Cytoplasmic p21 is a potential predictor for cisplatin sensitivity in ovarian cancer

Abstract

BackgroundP21(WAF1/Cip1) binds to cyclin-dependent kinase complexes and inhibits their activities. It was originally described as an inhibitor of cancer cell proliferation. However, many recent studies have shown that p21 promotes tumor progression when accumulated in the cell cytoplasm. So far, little is known about the correlation between cytoplasmic p21 and drug resistance. This study was aimed to investigate the role of p21 in the cisplatin resistance of ovarian cancer.MethodsRT-PCR, western blot and immunofluorescence were used to detect p21 expression and location in cisplatin-resistant ovarian cancer cell line C13* and its parental line OV2008. Regulation of cytoplasmic p21 was performed through transfection of p21 siRNA, Akt2 shRNA and Akt2 constitutively active vector in the two cell lines; their effects on cisplatin-induced apoptosis were evaluated by flow cytometry. Tumor tissue sections of clinical samples were analyzed by immunohistochemistry.Resultsp21 predominantly localizes to the cytoplasm in C13* compared to OV2008. Persistent exposure to low dose cisplatin in OV2008 leads to p21 translocation from nuclear to cytoplasm, while it had not impact on p21 localization in C13*. Knockdown of cytoplasmic p21 by p21 siRNA transfection in C13* notably increased cisplatin-induced apoptosis through activation of caspase 3. Inhibition of p21 translocation into the cytoplasm by transfection of Akt2 shRNA into C13* cells significantly increased cisplatin-induced apoptosis, while induction of p21 translocation into the cytoplasm by transfection of constitutively active Akt2 in OV2008 enhanced the resistance to cisplatin. Immunohistochemical analysis of clinical ovarian tumor tissues demonstrated that cytoplasmic p21 was negatively correlated with the response to cisplatin based treatment.ConclusionsCytoplasmic p21 is a novel biomarker of cisplatin resistance and it may represent a potential therapeutic target for ovarian tumors that are refractory to conventional treatment.

Adenovirus type 12 E1B 55-kilodalton oncoprotein promotes p53-mediated apoptotic response of ovarian cancer to cisplatin

“…P21 binds and inhibits the function of cellular cyclin-dependent kinase and proliferating cell nuclear antigen, thereby inhibiting their function and leading to cell cycle arrest, leading to blockade of DNA synthesis and inhibition of cell proliferation [26,27]. Recent study had also shown the involvement of p21 in drug resistance of human cancers [28]. In this study, we also found that changes in mRNA and protein expressions of Bax, p21, and Mdm2 in cisplatin-resistant and cisplatin-sensitive ovarian cancer, respectively, compared with their pericarcinous tissues.…”

Less understood issues: p21Cip1 in mitosis and its therapeutic potential

“…[168][169][170][171] The oncogenic potential of p21 raises the concept of its silencing, 99,153 specifically targeting increased cytoplasmic-localized p21. 172,173 Several small-molecule inhibitors against p21 have been identified and investigated: 163 butyrolactone, 174 LLW10, 175 sorafenib 176 and UC2288. 90,163 They showed some effects, yet unspecific.…”

Resistance and gain-of-resistance phenotypes in cancers harboring wild-type p53

“…A case in point is where p53 is functional and transactivates p21, but this Cdk inhibitor becomes inactivated through cytoplasmic sequestration after Akt-mediated phosphorylation, leading to resistance of testicular and ovarian cancers to antitumor agents such as cisplatin [60,61]. In this case, a possible mechanism for the resistance is the binding of phosphorylated form of p21 in the cytoplasm to procaspase-3, preventing its conversion to caspase-3 and thereby blocking apoptosis [62].…”