Endothelial cell-laminin interaction: modulation of LDH expression involves alpha6beta4 integrin-FAK-p38MAPK pathway.

One of the possible mechanisms of the angiogenic effect of laminin (Ln) involves modulation of the biological activity of VEGF by regulating poly ADP ribosylation (PAR). PAR modification of VEGF was found to be related with the changes in NAD(+) associated with a shift in LDH isoenzymes. Further investigations on LDH gene expression in HUVECs suggested that the effect of Ln was mediated through alpha(6)beta(4) integrin-FAK-src-p38 MAPK pathway. This was evidenced by (a) co-immunoprecipitation of beta(4) integrin with alpha(6) subunit, (b) activation by tyrosine phosphorylation of beta(4) integrin and FAK, (c) co-immunoprecipitation of FAK with beta(4) and with adapter protein, src, (d) increased phosphorylation of p38 MAPK in cells maintained on Ln and (e) blocking of effect of Ln on LDH-B gene expression by inhibition of p38 MAPK. Increase in serine phosphorylation of c-fos and c-jun and higher levels of heterodimers of AP-1 in the nucleus in cells maintained on Ln suggested activation of AP-1 transcription factor. These results provide evidence for modulation of endothelial cell function relevant to angiogenesis by Ln through alpha(6)beta(4) integrin.