The v-rel oncogene: insights into the mechanism of transcriptional activation, repression, and transformation.
The v-rel oncogene product from the avian reticuloendotheliosis virus strain T corresponds to a member of the Rel-related family of enhancer-binding proteins that includes both the mammalian 50- and 65-kDa subunits of the NF-kappa B transcription factor complex. However, in contrast to NF-kappa B, v-Rel has been shown to function as a dominant-negative repressor of kappa B-dependent transcription in many mature cell types. We now demonstrate that a highly conserved motif within the Rel homology domain of v-Rel containing a consensus protein kinase A phosphorylation site is required for DNA binding, transcriptional repression, and cellular transformation mediated by this oncoprotein. However, replacement of the serine phosphate acceptor within the protein kinase A site with an alanine did not alter any of these functions of v-Rel, suggesting that phosphorylation at this site is not central to the regulation of this oncogene product. Rather, the inactive mutations appear to identify a functional domain within v-Rel required for these various biological activities. It is notable that these same mutations do not impair the ability of v-Rel to heterodimerize with the 50-kDa subunit of NF-kappa B, suggesting that v-Rel-mediated transcriptional repression likely involves direct nuclear blockade of the kappa B enhancer rather than indirect alterations in the composition of preformed cytoplasmic NF-kappa B complexes. Paradoxically, when introduced into undifferentiated F9 cells, v-Rel functions as a kappa B-specific transcriptional activator rather than as a dominant-negative repressor. These stimulatory effects of v-Rel require both the conserved protein kinase A phosphorylation site and additional unique C-terminal sequences not needed for v-Rel-mediated repression in mature cells. Retinoic acid-induced differentiation of these F9 cells restores the repressor function of v-Rel. These opposing biological actions of v-Rel occurring in cells at distinct stages of differentiation may have important implications for the mechanism of v-Rel-mediated transformation occurring in avian splenocytes.
Walker
W H
WH
Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710.
Stein
B
B
Ganchi
P A
PA
Hoffman
J A
JA
Kaufman
P A
PA
Ballard
D W
DW
Hannink
M
M
Greene
W C
WC
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D015967:Gene Expression Regulation, Viral; D005822:Genetic Vectors; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000378:metabolism; D009838:Oligodeoxyribonucleotides; D020572:Oncogene Proteins v-rel; D009857:Oncogenes; D010957:Plasmids; D014176:Protein Biosynthesis; D011505:Protein-Tyrosine Kinases / Q000235:genetics; D001356:Reticuloendotheliosis virus / Q000235:genetics*; D015682:Retroviridae Proteins, Oncogenic / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D016385:TATA Box; D013724:Teratoma; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
D016328:NF-kappa B; D009838:Oligodeoxyribonucleotides; D020572:Oncogene Proteins v-rel; D015682:Retroviridae Proteins, Oncogenic; D015500:Chloramphenicol O-Acetyltransferase; D011505:Protein-Tyrosine Kinases