INSM1 functions as a transcriptional repressor of the neuroD/beta2 gene through the recruitment of cyclin D1 and histone deacetylases.
INSM1/IA-1 (insulinoma-associated 1) is a developmentally regulated zinc-finger transcription factor, exclusively expressed in the foetal pancreas and nervous system, and in tumours of neuroendocrine origin. We have identified an INSM1 binding site in the neuroD/beta2 promoter and demonstrated transcriptional repressor activity of INSM1 by transient transfection assay. A chromatin immunoprecipitation assay confirmed that in vivo INSM1 is situated on the promoter region of the neuroD/beta2 gene. In an attempt to elucidate the molecular mechanism of transcriptional repression by the INSM1 gene, cyclin D1 was identified as an interacting protein by using a 45-day-old human foetal brain cDNA library and a yeast two-hybrid screen. The physical association between INSM1 and cyclin D1 was confirmed by in vitro and in vivo pull-down assay. Cyclin D1 co-operates with INSM1 and suppresses neuroD/beta2 promoter activity. Co-immunoprecipitation of INSM1, cyclin D1 and HDACs (histone deacetylases) in mammalian cells revealed that INSM1 interacts with HDAC-1 and -3 and that this interaction is mediated through cyclin D1. Overexpression of cyclin D1 and HDAC-3 significantly enhanced the transcriptional repression activity of INSM1 on the neuroD/beta2 promoter. A further chromatin immunoprecipitation assay confirmed that HDAC-3 occupies this same region of the neuroD/beta2 promoter, by forming a transcription complex with INSM1. Thus we conclude that INSM1 recruits cyclin D1 and HDACs, which confer transcriptional repressor activity.
The Research Institute for Children, Children's Hospital, New Orleans, LA 70118, USA.
Wei-Dong
WD
Liu
Hong-Wei
HW
Wang
Michelle
M
Muguira
Mary B
MB
Breslin
Michael S
MS
Lan
D000256:Adenoviridae / Q000235:genetics; D051792:Basic Helix-Loop-Helix Proteins / Q000096:biosynthesis / Q000235:genetics*; D020295:Brain Stem Neoplasms; D047369:Chromatin Immunoprecipitation; D019938:Cyclin D1 / Q000502:physiology; D004268:DNA-Binding Proteins / Q000502:physiology*; D056284:Histone Deacetylase 1; D056464:Histone Deacetylase 2; D006655:Histone Deacetylases / Q000378:metabolism; D006801:Humans; D007668:Kidney / Q000166:cytology; D008527:Medulloblastoma; D010957:Plasmids; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic / Q000187:drug effects; D014407:Tumor Cells, Cultured; D020798:Two-Hybrid System Techniques
D051792:Basic Helix-Loop-Helix Proteins; D019938:Cyclin D1; D004268:DNA-Binding Proteins; D056284:Histone Deacetylase 1; D056464:Histone Deacetylase 2; D006655:Histone Deacetylases; D012097:Repressor Proteins; C093970:NEUROD1 protein, human; C087342:INSM1 protein, human; C110550:HDAC1 protein, human