title: The C-terminal sterile alpha motif and the extreme C terminus regulate the transcriptional activity of the alpha isoform of p73.
abstract: p73, a member of the p53 family, is expressed from two separate promoters, generating TA and DeltaN variants. Each variant potentially encodes at least seven alternatively spliced isoforms (alpha-eta). Interestingly, we and others have shown that the alpha isoform of p73 has a weaker transcriptional activity than the beta isoform. Because the alpha isoform has an extended C terminus consisting of a sterile alpha motif (SAM) and an extreme C terminus, it appears that the C terminus is inhibitory. However, how the C terminus inhibits the transcriptional activity of p73 has not been determined. Here, we found that both the SAM and the extreme C terminus exert their inhibitory activity by preventing the accessibility of p300/CBP to the activation domain in p73. Specifically, we showed that the SAM and the extreme C terminus together or individually are capable of repressing the function of p73 activation domain, but neither interacts directly with the activation domain, or suppresses the DNA-binding activity, of the p73 protein. We also showed that the intact state of the SAM and the extreme C terminus is essential for their inhibitory functions such that a small deletion of either the SAM or the extreme C terminus abolishes its inhibitory activity. Furthermore, we showed that both inhibitory domains in the C terminus are capable of suppressing the function of a cis heterologous activation domain from p53 or Gal4. Finally, we showed that both inhibitory domains suppress the ability of p73 to interact with the transcriptional coactivators p300/CBP that are necessary for the initiation of transcription.
authors.affiliation: Department of Cell Biology, The University of Alabama, Birmingham, 35294, USA.
authors.forename: Gang
authors.initials: G
authors.lastname: Liu
authors.forename: Xinbin
authors.initials: X
authors.lastname: Chen
mesh_terms: D020816:Amino Acid Motifs; D017209:Apoptosis; D001483:Base Sequence; D002460:Cell Line; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D016147:Genes, Tumor Suppressor; D006801:Humans; D009687:Nuclear Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins
chemical_list: D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011994:Recombinant Proteins; C000606460:TP73 protein, human; D015534:Trans-Activators; D014157:Transcription Factors; D000072160:Tumor Protein p73; D025521:Tumor Suppressor Proteins