Dynamic actin remodeling in response to lysophosphatidic acid

Abstract

Lysophosphatidic acid (LPA) is a multifunctional regulator of actin cytoskeleton that exerts a dramatic impact on the actin cytoskeleton to build a platform for diverse cellular processes including growth cone guidance, neurite retraction and cell motility. It has been implicated in the formation and dissociation of complexes between actin and actin binding proteins, supporting its role in actin remodeling. Several studies point towards its ability to facilitate formation of special cellular structures including focal adhesions and actin stress fibres by phosphoregulation of several actin associated proteins and their multiple regulatory kinases and phosphatases. In addition, multiple levels of crosstalk among the signaling cascades activated by LPA, affect actin cytoskeleton-mediated cell migration and chemotaxis which in turn play a crucial role in cancer metastasis. In the current review, we have attempted to highlight the role of LPA as an actin modulator which functions by controlling activities of specific cellular proteins that underlie mechanisms employed in cytoskeletal and pathophysiological events within the cell. Further studies on the actin affecting/remodeling activity of LPA in different cell types will no doubt throw up many surprises essential to gain a full understanding of its contribution in physiological processes as well as in diseases.

Communicated by Ramaswamy H. Sarma     

Does disturbance affect the structure of tropical fish assemblages? A test using null models

Null model analyses on fish presence-absence data from tropical river assemblages of the Western Ghats, India, revealed a difference in the extent of randomness in species assemblage structure among impacted and unimpacted rivers in the region.     

Slit signaling promotes the terminal asymmetric division of neural precursor cells in the Drosophila CNS.

The bipotential Ganglion Mother Cells, or GMCs, in the Drosophila CNS asymmetrically divide to generate two distinct post-mitotic neurons. Here, we show that the midline repellent Slit (Sli), via its receptor Roundabout (Robo), promotes the terminal asymmetric division of GMCs. In GMC-1 of the RP2/sib lineage, Slit promotes asymmetric division by down regulating two POU proteins, Nubbin and Mitimere. The down regulation of these proteins allows the asymmetric localization of Inscuteable, leading to the asymmetric division of GMC-1. Consistent with this, over-expression of these POU genes in a late GMC-1 causes mis-localization of Insc and symmetric division of GMC-1 to generate two RP2s. Similarly, increasing the dosage of the two POU genes in sli mutant background enhances the penetrance of the RP2 lineage defects whereas reducing the dosage of the two genes reduces the penetrance of the phenotype. These results tie a cell-non-autonomous signaling pathway to the asymmetric division of precursor cells during neurogenesis.     

Dose dependent pharmacokinetics,tissue distribution,and anti-tumor efficacy of a humanized monoclonal antibody against DLL4 in mice

Delta-like-4 ligand (DLL4) plays an important role in vascular development and is widely expressed on the vasculature of normal and tumor tissues. Anti-DLL4 is a humanized IgG1 monoclonal antibody against DLL4. The purpose of these studies was to characterize the pharmacokinetics (PK), tissue distribution, and anti-tumor efficacy of anti-DLL4 in mice over a range of doses. PK and tissue distribution of anti-DLL4 were determined in athymic nude mice after administration of single intravenous (IV) doses. In the tissue distribution study, radiolabeled anti-DLL4 (mixture of ¹²⁵Iodide and ¹¹¹Indium) was administered in the presence of increasing amounts of unlabeled anti-DLL4. Dose ranging anti-DLL4 anti-tumor efficacy was evaluated in athymic nude mice bearing MV522 human lung tumor xenografts. Anti-DLL4 had nonlinear PK in mice with rapid serum clearance at low doses and slower clearance at higher doses suggesting the involvement of target mediated clearance. Consistent with the PK data, anti-DLL4 was shown to specifically distribute to several normal tissues known to express DLL4 including the lung and liver. Maximal efficacy in the xenograft model was seen at doses ≥ 10 mg/kg when tissue sinks were presumably saturated, consistent with the PK and tissue distribution profiles. These findings highlight the importance of mechanistic understanding of antibody disposition to enable dosing strategies for maximizing efficacy.     

A Rare HBV Subgenotype D4 with Unique Genomic Signatures Identified in North-Eastern India –An Emerging Clinical Challenge?

Background/Aims

HBV has been classified into ten genotypes (A–J) and multiple subgenotypes, some of which strongly influence disease outcome and their distribution also correlate with human migration. HBV infection is highly prevalent in India and its diverse population provides an excellent opportunity to study the distinctiveness of HBV, its evolution and disease biology in variegated ethnic groups. The North-East India, having international frontiers on three sides, is one of the most ethnically and linguistically diverse region of the country. Given the paucity of information on molecular epidemiology of HBV in this region, the study aimed to carry out an in-depth genetic characterization of HBV prevailing in North-East state of Tripura.

Methods

From sera of chronically HBV infected patients biochemical/serological tests, HBV DNA quantification, PCR-amplification, sequencing of PreS/S or full-length HBV genomes were done. HBV genotype/subgenotype determination and sequence variability were assessed by MEGA5-software. The evolutionary divergence times of different HBV subgenotypes were estimated by DNAMLK/PHYLIP program while jpHMM method was used to detect any recombination event in HBV genomes.

