Transcriptional activation by pRB and its coordination with SWI/SNF recruitment.
A central question in cancer biology is why most tumor susceptibility genes are linked with only limited types of cancer. Human germ-line mutation of the retinoblastoma susceptibility gene Rb1 is closely linked with just retinoblastoma and osteosarcoma, although the gene is universally expressed. Functional analysis of pRB and its close relatives, p107 and p130, has largely focused on their roles in repression of proliferation across all tissue types, but genetic evidence indicates an active requirement for pRB in osteoblast differentiation that correlates more directly with osteosarcoma susceptibility. Still, potential promoter targets of pRB and its role in normally differentiating osteoblasts remain insufficiently characterized. Here, an early marker of osteoblast differentiation, alkaline phosphatase, is identified as a direct promoter activation target of pRB. One role of pRB on this promoter is to displace the histone lysine demethylase KDM5A, thereby favoring trimethylation of H3K4, a promoter activation mark. A major new aspect of pRB-mediated transcriptional activation revealed in this promoter analysis is its role in recruitment of an activating SWI/SNF chromatin-remodeling complex. SWI/SNF is a critical coordinator of tissue-specific gene expression. In osteoblasts, SWI/SNF complexes containing the BRM ATPase repress osteoblast-specific genes to maintain the precursor state, whereas the alternative ATPase BRG1 distinguishes an activating SWI/SNF complex necessary for RNA polymerase-II recruitment. A switch from BRM to BRG1 on the alkaline phosphatase promoter marks the onset of differentiation and is accomplished in a precise two-step mechanism. Dissociation of BRM-containing SWI/SNF depends on p300, and association of BRG1-containing SWI/SNF depends on pRB.
Flowers
Stephen
S
Department of Orthopaedics, New Jersey Medical School-University Hospital Cancer Center, UMDNJ, Newark, New Jersey 07103, USA.
Beck
George R
GR
Moran
Elizabeth
E
D000469:Alkaline Phosphatase / Q000235:genetics* / Q000378:metabolism; D015152:Blotting, Northern; D002454:Cell Differentiation; D002478:Cells, Cultured; D047369:Chromatin Immunoprecipitation; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism*; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation; D012321:DNA-Directed RNA Polymerases / Q000235:genetics / Q000378:metabolism; D006657:Histones / Q000235:genetics / Q000378:metabolism; D006801:Humans; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D016160:Retinoblastoma Protein / Q000502:physiology*; D056485:Retinoblastoma-Binding Protein 2 / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
D002868:Chromosomal Proteins, Non-Histone; D006657:Histones; D009687:Nuclear Proteins; D012333:RNA, Messenger; D016160:Retinoblastoma Protein; C084011:SMARCA2 protein, human; C445179:SWI-SNF-B chromatin-remodeling complex; D014157:Transcription Factors; C070050:KDM5A protein, human; D056485:Retinoblastoma-Binding Protein 2; D012321:DNA-Directed RNA Polymerases; D000469:Alkaline Phosphatase; C084108:SMARCA4 protein, human; D004265:DNA Helicases