COMMUNICATION OF POST-GOLGI ELEMENTS WITH EARLY ENDOCYTIC PATHWAY - REGULATION OF ENDOPROTEOLYTIC CLEAVAGE OF SEMLIKI FOREST VIRUS-P62 PRECURSOR

A number of cellular proteins and viral spike proteins are cleaved at a basic recognition sequence. To characterize the membrane traffic ste p at which this proteolysis occurs we have studied the intracellular p rocessing site of Semliki Forest virus (SFV) spike precursor p62 in BH K21 cells. The p62 is endoproteolytically cleaved at a tetrabasic Arg- His-Arg-Arg recognition sequence. Previously, it has been shown that t he SFV p62 remains uncleaved when accumulated to the trans-Golgi netwo rk (TGN/20 degrees C block site). We show here that exit from the tran s-Golgi is required for the cleavage of p62. Proteolytic processing wa s inhibited in synchronized assays when the 20 degrees C transport blo ck was released in the presence of brefeldin A, energy inhibitors (azi de and deoxyglucose; carbonyl cyanide m-chlorophenylhydrazone, CCCP) o r an effector of trimeric G proteins, AlFn. Endocytosed antibodies aga inst the SFV spike glycoproteins or antibodies against a peptide corre sponding to the enzymatically active motif of furin inhibited cleavage of p62 at a post-TGN location. The results indicate a post-TGN commun ication step between exocytic and endocytic elements. Kinetic experime nts suggested that this communication may involve an early compartment of the endocytic pathway.