Enhanced migration of the acute promyelocytic leukemia cell line NB4 underin vitro conditions during short-term all-trans-retinoic acid treatment

All-trans-retinoic acid (RA) is a potent differentiating agent that is very effective in the treatment of patients with acute promyelocytic leukemia ( APL). Since clinical response can be accompanied by extramedullary manifest ations, we have investigated the influence of RA on cell adhesion to and mi gration through reconstituted basement membranes (Matrigel) in the APL cell line NB4. No apparent cellular differentiation was observed during a 24-h incubation with 1 mu M RA, as indicated by the nitroblue tetrazolium reduct ion test. However, exposure to RA significantly enhanced NB4 cell adhesion to Matrigel and consecutive migration through Matrigel barriers in a dose-d ependent manner. Several integrin molecules potentially involved in this pr ocess, i.e., CD29, CD18, CD11a, CD11b and CD11c, were therefore studied by fluorescence-activated cell sorting analysis. The expression of the beta su bunit of the beta 2 integrins (CD 18), but not that of beta 1 integrins (CD 29), was increased during 24-h RA treatment. Among the PZ integrins, the ex pression of LFA-1 (CD11a) and of Mac-1 (CD11b), but not of p150,95 (CD11c), was induced by RA. When monoclonal antibodies that specifically block the interaction of these integrins with their ligands were used, we observed th at CD29 is only involved in adhesion and CD11b only in migration, whereas C D11a participates in both processes. NB4 cells constitutively secreted the matrix metalloproteinases MMP-9 and MMP-2, which are known to promote cellu lar invasion processes by degradation of the extracellular matrix. RA treat ment had no influence on the quantity of secreted MMP-9 or MMP-2 in these c ells as determined by zymography. Addition of Batimastat (BB-94), a synthet ic inhibitor of matrix metalloproteinases, blocked RA-induced cell migratio n without affecting cellular adhesion to Matrigel. These findings indicate that adhesion molecules as well as matrix metalloproteinases are involved i n RA-stimulated migration of NB4 cells through Matrigel, possibly providing some explanation of tissue infiltration by leukemic cells as observed duri ng treatment of APL patients with RA.