Isolation and characterization of a novel transcription factor that binds to and activates insulin control element-mediated expression.
Pancreatic beta-cell-type-specific transcription of the insulin gene is principally regulated by a single cis-acting DNA sequence element, termed the insulin control element (ICE), which is found within the 5'-flanking region of the gene. The ICE activator is a heteromeric complex composed of an islet alpha/beta-cell-specific factor associated with the ubiquitously distributed E2A-encoded proteins (E12, E47, and E2-5). We describe the isolation and characterization of a cDNA for a protein present in alpha and beta cells, termed INSAF for insulin activator factor, which binds to and activates ICE-mediated expression. INSAF was isolated from a human insulinoma cDNA library. Transfection experiments demonstrated that INSAF activates ICE expression in insulin-expressing cells but not in non-insulin-expressing cells. Cotransfection experiments showed that activation by INSAF was inhibited by Id, a negative regulator of basic helix-loop-helix (bHLH) protein function. INSAF was also shown to associate in vitro with the bHLH protein E12. In addition, affinity-purified INSAF antiserum abolished the formation of the activator-specific ICE-binding complex. Immunohistochemical studies indicate that INSAF is restricted in terms of its expression pattern, in that INSAF appears to be detected only within the nuclei of islet pancreatic alpha and beta cells. All of these data are consistent with the proposal that INSAF is either part of the ICE activator or is antigenically related to the specific activator required for insulin gene transcription.
Robinson
G L
GL
Department of Molecular Physiology and Biophysics, Vanderbilt University Medical Center, Nashville, Tennessee 37232.
Cordle
S R
SR
Henderson
E
E
Weil
P A
PA
Teitelman
G
G
Stein
R
R
D000595:Amino Acid Sequence; D001483:Base Sequence; D002451:Cell Compartmentation; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D051798:Inhibitor of Differentiation Protein 1; D007328:Insulin / Q000494:pharmacology*; D007340:Insulinoma / Q000235:genetics; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D009928:Organ Specificity; D010179:Pancreas / Q000502:physiology*; D010190:Pancreatic Neoplasms / Q000235:genetics; D011485:Protein Binding; D012045:Regulatory Sequences, Nucleic Acid; D012097:Repressor Proteins; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D051820:TCF Transcription Factors; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors; D015533:Transcriptional Activation
D004268:DNA-Binding Proteins; C497453:ID1 protein, human; C089509:INSAF protein, human; D051798:Inhibitor of Differentiation Protein 1; D007328:Insulin; D009687:Nuclear Proteins; D012097:Repressor Proteins; D051820:TCF Transcription Factors; C544912:TCF7L1 protein, human; D015534:Trans-Activators; D058125:Transcription Factor 7-Like 1 Protein; D014157:Transcription Factors