Tyrosine kinase signaling pathways control the expression of retinoic acid receptor-alpha in SK-BR-3 breast cancer cells

Breast carcinomas are frequently characterized by hyperactivated c-erbB receptor tyrosine kinase signaling. Combination of anti-proliferative retinoids with growth-inhibitory c-erbB-specific agents might induce therapeutic benefit. We demonstrate close interactions between the c-erbB and the retinoic acid receptor system in SK-BR-3 breast cancer cells, Epidermal growth factor and heregulin-beta 1 activate c-erbB receptors and dose- and time-dependently up-regulate retinoic acid receptor-alpha (RAR-alpha) mRNA. Similar effects have been found for the growth-inhibitory c-erbB-2 receptor tyrosine kinase-activating antibody 4D5 and the tyrosine phosphatase inhibitor orthovanadate. In contrast, the tyrosine kinase-inhibitor herbimycin A reduces tyrosine-specific protein phosphorylation and down-regulates RAR-alpha. Our data demonstrate that the expression of RAR-alpha, which represents a key mediator of the anti-proliferative effects of retinoids in breast cancer cells, is regulated by modulators of tyrosine kinase signaling. The levels of RAR-beta and -gamma mRNAs, however, are not affected by such agents. (C) 1997 Elsevier Science Ireland Ltd.