Single‐cell analysis of p16INK4a and p21WAF1 expression suggests distinct mechanisms of senescence in normal human and Li‐Fraumeni Syndrome fibroblasts

Herein we used single‐cell observation methods to gain insight into the roles of p16^INK4A and p21^WAF1 (hereafter p16 and p21) in replicative senescence and ionizing radiation‐induced accelerated senescence in human [normal, ataxia telangiectasia (AT) and Li‐Fraumeni syndrome (LFS)] fibroblast strains. Cultures of all strains entered a state of replicative senescence at late passages, as evident from inhibition of growth, acquisition of flattened and enlarged cell morphology, and positive staining for senescence‐associated β‐galactosidase. In addition, proliferating early‐passage cultures of these strains exhibited accelerated senescence in response to ionizing radiation. Immunofluorescence microscopy revealed the heterogeneous expression of p16 in normal and AT fibroblast strains, with the majority of the cells exhibiting undetectable levels of p16 irrespective of in vitro culture age. Importantly, replicative senescence as well as accelerated senescence triggered by ionizing radiation were accompanied by sustained nuclear accumulation of p21, but did not correlate with p16 expression in p53‐proficient (normal and AT) fibroblasts. In p53‐deficient (LFS) fibroblasts, on the other hand, replicative senescence and ionizing radiation‐triggered accelerated senescence strongly correlated with expression of p16 but not of p21. Furthermore, senescence in LFS fibroblasts was associated with genomic instability encompassing polyploidy. Our findings are compatible with a model in which p16 serves as a backup regulator of senescence, triggering this response preferentially in the absence of wild‐type p53 activity. The possibility that one of the tumor‐suppressor functions of p16 may be associated with genomic instability, preventing the emergence of malignant progeny from polyploid giant cells, is also supported by these results. J. Cell. Physiol. 223: 57–67, 2010. © 2009 Wiley‐Liss, Inc.     

Spectroscopic investigation of the interaction of water-soluble azocalix[4]arenes with bovine serum albumin

In this work, three hydrosoluble azocalix[4]arene derivatives, 5-(o-methylphenylazo)-25,26,27-tris(carboxymethoxy)-28-hydroxycalix[4]arene (o-MAC-Calix), 5-(m-methylphenylazo)-25,26,27-tris(carboxymethoxy)-28-hydroxycalix[4]arene (m-MAC-Calix) and 5-(p-methylphenylazo)-25,26,27-tris(carboxymethoxy)-28-hydroxycalix[4]arene (p-MAC-Calix) were synthesized. Their structures were characterized by infrared spectrum (IR), nuclear magnetic resonance spectrum (¹H NMR and ¹³C NMR) and mass spectrum (MS). The interactions between these compounds and bovine serum albumin (BSA) were studied by fluorescence spectroscopy, UV–vis spectrophotometry and circular dichroic spectroscopy. According to experimental results, three azocalix[4]arene derivatives can efficiently bind to BSA molecules and the o-MAC-Calix displays more efficient interactions with BSA molecules than m-MAC-Calix and p-MAC-Calix. Molecular docking showed that the o-MAC-Calix was embedded in the hydrophobic cavity of helical structure of BSA molecular and the tryptophan (Trp) residue of BSA molecular had strong interaction with o-MAC-Calix. The fluorescence quenching of BSA caused by azocalix[4]arene derivatives is attributed to the static quenching process. In addition, the synchronous fluorescence spectroscopy indicates that these azocalix[4]arene derivatives are more accessible to Trp residues of BSA molecules than the tyrosine (Tyr) residues. The circular dichroic spectroscopy further verified the binding of azocalix[4]arene derivatives and BSA.     

