The dichotomy of p53 regulation by noncoding RNAs

The p53 tumor suppressor gene is the most frequently mutated gene in cancer. Significant progress has been made to discern the im- portance of p53 in coordinating cellular responses to DNA damage, oncogene activation, and other stresses. Noncoding RNAs are RNA molecules functioning without being translated into proteins. In this work, we discuss the dichotomy of p53 regulation by noncoding RNAs with four unconventional questions. First, is overexpression of microRNAs responsible for p53 inactivation in the absence of p53 mutation？ Second, are there somatic mutations in the noncoding regions of the p53 gene？ Third, is there a germline mutant in the non- coding regions of the p53 gene that predisposes carriers to cancer？ Fourth, can p53 activation mediated by a noncoding RNA mutation cause cancer？ This work highUghts the prominence of noncoding RNAs in p53 dysregutation and tumorigenesis.     

Role ofthe IncRNA-p53 regulatory network in cancer

Advances in functional genomics have led to discovery of a large group of previous uncharacterized long non-coding RNAs （IncRNAs）. Emerging evidence indicates that IncRNAs may serve as master gene regulators through various mechanisms. Dysregulation of IncRNAs is often associated with a variety of human diseases including cancer. Of significant interest, recent studies suggest that IncRNAs participate in the p53 tumor suppressor regulatory network. In this review, we discuss how IncRNAs serve as p53 regulators or p53 effectors. Further characterization of these p53-associated IncRNAs in cancer will provide a better understanding of lncRNA- mediated gene regulation in the p53 pathway. As a result, IncRNAs may prove to be valuable biomarkers for cancer diagnosis or poten- tial targets for cancer therapy.     

In situ quantification of aberrant p53 in colorectal neoplasia

Aberrant p53 protein accumulation was measured immunohistologically in 342 colorectal paraffin-embedded tissue sections from 115 patients (24 with adenocarcinoma, 59 with adenoma and 32 'hospital controls'). Subjective scoring was compared with quantitative cell imaging, including dichotomous (p53⁺/p53^-) status, ng p53^mut mg^-1 enterocyte protein, and tumour burden and patient body 'burden' of aberrant p53. A total of 62.5% cancer patients, 23.7% adenoma patients and 3.1% hospital controls were accorded p53⁺ status on the basis of p53 quantification. Quantitative p53⁺/p53^- assignment had a stronger inverse association with survival (χ²=6.17, p=0.013, Kaplan-Meier test) than subjective 'visual estimation' (χ²=0.57, p=0.449). There was a strong inverse relationship between the p53 'body burden' and the months of post-diagnosis survival (hazard ratio=1.42, p=0.0004, Cox proportional hazards). Absolute quantification for inactivated p53 permits objective and reproducible scoring, adjusts for intra-laboratory immunostaining 'batch effects', corrects for fixation artefacts, and standardizes for inter-laboratory differences in fixation, antibody selection and staining method. Clinically, in situ quantification of p53 will permit more accurate survival prognoses and will inform therapy selection and dose. Ultimately, accurate quantitative tissue/blood p53 correlations may provide a minimally invasive and systemic surrogate measure for these same clinical purposes.     

Reversible acetylation regulates vascular endothelial growth factor receptor-2 activity

The tyrosine kinase receptor vascular endothelial growth factor receptor 2 （VEG FR2） is a key regulator of angiogenesis. Here we show that VEGFR2 is acetylated in endothelial cells both at four lysine residues forming a dense cluster in the kinase insert domain and at a single lysine located in the receptor activation loop. These modifications are under dynamic control of the acetyltransferase p300 and two deacetyiases HDAC5 and HDAC6. We demonstrate that VEGFR2 acetylation essentially regulates receptor phosphorylation. In par- ticular, VEGFR2 acetylation significantly alters the kinetics of receptor phosphorylation after ligand binding, allowing receptor phos- phoryiation and intraceUular signaling upon proLonged stimulation with VEGF. Molecular dynamics simulations indicate that acetylation of the lysine in the activation loop contributes to the transition to an open active state, in which tyrosine phosphorylation is favored by better exposure of the kinase target residues. These findings indicate that post-translational modification by acetyiation is a critical mechanism that directLy affects VEGFR2 function.     

