Cell-to-Cell Contact Modulates the Expression of the β1 Family of Integrins in Primary Cultures of Thyroid Cells

Abstract

The expression of the β1 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 α3 subunit on the cell membrane progressively increased soon after plating, reaching a 30-fold higher intensity. The α2 subunit, not detectable in native follicular cells, was expressed de novo and reached a remarkable high level. Up-regulation of α2 and α3 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 β1 integrin mRNA. The increase of α2 and α3 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 β1 integrins in thyroid primary cultures.