TNFα induces NFκB/p50 in association with the growth and morphogenesis of normal and transformed rat mammary epithelial cells

In contrast to the cytotoxic or cytostatic effect of TNF alpha on many breast cancer cell lines, TNF alpha stimulates growth and morphogenesis of normal rat mammary epithelial cells (MEC). The present studies were carried out to determine whether there are intrinsic differences between normal and malignant MEC which may explain the differing responsiveness to TNF alpha. Freshly isolated rat MEC organoids from normal mammary gland or 1-methyl-1-nitrosourea-induced mammary tumors were treated with TNF alpha for 21 days. Unexpectedly, TNF alpha stimulated growth and morphogenesis of both normal and transformed MEC in primary culture, although in transformed cells its effects were delayed and the majority of the colonies were histologically abnormal, with multiple cell layers and no lumen. Since NF kappaB is a key mediator of TNF alpha action and has been implicated in carcinogenesis, the expression of the p50, p52, p65, and c-rel NF kappa -B proteins in normal and transformed MEC was determined. Expression of p52 was significantly reduced in tumor cells, and p50 was absent, although its putative precursor, p105 was abundant. There were no changes in the levels of p65 or c-rel. TNF alpha induced a pronounced and sustained increase of a p50 homodimeric NF kappaB/DNA complex in both normal and transformed MEC. However, in transformed MEC, NF kappaB binding was initially undetectable but then increased in response to TNF alpha. Thus, NF kappaB expression and DNA binding activity are altered during mammary carcinogenesis. In addition, the significant increase in NF kappaB/p50 DNA-binding was temporally coincident with TNF alpha -induced growth and morphogenesis, suggesting that it may play a significant role in both normal development and carcinogenesis. (C) 2001 Wiley-Liss Inc.