CONICET | Buscador de Institutos y Recursos Humanos

Most of human breast cancers are aneuploid because of chromosome missegregation occurring during mitosis. Deregulation in the control of cell cycle progression is frequently found in mammary carcinomas and is associated with mitotic spindle checkpoint defects and aneuploidy. The Laboratory of Hormonal Carcinogenesis has developed an experimental model of mammary carcinomas by the administration of medroxyprogesterone acetate (MPA) to BALB/c mice. These tumors are metastatic luminal ductal carcinomas, which express estrogen and progesterone receptors (PR) and show different responses to antiprogestin treatment. An association between PR isoform expression and endocrine therapy resistance was found in these mammary carcinomas. Tumors with higher levels of isoform A of PR (PRA) than isoform B (PRB) are inhibited by antiprogestin treatment while those with the opposite ratio are antiprogestin resistant tumors. The cytogenetic analysis of these MPA-induced mammary carcinomas showed that all the diploid mammary tumors respond to antiprogestin treatment, whereas aneuploid mammary tumors can be responsive or resistant to the endocrine therapy. Taking into account that Cyclin A has been related to chromosome instability and has also been involved in PR activation, in this study we evaluated its role in aneuploidy and hormone resistance using the MPA breast cancer model. We analyzed the Cyclin A expression by Western blot (WB) and immunohistochemistry (IHC) in the hormone dependent and the independent (HI) derived variants with different antiprogestin responsiveness and ploidy levels. WB studies revealed for Cyclin A two bands of estimated molecular weights of 52 kDa and 48 kDa in all the mammary tumors analyzed. The 52 kDa form of Cyclin A was overexpressed in the aneuploid unresponsive C4-2-HI tumor (10 fold; p