α3β1-integrin as a critical mediator of the hepatic differentiation response to the extracellular matrix

Abstract

The extracellular matrix (ECM) promotes the differentiation of many cell types, and ECM remodeling in the liver has been implicated in embryonic development, tissue injury, and oncogenesis. Integrins are heterodimeric ECM receptors that play critical roles in transducing the composition of the ECM in the cell environment. We previously showed that mouse H2.35 cells, a conditionally transformed, liver-derived cell line, assume a more differentiated hepatocyte morphology and enhanced liver-specific gene expression when the cells are cultured on gelatinous ECM substrata. Here we show that H2.35 cells express relatively high levels of ␣ 3 ␤ 1 -integrins, similar to that previously shown for immature hepatocytes, transformed hepatocytes, and biliary cells. However, the cell morphological responses that depend on ␣ 3 ␤ 1 -integrin have not been defined. We found that transfecting H2.35 cells with antisense RNA construct directed to ␣ 3 -subunit messenger RNA perturbs the initial cell attachment to laminin and collagen, and strongly inhibits cell morphological, proliferative, and gene expression responses to a collagen gel substratum. In situ hybridization to mouse embryo tissues demonstrates the presence of ␣ 3 -subunit messenger RNAs in newly formed hepatocytes. We suggest that ␣ 3 ␤ 1 -integrins are important for immature and transformed hepatocytes to respond morphologically to the extracellular matrix. (HEPATOLOGY 1998;28:1095-1104.)Tissue-specific gene expression, morphogenesis, and cell migration are promoted by interactions between cells and the surrounding extracellular matrix (ECM). For example, early hepatocyte differentiation begins as foregut endodermal cells enter the new collagenous environment of the surrounding mesenchyme, 1 and the role of the ECM in adult hepatocyte differentiation is well established. [2][3][4][5][6][7][8] Other examples of ECMpromoted differentiation include the differentiation of keratinocytes, 9 gastrulation in Pleurodeles embryos, 10 and the epithelial conversion of kidney mesenchyme 11 (for review, see Adams and Watt 12 ). The ECM is present in all animals from the earliest stages of development and is composed of a mixture of proteins and proteoglycans such as collagens, laminin, and fibronectin. An important set of membrane receptors for ECM molecules is the integrin family of proteins. [13][14][15] Integrins are heterodimers of ␣ and ␤ subunits, with each subunit containing an N-terminal extracellular domain, a transmembrane domain, and a C-terminal intracellular domain. Integrins activate common as well as subgroupspecific intracellular signaling pathways in response to the ECM. 16,17 Membrane proximal events triggered by integrin ligation include the activation of the focal adhesion kinase 18 by the ␤ subunit and the recruitment of adapter protein Shc by certain ␣ subunits within heterodimers. 19 More ␣ subunits are known than ␤ subunits, and the particular combination of ␣ and ␤ partners determines the ligand specificity for ECM molecules. An ECM protein can be recognized...

Human Hepatocellular Carcinoma (HCC) Cells Require Both α3β1 Integrin and Matrix Metalloproteinases Activity for Migration and Invasion

“…However, noninvasive HCC cells express MT1-MMP but do not migrate on Ln-5, even in the presence of added exogenous MMP-2. These contradictory results might be explained by the fact that nonmigratory cells hardly express ␣3␤1 integrin, which is also absent in normal adult hepatocytes; whereas it is highly expressed in hepatocytes that are migrating from the endoderm germ layer to the mesenchyme of the septum transversum during embryogenesis (Lora et al, 1998;Nejjari et al, 1999;Scoazec et al, 1996). We found that ␣3␤1 was expressed in HCC tissue, suggesting a role for this integrin in migration on ECM components such as Ln-5 and in metastasis formations.…”

The Role of Collagen Structure in Mitogen Stimulation of ERK, Cyclin D1 Expression, and G1-S Progression in Rat Hepatocytes

“…2 It is possible, however, that other integrin ␣ subunits that block growth factor signaling are involved in adhesion to polymerized collagen gel. Primary hepatocytes do not express ␣ 2 subunits (58), however, it has been reported that the ␣ 3 subunit is expressed in primary hepatocytes (58) and expression of this subunit in a conditionally transformed mouse hepatocyte cell line is involved in the differentiated response to collagen gel (59). Investigation of this and other ␣ subunits that may be involved in adhesion specifically to the collagen gel is an area currently under investigation.…”

Embryonic development of the liver

“…83,124 In addition, cells lacking ␤1-integrin, a subunit of a heterodimeric protein complex that contributes to cell-matrix interactions, are unable to colonize the liver, and inhibition of the ␣3-integrin subunit expression blocks extracellular matrixinduced differentiation of a hepatic cell line. 125,126 One fruitful direction for future research is to clearly define the mechanisms through which extracellular matrix signaling controls biliary epithelial cell gene expression.…”