Treacher Collins syndrome: Unmasking the role of Tcof1/treacle

Treacher Collins syndrome (TCS) is a rare congenital birth disorder characterized by severe craniofacial defects. The syndrome is associated with mutations in the TCOF1 gene which encodes a putative nucleolar phosphoprotein known as treacle. An animal model of the severe form of TCS, generated through mutation of the mouse homologue Tcof1 has recently revealed significant insights into the etiology and pathogenesis of TCS (Dixon and Dixon, 2004; Dixon et al., 2006; Jones et al 2008). During early embryogenesis in a TCS individual, an excessive degree of neuroepithelial apoptosis diminishes the generation of neural crest cells. Neural crest cells are a migratory stem and progenitor cell population that generates most of the tissues of the head including much of the bone, cartilage and connective tissue. It has been hypothesized that mutations in Tcof1 disrupt ribosome biogenesis to a degree that is insufficient to meet the proliferative needs of the neuroepithelium and neural crest cells. This causes nucleolar stress activation of the p53-dependent apoptotic pathway which induces neuroepithelial cell death. Interestingly however, chemical and genetic inhibition of p53 activity can block the wave of apoptosis and prevent craniofacial anomalies in Tcof1 mutant mice [Jones NC, Lynn ML, Gaudenz K, Sakai D, Aoto K, Rey JP, et al. Prevention of the neurocristopathy Treacher Collins syndrome through inhibition of p53 function. Nat Med 2008;14:125–33]. These findings shed new light on potential therapeutic avenues for the prevention of not only TCS but also other congenital craniofacial disorders which share a similar etiology and pathogenesis.     

Leukemic and non-leukemic lymphocytes from patients with Li Fraumeni syndrome demonstrate loss of p53 function,Bcl-2 family dysregulation and intrinsic resistance to conventional chemotherapeutic drugs but not flavopiridol

Li Fraumeni syndrome (LFS) is characterised by a predisposition to the early onset of certain tumors and is associated with germline mutation of the anti-oncogene p53. In this study we analysed the in vitro responses of lymphocytes from two LFS patients to chemotherapeutic drugs in terms of apoptosis induction and the expression of key intracellular proteins that regulate this process. One of the LFS patients also suffered from B-cell chronic lymphocytic leukemia (B-CLL) and hence presented with a light-chain restricted B-cell lymphocytosis while the other patient had entirely normal blood counts. The B-lymphocytes from both LFS patients showed a marked degree of resistance to chlorambucil and fludarabine when compared to age-matched controls but were remarkably sensitive to the novel flavone, flavopiridol. Loss of function of p53 was demonstrated by a failure to induce Bax and p21 protein expression. In addition, altered basal expression patterns of Bcl-2 and Bax, two key regulators of apoptosis, were found in the LFS lymphocytes when compared with controls. These results suggest that LFS lymphocytes carrying a p53 mutation show intrinsic resistance to conventional chemotherapeutic drugs and this is associated with dysregulation of Bcl-2 family proteins. Furthermore, The innate resistance profile was similar in leukemic and non-leukemic lymphocytes and was therefore independent of genetic changes acquired during malignant transformation. Novel agents that induce p53-independent cell killing may be useful not only in the treatment of LFS-associated tumors but also drug resistant tumors in general where p53 and/or Bcl-2 family dysregulation is a feature.     

Calixarene-based phosphinic acids as inhibitors of protein tyrosine phosphatases

In the present work, the derivatives of calix[4]arene, thiacalix[4]arene, and sulfonylcalix[4]arene bearing four methylene(phenyl)phosphinic acid groups on the upper rim of the macrocycle were synthesized and studied as inhibitors of human protein tyrosine phosphatases. The inhibitory capacities of the three compounds towards PTP1B were higher than those for protein tyrosine phosphatases TC–PTP, MEG1, MEG2, and SHP2. The most potent sulfonylcalix[4]arene phosphinic acid displayed K_i value of 32?nM. The thiacalix[4]arene phosphinic acid was found to be a low micromolar inhibitor of PTP1B with selectivity over the other PTPs. The kinetic experiments showed that the inhibitors compete with the substrate for the active site of the enzyme. Molecular docking was performed to explain possible binding modes of the calixarene-based phosphinic inhibitors of PTP1B.     

