Converging signals synergistically activate the LAMC2 promoter and lead to accumulation of the laminin gamma2 chain in human colon carcinoma cells

Abstract

The trimeric extracellular matrix molecule laminin-5 and its constituent chains (alpha 3, beta 3, gamma 2) are normally not detectable intracellularly in intestinal epithelial cells but the laminin gamma 2 chain can be detected in cancer cells at the invasive front of a subset of colon carcinomas. These cells are subjected to cytokines such as transforming growth factor beta 1 (TGF-beta 1) and hepatocyte growth factor (HGF), produced by the tumour cells or by the surrounding stromal cells. The purpose of the present work was to investigate whether TGF-beta 1 and HGF, known to stimulate the LAMC2 gene encoding the laminin gamma 2 chain, might synergize to activate the LAMC2 promoter, and to identify the promoter elements involved. We find evidence for synergy between TGF-beta and HGF with respect to laminin gamma 2 chain expression and promoter activation and demonstrate that this requires the 5' activator protein-1 (AP-1) element of the promoter and an additional upstream element which is also responsive to co-expression of the Smad3 protein from the TGF-beta signalling pathway. The transcripts encoding the other laminin-5 chains are not synergistically activated by HGF and TGF-beta. Thus the synergistic activation of the LAMC2 gene is mediated via different cis-elements and results in an overproduction of the laminin gamma 2 chain relative to the other laminin-5 constituent chains. This difference may explain why laminin gamma 2 chains accumulate in the cells at the invasive front of colon carcinomas.

Basement membrane component laminin-5 is a target of the tumor suppressor Smad4

“…When b-catenin is overactivated in budding tumor cells presumably through stromal growth factors, LAMC2 is induced (Sordat et al, 2000;Hlubek et al, 2001). This pattern of regulation was also reflected in an in vitro study, where LAMC2, but not LAMA3 and LAMB3 was shown to be synergistically induced by TGF-b and hepatocyte growth factor in colorectal carcinoma cells (Olsen et al, 2003). Selective induction of the g2 (and b3) chain, but not the a3 chain by b-cateninmediated signals is consistent with the promoter composition: an in silico promoter analysis indicated 6 and 10 T-cell factor/lymphoid enhancing factor (TCF/Lef) consensus binding sequences in the 5 kb promoter regions of the LAMB3 and LAMC2 genes, respectively.…”

Suppression of laminin-5 expression leads to increased motility, tumorigenicity, and invasion

“…However, in many of these previous immunohistochemical studies, expression of the Ln-5 g2 chain was the only Ln-5 chain assayed and reported [21,23,24,46]. In addition, recent work has established that the Ln-5 g2 chain is over-expressed in invading carcinoma cells without any evidence of coexpression of the Ln-5 a3 and h3 chains [22,47,48]. This brings into question whether Ln-5 heterotrimer or just Ln-5 g2 chain was over-expressed in these earlier studies.…”

Laminin-332-Integrin Interaction: A Target For Cancer Therapy?

“…In addition, genetic inactivation through the methylation of the genes encoding laminin-332 subunits has been reported in lung and bladder cancer [35,36]. Moreover, in colon cancer, the laminin γ2 subunit mRNA (LAMC2) promoter has been observed to be activated by transforming growth factor β1 or hepatocyte growth factor (HGF), leading to overexpression of the laminin γ2 subunit protein [37]. Upregulation of expression of laminin-332 in cancer is also controled by a number of other molecules.…”