Dissociation between AKAP3 and PKARII Promotes AKAP3 Degradation in Sperm Capacitation

Ejaculated spermatozoa must undergo a series of biochemical modifications called capacitation, prior to fertilization. Protein-kinase A (PKA) mediates sperm capacitation, although its regulation is not fully understood. Sperm contain several A-kinase anchoring proteins (AKAPs), which are scaffold proteins that anchor PKA. In this study, we show that AKAP3 is degraded in bovine sperm incubated under capacitation conditions. The degradation rate is variable in sperm from different bulls and is correlated with the capacitation ability. The degradation of AKAP3 was significantly inhibited by MG-132, a proteasome inhibitor, indicating that AKAP3 degradation occurs via the proteasomal machinery. Treatment with Ca²⁺-ionophore induced further degradation of AKAP3; however, this effect was found to be enhanced in the absence of Ca²⁺ in the medium or when intracellular Ca²⁺ was chelated the degradation rate of AKAP3 was significantly enhanced when intracellular space was alkalized using NH₄Cl, or when sperm were treated with Ht31, a peptide that contains the PKA-binding domain of AKAPs. Moreover, inhibition of PKA activity by H89, or its activation using 8Br-cAMP, increased AKAP3 degradation rate. This apparent contradiction could be explained by assuming that binding of PKA to AKAP3 protects AKAP3 from degradation. We conclude that AKAP3 degradation is regulated by intracellular alkalization and PKA_RII anchoring during sperm capacitation.     

AKAP12 and AKAP5 form higher-order hetero-oligomers

Background

A-kinase-anchoring proteins, AKAPs, constitute a family of scaffolds that play an essential role in catalyzing the spatial-temporal, dynamic interactions of protein kinase A, protein kinase C, tyrosine kinases, G-protein-coupled receptors and ion channels. We studied AKAP5 (AKAP79; MW ~47 kDa) and AKAP12 (gravin, SSECKS; MW ~191 kDa) to probe if these AKAP scaffolds oligomerize.

Results

In gel analysis and sodium-dodecyl sulfate denaturation, AKAP12 behaved with a MW of a homo-dimer. Only in the presence of the chaotropic agent 8 M urea did gel analysis reveal a monomeric form of AKAP12. By separation by steric-exclusion chromatography, AKAP12 migrates with MW of ~840 kDa, suggestive of higher-order complexes such as a tetramer. Interestingly, the N-(1-840) and C-(840-1782) terminal regions of AKAP12 themselves retained the ability to form dimers, suggesting that the structural basis for the dimerization is not restricted to a single "domain" found within the molecule. In either sodium dodecyl sulfate or urea, AKAP5 displayed a relative mobility of a monomer, but by co-immunoprecipitation in native state was shown to oligomerize. When subjected to steric-exclusion chromatography, AKAP5 forms higher-order complexes with MW ~220 kDa, suggestive of tetrameric assemblies.

Conclusion

Both AKAP5 and AKAP12 display the capacity to form supermolecular homo-oligomeric structures that likely influence the localization and function of these molecular scaffolds.     

Re-expression of AKAP12 inhibits progression and metastasis potential of colorectal carcinoma in vivo and in vitro

Background

AKAP12/Gravin (A kinase anchor protein 12) is one of the A-kinase scaffold proteins and a potential tumor suppressor gene in human primary cancers. Our recent study demonstrated the highly recurrent loss of AKAP12 in colorectal cancer and AKAP12 reexpression inhibited proliferation and anchorage-independent growth in colorectal cancer cells, implicating AKAP12 in colorectal cancer pathogenesis.

Methods

To evaluate the effect of this gene on the progression and metastasis of colorectal cancer, we examined the impact of overexpressing AKAP12 in the AKAP12-negative human colorectal cancer cell line LoVo, the single clone (LoVo-AKAP12) compared to mock-transfected cells (LoVo-CON).

