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Alteration of fibronectin receptors (integrins) in phorbol ester-treated human promonocytic leukemia cells.

We describe the isolation of human fibronectin receptors (integrins) from two nonadherent promonocytic cell lines and from peripheral blood monocytes. Integrins purified from U-937 and THP-1 cells exhibited identical electrophoretic migrations on sodium dodecyl sulfate gels run under reducing (approximately Mr 150,000) and nonreducing (alpha, Mr 160,000; beta, Mr 130,000) conditions. Treatment of U-937 or THP-1 cells with phorbol esters induced these cells to express different integrins with electrophoretic mobilities (alpha, Mr 140,000; beta, Mr 115,000, nonreduced) identical to those from normal human peripheral blood monocytes. Receptors isolated from uninduced, nonadherent promonocytic leukemia cells (U-937 and THP-1) were distinct from glycoproteins IIb and IIIa and from leukocyte adhesion molecules (p150/95). However, receptors isolated here did react with an antibody known to block cell adhesion to fibronectin. The differences observed in apparent molecular masses of fibronectin receptors from uninduced and induced U-937 or THP-1 cells are removed by treatment of purified integrins with endoglycosidase F or N-glycanase. In summary, the data presented here demonstrate the purification of integrins by fibronectin affinity chromatography from human leukemia cells and normal peripheral blood monocytes. Our results suggest that these receptors differ in immature and mature monocytic cells, and are altered by glycosylation in the course of cellular maturation.