Penetration and uncoating of rotaviruses in cultured cells.

Early steps of replication (penetration and uncoating) of the OSU strain of porcine rotavirus were studied in MA-104 cells. After adsorption of trypsin-treated viruses at 4 degrees, followed by a shifting of the temperature to 37 degrees, particles were seen within coated pits, coated vesicles, and secondary lysosomes, indicating that virus entry occurred by receptor-mediated endocytosis, and that uncoating (removal of the outer capsid) could occur by the effect of lysosomal enzymes. This latter aspect was studied using lysosomotropic drugs (chloroquine and ammonium chloride), which were found not to inhibit rotavirus replication, indicating that the low intralysosomal pH is not responsible for virus uncoating. The effect of Ca2+ concentration on intracellular rotavirus uncoating was investigated by treating cells with the calcium ionophore A23187, to increase the intracellular Ca2+ concentration during the early stages of virus replication. Under these conditions rotavirus uncoating did not occur, suggesting that the low Ca2+ concentration in the intracellular microenvironment may be responsible for rotavirus uncoating.