Entry of poliovirus into cells is blocked by valinomycin and concanamycin A

Poliovirus contains a virus particle devoid of a lipid envelope that does n ot require an intact pH to enter into susceptible cells. Thus, the blockade of pH gradient generated in endosomes is not sufficient to impede the tran slocation of poliovirus particles to the cytoplasm, suggesting that translo cation takes place at the plasma membrane. Measuring both viral protein syn thesis and eIF4G-1 cleavage mediated by poliovirus protease 2A has been use d to monitor productive entry of poliovirus into cells. Translation of the input poliovirus RNA produces enough 2A(pro) to cleave eIF4G-1, providing a sensitive assay to estimate poliovirus RNA delivery to the cytoplasm follo wed by its translation. Combination of concanamycin A, a vacuolar proton-AT Pase inhibitor, and valinomycin, an ionophore that promotes K+ efflux from cells, powerfully prevented poliovirus infection. Moreover, modifying the i onic conditions of the culture medium (increasing the concentration of K+ a nd decreasing the concentration of Na+), together with concanamycin A, also significantly interfered with poliovirus entry. These findings suggest tha t poliovirus RNA requires an intact concentration of K+ ions inside the cel ls to be uncoated and to gain access to the cytoplasm. In addition, the act ual contribution of concanamycin A (as well as other inhibitors of endocyto sis) to the total inhibition of productive poliovirus entry points to the i dea that at least some percentage of polioviral subparticles translocates f rom the endosomes.