Mutations in iron-sulfur cluster scaffold genes NFU1 and BOLA3 cause a fatal deficiency of multiple respiratory chain and 2-oxoacid dehydrogenase enzymes

Severe combined deficiency of the 2-oxoacid dehydrogenases, associated with a defect in lipoate synthesis and accompanied by defects in complexes I, II, and III of the mitochondrial respiratory chain, is a rare autosomal recessive syndrome with no obvious causative gene defect. A candidate locus for this syndrome was mapped to chromosomal region 2p14 by microcell-mediated chromosome transfer in two unrelated families. Unexpectedly, analysis of genes in this area identified mutations in two different genes, both of which are involved in [Fe-S] cluster biogenesis. A homozygous missense mutation, c.545G>A, near the splice donor of exon 6 in NFU1 predicting a p.Arg182Gln substitution was found in one of the families. The mutation results in abnormal mRNA splicing of exon 6, and no mature protein could be detected in fibroblast mitochondria. A single base-pair duplication c.123dupA was identified in BOLA3 in the second family, causing a frame shift that produces a premature stop codon (p.Glu42Argfs^∗13). Transduction of fibroblast lines with retroviral vectors expressing the mitochondrial, but not the cytosolic isoform of NFU1 and with isoform 1, but not isoform 2 of BOLA3 restored both respiratory chain function and oxoacid dehydrogenase complexes. NFU1 was previously proposed to be an alternative scaffold to ISCU for the biogenesis of [Fe-S] centers in mitochondria, and the function of BOLA3 was previously unknown. Our results demonstrate that both play essential roles in the production of [Fe-S] centers for the normal maturation of lipoate-containing 2-oxoacid dehydrogenases, and for the assembly of the respiratory chain complexes.     

A rapid and reproducible assay for collagenase using [1-14C]acetylated collagen.

A rapid, continuous, and highly sensitive fluorescence assay is described for the measurement of epoxide hydrase activity. The method is based on the large differences between the fluorescence spectra of certain K-region arene oxides and their corresponding trans-dihydrodiols. Enzymatic hydration of K-region arene oxides of phenanthrene, pyrene, benzo[a]pyrene, and 7,12-dimethylbenzo[a]anthracene was studied. The assay was most sensitive with benzo[a]pyrene-4,5-oxide as substrate. With 10 μm benzo[a]pyrene-4,5-oxide, enzymatic rates of 30 pmol of dihydrodiol/min/mg of protein are three to five times those of the blank without enzyme. The fluorometric method described has been used to study site-directed inhibitors of epoxide hydrase and the stereoselective hydration of racemic arene oxides.     

Inhibition of Yersinia protein tyrosine phosphatase by phosphonate derivatives of calixarenes

Inhibition of Yersinia protein tyrosine phosphatase by calix[4]arene mono-, bis-, and tetrakis(methylenebisphosphonic) acids as well as calix[4]arene and thiacalix[4]arene tetrakis(methylphosphonic) acids have been investigated. The kinetic studies revealed that some compounds in this class are potent competitive inhibitors of Yersinia PTP with inhibition constants in the low micromolar range. The binding modes of macrocyclic phosphonate derivatives in the enzyme active center have been explained using computational docking approach. The results obtained indicate that calix[4]arenes are promising scaffolds for the development of inhibitors of Yersinia PTP.     

Association of p53 and MDM2 polymorphisms with risk of human papillomavirus (HPV)-related esophageal squamous cell carcinoma (ESCC)

PurposeThough polymorphisms of the tumor suppressor gene p53 have been extensively investigated in numerous tumors, particularly tumors associated with human papillomavirus (HPV) infection. However, the results remain controversial. Our previous study showed that HPV serostatus is not an independent risk factor for esophageal squamous cell carcinoma (ESCC) in nonsmokers and nondrinkers. Given the roles of p53 and HPV E6 as well as MDM2 oncoproteins in p53 degradation, we validated the association of p53 and MDM2 polymorphisms with ESCC risk stratified by HPV16 sero-status.MethodsSingle nucleotide polymorphisms of p53 Arg72Pro (rs1042522) and MDM2 (rs937283) in 307 ESCC patients and 311 healthy controls were genotyped. The presence or absence of HPV16 in serum was measured by enzyme-linked immunosorbent assay. Multivariable logistic regression analysis was used to evaluate the possible associations of p53 and MDM2 polymorphisms with ESCC risk stratified by HPV16 sero-status.ResultsPatients carrying p53 Arg/Arg or Arg/Pro had a higher risk of esophageal SCC (P < 0.001, Odds ratio [OR] 4.98, 95% confidential interval [CI] 3.46–7.17), however, not found in MDM2 rs937283. The risk of esophageal SCC increased significantly among patients carrying p53 Arg/Arg, or Arg/Pro and HPV16-seropositivity (P < 0.001, OR 9.33, 95% CI 5.44–16.0), but not for MDM2 rs937283. The risk of esophageal SCC was further elevated among patients carrying Arg/Arg or Arg/Pro and HPV16-seropositivity who were smokers (P < 0.001, OR 27.05, 95% CI 11.06–66.16) or drinkers (P < 0.001, OR 13.20, 95% CI 5.74–30.38).ConclusionHPV16 seropositivity synergized with p53 Arg/Arg or Arg/Pro and increased ESCC risk, especially in smokers or drinkers.     

