SV40 T antigen increases the expression and activities of p34cdc2, cyclin A, and cyclin B prior to immortalization of human diploid fibroblasts.
SV40 T antigen induces karyotype instability soon after it is expressed in human diploid fibroblasts and ultimately promotes cell immortalization and tumorigenesis. Protein levels and activities of mitotic cell cycle proteins have been shown to be elevated in several immortal cell lines relative to their normal parental cells, suggesting a possible role for the aberrant regulation of mitosis in karyotype instability. We show here that IMR-90 human diploid lung fibroblasts expressing the SV40 tumor antigens display increased protein levels and associated enzymatic activities of cyclin A, cyclin B, and p34cdc2 long before crisis and immortalization. These elevations cannot be explained by faster cell growth or altered cell cycle distributions. Increased protein levels were not totally accounted for by elevated levels of the corresponding mRNA, indicating that T antigen modulates expression at least partially by posttranscriptional mechanisms. These results indicate that perturbation of mitotic regulatory proteins precedes crisis, and imply that altered mitotic control is a direct consequence of T antigen expression rather than an outcome of secondary events associated with immortalization.
Chang
T H
TH
Department of Molecular and Cellular Toxicology, Harvard School of Public Health, Boston, Massachusetts 02115, USA.
Schlegel
R
R
D000595:Amino Acid Sequence; D000952:Antigens, Polyomavirus Transforming / Q000276:immunology*; D016203:CDC2 Protein Kinase / Q000096:biosynthesis* / Q000378:metabolism; D002453:Cell Cycle / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D002460:Cell Line; D002470:Cell Survival / Q000276:immunology; D016213:Cyclins / Q000096:biosynthesis* / Q000378:metabolism; D004171:Diploidy; D005347:Fibroblasts / Q000378:metabolism*; D006801:Humans; D008938:Mitosis / Q000276:immunology; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000096:biosynthesis
D000952:Antigens, Polyomavirus Transforming; D016213:Cyclins; D012333:RNA, Messenger; D016203:CDC2 Protein Kinase