Differential positive control by Oct-1 and Oct-2: activation of a transcriptionally silent motif through Oct-1 and VP16 corecruitment.
Transcriptional regulation by the ubiquitous human POU homeo domain protein Oct-1 and the related B-cell protein Oct-2 is a model for understanding how proteins that recognize the same regulatory site elicit different programs of gene transcription. Here, we describe a mechanism for differential promoter activation whereby only Oct-1, through selective corecruitment with the herpesvirus trans-activator VP16, acquires the ability to stimulate transcription from a TAATGARAT-containing site that responds to neither Oct-1 nor Oct-2 alone. To measure differential in vivo activation by human Oct-1 and Oct-2 in response to VP16, we have developed a transient assay in murine NIH-3T3 cells. Surprisingly, murine Oct-1 associates with VP16 much less effectively than its human counterpart, most likely because the murine Oct-1 homeo domain differs at four positions from the human Oct-1 homeo domain. The murine cell transient assay shows directly that human Oct-1, but not human Oct-2, can respond to VP16 in vivo. The Oct-1 DNA-binding POU domain is sufficient and the Oct-1 homeo domain is critical for this response, because an Oct-1 POU domain containing the Oct-2 homeo domain fails to respond to the VP16-induced positive control of transcription. Thus, by selective homeo domain interaction and corecruitment to an otherwise silent regulatory element, VP16 expands the repertoire of sites responsive to Oct-1 without affecting the activity of its close relative Oct-2.
Cleary
M A
MA
Cold Spring Harbor Laboratory, New York 11724.
Stern
S
S
Tanaka
M
M
Herr
W
W
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D004247:DNA; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D005914:Globins / Q000235:genetics; D006367:HeLa Cells; D017405:Herpes Simplex Virus Protein Vmw65 / Q000378:metabolism*; D051863:Host Cell Factor C1; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D050811:Octamer Transcription Factor-1; D050813:Octamer Transcription Factor-2; D050809:POU Domain Factors; D011401:Promoter Regions, Genetic; D017413:Ribonucleoprotein, U2 Small Nuclear / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
D004268:DNA-Binding Proteins; C497692:HCFC1 protein, human; C497693:Hcfc1 protein, mouse; D017405:Herpes Simplex Virus Protein Vmw65; D051863:Host Cell Factor C1; D050811:Octamer Transcription Factor-1; D050813:Octamer Transcription Factor-2; D050809:POU Domain Factors; C494165:POU2F1 protein, human; C058435:POU2F2 protein, human; C494166:Pou2f1 protein, mouse; C489206:Pou2f2 protein, mouse; D017413:Ribonucleoprotein, U2 Small Nuclear; D014157:Transcription Factors; D005914:Globins; D004247:DNA