PINCH1 is composed of 5 LIM domains, binds integrin-linked kinase (ILK) and locates to integrin-mediated adhesion sites. In order to investigate PINCH1 function we generated mice and embryonic stem (ES) cell-derived embryoid bodies (EBs) lacking the PINCH1 gene. Similar to mice lacking β1 integrin or Ilk, loss of PINCH1 arrested development at the peri-implantation stage. In contrast to β1 integrin or Ilk mutants, however, disruption of the PINCH1 gene produced implantation chambers with visible cell clumps even at embryonic day 9.5. In order to define the phenotype leading to the peri-implantation lethality we made PINCH1-null EBs and found similar but also additional defects not observed in β1 integrin or Ilk mutant EBs. The similarities included abnormal epiblast polarity, impaired cavitation and detachment of endoderm and epiblast from basement membranes. Additional defects, which were not observed in β1 integrin- or ILK-deficient mice or EBs, included abnormal cell-cell adhesion of endoderm and epiblast as well as the presence of apoptotic cells in the endodermal cell layer. Although ILK and PINCH1 were shown to be involved in the phosphorylation of serine-473 of PKB/Akt, immunostaining with specific antibodies revealed no apparent alteration of PKB/Akt phosphorylation in PINCH1-deficient EBs. Altogether these data demonstrate an important role of PINCH1 for integrin function, actin organization, cell-cell adhesion and endodermal cell survival during the implanting of mouse embryos.

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PINCH2 belongs, together with PINCH1, to a new family of focal adhesion proteins, the members of which are composed of five LIM domains. PINCH1 and PINCH2 interact, through their first LIM domain, with the integrin-linked kinase and thereby link integrins with several signal transduction pathways. Despite their high similarity, it has been shown that PINCH1 and PINCH2 could exert distinct functions during cell spreading and cell survival. To investigate the function of PINCH2 in vivo, we deleted PINCH2 in mouse using the loxP/Cre system. In contrast to the PINCH1-deficient mice, which die at the peri-implantation stage, PINCH2-null mice are viable, fertile and show no overt phenotype. Histological analysis of tissues that express high levels of PINCH2 such as bladder and kidney revealed no apparent abnormalities, but showed a significant upregulation of PINCH1, suggesting that the two PINCH proteins may have, at least in part, overlapping function in vivo. To further test this possibility, we established PINCH1-null mouse embryonic fibroblasts, which express neither PINCH1 nor PINCH2. We found that in fibroblasts with a PINCH1/2-null background, PINCH2 is able to rescue the spreading and adhesion defects of mutant fibroblasts to the same extent as PINCH1. Furthermore, we show that the LIM1 domain only of either PINCH1 or PINCH2 can prevent ILK degradation despite their failure to localize to focal adhesions. Altogether these results suggest that PINCH1 and PINCH2 share overlapping functions and operate dependently and independently of their subcellular localization.

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.