Skeletal muscle myogenesis is regulated by G protein-coupled receptor kinase 2

G protein-coupled receptor kinase 2 （GRK2） is an important serine/threonine-kinase regulating different membrane receptors and intraceUular proteins. Attenuation of Drosophila Gprk2 in embryos or adult flies induced a defective differentiation of somatic muscles, loss of fibers, and a flightless phenotype. In vertebrates, GRK2 hemizygous mice contained less but more hypertrophied skeletal muscle fibers than wild-type littermates. In C2C12 myoblasts, overexpression of a GRK2 kinase-deficient mutant （K220R） caused precocious differentiation of ceUs into immature myotubes, which were wider in size and contained more fused nuclei, while GRK2 overexpression blunted differentiation. Moreover, p38MAPK and Akt pathways were activated at an earlier stage and to a greater extent in K220R-expressing cells or upon kinase downregulation, while the activation of both kinases was impaired in GRK2-overexpressing cells. The impaired differentiation and fewer fusion events promoted by enhanced GRK2 levels were recapitulated by a p38MAPK mutant, which was able to mimic the inhibitory phosphorylation of p38MAPK by GRK2, whereas the blunted differentiation observed in GRK2-expressing clones was rescued in the presence of a constitutively active upstream stimulator of the p38MAPK pathway. These results suggest that balanced GRK2 function is necessary for a timely and complete myogenic process.     

CD4+ T cell responses to self- and mutated p53 determinants during tumorigenesis in mice

We analyzed CD4+ T helper responses to wild-type (wt) and mutated (mut) p53 protein in normal and tumor-bearing mice. In normal mice, we observed that although some self-p53 determinants induced negative selection of p53-reactive CD4+ T cells, other p53 determinants (cryptic) were immunogenic. Next, BALB/c mice were inoculated with J774 syngeneic tumor cell line expressing mut p53. BALB/c tumor-bearing mice mounted potent CD4+ T cell responses to two formerly cryptic peptides on self-p53. This response was characterized by massive production of IL-5, a Th2-type lymphokine. Interestingly, we found that T cell response was induced by different p53 peptides depending upon the stage of cancer. Mut p53 gene was shown to contain a single mutation resulting in the substitution of a tyrosine by a histidine at position 231 of the protein. Two peptides corresponding to wt and mutated sequences of this region were synthesized. Both peptides bound to the MHC class II-presenting molecule (Ed) with similar affinities. However, only mut p53.225-239 induced T cell responses in normal BALB/c mice, a result strongly suggesting that high-affinity wt p53.225-239 autoreactive T cells had been eliminated in these mice. Surprisingly, CD4+ T cell responses to both mut and wt p53.225-239 peptides were recorded in J774 tumor-bearing mice, a phenomenon attributed to the recruitment of low-avidity p53.225-239 self-reactive T cells.     

Fucoxanthin induces growth arrest and apoptosis in human bladder cancer T24 cells by up-regulation of p21 and down-regulation of mortalin

Fucoxanthin, a natural carotenoid, has been reported to have anti-cancer activity in human colon cancer cells, human prostate cancer cells, human leukemia cells, and human epithelial cervical cancer cells. This study was undertaken to evaluate the molecular mechanisms of fuco- xanthin against human bladder cancer T24 cell line. MTT analysis results showed that 5 and 10 ixM fucoxanthin inhibited the proliferation of T24 cells in a dose- and time- dependent manner accompanied by the growth arrest at Go/G1 phase of cell cycle, which is mediated by the up-regu- lation of p21, a cyclin-dependent kinase （CDK）-inhibitory protein and the down-regulation of CDK-2, CDK-4, cyclin D1, and cyclin E. In addition, 20 and 40 μM fucoxanthin induced apoptosis of T24 cells by the abrogation of morta- lin-p53 complex and the reactivation of nuclear mutant- type p53, which also had tumor suppressor function as wild-type p53. All these results demonstrated that the anti- cancer activity of fucoxanthin on T24 cells was associated with cell cycle arrest at Go/G1 phase by up-regulation of p21 at low doses and apoptosis via decrease in the expres- sion level of mortalin, which is a stress regulator and a mem- ber of heat shock protein 70, followed by up-regulation of cleaved caspase-3 at high doses.     