Results

pCMV6-AKAP12-mediated AKAP12 re-expression induced apoptosis (3% to 12.7%, p<0.01), migration (89.6±7.5 cells to 31.0±4.1 cells, p<0.01) and invasion (82.7±5.2 cells to 24.7±3.3 cells, p<0.01) of LoVo cells in vitro compared to control cells. Nude mice injected with LoVo-AKAP12 cells had both significantly reduced tumor volume (p<0.01) and increased apoptosis compared to mice given AKAP12-CON. The quantitative human-specific Alu PCR analysis showed overexpression of AKAP12 suppressed the number of intravasated cells in vivo (p<0.01).

Conclusion

These results demonstrate that AKAP12 may play an important role in tumor growth suppression and the survival of human colorectal cancer.     

AKAP79/150 Interacts with AC8 and Regulates Ca2+-dependent cAMP Synthesis in Pancreatic and Neuronal Systems

Protein kinase A anchoring proteins (AKAPs) provide the backbone for targeted multimolecular signaling complexes that serve to localize the activities of cAMP. Evidence is accumulating of direct associations between AKAPs and specific adenylyl cyclase (AC) isoforms to facilitate the actions of protein kinase A on cAMP production. It happens that some of the AC isoforms (AC1 and AC5/6) that bind specific AKAPs are regulated by submicromolar shifts in intracellular Ca²⁺. However, whether AKAPs play a role in the control of AC activity by Ca²⁺ is unknown. Using a combination of co-immunoprecipitation and high resolution live cell imaging techniques, we reveal an association of the Ca²⁺-stimulable AC8 with AKAP79/150 that limits the sensitivity of AC8 to intracellular Ca²⁺ events. This functional interaction between AKAP79/150 and AC8 was observed in HEK293 cells overexpressing the two signaling molecules. Similar findings were made in pancreatic insulin-secreting cells and cultured hippocampal neurons that endogenously express AKAP79/150 and AC8, which suggests important physiological implications for this protein-protein interaction with respect to Ca²⁺-stimulated cAMP production.     

PKA Compartmentalization via AKAP220 and AKAP12 Contributes to Endothelial Barrier Regulation

cAMP-mediated PKA signaling is the main known pathway involved in maintenance of the endothelial barrier. Tight regulation of PKA function can be achieved by discrete compartmentalization of the enzyme via physical interaction with A-kinase anchoring proteins (AKAPs). Here, we investigated the role of AKAPs 220 and 12 in endothelial barrier regulation. Analysis of human and mouse microvascular endothelial cells as well as isolated rat mesenteric microvessels was performed using TAT-Ahx-AKAPis peptide, designed to competitively inhibit PKA-AKAP interaction. In vivo microvessel hydraulic conductivity and in vitro transendothelial electrical resistance measurements showed that this peptide destabilized endothelial barrier properties, and dampened the cAMP-mediated endothelial barrier stabilization induced by forskolin and rolipram. Immunofluorescence analysis revealed that TAT-Ahx-AKAPis led to both adherens junctions and actin cytoskeleton reorganization. Those effects were paralleled by redistribution of PKA and Rac1 from endothelial junctions and by Rac1 inactivation. Similarly, membrane localization of AKAP220 was also reduced. In addition, depletion of either AKAP12 or AKAP220 significantly impaired endothelial barrier function and AKAP12 was also shown to interfere with cAMP-mediated barrier enhancement. Furthermore, immunoprecipitation analysis demonstrated that AKAP220 interacts not only with PKA but also with VE-cadherin and ß-catenin. Taken together, these results indicate that AKAP-mediated PKA subcellular compartmentalization is involved in endothelial barrier regulation. More specifically, AKAP220 and AKAP12 contribute to endothelial barrier function and AKAP12 is required for cAMP-mediated barrier stabilization.     

A Novel Cancer Testis Antigen,A-Kinase Anchor Protein 4 (AKAP4) Is a Potential Biomarker for Breast Cancer

Background

Breast cancer is the second leading cause of cancer related deaths in women worldwide. Reports about the early diagnosis of breast cancer are suggestive of an improved clinical outcome and overall survival rate in cancer patients. Therefore, cancer screening biomarker for early detection and diagnosis is urgently required for timely treatment and better cancer management. In this context, we investigated an association of cancer testis antigen, A-Kinase anchor protein 4 (AKAP4) with breast carcinoma.

