Cell-to-cell contact modulates the expression of the beta 1 family of integrins in primary cultures of thyroid cells.

The expression of the beta 1 family of integrins was studied in normal thyroid tissue cultures and monolayer cell cultures. The expression of the various subunits was measured by flow cytofluorometry with specific monoclonal antibodies and by Northern analysis. In monolayer cell cultures but not in tissue cultures, the expression of the alpha 3 subunit on the cell membrane progressively increased soon after plating, reaching a 30-fold higher intensity. The alpha 2 subunit, not detectable in native follicular cells, was expressed de novo and reached a remarkable high level. Up-regulation of alpha 2 and alpha 3 in monolayer cell cultures was serum-independent and preceded the expression of proliferating cell nuclear antigen, [3H]thymidine incorporation, and cell replication. Northern analysis demonstrated an increased level of beta 1 integrin mRNA. The increase of alpha 2 and alpha 3 was readily reversible since the expression of these molecules returned to a lower level when cultures reached a high cell density. Down-regulation did not occur until cell cultures were confluent. When cells from high cell density and low integrin expression were harvested and sparsely seeded in culture, up-regulation of integrins was observed again, while rapid reaggregation of isolated cells inhibited this phenomenon. Altogether these data suggest that cell-to-cell contact may regulate the expression of beta 1 integrins in thyroid primary cultures.