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.
Liu
Wei-Dong
WD
The Research Institute for Children, Children's Hospital, New Orleans, LA 70118, USA.
Wang
Hong-Wei
HW
Muguira
Michelle
M
Breslin
Mary B
MB
Lan
Michael S
MS
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