Differential expression of transforming growth factor-beta 1 (TGF-beta 1) receptors in murine myeloid cell lines transformed with oncogenes. Correlation with differential growth inhibition by TGF-beta 1.

Transforming growth factor-beta 1 (TGF-beta 1) is a pleiotropic polypeptide hormone known to play an important role as a modulator of hematopoietic processes in human and murine cells. One of the characteristics of TGF-beta 1 is the ability to inhibit the growth of several cell types, including cells of the myeloid lineage. To study the mechanism by which TGF-beta 1 inhibits the growth of myeloid cells, we have used three murine myeloid cell lines, the parental interleukin-3-dependent 32D-123 cell line and two retrovirally infected interleukin-3-independent cell lines (32D-abl, 32D-src), all of which are growth inhibited by TGF-beta 1. Each of these oncogene-transfected cells expresses a greater number of TGF-beta 1 receptors than the parental cell line and responds to TGF-beta 1 with increased sensitivity; 32D and 32D-src cells are 2- and 58-fold more sensitive to TGF-beta 1 inhibition than the parental cell line (ED50 = 35 pM). Both 32D-abl- and 32D-src-transformed cell lines expressed higher levels of the 65- and 85-kDa TGF-beta 1 receptor species than did the parental cells. We observed a correlation between the greater sensitivity of 32D-src cells to TGF-beta 1 and the more rapid down-modulation and reappearance of cell surface TGF-beta 1 receptors on 32D-src cells. Thus, the level of TGF-beta 1 receptor expression and rate of reexpression both have a crucial regulatory effect on the functional activity of the TGF-beta 1 ligand.     

Transforming growth factor-beta 1-induced activation of the ERK pathway/activator protein-1 in human lung fibroblasts requires the autocrine induction of basic fibroblast growth factor

Transforming growth factor-beta (TGF-beta) is involved in multiple processes including cell growth and differentiation. In particular, TGF-beta has been implicated in the pathogenesis of fibrotic lung diseases. In this study, we examined regulation of the mitogen-activated protein kinase pathway by TGF-beta1 in primary human lung fibroblasts. TGF-beta1 treatment resulted in extracellular signal-regulated kinase (ERK) pathway activation in a delayed manner, with maximal activity at 16 h. ERK activation occurred concomitantly with the induction of activator protein-1 (AP-1) binding, a nuclear factor required for activation of multiple genes involved in fibrosis. AP-1 binding was dependent on ERK activation, since the MEK-1 (mitogen-activated protein kinase kinase) inhibitor PD98059 inhibited TGF-beta1-induced binding. Induction of the receptor tyrosine kinase-linked growth factor, basic fibroblast growth factor (bFGF) protein expression temporally paralleled the activation of ERK/AP-1. Induction of AP-1 by TGF-beta1-conditioned medium was observed at 2 h, similar to AP-1 induction in response to exogenous bFGF. Dependence of ERK/AP-1 activation on bFGF induction was demonstrated by inhibition of TGF-beta1-induced ERK/AP-1 activation when conditioned medium from TGF-beta1-treated cells was incubated with bFGF-neutralizing antibody. Together, these results demonstrate that TGF-beta1 regulates the autocrine induction of bFGF, resulting in activation of the ERK mitogen-activated protein kinase pathway and induction of AP-1 binding.