EXPRESSION OF TRANSFORMING GROWTH-FACTOR-ALPHA ANTISENSE MESSENGER-RNA INHIBITS THE ESTROGEN-INDUCED PRODUCTION OF TGF-ALPHA AND ESTROGEN-INDUCED PROLIFERATION OF ESTROGEN-RESPONSIVE HUMAN BREAST-CANCER CELLS

To ascertain if 17beta-estradiol (E2)-induced proliferation could be attenuated by blocking the expression of endogenous transforming growth factor alpha (TGFalpha), estrogen receptor (ER)-positive, estrogen-responsive MCF-7 or ZR-75-1 cells and ER-negative, estrogen-nonresponsive MDA-MB-468 or HS-578T cells were infected with a recombinant amphotropic, replication-defective retroviral expression vector containing a 435 base pair (bp) Apa1-Eco R1 coding fragment of the human TGFalpha cDNA oriented in the 3' to 5' direction and under the transcriptional control of an internal heavy metal-inducible mouse metallothionein (MT-1) promoter and containing the neomycin (neo) resistance gene. E2-stimulated expression of endogenous TGFalpha mRNA was inhibited by 4-5-fold, and the production of TGFalpha protein was inhibited by 50-80% when M-1 mass-infected MCF-7 or MZ-1 mass-infected ZR-75-1 cells were treated with 0.75-1 muM CdCl2, whereas in comparably treated parental MCF-7 or ZR-75-1 cells there was no significant effect upon these parameters. E2-stimulated anchorage-dependent growth (ADG) and anchorage-independent growth (AIG) of the M-1 or MZ-1 cells was inhibited by 60-90% following CdCl2 treatment. In contrast, neither the ADG nor AIG of the parental noninfected MCF-7 or ZR-75-1 cells that were maintained in the absence or presence of E2 was affected by comparable concentrations of CdCl2. The ADG and AIG of TGFalpha antisense MD-1 mass-infected MDA-MB-468 cells that express high levels of endogenous TGFalpha mRNA were also inhibited by 1 muM CdCl2, whereas the ADG and AIG of MH-1 mass-infected HS-578T cells, a TGFalpha-negative cell line, were unaffected by CdCl2 treatment. These results suggest that TGFalpha may be one important autocrine intermediary in regulating estrogen-induced cell proliferation. (C) 1993 Wiley-Liss, Inc.