Influence of the Viral Regulatory Region on Tumor Induction by Simian Virus 40 in Hamsters

ABSTRACT Most of the simian virus 40 (SV40) genome is conserved among isolates, but the noncoding regulatory region and the genomic region encoding the large T-antigen C terminus (T-ag-C) may exhibit considerable variation. We demonstrate here that SV40 isolates differ in their oncogenic potentials in Syrian golden hamsters. Experimental animals were inoculated intraperitoneally with 107 PFU of parental or recombinant SV40 viruses and were observed for 12 months to identify genetic determinants of oncogenicity. The viral regulatory region was found to exert a statistically significant influence on tumor incidence, whereas the T-ag-C played a minor role. Viruses with a single enhancer (1E) were more oncogenic than those with a two-enhancer (2E) structure. Rearrangements in the 1E viral regulatory region were detected in 4 of 60 (6.7%) tumors. Viral loads in tumors varied, with a median of 5.4 SV40 genome copies per cell. Infectious SV40 was rescued from 15 of 37 (40%) cell lines established from tumors. Most hamsters with tumors and many without tumors produced antibodies to T antigen. All viruses displayed similar transforming frequencies in vitro, suggesting that differences in oncogenic potential in vivo were due to host responses to viral infection. This study shows that SV40 strains differ in their biological properties, suggests that SV40 replicates to some level in hamsters, and indicates that the outcome of an SV40 infection may depend on the viral strain present.

Activation of the simian virus 40 (SV40) genome abrogates sensitivity to AVP in a rabbit collecting tubule cell line by repressing membrane expression of AVP receptors.

To analyze the role of SV40 genome in the phenotypic alterations previously observed in SV40-transformed cell lines, we infected rabbit renal cortical cells with a temperature-sensitive SV40 mutant strain (tsA58) and compared the cell phenotypes at temperatures permissive (33 degrees C) and restrictive (39.5 degrees C) for SV40 genome expression. At both temperatures, the resulting cell line (RC.SVtsA58) expresses cytokeratin and uvomorulin, but epithelial differentiation is more elaborate at 39.5 degrees C as shown by the formation of a well-organized cuboidal monolayer with numerous tight junctions and desmosomes. Functional characteristics are also markedly influenced by the culture temperature: cells grown at 33 degrees C respond only to isoproterenol (ISO, 10(-6) M) by a sevenfold increase in cAMP cell content above basal values; in contrast, when transferred to 39.5 degrees C, they exhibit increased sensitivity to ISO (ISO/basal: 19.1) and a dramatic response to 10(-7) M dDarginine vasopressin (dDAVP/basal: 18.2, apparent Ka: 5 X 10(-9) M) which peaks 48 h after the temperature shift. The latter is associated with membrane expression of V2-type AVP receptors (approximately 50 fmol/10(6) cells) which are undetectable when SV40 genome is activated (33 degrees C). Clonal analysis, additivity studies, and desensitization experiments argue for the presence of a single cell type responsive to both AVP and ISO. The characteristics of the RC. SVtsA58 cell line at 39.5 degrees C (effector-stimulated cAMP profile, lack of expression of brush-border hydrolases and Tamm-Horsfall protein) suggest that it originates from the cortical collecting tubule, and probably from principal cells.