Lm. Gangarosa et al., A RAF-INDEPENDENT EPIDERMAL GROWTH-FACTOR RECEPTOR AUTOCRINE LOOP IS NECESSARY FOR RAS TRANSFORMATION OF RAT INTESTINAL EPITHELIAL-CELLS, The Journal of biological chemistry, 272(30), 1997, pp. 18926-18931
We recently have shown that activated Ras, but not Raf, causes transfo
rmation of intestinal (RIE-1, IEC-6) epithelial cells, whereas both ac
tivated Ras and Raf transform NIH 3T3 fibroblasts (Oldham, S. M., Clar
k, G. J., Gangarosa, L. M., Coffey, R. J., and Her, C. J. (1996) Proc.
Natl. Acad. Sci. U. S. A. 93, 6924-6928). The observations that condi
tioned medium from Ras-, but not Raf-, transfected RIE-1 cells, as wel
l as exogenous transforming growth factor alpha (TGF alpha), promoted
morphological transformation of parental RIE-1 cells prompted us to id
entify epidermal growth factor (EGF) receptor (EGFR) ligands produced
by Ras-transformed RIE-1 cells responsible for this autocrine effect.
Since studies in fibroblasts have shown that v-Src is transforming, we
also determined if v-Src could transform RIE-1 cells. H- or K-Ras-tra
nsformed cells secreted significant amounts of TGF alpha protein, and
mRNA transcripts for TGF alpha, amphiregulin (AR), and heparin-binding
EGF-like growth factor (HB-EGF) were induced. Like Ras, v-Src caused
morphological and growth transformation of parental RIE-1 cells. Howev
er, TGF alpha protein was not secreted by RIE-1 cells stably expressin
g v-Src or activated Raf, and only minor increases in EGFR ligand mRNA
expression were detected in these cells. A selective EGFR tyrosine ki
nase inhibitor PD153035 attenuated the Ras-, but not Src-, transformed
phenotype. Taken together, these observations provide a mechanistic a
nd biochemical basis for the ability of activated Ras, but not activat
ed Raf, to cause transformation of RIE-1 cells. Finally, we suggest th
at an EGFR dependent mechanism is necessary for Ras, but not Src, tran
sformation of these intestinal epithelial cells.