Enhancement of serum-response factor-dependent transcription and DNA binding by the architectural transcription factor HMG-I(Y).
The mechanisms by which HMG-I proteins regulate cell growth are unknown, and their effects on gene expression have only been partially elucidated. We explored the potential interaction between HMG-I proteins and serum-response factor (SRF), a member of the MADS-box family of transcription factors. In cotransfection experiments, HMG-I(Y) potentiated SRF-dependent activation (by more than 5-fold) of two distinct SRF-responsive promoters, c-fos and the smooth muscle-specific gene SM22alpha. This effect was also observed with a heterologous promoter containing multiple copies of the CC(A/T)6GG (CArG) box. HMG-I proteins bound specifically to the CArG boxes of c-fos and SM22alpha in gel mobility shift analysis and enhanced binding of SRF to these CArG boxes. By chelating peptide-immobilized metal affinity chromatography, we mapped the domain of HMG-I(Y) that interacts with SRF to amino acids 50-81, a region that does not bind specifically to DNA in electrophoretic mobility shift assays even though it includes the third AT-hook DNA-binding domain. Surprisingly, HMG-I(Y) mutants that failed to bind DNA still enhanced SRF binding to DNA and SRF-dependent transcription. In contrast, deletion of the HMG-I(Y) 50-81 domain that bound SRF prevented enhancement of transcription. To our knowledge, this is the first report of an HMG-I protein interacting with a MADS-box transcription factor. Our observations suggest that members of the HMG-I family play an important role in SRF-dependent transcription and that their effect is mediated primarily by a protein-protein interaction.
Chin
M T
MT
Cardiovascular Biology Laboratory, Harvard School of Public Health, Boston, Massachusetts 02115, USA.
Pellacani
A
A
Wang
H
H
Lin
S S
SS
Jain
M K
MK
Perrella
M A
MA
Lee
M E
ME
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004330:Drosophila; D016762:Genes, fos; D025741:HMGA1a Protein; D006609:High Mobility Group Proteins / Q000378:metabolism*; D007700:Kinetics; D008840:Microfilament Proteins; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000096:biosynthesis*; D009130:Muscle, Smooth / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides; D011401:Promoter Regions, Genetic; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D026362:Serum Response Factor; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection
D004268:DNA-Binding Proteins; D006609:High Mobility Group Proteins; D008840:Microfilament Proteins; D009124:Muscle Proteins; D009687:Nuclear Proteins; D009838:Oligodeoxyribonucleotides; D016760:Proto-Oncogene Proteins c-fos; D011994:Recombinant Proteins; D026362:Serum Response Factor; C058992:Tagln protein, mouse; D014157:Transcription Factors; C051615:transgelin; D025741:HMGA1a Protein