INHIBITION OF ESTROGEN-INDUCED BREAST-CANCER CELL-PROLIFERATION BY REDUCTION IN AUTOCRINE TRANSFORMING GROWTH-FACTOR-ALPHA EXPRESSION

Breast cancer cell lines have been shown to secrete transforming growt h factor alpha (TGF alpha) and other polypeptide growth factors in res ponse to estrogen (E(2)) stimulation. In this study, we investigated w hether cellular-derived TGF alpha mediates the growth-stimulatory effe cts of E(2) in ER-positive breast cancer cells. To test this hypothesi s, we introduced an antisense TGF alpha mRNA expression vector under c ontrol of a human metallothionein promoter into E(2)-responsive T47D h uman breast cancer cells. In stably transfected cells, cadmium induced antisense mRNA and reduced expression of TGF alpha mRNA and protein i n antisense clones (AS1). TGF alpha expression was increased in sense clones (S2), while wild-type T47D cells (W3) or pSV2 neomycin resistan ce-transfected cells showed no change in TGF alpha expression in respo nse to cadmium. The basal proliferative capacity of antisense transfec ted cells was equivalent to that of the wild-type. E(2) increased TGF alpha synthesis and cell proliferation in transfected and wildtype cel ls. In AS1 cells, the simultaneous addition of cadmium with E(2) block ed most of the E(2)-induced increase in TGF alpha mRNA and protein and nearly abolished the stimulatory effects of E(2) on DNA synthesis and cell number. In contrast, no reduction in cell proliferation was obse rved with cadmium in antisense-transfected cells with a low level of a ntisense expression or in the S2 or W3 cells. Our results are compatib le with the hypothesis that autocrine production of TGF alpha may be a n important contributor to E(2)-induced growth in T47D cells.