SPECIFIC ALTERATIONS IN THE EXPRESSION OF ALPHA-3-BETA-1 AND ALPHA-6-BETA-4 INTEGRINS IN HIGHLY INVASIVE AND METASTATIC VARIANTS OF HUMAN PROSTATE CARCINOMA-CELLS SELECTED BY IN-VITRO INVASION THROUGH RECONSTITUTED BASEMENT-MEMBRANE

Highly invasive cell subpopulations from a human prostate carcinoma ce ll line, PC-3, were selected for by allowing the parental PC-3 cells t o invade through reconstituted basement membrane, Matrigel. These cell s were collected, cultured and then selected further by repeated invas ion through the in vitro invasion chamber. The invasive subpopulations (I-PC3 (2) and (3)) were found to be approximately 15-fold more invas ive in vitro than the parental cells, had a distinct rounded morpholog y in culture, and proliferated more rapidly than the parental cells. W hen injected either subcutaneously or intraperitoneally into immunocom promised SCID mice, the I-PC3 cells were found to form tumors at the p rimary sites and to be highly invasive and metastatic. In contrast, th e parental PC-3 cells formed tumors at the site of inoculation in thes e mice but failed to invade or metastasize. The I-PC3 cells attached e qually as well as PC-3 cells to fibronectin, laminin, collagen type IV and vitronectin, but unlike the parental PC-3 cells these invasive va riants failed to spread on any of these substrates. On Matrigel, the P C-3 cells became highly organized, whereas the I-PC3 cells remained ro unded, clumped together and penetrated into the Matrigel. Biochemical analysis of the expression of adhesion proteins and integrins demonstr ated that whereas the parental cells synthesized and secreted substant ial amounts of fibronectin, the I-PC3 cell variants did not secrete an y fibronectin. Although both PC-3 and I-PC3 cells expressed equivalent levels of cell surface alphavbeta3, alpha2beta1 and alpha5beta1 integ rins, the expression of the alpha3beta1 integrin, which is expressed a t very high levels on the parental PC-3 cells, was drastically reduced on the invasive I-PC3 cells. This decrease in expression of alpha3 oc curred also at the level of mRNA expression. Finally, whereas the PC-3 cells express alpha6beta1, in the invasive I-PC3 cells the alpha6 sub unit was associated mostly with the beta4 subunit. Since the alpha6bet a4 integrin is analogous to the A9 tumor antigen which is associated w ith aggressive human squamous cell carcinomas, the apparent overexpres sion of alpha6beta4 may also participate in the aggressive behavior of these variant prostate carcinoma cells. Alterations in the expression of the alpha3beta1 and alpha6beta4 integrins may thus allow these cel ls to become more invasive, and lead to an increased propensity for me tastasis.