Adenomatous transformation of the human anterior pituitary is associated with alterations in integrin expression.

Integrins are heterodimeric transmembrane molecules that mediate cell-cell and cell-substratum adhesion. Because alterations in the adhesive properties of tumor cells influence tumor growth and progression, the distribution of different alpha and beta integrin subunits was studied in both the parenchyma and the connective tissue in 6 normal and 25 adenomatous human anterior pituitaries. All normal parenchymal cells expressed the alpha3beta1 and alpha6beta4 integrins. By contrast, in adenomatous parenchymal cells the expression of alpha3beta1 was down-regulated and that of alpha6beta4 abrogated. Neoexpression of alphavbeta3 Occurred in the parenchyma of a subset of adenomas. All normal connective tissue cells expressed the alpha1 and beta1 subunits, a third subunit (alpha5) being present in the normal endothelium. By comparison, all adenomatous stromal cells expressed many more integrin subunits (alpha1, alpha3, alpha5, alphav, beta1 and beta3), adenomatous endothelial cells bearing additional subunits (alpha6, beta4 and beta5). Vitronectin, absent from the normal connective tissue, was constantly observed in the adenomatous stroma. To conclude, compared with cells of the normal gland, adenomatous anterior pituitary cells display a decreased expression of integrins whereas the adenomatous stroma expresses a rich repertoire of integrins. These changes are not related to the secretory type, grade or invasiveness of the adenoma. The resulting alterations in the adhesive properties of adenomatous cells could facilitate their dissemination. Enrichment of the integrin repertoire expressed by the adenomatous vasculature is indicative of its dual nature, systemic and tumoral.