Dominant negative murine serum response factor: alternative splicing within the activation domain inhibits transactivation of serum response factor binding targets.
Primary transcripts encoding the MADS box superfamily of proteins, such as MEF2 in animals and ZEMa in plants, are alternatively spliced, producing several isoformic species. We show here that murine serum response factor (SRF) primary RNA transcripts are alternatively spliced at the fifth exon, deleting approximately one-third of the C-terminal activation domain. Among the different muscle types examined, visceral smooth muscles have a very low ratio of SRFDelta5 to SRF. Increased levels of SRFDelta5 correlates well with reduced smooth muscle contractile gene activity within the elastic aortic arch, suggesting important biological roles for differential expression of SRFDelta5 variant relative to wild-type SRF. SRFDelta5 forms DNA binding-competent homodimers and heterodimers. SRFDelta5 acts as a naturally occurring dominant negative regulatory mutant that blocks SRF-dependent skeletal alpha-actin, cardiac alpha-actin, smooth alpha-actin, SM22alpha, and SRF promoter-luciferase reporter activities. Expression of SRFDelta5 interferes with differentiation of myogenic C2C12 cells and the appearance of skeletal alpha-actin and myogenin mRNAs. SRFDelta5 repressed the serum-induced activity of the c-fos serum response element. SRFDelta5 fused to the yeast Gal4 DNA binding domain displayed low transcriptional activity, which was complemented by overexpression of the coactivator ATF6. These results indicate that the absence of exon 5 might be bypassed through recruitment of transcription factors that interact with extra-exon 5 regions in the transcriptional activating domain. The novel alternatively spliced isoform of SRF, SRFDelta5, may play an important regulatory role in modulating SRF-dependent gene expression.
Belaguli
N S
NS
Departments of Cell Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
Zhou
W
W
Trinh
T H
TH
Majesky
M W
MW
Schwartz
R J
RJ
D016475:3T3 Cells; D051702:Activating Transcription Factor 6; D017398:Alternative Splicing; D000818:Animals; D001011:Aorta / Q000378:metabolism; D001665:Binding Sites; D002454:Cell Differentiation; D002460:Cell Line; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D019281:Dimerization; D005091:Exons; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D026362:Serum Response Factor; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation
D051702:Activating Transcription Factor 6; C497112:Atf6 protein, mouse; C497113:Atf6 protein, rat; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C052130:GAL4 protein, S cerevisiae; D009687:Nuclear Proteins; D016760:Proto-Oncogene Proteins c-fos; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D026362:Serum Response Factor; D014157:Transcription Factors