Number of rare germline CNVs and <Emphasis Type="Italic">TP53</Emphasis> mutation types

Background

The Li-Fraumeni syndrome (LFS), an inherited rare cancer predisposition syndrome characterized by a variety of early-onset tumors, is caused by different highly penetrant germline mutations in the TP53 gene; each separate mutation has dissimilar functional and phenotypic effects, which partially clarifies the reported heterogeneity between LFS families. Increases in copy number variation (CNV) have been reported in TP53 mutated individuals, and are also postulated to contribute to LFS phenotypic variability. The Brazilian p.R337H TP53 mutation has particular functional and regulatory properties that differ from most other common LFS TP53 mutations, by conferring a strikingly milder phenotype.

Methods

We compared the CNV profiles of controls, and LFS individuals carrying either p.R337H or DNA binding domain (DBD) TP53 mutations by high resolution array-CGH.

Results

Although we did not find any significant difference in the frequency of CNVs between LFS patients and controls, our data indicated an increased proportion of rare CNVs per genome in patients carrying DBD mutations compared to both controls (p=0.0002***) and p.R337H (0.0156*) mutants.

Conclusions

The larger accumulation of rare CNVs in DBD mutants may contribute to the reported anticipation and severity of the syndrome; likewise the fact that p.R337H individuals do not present the same magnitude of rare CNV accumulation may also explain the maintenance of this mutation at relatively high frequency in some populations.

     

De Novo Nonsense Mutations in KAT6A,a Lysine Acetyl-Transferase Gene,Cause a Syndrome Including Microcephaly and Global Developmental Delay

Chromatin remodeling through histone acetyltransferase (HAT) and histone deactylase (HDAC) enzymes affects fundamental cellular processes including the cell-cycle, cell differentiation, metabolism, and apoptosis. Nonsense mutations in genes that are involved in histone acetylation and deacetylation result in multiple congenital anomalies with most individuals displaying significant developmental delay, microcephaly and dysmorphism. Here, we report a syndrome caused by de novo heterozygous nonsense mutations in KAT6A (a.k.a., MOZ, MYST3) identified by clinical exome sequencing (CES) in four independent families. The same de novo nonsense mutation (c.3385C>T [p.Arg1129^∗]) was observed in three individuals, and the fourth individual had a nearby de novo nonsense mutation (c.3070C>T [p.Arg1024^∗]). Neither of these variants was present in 1,815 in-house exomes or in public databases. Common features among all four probands include primary microcephaly, global developmental delay including profound speech delay, and craniofacial dysmorphism, as well as more varied features such as feeding difficulties, cardiac defects, and ocular anomalies. We further demonstrate that KAT6A mutations result in dysregulation of H3K9 and H3K18 acetylation and altered P53 signaling. Through histone and non-histone acetylation, KAT6A affects multiple cellular processes and illustrates the complex role of acetylation in regulating development and disease.     

