Autocrine TGF? expression in the regulation of initiation of human colon carcinoma growth

Abstract

Previously, we reported that unaggressive, growth factor-dependent FET human colon carcinoma cells downregulated their transforming growth factor alpha (TGFalpha) expression in a quiescent state (G0/G1) induced by growth factor and nutrient deprivation (Mulder, 1991, Cancer Res., 51:2256-2262). In contrast, highly aggressive, growth factor-independent HCT116 human colon carcinoma cells aberrantly upregulated this autocrine activity in the quiescent state (Mulder, 1991, Cancer Res., 51:2256-2262; Howell et al., 1998, Mol. Cell. Biol., 18:303-313). In this report, the role of autocrine TGFalpha and the mechanism of its regulation of expression during reentry into the cell cycle from a noncycling growth state were determined in FET cells. Optimal induction of DNA synthesis from a quiescent state in FET cells is dependent upon autocrine TGFalpha as well as exogenous transferrin and insulin. Reentry into the cell cycle resulting from treatment with exogenous transferrin and insulin resulted in approximately 3-fold induction of TGFalpha expression within 1 hr. TGFalpha induction was controlled at the transcription level, and the cis-controlling element was localized to the region between bp -370 - -201 relative to the translation start codon within the TGFalpha promoter. Thus neutralization of autocrine TGFalpha protein revealed that the induced TGFalpha autocrine activity was necessary for DNA synthesis and acted only in the early G1 phase of the cell cycle. Blockade of autocrine TGFalpha expression early in the cell cycle resulted in the reduction of DNA synthesis, whereas treatment with neutralization antibody at later times had no effect. This suggested that autocrine TGFalpha functions to initiate cell growth from noncycling states. This was further confirmed by the dependence of FET cells upon autocrine TGFalpha for colony formation in experiments where the plating density was sufficiently low to generate a lag phase in tissue culture. In contrast, TGFalpha autocrine activity was not required for exponential phase cells, as evidenced by the failure of TGFalpha neutralizing antibody to inhibit proliferation in this growth state. Taken together, these results suggest that autocrine TGFalpha acts primarily in the process of growth initiation by moving cells from a noncycling state back into the cell cycle, rather than supporting cell growth already initiated.

Reorganization of ErbB Family and Cell Survival Signaling after Knock-down of ErbB2 in Colon Cancer Cells

“…In addition to overexpression, other mechanisms of constitutive activation have been established. For example, constitutive activation of normal levels of ErbB2 by ligand activation provides a signaling basis for several transformed properties in cancer cells (17,39). Disruption of constitutive activation may accomplish reversion of the malignant phenotype or initiation of cell death.…”

“…In patients with colon carcinoma, increased EGFR mRNA in the tumors is associated with a higher rate of liver metastasis (14). Previous work in this laboratory indicated that inappropriate expression of EGFR and its ligand, transforming growth factor-␣, associates with neoplastic transformation and induces malignant progression of human colon carcinoma (15,16) as well as activation of ErbB2 (17).…”

The Invasive Phenotype of Shigella flexneri Directs a Distinct Gene Expression Pattern in the Human Intestinal Epithelial Cell Line Caco-2

“…Amphiregulin also strongly induces secretion of the matrix metalloproteinases MMP-9 and MMP-2 in cancer cells (81) and is a potent antiapoptotic factor in non-small cell lung cancer cell lines (63). TGF-␣ is also an autocrine/paracrine growth factor acting primarily in the process of growth initiation by moving cells from the non-cycling state back into the cell cycle (69). Increased transcription of amphiregulin and TGF-␣ may reflect the neoplastic origin of Caco-2 cells.…”

Selective abrogation of the proinvasive activity of the trefoil peptides pS2 and spasmolytic polypeptide by disruption of the EGF receptor signaling pathways in kidney and colonic cancer cells

“…Both EGF and TGFa are overexpressed in the transformed gastrointestinal tract and are therefore acting as paracrine/autocrine agents during cancer progression (Ziober et al, 1993;Jiang et al, 1998;Messa et al, 1998;Wang et al, 1998;Normanno et al, 2001). In order to specify the role of EGFR activation in cellular invasion, we studied the invasion patterns of kidney and colonic cancer cells in response to its natural agonists including EGF, TGFa and amphiregulin.…”