IN-SITU EXPRESSION OF BETA-1, BETA-3 AND BETA-4 INTEGRIN SUBUNITS IN NONNEOPLASTIC ENDOTHELIUM AND VASCULAR TUMORS

Endothelial cells play an important role in adhesive interactions betw een circulating cells and extracellular matrix proteins. In vitro stud ies have shown that many of these processes are mediated by a superfam ily of alpha beta heterodimeric transmembrane glycoproteins called int egrins. The distribution patterns of beta 1, beta 3 and beta 4 integri n subunits in endothelial cells (EC) in situ were examined immunohisto chemically on serial frozen sections of a wide range of non-neoplastic tissues and of vascular tumours, both benign and malignant. Expressio n of the beta 1 subunit was a constitutive feature of EC. Among the be ta 1-associated alpha subunits, alpha 5 and alpha 6 were broadly distr ibuted in EC, irrespective of vessel size and microenvironment. The al pha 3 subunit displayed intermediate levels of expression with a sligh t preference for small vessel EC. Presence of alpha 1 was confined to EC of capillaries and venules/small veins. Expression of alpha 2 in EC was inconsistent. With rare exceptions, the alpha 4 chain was absent in EC. The beta 3 and alpha v subunits were expressed in most EC, thou gh not always concomitantly. In contrast to the beta 1 chain, however, these integrin subunits were absent in EC of glomerular capillaries a nd were expressed variably in sinusoidal EC. The beta 4 chain was even ly present in the great majority of EC, except for those of large vess els. In vascular tumours, the patterns of beta 1 and alpha 1 to alpha 6 subunit expression generally corresponded to those found in their no n-neoplastic counterparts. Expression of beta 3, alpha v and beta 4 ch ains, however, decreased in neoplasia, especially in angiosarcomas. Th ese data show that EC dispose of broad and at the same time differenti al repertoires of integrin subunits that presumably reflect vessel-typ e associated functional differences among these cells. In vascular tum ours, the orthologous distribution patterns of beta 1 and alpha 1 to a lpha 6 chains are conserved in most instances while the amounts of bet a 3, alpha v and beta 4 subunits expressed in EC tend to decrease in t he course of malignant transformation.