Methodology/Findings

We first compared the AKAP4 gene and protein expression in four breast cancer cells (MCF7, MDA-MB-231, SK-BR3 and BT474) and normal human mammary epithelial cells. In addition, 91 clinical specimens of breast cancer patients of various histotypes including ductal carcinoma in situ, infiltrating ductal carcinoma and infiltrating lobular carcinoma and 83 available matched adjacent non-cancerous tissues were examined for AKAP4 gene and protein expression by employing in situ RNA hybridization and immunohistochemistry respectively. Humoral response against AKAP4 was also investigated in breast cancer patients employing ELISA. Our in vitro studies in all breast cancer cells revealed AKAP4 gene and protein expression whereas, normal human mammary epithelial cells failed to show any expression. Using in situ RNA hybridization and immunohistochemistry, 85% (77/91) tissue specimens irrespective of histotypes, stages and grades of breast cancer clinical specimens revealed AKAP4 gene and protein expression. However, matched adjacent non-cancerous tissues failed to display any AKAP4 gene and protein expression. Furthermore, humoral response was observed in 79% (72/91) of total breast cancer patients. Interestingly, we observed that 94% (72/77) of breast cancer patients found positive for AKAP4 protein expression generated humoral response against AKAP4 protein.

Conclusions

Collectively, our data suggests that AKAP4 may be used as serum based diagnostic test for an early detection and diagnosis of breast cancer and may be a potential target for immunotherapeutic use.     

Molecular Cloning, Chromosomal Localization, and Cell Cycle-Dependent Subcellular Distribution of the A-Kinase Anchoring Protein, AKAP95

The cyclic AMP-dependent protein kinase (PKA) type II is directed to different subcellular loci through interaction of the RII subunits with A-kinase anchoring proteins (AKAPs). A full-length human clone encoding AKAP95 was identified and sequenced, and revealed a 692-amino acid open reading frame that was 89% homologous to the rat AKAP95 (V. M. Coghlan, L. K. Langeberg, A. Fernandez, N. J. Lamb, and J. D. Scott (1994)J. Biol. Chem.269, 7658–7665). The gene encoding AKAP95 was mapped to human chromosome 19p13.1-q12 using somatic cell hybrids and PCR. A fragment covering amino acids 414–692 of human AKAP95 was expressed inEscherichia coliand shown to bind RIIα. Competition with a peptide covering the RII-binding domain of AKAP Ht31 abolished RIIα binding to AKAP95. Immunofluorescence studies in quiescent human Hs-68 fibroblasts showed a nuclear localization of AKAP95, whereas RIIα was excluded from the nucleus. In contrast, during mitosis AKAP95 staining was markedly changed and appeared to be excluded from the condensed chromatin and localized outside the metaphase plate. Furthermore, the subcellular localizations of AKAP95 and RIIα overlapped in metaphase but started to segregate in anaphase and were again separated as AKAP95 reentered the nucleus in telophase. Finally, RIIα was coimmunoprecipitated with AKAP95 from HeLa cells arrested in mitosis, but not from interphase HeLa cells, demonstrating a physical association between these two molecules during mitosis. The results show a distinct redistribution of AKAP95 during mitosis, suggesting that the interaction between AKAP95 and RIIα may be cell cycle-dependent.     

Disruption of the autism-related gene Pak1 causes stereocilia disorganization,hair cell loss,and deafness in mice

Several clinical studies have reported that hearing loss is correlated with autism in children. However, little is known about the underlying mechanism between hearing loss and autism. p21-activated kinases(PAKs)are a family of serine/threonine kinases that can be activated by multiple signaling molecules, particularly the Rho family of small GTPases. Previous studies have shown that Pak1 mutations are associated with autism. In the present study, we take advantage of Pak1 knockout(Pak1à/à) mice to investigate the role of PAK1 in hearing function. We find that PAK1 is highly expressed in the postnatal mouse cochlea and that PAK1 deficiency leads to hair cell(HC) apoptosis and severe hearing loss. Further investigation indicates that PAK1 deficiency downregulates the phosphorylation of cofilin and ezrin-radixin-moesin and the expression of b II-spectrin, which further decreases the HC synapse density in the basal turn of cochlea and disorganized the HC stereocilia in all three turns of cochlea in Pak1à/àmice. Overall, our work demonstrates that the autism-related gene Pak1 plays a crucial role in hearing function. As the first candidate gene linking autism and hearing loss, Pak1 may serve as a potential target for the clinical diagnosis of autism-related hearing loss.     

