TGF beta regulation of mitogen-activated protein kinases in human breast cancer cells

We demonstrate herein the ability of transforming growth factor-beta-2 (TGF beta(2)) to potently activate extracellular signal-regulated kinase 2 (ERK2) in the highly TGF beta-sensitive breast cancer cell (BCC) line Hs578T. The ERK2 isoform was activated by 3-fold within 5 min of TGF beta(2) addition to Hs578T cells. However, TGF beta(2) only slightly activated ERK2 (1.5-fold) in the partially TGF beta-responsive BCC line MDA-MB-231. The magnitude of the difference in activation of ERK2 by TGF beta(2) in the two cell lines paralleled the difference in the IC50 values for TGF beta inhibition of DNA synthesis; the IC50 value in the MDA-MB-231 cells was 32-fold greater than that in the Hs578T cells. Further, our data demonstrate that TGF beta(2) activated the stress-activated protein kinase/Jun N-terminal kinase (SAPK/JNK) type of mitogen-activated protein kinases (MAPKs); maximal induction levels were 2.5-fold above basal values and were attained at 30 min after TGF beta(2) treatment. Transient co-transfection of a luciferase reporter construct (3TP-Lux) containing three AP-1 sites and the plasminogen activator inhibitor-1 (PAI-1) promoter, in conjunction with a construct that directs expression of a dominant-negative mutant ERK2 (TAYF) protein, did net block the ability of TGF beta to induce AP-1 or PAI-1 activity. In contrast, TAYF ERK2 was able to block EGF and insulin-induced 3TP-Lux-reporter activity. These results indicate that in these BCCs, the activation of ERK2 by TGF beta is more tightly linked to the ability of TGF beta to inhibit DNA synthesis than to the ability to stimulate promoter regions important for TGF beta production and control of the extracellular matrix. In addition, this is the first demonstration that TGF beta can activate the SAPK/JNK type of MAPK in TGF beta-sensitive human BCCs. (C) 1997 Elsevier Science Ireland Ltd.