Mutations of phosphorylation sites Ser10 and Thr187 of p27Kip1 abolish cytoplasmic redistribution but do not abrogate G0/1 phase arrest in the HepG2 cell line

High Expression of miR-196b Predicts Poor Prognosis in Patients with Ovarian Cancer

Background/Aims

To analyze the clinical significance of miR-196b expression in ovarian cancer and predict the function and possible mechanism of miR-196b.

Methods

Both Kaplan–Meier (K-M) and Cox proportional hazards regression model were used to analyze the prognostic factors of patients with ovarian cancer. MiR196-b was modulated in ovarian cancer cells, and the cell viability, cell cycle, and cell cycle-related gene expression were analyzed. The target genes of miR-196b were then predicted and checked the relationship between the target genes.

Results

MiR-196b was an independent risk factor, while high expression of miR-196b was associated with poor prognosis of ovarian cancer. MiR-196b overexpression increased cancer cell proliferation. Cdkn1b, as one of the targets of miR-196b, was related to cell viability and mitosis.

Conclusion

High expression of miR-196b was significantly associated with poor prognosis of the patients with ovarian cancer. MiR-196b could increase the cell proliferation of ovarian cancer by modulating Cdkn1b expression.

Hypoxia inducible prolyl hydroxylase PHD3 maintains carcinoma cell growth by decreasing the stability of p27

Background

Hypoxia can halt cell cycle progression of several cell types at the G1/S interface. The arrest needs to be overcome by cancer cells. We have previously shown that the hypoxia-inducible cellular oxygen sensor PHD3/EGLN3 enhances hypoxic cell cycle entry at the G1/S boundary.

Methods

We used PHD3 knockdown by siRNA and shRNA in HeLa and 786–0 renal cancer cells. Flow cytometry with cell synchronization was used to study cell growth at different cell cycle phases. Total and phosphospecific antibodies together with cycloheximide chase were used to study p27/CDKN1B expression and fractionations for subcellular protein localization.

Results

Here we show that PHD3 enhances cell cycle by decreasing the expression of the CDK inhibitor p27/CDKN1B. PHD3 reduction led to increased p27 expression under hypoxia or VHL mutation. p27 was both required and sufficient for the PHD3 knockdown induced cell cycle block. PHD3 knockdown did not affect p27 transcription and the effect was HIF-independent. In contrast, PHD3 depletion increased the p27 half-life from G0 to S-phase. PHD3 depletion led to an increase in p27 phosphorylation at serine 10 without affecting threonine phosphorylation. Intact serine 10 was required for normal hypoxic and PHD3-mediated degradation of p27.

Conclusions

The data demonstrates that PHD3 can drive cell cycle entry at the G1/S transition through decreasing the half-life of p27 that occurs by attenuating p27S10 phosphorylation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0410-5) contains supplementary material, which is available to authorized users.

Correlations of common polymorphism of EVI-1 gene targeted by miRNA-206/133b with the pathogenesis of breast cancer

The aim of this study was to identify the correlations of a common polymorphism (rs6774494 A > G) in the EVI-1 gene targeted by micro-RNA (miRNA)-206/133b with the pathogenesis of breast cancer (BC). A total of 196 unrelated ethnic Han Chinese women diagnosed with primary BC were consecutively recruited and 200 healthy controls were randomly selected from the same population-based cohort. Direct PCR sequencing assay was used to detection of rs6774494 A > G polymorphism in the EVI-1 gene. Real-time quantitative PCR (RT-PCR) analysis was performed to verify the alterations of the EVI1 messenger RNA (mRNA) levels. Kaplan-Meier analysis was used to investigate and to estimate the survival outcomes for each endpoint. All statistical analyses were performed with SPSS software (version 18.0, SPSS, Chicago, IL). Our results demonstrated that the carriers of EVI-1 AG genotype were more likely to develop BC when compared with the EVI-1 GG genotype (P = 0.034, OR = 1.26, 95% CI = 1.02 ∼ 1.57). In addition, it was found that patients with the G (AG + GG) allele of EVI-1 genetic variants were associated with higher risk of BC compared with the EVI-1 AA genotype (OR = 1.26, 95% CI = 1.02 ∼ 1.54, P = 0.028). The results of a subgroup analysis stratified by menopause revealed that in female post-menopause subgroup patients with the EVI-1 G allele were correlated with a higher risk of BC than those with the EVI-1 AA genotype (OR = 1.31, 95% CI = 1.00 ∼ 1.72, P = 0.054). Kaplan-Meier analyses suggested that carriers of the G allele (AG + GG) were associated with poorer overall survival (OS) and progression-free survival (PFS) compared with those with AA genotype (OS P = 0.042; PFS P = 0.036, respectively). The correlation analysis showed that EVI-1 mRNA levels were negatively associated with miRNA-206/133b levels in the carriers of the G allele (AG + GG) (r = -1.274, P < 0.05). Our findings provide evidence that the EVI-1 rs6774494 G > A polymorphism targeted by miRNA-206/133b may contribute to the pathogenesis of BC.

