Estrogen is known to increase the expression of type 1 inositol 1,4,5-trisphosphate receptor (ITPR1) in G-292 osteoblastic cell line.  Change in ITPR1 expression alters the growth capacity and signaling potential of many estrogen-sensitive cells.  The action of estrogen on ITPR1 expression is mediated by the –137/-113 region of the ITPR1 gene promoter.  The –137/-113 region lacks a consensus estrogen response element (ERE), but has a consensus AP-2 binding sequence [-134(GCCCAGGGG)-126].  Objectives: To analyze the binding of the estrogen receptor (ERβ) and the AP-2α transcription factor protein to the ITPR1 promoter in estrogen treated human osteosarcoma (G-292) cell lines in vivo.  A model is proposed that ERβ regulates transcription of ITPR1 through its interactions with AP-2α bound to -137/-113 region.  Methods: Chromatin immunoprecipitation (ChIP) using enzymatic shearing and polymerase chain reaction (PCR) for amplification of the specific DNA of the ITPR1 promoter.  Results: ChIP of the G-292 sheared DNA using anti-ERβ and anti-AP-2α antibodies, along with its corresponding PCR products showed amplification using the -222/-63 region of the ITPR1 promoter.  Conclusions: DNA immunoprecipitated with anti-ERβ and anti-AP-2α antibodies was used successfully to amplify the -222/-63 region of the promoter.  Data suggest that AP-2α and ERβ are bound to the -222/-63 region of the ITPR1 in vivo.  These studies support the hypothesis that estrogen receptors regulate expression of the ITPR1 gene through a possible interaction with AP-2α bound to the gene promoter.  This mechanism of ITPR1 regulation may contribute to the growth and signaling capacity of estrogen-sensitive cells.  This study was supported by the ADA Health Foundation through the 2006 AADR Student Research Fellowship.

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