The cyclin-dependent kinase inhibitor p27(kip1) is a putative tumor suppressor for human cancer. The mechanism underlying p27(kip1) deregulation in human cancer is, however, poorly understood. We demonstrate that the serine/threonine kinase Akt regulates cell proliferation in breast cancer cells by preventing p27(kip1)-mediated growth arrest. Threonine 157 (T157), which maps within the nuclear localization signal of p27(kip1), is a predicted Akt-phosphorylation site. Akt-induced T157 phosphorylation causes retention of p27(kip1) in the cytoplasm, precluding p27(kip1)-induced G1 arrest. Conversely, the p27(kip1)-T157A mutant accumulates in cell nuclei and Akt does not affect p27(kip1)-T157A-mediated cell cycle arrest. Lastly, T157-phosphorylated p27(kip1) accumulates in the cytoplasm of primary human breast cancer cells coincident with Akt activation. Thus, cytoplasmic relocalization of p27(kip1), secondary to Akt-mediated phosphorylation, is a novel mechanism whereby the growth inhibitory properties of p27(kip1) are functionally inactivated and the proliferation of breast cancer cells is sustained.

Epithelial ovarian cancer is the most lethal gynecologic malignancy; it is highly aggressive and causes almost 125,000 deaths yearly. Despite advances in detection and cytotoxic therapies, a low percentage of patients with advanced stage disease survive 5 y after the initial diagnosis. The high mortality of this disease is mainly caused by resistance to the available therapies. Here, we profiled microRNA (miR) expression in serous epithelial ovarian carcinomas to assess the possibility of a miR signature associated with chemoresistance. We analyzed tumor samples from 198 patients (86 patients as a training set and 112 patients as a validation set) for human miRs. A signature of 23 miRs associated with chemoresistance was generated by array analysis in the training set. Quantitative RT-PCR in the validation set confirmed that three miRs (miR-484, -642, and -217) were able to predict chemoresistance of these tumors. Additional analysis of miR-484 revealed that the sensitive phenotype is caused by a modulation of tumor vasculature through the regulation of the VEGFB and VEGFR2 pathways. We present compelling evidence that three miRs can classify the response to chemotherapy of ovarian cancer patients in a large multicenter cohort and that one of these three miRs is involved in the control of tumor angiogenesis, indicating an option in the treatment of these patients. Our results suggest, in fact, that blockage of VEGF through the use of an anti-VEGFA antibody may not be sufficient to improve survival in ovarian cancer patients unless VEGFB signaling is also blocked.

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The beta-thymosins comprise a family of structurally related, highly conserved acidic polypeptides, originally isolated from calf thymus. Recently, we have demonstrated the overexpression of thymosin beta-10 (TB10) in rat thyroid transformed cell lines and in human thyroid carcinoma tissues and cell lines. To verify whether TB10 overexpression is a general event in the process of carcinogenesis, we have analyzed TB10 mRNA levels in human colon carcinomas, germ cell tumors of different histological types, breast carcinomas, ovarian carcinomas, uterine carcinomas, colon and esophageal carcinoma cell lines. Overexpression of the TB10 gene was detected in all of the neoplastic tissues and cell lines compared to the respective normal tissues. Moreover, the mouse model of skin carcinogenesis induced by the combined action of chemical carcinogens and phorbol esters was used to identify the stage of TB10 gene induction. The expression was almost undetectable in normal keratinocytes, its induction occurred even at the papilloma stage, however a further increased expression was observed in the carcinoma derived cell lines. Finally, immunohistochemical analysis of some breast, colon and ovary carcinoma samples by using specific anti-TB10 antibodies revealed the presence of the TB10 protein in all of the neoplastic tissues, but not in the respective normal tissues. Therefore the TB10 detection may be considered a potential tool for the diagnosis of several human neoplasias.

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Functional inactivation of the tumor suppressor p27(kip1) in human cancer occurs either through loss of expression or through phosphorylation-dependent cytoplasmic sequestration. Here we demonstrate that dysregulation of the PI3K/AKT pathway is important in thyroid carcinogenesis and that p27(kip1) is a key target of the growth-regulatory activity exerted by this pathway in thyroid cancer cells. Using specific PI3K inhibitors (LY294002, wortmannin, and PTEN) and a dominant active AKT construct (myrAKT), we demonstrated that the PI3K/AKT pathway controlled thyroid cell proliferation by regulating the expression and subcellular localization of p27. Results obtained with phospho-specific antibodies and with transfection of nonphosphorylable p27(kip1) mutant constructs demonstrated that PI3K/AKT-dependent regulation of p27(kip1) mislocalization in thyroid cancer cells occurred via phosphorylation of p27(kip1) at T157 and T198 (but not at S10 or T187). Finally, we evaluated whether these results were applicable to human tumors. Analysis of 100 thyroid carcinomas indicated that p27(kip1) phosphorylation at T157/T198 and cytoplasmic mislocalization were preferentially associated with activation of the PI3K/AKT pathway. Thus the PI3/AKT pathway and its effector p27(kip1) play major roles in thyroid carcinogenesis.

The localization of the cyclin-dependent kinase inhibitor p27 kip1 is dependent on the phosphorylation of one of three key amino acid residues: S10, T157 and T198. However, it was unclear whether endogenous p27 kip1 is phosphorylated at T198 in the living cell. In the present work we describe the generation and characterization of a polyclonal antibody able to recognize recombinant, transfected as well as endogenous T198-phosphorylated p27 kip1. Using this antibody, we demonstrate that: (1) endogenous p27 kip1 is phosphorylated at T198 in 4 breast cancer cells lines (MCF7, MDA-MB231, MDA-MB436 and MDA-MB468); (2) T198 phosphorylation is increased in breast cancer cells compared with normal mammary epithelial cells (HMEC); (3) T198-phosphorylated p27 kip1 is exclusively cytoplasmic; (4) T198 phosphorylation is dependent on the activity of the PI3K-PKB/Akt pathway, being it drastically reduced by the pharmacological PI3K inhibitor LY294002 or stimulated by the constitutive activation of PKB/Akt. Finally, in primary human breast carcinomas, cytoplasmic accumulation of T198-phosphorylated p27 kip1 parallels Akt activation. We conclude that in breast cancer cells p27 kip1 is phosphorylated at T198 in a PI3K/Akt dependent manner and that this phosphorylation may contribute to p27 kip1 cytoplasmic mislocalization observed in breast cancer.