Results

HBV genotypes D (89.5%), C (6.6%) and A (3.9%) were detected among chronic carriers. While all HBV/A and HBV/C isolates belonged to subgenotype-A1 and C1 respectively, five subgenotypes of HBV/D (D1–D5) were identified including the first detection of rare D4. These non-recombinant Indian D4 (IndD4) formed a distinct phylogenetic clade, had 2.7% nucleotide divergence and recent evolutionary radiation than other global D4. Ten unique amino acids and 9 novel nucleotide substitutions were identified as IndD4 signatures. All IndD4 carried T¹²⁰ and R¹²⁹ in ORF-S that may cause immune/vaccine/diagnostic escape and N¹²⁸ in ORF-P, implicated as compensatory Lamivudine resistance mutation.

Conclusions

IndD4 has potential to undermine vaccination programs or anti-viral therapy and its introduction to North-East India is believed to be linked with the settlement of ancient Tibeto-Burman migrants from East-Asia.     

Acylation Stimulating Protein,Complement C3 and Lipid Metabolism in Ketosis-Prone Diabetic Subjects

Background

Ketosis-prone diabetes (KPDM) is new-onset diabetic ketoacidosis without precipitating factors in non-type 1 diabetic patients; after management, some are withdrawn from exogenous insulin, although determining factors remain unclear.

Methods

Twenty KPDM patients and twelve type 1 diabetic patients (T1DM), evaluated at baseline, 12 and 24 months with/without insulin maintenance underwent a standardized mixed-meal tolerance test (MMTT) for 2 h.

Results

At baseline, triglyceride and C3 were higher during MMTT in KPDM vs. T1DM (p<0.0001) with no differences in non-esterified fatty acids (NEFA) while Acylation Stimulating Protein (ASP) tended to be higher. Within 12 months, 11 KPDM were withdrawn from insulin treatment (KPDM-ins), while 9 were maintained (KPDM+ins). NEFA was lower in KPDM-ins vs. KPDM+ins at baseline (p = 0.0006), 12 months (p<0.0001) and 24 months (p<0.0001) during MMTT. NEFA in KPDM-ins decreased over 30–120 minutes (p<0.05), but not in KPDM+ins. Overall, C3 was higher in KPDM-ins vs KPDM+ins at 12 months (p = 0.0081) and 24 months (p = 0.0019), while ASP was lower at baseline (p = 0.0024) and 12 months (p = 0.0281), with a decrease in ASP/C3 ratio.

Conclusions

Notwithstanding greater adiposity in KPDM-ins, greater NEFA decreases and lower ASP levels during MMTT suggest better insulin and ASP sensitivity in these patients.     

Finding homes for orphan cytochrome P450s: CYP4V2 and CYP4F22 in disease states

The cytochrome P450 (CYP) 4 family of enzymes contains several recently identified membersthat are referred to as “orphan P450s” because their endogenous substrates are unknown.Human CYP4V2 and CYP4F22 are two such orphan P450s that are strongly linked to ocular andskin disease, respectively. Genetic analyses have identified a wide spectrum of mutations in the CYP4V2gene from patients suffering from Bietti’s crystalline corneoretinal dystrophy, and mutations in theCYP4F22 gene have been linked to lamellar ichthyosis. The strong gene–disease associations provideunique opportunities for elucidating the substrate specificity of these orphan P450s and unraveling thebiochemical pathways that may be impacted in patients with CYP4V2 and CYP4F22 functional deficits.     

Integrin-α5 coordinates assembly of posterior cranial placodes in zebrafish and enhances Fgf-dependent regulation of otic/epibranchial cells

Vertebrate sensory organs develop in part from cranial placodes, a series of ectodermal thickenings that coalesce from a common domain of preplacodal ectoderm. Mechanisms coordinating morphogenesis and differentiation of discrete placodes are still poorly understood. We have investigated whether placodal assembly in zebrafish requires Integrin- α5 (itga5), an extracellular matrix receptor initially expressed throughout the preplacodal ectoderm. Morpholino knockdown of itga5 had no detectable effect on anterior placodes (pituitary, nasal and lens), but posterior placodes developed abnormally, resulting in disorganization of trigeminal and epibranchial ganglia and reduction of the otic vesicle. Cell motion analysis in GFP-transgenic embryos showed that cell migration in itga5 morphants was highly erratic and unfocused, impairing convergence and blocking successive recruitment of new cells into these placodes. Further studies revealed genetic interactions between itga5 and Fgf signaling. First, itga5 morphants showed changes in gene expression mimicking modest reduction in Fgf signaling. Second, itga5 morphants showed elevated apoptosis in the otic/epibranchial domain, which was rescued by misexpression of Fgf8. Third, knockdown of the Fgf effector erm had no effect by itself but strongly enhanced defects in itga5 morphants. Finally, proper regulation of itga5 requires dlx3b/4b and pax8, which are themselves regulated by Fgf. These findings support a model in which itga5 coordinates cell migration into posterior placodes and augments Fgf signaling required for patterning of these tissues and cell survival in otic/epibranchial placodes.