A novel mutation in MID1 in a patient with X-linked Opitz G/BBB syndrome

Opitz G/BBB syndrome (OS) is a genetically heterogeneous disease. We report on an OS patient with a novel inherited mutation in MID1. Metaphase analysis showed a normal male karyotype. Array CGH revealed a maternally inherited duplication at Xp22.31 (6,467,203–7,992,261, hg18), the size was estimated to 1.5 Mb. Sequence analysis of the MID1 coding region revealed a novel missense mutation in exon 8 (c.1561C>T/p. R521C) which resulted in an ammonia acid substitution (R521C) in the PRX domain of the MID1 protein. The mutation was inherited from unaffected grandmother and mildly affected mother. Prenatal diagnosis was performed for the third pregnancy after identification of the causative mutation in the family. The third fetus was found to be a female carrier. Postnatal follow-up at 2-month-old showed normal phenotype. In conclusion, we reported a familial OS patient with a novel mutation in exon 8 which provided another evidence for that mutation clustered in C-terminal domain of MID1. The newly identified mutation in our patient expands mutation spectrum in MID1 gene.     

Comprehensive Evolutionary and Expression Analysis of FCS-Like Zinc finger Gene Family Yields Insights into Their Origin,Expansion and Divergence

Plant evolution is characterized by frequent genome duplication events. Expansion of habitat resulted in the origin of many novel genes and genome duplication events which in turn resulted in the expansion of many regulatory gene families. The plant-specific FCS-Like Zinc finger (FLZ) gene family is characterized by the presence of a FCS-Like Zinc finger (FLZ) domain which mediates the protein-protein interaction. In this study, we identified that the expansion of FLZ gene family size in different species is correlated with ancestral and lineage-specific whole genome duplication events. The subsequent gene loss found to have a greater role in determining the size of this gene family in many species. However, genomic block duplications played the significant role in the expansion of FLZ gene family in some species. Comparison of Arabidopsis thaliana and Oryza sativa FLZ gene family revealed monocot and dicot specific evolutionary trends. The FLZ genes were found to be under high purifying selection. The spatiotemporal expression analyses of Arabidopsis thaliana FLZ gene family revealed that majority of the members are highly expressed in reproductive organs. FLZ genes were also found to be highly expressed during vegetative-to-reproductive phase transition which is correlated with the proposed role of this gene family in sugar signaling. The comparison of sequence, structural and expression features of duplicated genes identified lineage-specific redundancy and divergence. This extensive evolutionary analysis and expression analysis of Arabidopsis thaliana FLZ genes will pave the way for further functional analysis of FLZ genes.     

Distinct but overlapping domains of AKAP95 are implicated in chromosome condensation and condensin targeting

A-kinase (or PKA)-anchoring protein AKAP95 is a zinc-finger protein implicated in mitotic chromosome condensation by acting as a targeting molecule for the condensin complex. We have identified determinants of chromatin-binding, condensin-targeting and chromosome-condensation activities of AKAP95. Binding of AKAP95 to chromatin is conferred by residues 387–450 and requires zinc finger ZF1. Residues 525–569 are essential for condensation of AKAP95-free chromatin and condensin recruitment to chromosomes. Mutation of either zinc finger of AKAP95 abolishes condensation. However, ZF1 is dispensable for condensin targeting, whereas the C-terminal ZF2 is required. AKAP95 interacts with Xenopus XCAP-H condensin subunit in vitro and in vivo but not with the human hCAP-D2 subunit. The data illustrate the involvement of overlapping, but distinct, domains of AKAP95 for condensin recruitment and chromosome condensation and argue for a key role of ZF1 in chromosome condensation and ZF2 in condensin targeting. Moreover, condensin recruitment to chromatin is not sufficient to promote condensation.     

