RECOMBINANT EXPRESSION OF THE MAL PROTEOLIPID, A COMPONENT OF GLYCOLIPID-ENRICHED MEMBRANE MICRODOMAINS, INDUCES THE FORMATION OF VESICULARSTRUCTURES IN INSECT CELLS

The MAL proteolipid has been identified as a component of glycolipid-e nriched membrane microdomains resistant to detergent solubilization in epithelial Madin-Darby canine cells, as well as in T lymphocytes and in myelin-forming cells, To study the function of the MAL proteolipid we have ectopically expressed a tagged form of MAL in both mammalian a nd insect cellular backgrounds, Immunofluorescence analysis in transie ntly transfected COS-7 cells showed the presence of MAL in large vesic ular structures, and biochemical analysis identified MAL in the fracti on of membranes resistant to Triton X-100 solubilization, Electron mic roscopic analysis showed that the expression of MAL in Sf21 cells morp hologically resulted in the intracellular accumulation of large vesicl es with a diameter from 200 to greater than 700 nm that were absent in uninfected or control infected cultures, Thus, ectopic expression of MAL in this heterologous expression system was sufficient to drive the formation of vesicles with a size similar to that of the vesicles det ected in mammalian cells, These vesicles were clearly different from t he caveolae-like vesicles induced by caveolin expression, as evidenced by co-infection experiments using a recombinant caveolin baculovirus. Taken together, these results suggest that the MAL proteolipid might play a role as a component of the machinery of vesiculation of glycoli pid-enriched membranes.