p53 expression in leukoplakia and carcinoma of the tongue

There is growing interest in assessing multistep carcinogenesis and predicting its course using different molecular markers. TP53 is a tumor suppressor gene and appears to be one of the molecular targets of tobacco-related carcinogens in oral cancer. The present study evaluated the role of p53 expression in patients with leukoplakia and carcinoma of the tongue. p53 expression was studied by immunohistochemistry. All patients with leukoplakia of the tongue were male tobacco users. Nuclear staining of p53 was observed in 79% of those patients. Fifty percent, 25% and 4% of the patients expressed 1+, 2+ and 3+ nuclear staining, respectively. When leukoplakia patients were graded according to histopathology, 67% had hyperplasia and 33% had dysplasia. Nuclear p53 accumulation was 88% in hyperplasia and 62% in dysplasia. In patients with tongue cancer, nuclear accumulation of p53 was seen in only 19% of the tumors, with a staining intensity of 1+ in 13%, 2+ in 2% and 3+ in 4% of the tumors. The prevalence of nuclear p53 positivity (79%) was significantly higher in patients with leukoplakia than in patients with tongue cancer (19%; chi2 = 34.32, r = -0.45, df = 1, p = 0.0001; odds ratio (OR) = 16.66, 95% CI, 5.25-52.86). Therefore, leukoplakia patients who show p53 expression have a higher risk of developing tongue cancer than those who do not show p53 expression. As the percentage of positivity of nuclear p53 was very low, none of the clinicopathological parameters or disease status showed any significant association with it. The interesting finding is that none of the female cancer patients showed nuclear p53 expression. Therefore, p53 accumulation is believed to be an early event in neoplastic progression of the tongue.     

Prostaglandin E2 stimulates p53 transactivational activity through specific serine 15 phosphorylation in human synovial fibroblasts. Role in suppression of c/EBP/NF-kappaB-mediated MEKK1-induced MMP-1 expression

Cyclooxygenase-2 (COX-2) overexpression has been linked to cell survival, transformation, and hyperproliferation. We examined the regulation of the tumor suppressor gene p53 and p53 target genes by prostaglandin E(2) (PGE(2)) in human synovial fibroblasts (HSF). PGE(2) induced a time-dependent increase in p53 Ser(15) phosphorylation, with no discernible change in overall p53 levels. PGE(2)-dependent Ser(15) phosphorylation was apparently mediated by activated p38 MAP kinase as SB202190, a p38 kinase inhibitor, blocked the response. Overexpression of a MKK3 construct, but not MKK1, stimulated SB202190-sensitive p53 Ser(15) phosphorylation. PGE(2)-stimulated [phospho-Ser(15)]p53 transactivated a p53 response element (GADD45)-luciferase reporter in transiently transfected HSF (SN7); the effect was compromised by overexpression of a dominant-negative mutant (dnm) of p53 or excess p53S15A expression plasmid but mimicked by a constitutively active p53S15E expression construct. PGE(2), wtp53 expression in the presence of PGE(2), and p53S15E suppressed steady-state levels of MEKK1-induced MMP-1 mRNA, effects nullified with co-transfection of p53 dnm or p53S15A. MEKK1-induced MMP-1 promoter-driven luciferase activity was largely dependent on a c/EBPbeta-NF-kappaB-like enhancer site at -2008 to -1972 bp, as judged by deletion and point mutation analyses. PGE(2), overexpression of p53wt with PGE(2), or p53S15E abolished the MEKK1-induced MMP-1 promoter luciferase activity. Gel-shift/super gel-shift analyses identified c/EBPbeta dimers and c/EBPbeta/NF-kappaB p65 heterodimers as binding species at the apparent site of MEKK1-dependent transactivation. PGE(2)-stimulated [phospho-Ser(15)]p53 abrogated the DNA binding of c/EBPbeta dimers and c/EBPbeta/NF-kappaB p65 heterodimers. Our data suggest that COX-2 prostaglandins may be implicated in p53 function and p53 target gene expression.     