AKAP13 couples GPCR signaling to mTORC1 inhibition

The mammalian target of rapamycin complex 1 (mTORC1) senses multiple stimuli to regulate anabolic and catabolic processes. mTORC1 is typically hyperactivated in multiple human diseases such as cancer and type 2 diabetes. Extensive research has focused on signaling pathways that can activate mTORC1 such as growth factors and amino acids. However, less is known about signaling cues that can directly inhibit mTORC1 activity. Here, we identify A-kinase anchoring protein 13 (AKAP13) as an mTORC1 binding protein, and a crucial regulator of mTORC1 inhibition by G-protein coupled receptor (GPCR) signaling. GPCRs paired to Gα_s proteins increase cyclic adenosine 3’5’ monophosphate (cAMP) to activate protein kinase A (PKA). Mechanistically, AKAP13 acts as a scaffold for PKA and mTORC1, where PKA inhibits mTORC1 through the phosphorylation of Raptor on Ser 791. Importantly, AKAP13 mediates mTORC1-induced cell proliferation, cell size, and colony formation. AKAP13 expression correlates with mTORC1 activation and overall lung adenocarcinoma patient survival, as well as lung cancer tumor growth in vivo. Our study identifies AKAP13 as an important player in mTORC1 inhibition by GPCRs, and targeting this pathway may be beneficial for human diseases with hyperactivated mTORC1.     

Resonance assignments of the human AKAP13-PH domain and stabilizing DH helix

The human AKAP13 protein contains DH and PH domains, which are responsible for its cell transforming activity. Despite its biomedical importance, the contribution of the PH domain to AKAP13 activity remains unclear and no three dimensional structure is available to date. Here we report the backbone and side chain ¹H, ¹³C and ¹⁵N resonance assignments of a 20 kDa construct comprising the uniformly ¹³C and ¹⁵N labeled AKAP13-PH domain and an associated helix from the DH domain which is required for its stable expression. Resonance assignment has been achieved using conventional triple resonance experiments; 95% of all back bone resonances and more than 90% of side chain resonances have been successfully assigned. The ¹H, ¹³C and ¹⁵N chemical shifts have been deposited in BMRB with accession number of 16195.     

AKAP18 contains a phosphoesterase domain that binds AMP

Protein kinase A anchoring proteins (AKAPs), defined by their capacity to target the cAMP-dependent protein kinase to distinct subcellular locations, function as molecular scaffolds mediating the assembly of multicomponent complexes to integrate and organise multiple signalling events. Despite their central importance in regulating cellular processes, little is known regarding their diverse structures and molecular mechanisms. Here, using bioinformatics and X-ray crystallography, we define a central domain of AKAP18δ (AKAP18^CD) as a member of the 2H phosphoesterase family. The domain features two conserved His-x-Thr motifs positioned at the base of a groove located between two lobes related by pseudo 2-fold symmetry. Nucleotide co-crystallisation screening revealed that this groove binds specifically to adenosine 5'-monophosphate (5'AMP) and cytosine 5'-monophosphate (5'CMP), with the affinity constant for AMP in the physiological concentration range. This is the first example of an AKAP capable of binding a small molecule. Our data generate two functional hypotheses for the AKAP18 central domain. It may act as a phosphoesterase, although we did not identify a substrate, or as an AMP sensor with the potential to couple intracellular AMP levels to PKA signalling events.     

