DEFICIENCY OF BETA-1 INTEGRINS IN TERATOMA INTERFERES WITH BASEMENT-MEMBRANE ASSEMBLY AND LAMININ-1 EXPRESSION

Subcutaneous injection of beta 1 integrin-deficient embryonic stem cel ls in mice causes the formation of teratomas although they occur with a lower frequency and are smaller than wild-type cells. Immunofluoresc ence analysis of these deficient tumors indicates a disorganized depos ition of several basement membrane proteins, This was confirmed by ele ctron microscopy which demonstrated frequent gaps in cell-associated b asement membranes or loss of close contacts lo the cells. Further aber rant features were multilaminar structures and amorphous deposits, ind icating a strong impairment of correct basement membrane assembly. Qua ntitative radio immunoassays were used to determine the levels of spec ific proteins in successive tissue extracts with neutral buffer in the absence and presence of EDTA and with 6 M guanidine. This demonstrate d a more than 90% decrease in the content of laminin-1 (alpha 1 beta 1 gamma 1) and a 70% decrease in nidogen in the beta 1 integrin-deficie nt teratomas. No significant changes were detected far other matrix pr oteins (perlecan, fibronectin, fibulins), This selective change impair ed the formation of laminin-nidogen complex and enhanced nidogen degra dation. Northern blots also demonstrated a distinctly reduced expressi on of laminin alpha 1, beta 1, and gamma 1 chains. Similar reductions were also observed in cultured embryonic stem cells prior to any diffe rentiation. No or only smaller changes were observed for laminin alpha 2 and beta 2 chain, nidogen, and perlecan mRNA. These data emphasize a distinct role of beta 1 integrins in the correct assembly of basemen t membranes which may occur through direct ligand binding and/or regul atory events at the transcriptional level. (C) 1988 Academic Press.