In situ quantification of aberrant p53 in colorectal neoplasia.

Aberrant p53 protein accumulation was measured immunohistologically in 342 colorectal paraffin-embedded tissue sections from 115 patients (24 with adenocarcinoma, 59 with adenoma and 32 'hospital controls'). Subjective scoring was compared with quantitative cell imaging, including dichotomous (p53+/p53-) status, ng p53mut mg(-1) enterocyte protein, and tumour burden and patient body 'burden' of aberrant p53. A total of 62.5% cancer patients, 23.7% adenoma patients and 3.1% hospital controls were accorded p53+ status on the basis of p53 quantification. Quantitative p53+/p53- assignment had a stronger inverse association with survival (chi2=6.17, p=0.013, Kaplan-Meier test) than subjective 'visual estimation' (chi2=0.57, p=0.449). There was a strong inverse relationship between the p53 'body burden' and the months of post-diagnosis survival (hazard ratio=1.42, p=0.0004, Cox proportional hazards). Absolute quantification for inactivated p53 permits objective and reproducible scoring, adjusts for intra-laboratory immunostaining 'batch effects', corrects for fixation artefacts, and standardizes for inter-laboratory differences in fixation, antibody selection and staining method. Clinically, in situ quantification of p53 will permit more accurate survival prognoses and will inform therapy selection and dose. Ultimately, accurate quantitative tissue/blood p53 correlations may provide a minimally invasive and systemic surrogate measure for these same clinical purposes.     

“Super p53” Mice Display Retinal Astroglial Changes

Tumour-suppressor genes, such as the p53 gene, produce proteins that inhibit cell division under adverse conditions, as in the case of DNA damage, radiation, hypoxia, or oxidative stress (OS). The p53 gene can arrest proliferation and trigger death by apoptosis subsequent to several factors. In astrocytes, p53 promotes cell-cycle arrest and is involved in oxidative stress-mediated astrocyte cell death. Increasingly, astrocytic p53 is proving fundamental in orchestrating neurodegenerative disease pathogenesis. In terms of ocular disease, p53 may play a role in hypoxia due to ischaemia and may be involved in the retinal response to oxidative stress (OS). We studied the influence of the p53 gene in the structural and quantitative characteristics of astrocytes in the retina. Adult mice of the C57BL/6 strain (12 months old) were distributed into two groups: 1) mice with two extra copies of p53 (“super p53”; n = 6) and 2) wild-type p53 age-matched control, as the control group (WT; n = 6). Retinas from each group were immunohistochemically processed to locate the glial fibrillary acidic protein (GFAP). GFAP+ astrocytes were manually counted and the mean area occupied for one astrocyte was quantified. Retinal-astrocyte distribution followed established patterns; however, morphological changes were seen through the retinas in relation to p53 availability. The mean GFAP+ area occupied by one astrocyte in “super p53” eyes was significantly higher (p<0.05; Student’s t-test) than in the WT. In addition, astroglial density was significantly higher in the “super p53” retinas than in the WT ones, both in the whole-retina (p<0,01 Student’s t-test) and in the intermediate and peripheral concentric areas of the retina (p<0.05 Student’s t-test). This fact might improve the resistance of the retinal cells against OS and its downstream signalling pathways.     

