The integrins alpha(3)beta(1) and alpha(6)beta(1) physically and functionally associate with CD36 in human melanoma cells - Requirement for the extracellular domain of CD36

Lateral association between different transmembrane glycoproteins Can serve to modulate integrin function. Here we characterize a physical association between the integrins alpha (3)beta (1) and alpha (6)beta (1) and CD36 on the surface of melanoma cells and show that ectopic expression of CD36 by C D36-negative MV3 melanoma cells increases their haptotactic migration on ex tracellular matrix components. The association was demonstrated by co-immun oprecipitation, reimmunoprecipitation, and immunoblotting of surface-labele d cells lysed in Brij 96 detergent. Confocal microscopy illustrated the co- association of alpha (3) and CD36 in cell membrane projections and ruffles. A requirement for the extracellular domain of CD36 in this association was shown by co-immunoprecipitation experiments using surface-labeled MV3 mela noma or COS-7 cells:that had been transiently transfected with chimeric con structs between CD36 and intercellular adhesion molecule 1 (ICAM-1) or with a truncation mutant of CD36. CD36 is known to engage in signal transductio n and to localize to membrane microdomains or rafts in several-cell types. Toward a mechanistic explanation for the functional effects of CD36 express ion, we demonstrate that in fractionated Triton X-100 lysates of the MV3 ce lls stably transfected with CD36, CD36 was greatly enriched with the deterg ent-insoluble fractions that represent plasma membrane rafts. Significantly , when these fractionated lysates were reprobed for endogenous beta (1) int egrin, it was found that a 4-fold increase in the proportion of the mature protein was contained within the detergent-insoluble fractions when extract ed from the CD36-transfected cells compared with MV3 cells transfected with vector only. These results suggest that in melanoma cells CD36 expression may induce the sequestration:of certain integrins into membrane microdomain s and promote cell migration.