Obesity is a risk factor for breast cancer, largely due to altered expression of various adipocytokines. As it concerns adiponectin, there are not univocal results regarding its role in breast cancer occurrence and progression. Here, we demonstrate that in animals injected with human estrogen receptor (ER)-alpha-negative MDA-MB-231 cells pretreated with adiponectin (1 and 5 mu g/ml), a significant reduction (60 and 40%, respectively) in tumor volume is observed, whereas an increased tumor growth (54 and 109%, respectively) is evidenced in the animals receiving human ER-positive MCF-7 cells. Moreover, cyclin D1 (CD1) mRNA and protein levels are decreased in MDA-MB-231 cells, whereas they are up-regulated in ER-alpha-positive cells by adiponectin. These findings fit with the opposite effects of adiponectin on CD1 promoter: 0.44- and 0.34-fold decrease in MDA-MB-231 cells and 0.63- and 0.95-fold increase in MCF-7 cells, treated with 1 and 5 mu g/ml, respectively. Functional studies indicate that these effects are mediated by the specific protein 1 motif located in the CD1 promoter. In the absence of ER-alpha, the adiponectin-mediated down-regulation of CD1 involves the recruitment of corepressors. In the presence of ER-alpha, the adiponectin-induced expression of CD1 requires the involvement of an activator complex. In conclusion, we propose that a possible mechanism through which adiponectin differently affects breast cancer growth is the opposite modulation of CD1 levels accordingly to ER-alpha expression.
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