人肝癌细胞基因组中HBV DNA的整合与c-fos、p53基因表达之间的关系

为了探讨HBVDNA、c-fos和p53在肝癌发生中的作用及其关系。利用PCR技术和免疫组化ABC法,检测了肝癌基因组中HBVDNA的整合、c-fos和突变p53的表达。HBVDNA整合率为67%,C-FOS蛋白阳性率为67%,突变P53蛋白阳性率为58%。HBVDNA整合与c-fos激活、p53突变有显著的一致性(P＞0.05;P＞0.05),c-fos激活与p53突变之间呈负相关,但无显著意义(r=-0.2816,P＞0.05)。HBVDNA的整合可能引起c-fos的激活和/或p53的突变,从而导致肝癌的发生。     

Immunohistochemical expression of the p53, mdm2, p21/Waf-1, Rb, p16, Ki67, cyclin D1, cyclin A and cyclin B1 proteins and apoptotic index in T-cell lymphomas

Fifty-seven cases of T-cell lymphomas (TCL) including 5 lymphoblastic (T-LBL) and 52 peripheral TCL (PTCL) were analyzed by immunohistochemistry for the expression of p53, mdm2, p21, Rb, cyclin D1, cyclin A, cyclin B1, and Ki67/MIB1 proteins and 39/52 PTCL were also analyzed for the expression of p16 protein and for the presence of apoptotic cells by the TUNEL method. The aim was to search for abnormal immunoprofiles of p53 and Rb growth control pathways and to determine the proliferative activity and the apoptotic index of TCL. Abnormal overexpression of p53, p21 and mdm2, in comparison to normal lymph nodes, was found in 12/57, 10/57 and 2/57 cases of TCL, respectively. Abnormal loss of Rb and p16 expression was found in 1/57 and 2/39 cases, respectively, whereas abnormal overexpression of cyclin D1 was not detected in any of the 57 cases. Our data revealed entity-related p53/p21/mdm2 phenotypes. Indeed, most nodal and cutaneous CD30+ anaplastic large cell lymphomas (ALCL) showed concomitant overexpression of p53 and p21 proteins (7/8 cases), and mdm2 was overexpressed in 2 p53-positive nodal ALCL. In contrast, overexpression of p53 was found in 3/17 cases of nodal peripheral TCL unspecified (PTCL-UC) and 2/7 non-ALCL cutaneous pleomorphic TCL. Overexpression of p21 protein was detected in 2/3 p53-positive PTCL-UC and in 1/2 p53-positive non-ALCL cutaneous pleomorphic TCL. Finally, all the remaining 25 cases of TCL did not show p53 and p21 overexpression. Overall, the p53+/p21+ phenotype in 10/57 TCL suggests wild-type p53 capable of inducing p21 expression. The highest apoptotic index (AI) was found in ALCL and a positive correlation between apoptotic index and Ki67 index (p<0.001) was detected. Ki67, cyclin A and cyclin B1 expression was found in all 57 TCL and on the basis of the combined use of these 3 variables, 3 groups of proliferative activity could be determined: a) high in ALCL and T-LBL, b) low in mycosis fungoides (MF) and gammadelta hepatosplenic TCL, and c) intermediate in the remaining TCL entities. The proliferative activity in the 12 p53 overexpressing cases was higher in comparison to the 45 p53-negative cases. Ki67 expresion in more than 25% of tumour cells showed significant correlation with p53 overexpression (p<0.001). Rb expression tended to be parallel to Ki67, cyclin A and cyclin B1 expression in all but one case of nodal PTCL-UC which displayed loss of RB expression. Interestingly, this case was p53-negative, whereas the p53-positive cases were Rb-positive. These findings suggest that different pathogenetic routes may function in some TCL, involving either the p53 or, less frequently, the Rb pathways.     

