Mutations selected in rotavirus enterotoxin NSP4 depend on the context of its expression

The rotavirus NSP4 protein is cytotoxic when transiently expressed in cells and is capable of inducing secretory diarrhea in neonatal mice. NSP4 consi sts of 175 amino acids, and sequences important for its toxic effects have been mapped to the carboxy-terminal half of the protein. In this report, we compared NSP4-enccding nucleotide sequences recovered from cell lines engi neered to express NSP4 from human rotavirus strain Wa with NSP4 sequences r ecovered from cells persistently infected with either Wa or simian rotaviru s strain SA11. In cells stably transfected with Wa NSP4, we found that prol ine(138) was changed to either serine or threonine. However, in cells persi stently infected with SA11, we found that phenylalanine(33) was changed to leucine, and in cells persistently infected with Wa, no changes were observ ed in NSP4, Expression of Wa NSP4 in Caco-2 cells resulted in increased cel l-doubling times and decreased cell viability in comparison to cells expres sing NSP4-serine(138) or NSP4-threonine(138). This result suggests that seq uence polymorphism at residue 138 in Wa NSP4 influences the cytotoxicity of the protein. Therefore, mutations in the carboxy-terminal half of NSP4 are selected when NSP4 is expressed in cells in the absence of other viral pro teins, but not in the context of viral replication. These findings suggest that cytotoxic functions of NSP4 are not operant during natural rotavirus i nfection. (C) 2000 Academic Press.