Setting sail for glucose homeostasis with the AKAP150‐PP2B‐anchor

EMBO J (2012) 31 20, 3991–4004 doi:10.1038/emboj.2012.244; published online August312012Glucose-stimulated insulin secretion, controlled by multiple protein phosphorylation events, is critical for the regulation of glucose homeostasis. Protein kinase A (PKA) is known to play a role in β cell physiology, but the role of its anchoring protein is not fully understood. Hinke et al (2012) illustrate the significance of A-kinase anchoring protein 150 in tethering protein phosphatase 2B to mediate nutrient-stimulated insulin secretion and thus modulate glucose homeostasis.Insulin secretion is a key component in the regulation of glucose homeostasis. The initiation of glucose-stimulated insulin secretion (GSIS) is coordinated by numerous protein phosphorylation and dephosphorylation events in the β cell (Jones and Persaud, 1998). PKA and protein phosphatase 2B (PP2B or calcineurin—a Ca²⁺/calmodulin-dependent enzyme) are examples of enzymes that can influence the release of insulin. The combined effects of these enzymes propagate GSIS, which is mediated intracellularly via an increase in ATP concentration, Ca²⁺ influx via the voltage-dependent Ca²⁺ channel (VDCC) and cyclic AMP (cAMP) signalling. At the same time, these enzymes can also regulate glucose usage (e.g., via glycogen synthase) in insulin-sensitive tissues such as the skeletal muscle.cAMP signalling serves to potentiate GSIS via either (1) PKA-dependent or (2) PKA-independent mechanisms (involving cAMP-binding protein Epac2A (exchange protein directly activated by cAMP 2)). A-kinase anchoring protein (AKAP) belongs to a group of regulatory proteins that interacts with cAMP-dependent PKA (Pidoux and Tasken, 2010; Welch et al, 2010). It can regulate the differential usage of kinase versus phosphatase, thereby controlling metabolic outcomes in specific tissues. Although it is known that PKA phosphorylation regulates β cell physiology, the role of such anchoring proteins is less clear (Faruque et al, 2009; Lester et al, 2001). For example, while disruption of the AKAP–PKA interaction has been reported to decrease insulin secretion (Lester et al, 1997), the specific regulatory protein that anchors PKA has yet to be identified.In this study, Hinke et al (2012) sought to identify the specific anchoring protein that tethers PKA, and to elucidate its function. Two AKAP proteins, namely, AKAP150 and AKAP220 were first shortlisted from an overlay assay used to detect RII (regulatory subunit of PKA) binding proteins. Subsequently, only AKAP150 was found to be important for nutrient-stimulated insulin secretion. Mice with a global knockout of AKAP150 (AKAP150KO) exhibited insulin secretory defects. AKAP150 binds to and regulates the phosphorylation-dependent VDCC. Thus, these AKAP150KO mice exhibited decreased basal Ca²⁺ current and glucose-stimulated Ca²⁺ influx in isolated β cells. One reason for the decrease in Ca²⁺ current could be attributed to a mislocation of its binding partner PP2B (discussed below). Glucose-stimulated cAMP fluctuation which is necessary for insulin secretion (Dyachok et al, 2008) was also abolished in AKAP150KO mice. Therefore, AKAP150KO mice exhibit an insulin secretory defect due to multiple impairments including (1) decreased Ca²⁺ influx and (2) defective cAMP production.Surprisingly, while the authors report that global AKAP150KO mice secrete less insulin, the skeletal muscle, an insulin-sensitive peripheral tissue, exhibited improved blood glucose clearance likely due to increased phosphorylation of IRS-1 and Akt/PKB, and activation of AMPK that resulted in improved insulin sensitivity. On the other hand, β cell-specific AKAP150KO mice secrete less insulin upon glucose stimulation despite increased insulin content in the β cell that occurs as an adaptation to the impaired glucose tolerance. These mice clearly exhibited an impaired glucose tolerance that is due to defective insulin secretion because they do not exhibit an increase in insulin sensitivity. Together, these data indicate that the skeletal muscle selectively adapts to the global absence of AKAP150 to compensate for the decrease in insulin in the body. Notably, AKAP150 is also expressed in the liver but does not exhibit compensatory effects while AKAP150 is not expressed in the adipose tissue.AKAP150 can anchor numerous enzymes with different metabolic activities. For instance, it binds PKA and PP2B, two enzymes with opposing functions, to the cell surface membrane. Hinke et al (2012) further investigated the impact of disrupting specific binding partners of AKAP150. Unexpectedly, AKAP150Δ36 mice that lack residues 705–724 and therefore cannot bind PKA exclusively are effectively metabolically normal. It is thus surprising that the anchoring of PKA to AKAP150 is not necessary for proper insulin release although this interaction is important in other cellular systems (Lu et al, 2008, 2011). AKAP150ΔPIX mice lacking residues 655–661 and thus unable to tether to PP2B at a seven-residue PIxIxIT motif demonstrate the same metabolic phenotype as global AKAP150KO mice. This suggests that AKAP150 is critical for tethering PP2B, and that PP2B is the key molecule necessary for insulin secretion in β cells. PP2B is also a determinant of the metabolic phenotypes such as improved insulin sensitivity and glucose handling upon loss of anchorage of PP2B.Overall, Hinke et al (2012) used complementary in vivo approaches including animal physiology, and in vitro islet culture and live-cell imaging to demonstrate the importance of the kinase/phosphatase anchoring protein AKAP150 in regulating nutrient-stimulated insulin secretion and modulating glucose homeostasis in mice (Figure 1). However, it is likely that there are AKAP150-independent mechanisms regulating insulin secretion since islets from AKAP150KO mice continued to respond to glucose stimulation and secrete insulin in both static and dynamic conditions, albeit at lower levels compared to wild-type mice. Importantly, the authors also identified AKAP150 tethering to PP2B as a key molecular event that regulates insulin secretion and glucose homeostasis (Figure 1). Thus, targeting the AKAP150–PP2B interface and the PIxIxIT motif could be therapeutically useful for increasing insulin sensitivity in patients with diabetes and metabolic syndromes. This could involve designing molecules or chemical compounds to bind the motif and block interaction between AKAP150 and PP2B. In parallel, the safety of systemic blockade of this interaction needs to be ascertained. Alternatively, skeletal muscle-specific AKAP150ΔPIX mice could be generated to determine if the metabolic phenotype is similar to global AKAP150ΔPIX mice. Should this be the case, then localized pharmacological blockade of AKAP150–PP2B interaction could be considered.Open in a separate windowFigure 1AKAP150 tethered to PP2B at a seven-residue PIxIxIT motif mediates nutrient-stimulated insulin secretion and glucose homeostasis. Both global AKAP150KO and AKAP150ΔPIX (AKAP150-PP2B binding abolished) mice exhibit insulin secretory defects, enhanced insulin sensitivity in skeletal muscle and overall improved glucose tolerance. This infers the importance of AKAP150-PP2B tethering for glucose homeostasis. ‘Tick'' indicates an increase or improvement. ‘Cross'' indicates a defect or impairment. ‘Equal sign'' indicates no change or no effect. Questions emerging from this study are highlighted in red.Several issues worth pursuing include (1) determining the differential adaptive response of the skeletal muscle versus the liver to alterations in insulin sensitivity in global AKAP150KO mice, (2) further investigating the functional relevance of AKAP150 tethering to PKA (by generating β cell-specific AKAP150Δ36 mice) as there is probably a biological rationale for their interaction, (3) exploring whether AKAP150-related or other proteins are expressed and act in different adipose tissue depots, (4) determining whether AKAP150 acts in a similar manner in ‘human'' skeletal muscle and β cells, and (5) examining if polymorphisms in human genes that encode AKAP150 tethering proteins are linked to disorders of glucose metabolism.     

