HUMAN CYTOMEGALOVIRUS MTRII ONCOPROTEIN BINDS TO P53 AND DOWN-REGULATES P53-ACTIVATED TRANSCRIPTION

The 79-amino-acid (79-aa) open reading frame (UL111a) gene within morp hological transforming region II (mtrII) of human cytomegalovirus stra in Towne has been shown to transform rodent cells in vitro (J. Thompso n, J. Doniger, and L. J. Rosenthal, Arch. Virol. 136:161-172, 1994). M oreover, a translation termination linker (TTL) mutant of mtrII that c oded for the first 49 aa of mtrII oncoprotein (designated TTL(49)) was sufficient for malignant transformation, whereas a TTL mutant that co ded for the first 24 aa (designated TTL(24)) was not. The current stud y demonstrates the binding of mtrII oncoprotein to the tumor suppresso r protein p53 both in vivo using transiently transfected cells and in vitro using labeled proteins, Furthermore, the C-terminally truncated mtrII protein TTL(49), but not truncated protein TTL(24), bound to p53 . The mtrII binding domain mapped to the N-terminal region of p53, res idues 1 to 106, with a critical region from aa 27 to 44, whereas the p 53 binding domain of mtrII protein was the first 49 aa, Furthermore, m trII inhibited p53-activated transcription, indicating its ability to alter p53-directed cellular regulatory mechanisms, mtrII oncoprotein w as detected both in stably transfected NIH 3T3 cell lines and human cy tomegalovirus-infected HEL 299 cells (as early as 12 h after infection ) in the perinuclear region and in the nucleus, mtrII-transformed cell lines, at both early and late passage, exhibited high levels of p53 w ith a 15-fold-extended half-life, However, p53-activated transcription was suppressed in these cells in spite of the increased p53 levels, F inally, the results with wild-type mtrII and its TTL mutants with resp ect to p53 binding, p53-activated transcription, and transforming abil ity suggest that the mechanism of mtrII transformation is linked to bo th p53 binding and disruption of p53 cell regulation.