Increased adhesion of the promyelocytic leukaemia cell line, NB4, to fibronectin and thrombospondin upon all-trans-retinoic acid treatment

We have evaluated the effects of all-trans-retinoic acid (RA) on the adhesion of the human promyelocytic tic cell Line NB4 to various components of the extracellular matrix. NB4 cells, radiolabelled with (111)Indium, showed a 2-3-fold increase(P < 0.001) in adhesion to fibronectin and thrombospondin upon RA (3x10(-7) M) treatment, whereas adhesion to collagen I. laminin and vitronectin was not modified, The increase in cell adhesion, observed as early as day 1, preceded cell differentiation and was concomitant with tyrosine phosphorylation events. Using now cytometry, we analysed the expression of major receptors for fibronectin (alpha 4 beta 1 and alpha 5 beta 1) and for thrombospondin (alpha nu beta 3, alpha IIb beta 3. CD36 and CD47) on NB4 cells before and after RA treatment. Except for alpha IIb beta 3. which was induced on RA-treated cells, we found no significant increase in the expression of the other receptors, and a decrease in the expression of CD36, upon RX treatment. Preincubation of RX-treated cells with blocking antibodies demonstrated a role for alpha 4 beta 1 and alpha 5 beta 1 in cell adhesion to fibronectin and alpha 5 beta 1, alpha IIb beta 3, CD36 and CD47 in cell adhesion to thrombospondin. Experiments with the synthetic peptides GRGDS(0.2mM) and CSVTCG (0.2 mM) confirmed the participation of integrins, and integrins and CD36, in adhesion of RA-treated cells to fibronectin and thrombospondin, respectively Further inhibition by heparin (10pg/ml) and/or recombinant heparin-binding domain of thrombospondin (TSP18) indicated the additional participation of heparin-like receptors in cell adhesion to thrombospondin. Our results indicate that increase in NB4 cell adhesion to fibronectin and thrombospondin upon RX treatment is Likely to occur through a modulation of the functional state of several receptors for these proteins.