A crosstalk imbalance between p27(Kip1) and its interacting molecules enhances breast carcinogenesis

p27(Kip1) (p27) is an inhibitor of cyclin/cyclin-dependent kinase complexes, the nuclear loss of which indicates poor prognoses in various solid tumors. In breast cancer cells, the p27 expression level usually decreases during tumor development and progression. In addition, p27 cytoplasmic mislocalization has been reported, but the exact molecular mechanisms remain unclear. Studies have indicated that its phosphorylation status is the key regulator and that several signal transduction pathways are involved in the regulation of both the expression and distribution of p27. To further understand the signals involved, the differences in the profiles of interacting proteins between tumor and normal cells should be elucidated. It is well known that p27 has various interacting partners, such as cyclin, cyclin-depend kinases, CRM1, Jab1, SKP2, and Spy1. Assays used to profile these proteins show differing intracellular p27 expression and localization depending on the cell-cycle phase. We hypothesize that the imbalance of crosstalk between p27 and the other molecules involved in the same signaling pathways plays an indispensable role in breast cancer carcinogenesis.

Variation of gene expression profile linked to p27 (Kip1) Ser(10) phosphorylation status in MCF-7 cell line

Ser(10) was the major phosphorylation site in p27(Kip1) (here after referred to as p27), accounting for 70% of the total phosphorylation of this protein, due to cytoplasmic shuttling. To further elucidate the mechanism for Ser(10)-mediated dysfunction of p27 during breast cancer progression. Affymetrix Human Genome U133A Array was used to identify differentially regulated genes between MCF-7 breast cancer cell lines stably-transfected with wild type and Ser(10) mutant (substitution of Ser(10) with Ala, S10A), alternatively. Then to confirm by RT-PCR then western blot partly. Microarray analysis showing that S10A, then abrogation of Ser(10) phosphorylation, result in important changes in a large number of genes involved in the control of cell cycle, cell differentiation, metabolism, immune response and signal transduction. S10A induced cell cycle G(0) phase arrest by FACS method. And cell growth inhibition and abrogation of cytoplasmic translation. Our data indicate that abrogation of phosphorylation of Ser(10) resulted in significant changes in gene expression profiles which mediate cell cycle redistribution, sub-cellular localization.

CaMKII phosphorylates serine 10 of p27 and confers apoptosis resistance to HeLa cells

Protein phosphatase (PP) 6 is a serine threonine phosphatase which belongs to the PP2A subfamily of protein phosphatases. PP6 has been implicated in the control of apoptosis. A dominant negative form PP6 (DN-PP6) mutant cDNA was prepared and transfected into HeLa cells to investigate the regulation of apoptosis. HeLa cells expressing DN-PP6 showed increased resistance to apoptosis induced by TNF and cycloheximide. CaMKII phosphorylation and the expression of p27 were increased in DN-PP6 transfectants. Transient expression or activation of CaMKII increased the expression of p27. Furthermore, CaMKII phosphorylated serine 10 of p27, which induces the translocation of p27 from nucleus to cytoplasm and increases the stability of p27. Overexpression of wild type but not the S10A mutant p27 cDNA increased the expression of Bcl-xL and conferred apoptosis resistance to HeLa cells. These results indicated that PP6 and CaMKII regulated apoptosis by controlling the expression level of p27.

Expression of CRM1 in human gliomas and its significance in p27 expression and clinical prognosis

OBJECTIVE

Gliomas are the most common type of primary intracranial tumor. Although tumor grade predicts the clinical course of most patients, molecular characteristics of individual tumors have emerged as important prognostic factors for patients with gliomas. Reduced expression of p27 protein is known as an independent prognostic marker in a large variety of cancers and is associated with an unfavorable prognosis. It is believed that phosphorylation of p27 on Ser10 has been shown to be required for the binding of CRM1, a carrier protein for nuclear export. This study assessed whether CRM1, Ser10-phosphorylated p27, and p27 correlated with each other, with glioma pathological stage, and with patient outcome.

METHODS

Immunohistochemical and Western blot analysis were performed in 70 cases of human gliomas and normal brain tissues. Survival analyses were performed using the Kaplan-Meier method.

RESULTS

High CRM1 expression (80% of cancer cell nuclei stained) was observed in 70 specimens and was related to the grade of malignancy. A strong inverse correlation was evident between p27 levels and both Ser10-phosphorylated p27 (P < 0.001) and CRM1 level (P < 0.001). We also reviewed each grade of tumors separately and investigated whether CRM1 expression predicted patient survival within each subgroup. In brief, CRM1 overexpression was significantly associated with overall survival (P < 0.001).

CONCLUSION

The current results showed that CRM1 and p27 expression were associated with glioma grade and that high CRM1 protein expression might be related to poor outcome.

Protein profiling: a possible molecular mechanism to mislocalization and down-expression of p27(Kip1) in tumor cells

p27(Kip1) (here after referred to as p27) is a member of a family of cyclin-dependent kinase inhibitors that control cell cycle. There is a considerable evidence that p27 plays a pivotal role in multiple foundational cellular processes, including cell proliferation, cell differentiation, and apoptosis. A large number of studies have characterized p27 as an independent prognostic factor in various human cancers and as a target for cancer therapeutics. The function of p27 is regulated by changes in its intracellular concentration as well as in its sub-cellular localization in the cell. Many tumor cells show p27 down-regulated or no detectable expression, p27 might act as an adverse prognostic marker for various types of cancers. Until recently, displacement of p27 into the cytoplasm has been identified as a mechanism of which cancer cells promote cancerogenesis in human. But much less is known about the molecular mechanisms of its abnormal expression and mislocalization in tumor cell. p27 protein has various interacting molecules. The different formation of p27 complexes maybe cause disregulation of p27 expression and localization in human cancer. We hypothesize here that different interacting protein profile may be a fundamentional step for the abnormal expression and cytoplasmic localization in tumor cells.