Loss of polarity and De novo expression of the β1 family of integrins in thyroid tumors

The expression and cell-membrane distribution of the beta 1 family of integrins (very-late-activation antigens, VLA) were investigated in benign and malignant human thyroid tumors. We compared tissue samples of normal glands, nodular goiters, adenomas and carcinomas. We also examined 3 thyroid-carcinoma cell lines cultured in vitro. The expression of subunits of the beta 1 family of integrins was assessed by flow cytometry and specific antibodies in dispersed single-cell suspensions and by immunofluorescence on frozen tissue sections. In contrast to the heterogeneity of the expression of beta 1 integrins observed in other tumors, thyroid neoplastic lesions showed a remarkably constant VLA profile. In all tumors, benign as well as malignant, and in carcinoma cell lines, all sub-units of beta 1 integrins were expressed at high levels. While sub-units alpha 1, alpha 3, alpha 5, alpha 6 and occasionally alpha 2 were also present in a cell sub-set of normal glands and nodular goiters, expression of alpha 4 was restricted to neoplastic lesions; this integrin can be therefore considered an antigen associated with thyroid tumors. It has been reported that in normal glands and in nodular goiters, the expression of beta 1 integrins is restricted to the basal-cell membrane. Immunofluorescence on tissue sections showed instead that, in adenomas and carcinomas, the polarized distribution of these integrins on the cell membrane is lost.