Calix[4]arene C-90 selectively inhibits Ca2+,Mg2+-ATPase of myometrium cell plasma membrane

The supramolecular compound calix[4]arene C-90 (5,11,17,23-tetra(trifluoro)methyl(phenylsulfonylimino)-methylamino-25,26,27,28-tetrapropoxycalix[4]arene) is shown to efficiently inhibit the ATP hydrolase activity of Ca²⁺,Mg²⁺-ATPase in the myometrium cell plasma membrane fraction and also in a preparation of the purified enzyme solubilized from this subcellular fraction. The inhibition coefficient I _0.5 values were 20.2 ± 0.5 and 58.5 ± 6.4 μM for the membrane fraction and the solubilized enzyme, respectively. The inhibitory effect of calix[4]arene C-90 was selective comparatively to other ATPases localized in the plasma membrane: calix[4]arene C-90 did not influence the activities of Na⁺,K⁺-ATPase and “basal” Mg²⁺-ATPase. The inhibitory effect of calix[4]arene C-90 on the Ca²⁺,Mg²⁺-ATPase activity was associated with the cooperative action of four trifluoromethylphenyl sulfonylimine (sulfonylamidine) groups oriented similarly on the upper rim of the calix[4]arene macrocycle (the calix[4]arene “bowl”). The experimental findings seem to be of importance for studies, using calix[4]arene C-90, of membrane mechanisms of regulation of calcium homeostasis in smooth muscle cells and also for investigation of the participation of the plasma membrane Ca²⁺-pump in control of electro- and pharmacomechanical coupling in myocytes.     

Proteasome Control of [URE3] Prion Propagation by Degradation of Anti-Prion Proteins Cur1 and Btn2 in Saccharomyces cerevisiae

[URE3] is a prion of the nitrogen catabolism controller, Ure2p, and [PSI+] is a prion of the translation termination factor Sup35p in S. cerevisiae. Btn2p cures [URE3] by sequestration of Ure2p amyloid filaments. Cur1p, paralogous to Btn2p, also cures [URE3], but by a different (unknown) mechanism. We find that an array of mutations impairing proteasome assembly or MG132 inhibition of proteasome activity result in loss of [URE3]. In proportion to their prion—curing effects, each mutation affecting proteasomes elevates the cellular concentration of the anti-prion proteins Btn2 and Cur1. Of >4,600 proteins detected by SILAC, Btn2p was easily the most overexpressed in a pre9Δ (α3 core subunit) strain. Indeed, deletion of BTN2 and CUR1 prevents the prion—curing effects of proteasome impairment. Surprisingly, the 15 most unstable yeast proteins are not increased in pre9Δ cells suggesting altered proteasome specificity rather than simple inactivation. Hsp42, a chaperone that cooperates with Btn2 and Cur1 in curing [URE3], is also necessary for the curing produced by proteasome defects, although Hsp42p levels are not substantially altered by a proteasome defect. We find that pre9Δ and proteasome chaperone mutants that most efficiently lose [URE3], do not destabilize [PSI+] or alter cellular levels of Sup35p. A tof2 mutation or deletion likewise destabilizes [URE3], and elevates Btn2p, suggesting that Tof2p deficiency inactivates proteasomes. We suggest that when proteasomes are saturated with denatured/misfolded proteins, their reduced degradation of Btn2p and Cur1p automatically upregulates these aggregate-handling systems to assist in the clean-up.     

R516Q mutation in Melanoma differentiation-associated protein 5 (MDA5) and its pathogenic role towards rare Singleton-Merten syndrome; a signature associated molecular dynamics study

Singleton-Merten syndrome, a critical and rare multifactorial disorder that is closely linked to R516Q mutation in MDA5 protein associated with an enhanced interferon response in the affected individual. In the present study, we provide conclusive key evidence on R516Q mutation and their connectivity towards sequence-structural basis dysfunction of MDA5 protein. Among the various mutations, we found R516Q is the most pathogenic mutation based on mutational signature Q-A-[RE]-G-R-[GA]-R-A-[ED]-[DE]-S-[ST]-Y-[TSAV]-L-V designed from our work. Further, we derived a distant ortholog for this mutational signature from which we identified 343 intra-residue interactions that fall communally in the position required to maintain the structural and functional integration of protein architecture. This identification served us to understand the critical role of hot spots in residual aggregation that holds a native form of folding conformation in the functional region. In addition, the long-range molecular dynamics simulation demarcated the residual dependencies of conformational transition in distinct regions (_L29360–370_α18, _α19380–410_L31, _α21430–480_L33-α22-L35 and _α24510–520_L38) occurring upon R516Q mutation. Together, our results emphasise that the dislocation of functional hot spots Pro229, Arg414, Val498, Met510, Ala513, Gly515 and Arg516 in MDA5 protein which is important for interior structural packing and fold arrangements. In a nutshell, our findings are perfectly conceded with other experimental reports and will have potential implications in immune therapeutical advancement for rare singleton-merten syndrome.     