DUF1220-Domain Copy Number Implicated in Human Brain-Size Pathology and Evolution

DUF1220 domains show the largest human-lineage-specific increase in copy number of any protein-coding region in the human genome and map primarily to 1q21, where deletions and reciprocal duplications have been associated with microcephaly and macrocephaly, respectively. Given these findings and the high correlation between DUF1220 copy number and brain size across primate lineages (R² = 0.98; p = 1.8 × 10⁻⁶), DUF1220 sequences represent plausible candidates for underlying 1q21-associated brain-size pathologies. To investigate this possibility, we used specialized bioinformatics tools developed for scoring highly duplicated DUF1220 sequences to implement targeted 1q21 array comparative genomic hybridization on individuals (n = 42) with 1q21-associated microcephaly and macrocephaly. We show that of all the 1q21 genes examined (n = 53), DUF1220 copy number shows the strongest association with brain size among individuals with 1q21-associated microcephaly, particularly with respect to the three evolutionarily conserved DUF1220 clades CON1(p = 0.0079), CON2 (p = 0.0134), and CON3 (p = 0.0116). Interestingly, all 1q21 DUF1220-encoding genes belonging to the NBPF family show significant correlations with frontal-occipital-circumference Z scores in the deletion group. In a similar survey of a nondisease population, we show that DUF1220 copy number exhibits the strongest correlation with brain gray-matter volume (CON1, p = 0.0246; and CON2, p = 0.0334). Notably, only DUF1220 sequences are consistently significant in both disease and nondisease populations. Taken together, these data strongly implicate the loss of DUF1220 copy number in the etiology of 1q21-associated microcephaly and support the view that DUF1220 domains function as general effectors of evolutionary, pathological, and normal variation in brain size.     

