Intracellular processing and transport of influenza-virus envelope proteins in Madin-Darby canine kidney cells. Effects of the carboxylic ionophores monensin and nigericin.

We have investigated the effects of the carboxylic ionophores monensin and nigericin on the intracellular processing and transport of the influenza-virus envelope proteins haemagglutinin and neuraminidase in Madin-Darby-canine-kidney-cell monolayers. In the presence of either ionophore, haemagglutinin acquires resistance to the enzyme endoglycosidase H more slowly than it does in untreated cells. In addition, the ionophores cause a block in oligosaccharide-processing events that are believed to occur normally in the trans elements of the Golgi complex. This block is not overcome even at long chase times. Finally, the ionophores cause a substantial slowing of the delivery of both haemagglutinin and neuraminidase to the plasma membrane. We conclude that the ionophores cause delays in the intracellular transport of these proteins both early and late in the pathway, that is, before and after passage through the trans-Golgi, and perturb the processing functions of this compartment. The possible significance of these observations with regard to the intracellular transport of newly synthesized plasma-membrane proteins in epithelial cells is discussed.