Hypoxia-inducible factor 1 alpha is essential for hypoxic p27 induction in endometrioid endometrial carcinoma.

Hypoxia-inducible factor 1alpha (HIF-1alpha) plays an essential role in the adaptive response of cells to hypoxia. The cyclin-dependent kinase inhibitor p27(Kip1) is highly expressed in the normal endometrium but is lost during endometrial carcinogenesis. However, in high-grade cancers, p27 re-expression is observed. We analysed the role of HIF-1alpha in hypoxia-induced expression of p27 in vitro and in vivo in endometrial cancer. Paraffin-embedded specimens from endometrioid endometrial carcinoma (n = 39) were stained immunohistochemically for HIF-1alpha, p27, and Ki67. HEC1B, an endometrial carcinoma cell line, was cultured under normoxic or hypoxic conditions in the presence or absence of transiently expressed short hairpin RNAs targeting HIF-1alpha. Protein expression of p27 and HIF-1alpha was assessed by western blotting. Immunohistochemical staining revealed perinecrotic HIF-1alpha expression in 67% of the cases and p27 staining centrally in the tumour islands, mostly around necrosis, in 46% of the cases. In 50% of the tumours with perinecrotic HIF-1alpha expression, p27 and HIF-1alpha perinecrotic/central co-localization was observed. In these tumour sections, hypoxia-associated p27 expression showed less proliferation around necrosis. Analysis of cultured endometrial carcinoma cells demonstrated that p27 protein expression is induced by hypoxia. This induction was abrogated by transient knockdown of HIF-1alpha using RNAi. Furthermore, hypoxia induced cell cycle arrest in HEC1B cells. We conclude that, in endometrioid endometrial carcinoma, p27 re-expression by hypoxia is HIF-1alpha-dependent and leads to cell cycle arrest. This may contribute to the survival of cancer cells in hypoxic parts of the tumour.

Progressive derailment of cell cycle regulators in endometrial carcinogenesis.

BACKGROUND: Derailments of the control mechanisms of the cell cycle can initiate carcinogenesis, and play a role in progression to cancer. AIM: To explore the expression of cell cycle proteins in normal, premalignant and malignant endometrial lesions representing the morphologically well defined stepwise model of human endometrial carcinogenesis METHODS: Observational study. Paraffin-embedded specimens from inactive endometrium (n = 16), endometrial hyperplasia (n = 23) and endometrioid endometrial carcinoma (n = 39) were stained immunohistochemically for cyclin A, cyclin B1, cyclin D1, cyclin E, cdk2, p16, p21, p27, p53 and Ki67(MIB-1)). Differences in expression between the tissues, and correlation with classical prognostic factors for the carcinomas were analysed. RESULTS: Expression of cyclin A and Ki67 gradually increased from normal through hyperplasia to carcinoma, indicating that proliferation increases over the carcinogenetic spectrum. cdk2, p16 and p21 gradually increased from normal through hyperplasia to carcinoma, indicating their potential importance in both early and late carcinogenesis. Cyclin D1, cyclin E and p53 especially increased and p27 decreased from hyperplasia to carcinoma, underlining their role in late carcinogenesis. In cancers, expression of cyclin A, p53 and Ki67 was positively correlated to grade, and cyclin A was positively correlated with cdk2, p21, Ki67, cyclin E and p53. CONCLUSION: During (endometrioid) endometrial carcinogenesis, there is increasing proliferation paralleled by progressive derailment of cyclin B1, cyclin D1, cyclin E, p16, p21, p27, p53, and cdk2, indicating the importance of these cell cycle regulators in endometrial carcinogenesis.

p16 is consistently expressed in endometrial tubal metaplasia.

BACKGROUND: Cell cycle proteins and HIF-1alpha with downstream factors are often abberrantly expressed in (pre)neoplastic tissue. METHODS: Paraffin-embedded specimens of inactive endometrium with TM (n=15), ovarian inclusion cysts (n=6), cervix with TM (tubal metaplasia) (n=3), Fallopian tubes (n=7), cycling endometrium (n=9) and a ciliated cell tumor of the ovary were stained for p16 and LhS28. 39 Endometrioid endometrial carcinomas and 5 serous endometrial carcinomas were stained for p16. Additionally, inactive endometrium (n=15) was immunohistochemically stained for p21, p27, p53, cyclin A, cyclin D1, cyclin E, HIF-1alpha, CAIX, Glut-1 and MIB-1. RESULTS: A mosaic pattern of expression of p16 was seen throughout in all cases of endometrial TM (15/15), in 2/6 of the ovarian inclusion cysts with TM, in all (3/3) cervical TM and focal in 5/7 of Fallopian tube cases. Mosaic expression was also seen in a ciliated cell tumor of the ovary and in 18/39 of endometrioid endometrial carcinomas, and diffuse p16 expression was seen in 5/5 serous carcinomas. In comparison with normal endometrium, TM areas in the endometrium showed significantly increased expression of HIF-1alpha, cyclin E, p21 and cyclin A, and decreased expression of p27. Membranous expression of CAIX and Glut-1 was only seen in TM areas, pointing to functional HIF-1alpha. CONCLUSION: As p16 is consistently expressed in TM, less and only patchy expressed in the normal Fallopian tube, is paralleled by aberrant expression of cell cycle proteins, HIF-1alpha, CAIX and Glut-1 and resembles the pattern of p16 expression frequently seen in endometrial carcinomas, we propose endometrial TM to be a potential premalignant endometrial lesion.