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 a ttenuated by blocking the expression of endogenous transforming growth factor alpha (TGFalpha), estrogen receptor (ER)-positive, estrogen-re sponsive MCF-7 or ZR-75-1 cells and ER-negative, estrogen-nonresponsiv e MDA-MB-468 or HS-578T cells were infected with a recombinant amphotr opic, replication-defective retroviral expression vector containing a 435 base pair (bp) Apa1-Eco R1 coding fragment of the human TGFalpha c DNA oriented in the 3' to 5' direction and under the transcriptional c ontrol of an internal heavy metal-inducible mouse metallothionein (MT- 1) promoter and containing the neomycin (neo) resistance gene. E2-stim ulated expression of endogenous TGFalpha mRNA was inhibited by 4-5-fol d, 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 trea ted 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 paramete rs. E2-stimulated anchorage-dependent growth (ADG) and anchorage-indep endent growth (AIG) of the M-1 or MZ-1 cells was inhibited by 60-90% f ollowing CdCl2 treatment. In contrast, neither the ADG nor AIG of the parental noninfected MCF-7 or ZR-75-1 cells that were maintained in th e 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 wer e 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 im portant autocrine intermediary in regulating estrogen-induced cell pro liferation. (C) 1993 Wiley-Liss, Inc.