HUMAN PROSTATE CARCINOMA-CELLS EXPRESS FUNCTIONAL ALPHA-IIB-BETA-3 INTEGRIN

The integrin alpha IIb beta 3 was initially believed to be expressed o nly in cells from the megakaryocytic lineage, such as platelets or HEL cells. In this study, we report for the first time that human prostat e carcinoma PC-3 and DU-145 cells express alpha IIb beta 3. Reverse tr anscription-PCR from HEL (positive control), PC-3, and DU-145 cells am plified a predicted alpha II beta fragment that hybridized to the full -length alpha II beta cDNA probe. DNA sequencing of the PCR fragments revealed 100% sequence homology to the corresponding extracellular dom ain of platelet alpha II beta but minimal sequence homology to integri ns alpha v or alpha 5. An RNase protection assay was used to confirm t he results from reverse transcription-PCR. An antisense riboprobe to a lpha IIb mRNA hybridized to total RNA from HEL, PC-3, and DU-145 cells , suggesting that alpha IIb mRNA is transcribed in these tumor cells. In situ hybridization on surgical specimens from human prostate tumor tissue stained positive,vith an antisense riboprobe to alpha IIb mRNA, The expression of alpha IIb beta 3 protein in PC-3 and DU-145 cells w as demonstrated by Western and dot blotting and flow cytometry with mo noclonal antibodies (mAbs) to alpha IIb (MAB 1990), beta 3, and alpha IIb beta 3 (AP-2). A protein kinase C activator, phorbol 12-myristate 13-acetate, increased the adhesion of PC-3 cells to PAC-1, a mAb speci fic to the high-affinity state of alpha IIb beta 3, by more than 80-fo ld. The invasion of DU-145 cells through a reconstituted basement memb rane was blocked 40-50% by mAbs AP-2 or PAC-1. These data collectively suggest that: (a) prostate tumor cells express alpha IIb beta 3; (b) surface expression of alpha IIb beta 3 integrin is regulated by protei n kinase C; and (c) mAbs to this receptor inhibit invasion of prostate cancer cells through a reconstituted basement membrane.