DIFFERENTIAL TARGETING OF VESICULAR STOMATITIS-VIRUS G-PROTEIN AND INFLUENZA-VIRUS HEMAGGLUTININ APPEARS DURING MYOGENESIS OF L6 MUSCLE-CELLS

Exocytic organelles undergo profound reorganization during myoblast di fferentiation and fusion. Here, we analyzed whether glycoprotein proce ssing and targeting changed during this process by using vesicular sto matitis virus (VSV) G protein and influenza virus hemagglutinin (HA) a s models. After the induction of differentiation, the maturation and t ransport of the VSV G protein changed dramatically. Thus, only half of the G protein was processed and traveled through the Golgi, whereas t he other half remained unprocessed. Experiments with the VSV tsO45 mut ant indicated that the unprocessed form folded and trimerized normally and then exited the ER, It did not, however, travel through the Golgi since brefeldin A recalled it back to the ER. Influenza virus HA glyc oprotein, on the contrary, acquired resistance to endoglycosidase H an d insolubility in Triton X-100, indicating passage through the Golgi. Biochemical and morphological assays indicated that the HA appeared at the myotube surface. A major fraction of the Golgi-processed VSV G pr otein, however, did not appear at the myotube surface, but was found i n intracellular vesicles that partially colocalized with the regulatab le glucose transporter. Taken together, the results su during early my ogenic differentiation, the VSV G protein was rerouted into developing , muscle-specific membrane compartments, Influenza virus HA, on the co ntrary, was targeted to the myotube surface.