LOCALIZATION OF ALPHA-2, ALPHA-5 AND ALPHA-6 INTEGRIN SUBUNITS IN HUMAN ENDOMETRIUM, DECIDUA AND TROPHOBLAST

Integrins are heterodimeric glycoproteins acting as membrane receptors for extracellular matrix components. The specificity of these receptors towards one particular matrix glycoprotein depends on the type of alpha and beta subunit combination. Since integrins are involved in the migratory behaviour of cells and since cytotrophoblastic cells are constitutively invasive, we undertook to immunolocalize the alpha2, alpha5 and alpha6 integrin subunits in normal and hydatidiform molar trophoblast, in an implantation site as well as in decidualized and non-decidualized endometrium. Alpha6 positivity was confined to villous cytotrophoblast and was clearly polarized towards the basement membrane. Extravillous cytotrophoblastic cells were alpha6-negative but became alpha5-positive. In contrast to normal trophoblast, villous cytotrophoblast from hydatidiform molar tissue was alpha5-positive. We conclude that the expression of a alpha5 integrin subunit on cytotropholastic cell surfaces is correlated with the appearance of an invasive phenotype. Alpha6 and alpha2 integrin subunits were both localized on the surface and glandular epithelium of the endometrium and their expression was increased during the secretory phase but became low or undetectable after decidualization. In contrast, alpha5 subunit positivity was weak in the same epithelia during the first half of the cycle but disappeared after ovulation. Stromal cell alpha5 positivity was present throughout the cycle but increased dramatically in decidualized endometria. We conclude that the alpha5 integrin subunit which disappears from the epithelium at the end of the cycle might allow migration of the epithelial cells and repair of the endometrium after menses. We also wonder if alpha5 positivity is part of a change in the stromal cell phenotype induced by decidualization.