Effects of steroids on laminin-binding integrins in a human melanoma cell line

The MEL-85 human melanoma cell line was used to investigate the effects of both estradiol and dexamethasone on expression of laminin (LM) receptors and cell adhesion capacity. Immunoblotting of eluates from whole-cell extracts applied to LM Sepharose indicates the presence of an LM-binding protein of 116-130 kDa that reacted with an anti-beta 1 integrin antibody, suggesting that the putative LM receptor of MEL-85 cells is a member of the integrin family. Analysis of 125I-LM binding to whole cells indicates the existence of low-affinity components which display positive co-operativity. LM-fragment-8 competes for this binding to the same extent as unlabelled LM (75%), while fragment PI is inactive and fibronectin (FN) competes by about 30% only. Binding of labelled fragment-8 exhibits a pattern similar to that of intact LM. Cell adhesion to substrates coated with LM and LM fragments closely parallels binding to cells in suspension. MEL-85 cells were estradiol-receptor-negative. Estradiol treatment did not stimulate LM receptor levels or attachment to LM. Growth rate also remained unaltered. To characterize the glucocorticoid dependence of MEL-85 cells, we first established the presence of glucocorticoid receptors and an inhibitory effect on growth rate. Dexamethasone treatment resulted in marked enhancement of adhesion to LM, without altering LM receptor number or affinity. In addition, dexamethasone changed the morphology of MEL-85 cells in conjunction with higher LM expression as evaluated by immunofluorescence.