Rare inherited missense variants of POGZ associate with autism risk and disrupt neuronal development

Excess de novo likely gene-disruptive and missense variants within dozens of genes have been identified in autism spectrum disorder(ASD)and other neurodevelopmental disorders.However,many rare inherited missense variants of these high-risk genes have not been thoroughly evaluated.In this study,we analyzed the rare missense variant burden of POGZ in a large cohort of ASD patients from the Autism Clinical and Genetic Resources in China(ACGC)and further dissected the functional effect of diseaseassociated missense variants on neuronal development.Our results showed a significant burden of rare missense variants in ASD patients compared to the control population(P=4.6×10-5,OR=3.96),and missense variants in ASD patients showed more severe predicted functional outcomes than those in controls.Furthermore,by leveraging published large-scale sequencing data of neurodevelopmental disorders(NDDs)and sporadic case reports,we identified 8 de novo missense variants of POGZ in NDD patients.Functional analysis revealed that two inherited,but not de novo,missense variants influenced the cellular localization of POGZ and failed to rescue the defects in neurite and dendritic spine development caused by Pogz knockdown in cultured mouse primary cortical neurons.Significantly,L1CAM,an autism candidate risk gene,is differentially expressed in POGZ deficient cell lines.Reduced expression of L1cam was able to partially rescue the neurite length defects caused by Pogz knockdown.Our study showed the important roles of rare inherited missense variants of POGZ in ASD risk and neuronal development and identified the potential downstream targets of POGZ,which are important for further molecular mechanism studies.     

Molecular evolution of a-kinase anchoring protein (AKAP)-7: implications in comparative PKA compartmentalization

ABSTRACT: BACKGROUND: A-Kinase Anchoring Proteins (AKAPs) are molecular scaffolding proteins mediating the assembly of multi-protein complexes containing cAMP-dependent protein kinase A (PKA), directing the kinase in discrete subcellular locations. Splice variants from the AKAP7 gene (AKAP15/18) are vital components of neuronal and cardiac phosphatase complexes, ion channels, cardiac Ca2+ handling and renal water transport. RESULTS: Shown in evolutionary analyses, the formation of the AKAP7-RI/RII binding domain (required for AKAP/PKA-R interaction) corresponds to vertebrate-specific gene duplication events in the PKA-RI/RII subunits. Species analyses of AKAP7 splice variants shows the ancestral AKAP7 splice variant is AKAP7alpha, while the ancestral long form AKAP7 splice variant is AKAP7gamma. Multi-species AKAP7 gene alignments, show the recent formation of AKAP7delta occurs with the loss of native AKAP7gamma in rats and basal primates. AKAP7 gene alignments and two dimensional Western analyses indicate that AKAP7gamma is produced from an internal translation-start site that is present in the AKAP7delta cDNA of mice and humans but absent in rats. Immunofluorescence analysis of AKAP7 protein localization in both rat and mouse heart suggests AKAP7gamma replaces AKAP7delta at the cardiac sarcoplasmic reticulum in species other than rat. DNA sequencing identified Human AKAP7delta insertion-deletions (indels) that promote the production of AKAP7gamma instead of AKAP7delta. CONCLUSIONS: This AKAP7 molecular evolution study shows that these vital scaffolding proteins developed in ancestral vertebrates and that independent mutations in the AKAP7 genes of rodents and early primates has resulted in the recent formation of AKAP7delta, a splice variant of likely lesser importance in humans than currently described.