辛伐他汀对大鼠糖尿病所致心肌细胞凋亡的影响及其机制

目的：探讨辛伐他汀对糖尿病所致心肌损伤的保护作用及可能机制。方法：24只SD大鼠（180~220） g随机分为对照组（control组,n=8）和模型组（n=16）,模型组给予链脲佐菌素（STZ）腹腔注射建立糖尿病模型,然后随机将模型组分为糖尿病组（DM组,n=8）和糖尿病+辛伐他汀组（DM+S组,n=8）,DM+S组给予辛伐他汀40 mg/（kg·d）灌胃四周,其余两组给予的等量生理盐水。实验结束后,取心脏,分光光度测定法测定大鼠心肌组织脂质过氧化物丙二醛（MDA）含量、超氧化物歧化酶（SOD）的活性,HE染色观察大鼠心肌病理学改变,TUNEL法检测大鼠心肌细胞凋亡,免疫组织化学法测定大鼠p53的表达;Western blot检测心肌组织p53,p53-phospho-serine15,Bax,Bcl-2等蛋白的表达。结果：①与对照组比较,DM组大鼠心肌组织MDA含量显著升高（P<0.01）,SOD活性明显下降（P<0.01）,与DM组比较,DM+S组大鼠SOD活性显著增加（P<0.01）,MDA含量显著下降（P<0.01）。②HE染色结果表明,与对照组比较,DM组大鼠心肌细胞排列紊乱,结构不清晰,有大量炎性细胞浸润;与DM组比较,DM+S组的心肌细胞结构明显改善。③ TUNEL细胞凋亡检测结果表明,与control组相比,DM组心肌凋亡细胞阳性率显著增加（P<0.01）,给予辛伐他汀后细胞凋亡明显减少（P<0.01）;④免疫组织学检测结果显示,与对照组比较,DM组p53表达量显著增加,且p53在细胞质和细胞核中均有表达（P<0.01）;与DM组比较,DM+S组p53表达量明显下降,p53在细胞质和核中均有表达,但核内表达量减少（P<0.01）。⑤ Western blot检测结果表明,与对照组比较,DM组大鼠p53,p53-Phospho-Serine15,Bax表达量显著升高（P<0.01）,Bcl-2表达量减少（P<0.01）;与DM组比较,DM+S组p53（P<0.01）,p53-Phospho-Serine15（P<0.01）,Bax （P<0.05）表达量显著下降,Bcl-2（P< 0.05）表达量显著增加。结论：辛伐他汀通过改善心肌结构异常、抑制氧化应激和心肌细胞凋亡对糖尿病导致的心肌损伤起到保护作用,其机制与p53介导的细胞凋亡通路相关蛋白的调控有关。     

S100B(betabeta) inhibits the protein kinase C-dependent phosphorylation of a peptide derived from p53 in a Ca2+-dependent manner.

S100B(betabeta) is a dimeric Ca2+-binding protein that is known to inhibit the protein kinase C (PKC)-dependent phosphorylation of several proteins. To further characterize this inhibition, we synthesized peptides based on the PKC phosphorylation domains of p53 (residues 367-388), neuromodulin (residues 37-53), and the regulatory domain of PKC (residues 19-31), and tested them as substrates for PKC. All three peptides were shown to be good substrates for the catalytic domain of PKC. As for full-length p53 (Baudier J, Delphin C, Grunwald D, Khochbin S, Lawrence JJ. 1992. Proc Natl Acad Sci USA 89:11627-11631), S100B(betabeta) binds the p53 peptide and inhibits its PKC-dependent phosphorylation (IC50 = 10 +/- 7 microM) in a Ca2+-dependent manner. Similarly, phosphorylation of the neuromodulin peptide and the PKC regulatory domain peptide were inhibited by S100B(betabeta) in the presence of Ca2+ (IC50 = 17 +/- 5 microM; IC50 = 1 +/- 0.5 microM, respectively). At a minimum, the C-terminal EF-hand Ca2+-binding domain (residues 61-72) of each S100beta subunit must be saturated to inhibit phosphorylation of the p53 peptide as determined by comparing the Ca2+ dependence of inhibition ([Ca]IC50 = 29.3 +/- 17.6 microM) to the dissociation of Ca2+ from the C-terminal EF-hand Ca2+-binding domain of S100B(betabeta).