Clinical Evaluation of BRCA1/2 Mutation in Mexican Ovarian Cancer Patients

Ovarian cancer (OC) is an important cause of gynecologic cancer-related deaths. In Mexico, around 4700 new cases of OC are diagnosed per year and it represents the second cause of gynecological cancer mortality with more than 2700 deaths. Germline mutations in BRCA1/2 genes are present in 13–18% of OC cases. Few studies have evaluated the presence of mutations in BRCA genes in a population of OC Mexican patients and their relationship with clinical response and survival rates.A total of 179 OC patients were studied by molecular testing for BRCA1/2 through next-generation sequencing and multiplex ligation-dependent probe amplification. Recurrence-free survival (RFS) was estimated by the Kaplan–Meier method. BRCA mutation was detected in 33% of patients. A percentage of 66.1% were BRCA1 mutated and 33.9% were BRCA2 mutated. BRCA1 mutation carriers had a worst RFS compared with BRCA2 mutation carriers (37.6 [29–46.2] vs 72.7 [38.4–107.2]; P = 0.030). The most common mutation for BRCA1 was ex9-12del (28.2%) (Mexican founder mutation). The Mexican founder mutation had a better RFS than other BRCA1 mutations (86.1 [37.2–135.1] vs 34.5 [20.7–48.2]; P = 0.033). The presence of BRCA2 mutations in the ovarian cancer cluster region (OCCR) had a significantly better RFS than mutations in breast cancer cluster regions (BCCR) and not-related risk region (NRR) (NR vs 72.8 [39–106.6] vs 25.8 [8.3–43.2]; P = 0.013). These results demonstrate that the prevalence of BRCA1/2 positive patients in OC Mexican patients are the highest reported. Patients with mutations in BRCA2 have a better prognosis than those mutated in BRCA1. The Mexican founder mutation has an important role in clinical outcomes. These results highlight the importance to test all the HGSP (high-grade serous papillary) OC patients with or without cancer family history (CFH) in Mexican population.     

Expression of a Homeostatic Regulator, Wip1 (Wild-type p53-induced Phosphatase), Is Temporally Induced by c-Jun and p53 in Response to UV Irradiation

Wild-type p53-induced phosphatase (Wip1) is induced by p53 in response to stress, which results in the dephosphorylation of proteins (i.e. p38 MAPK, p53, and uracil DNA glycosylase) involved in DNA repair and cell cycle checkpoint pathways. p38 MAPK-p53 signaling is a unique way to induce Wip1 in response to stress. Here, we show that c-Jun directly binds to and activates the Wip1 promoter in response to UV irradiation. The binding of p53 to the promoter occurs earlier than that of c-Jun. In experiments, mutation of the p53 response element (p53RE) or c-Jun consensus sites reduced promoter activity in both non-stressed and stressed A549 cells. Overexpression of p53 significantly decreased Wip1 expression in HCT116 p53^+/+ cells but increased it in HCT116 p53^−/− cells. Adenovirus-mediated p53 overexpression greatly decreased JNK activity. Up-regulation of Wip1 via the p38 MAPK-p53 and JNK-c-Jun pathways is specific, as demonstrated by our findings that p38 MAPK and JNK inhibitors affected the expression of the Wip1 protein, whereas an ERK inhibitor did not. c-Jun activation occurred much more quickly, and to a greater extent, in A549-E6 cells than in A549 cells, with delayed but fully induced Wip1 expression. These data indicate that Wip1 is activated via both the JNK-c-Jun and p38 MAPK-p53 signaling pathways and that temporal induction of Wip1 depends largely on the balance between c-Jun and p53, which compete for JNK binding. Moreover, our results suggest that JNK-c-Jun-mediated Wip1 induction could serve as a major signaling pathway in human tumors in response to frequent p53 mutation.