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Articles by A Kamat
Total Records ( 1 ) for A Kamat
  P Kumar , A Kamat and C. R. Mendelson

A 246-bp region upstream of placenta-specific exon I.1 of the human aromatase (hCYP19) gene mediates placenta-specific, developmental, and O2 regulation of expression. In this study, trophoblast differentiation and associated induction of CYP19 expression were prevented when cytotrophoblasts were cultured in phenol red-free medium containing charcoal-stripped serum or with the estrogen receptor (ER) antagonist, ICI 182,780, suggesting a stimulatory role of estrogen/ER. ER protein was expressed in human trophoblasts and increased during syncytiotrophoblast differentiation, whereas ERβ was undetectable. Mutational analysis revealed that an estrogen response element-like sequence (ERE-LS) at –208 bp is required for inductive effects of estradiol/ER on hCYP19I.1 promoter activity in transfected COS-7 cells. Increased binding of syncytiotrophoblast compared with cytotrophoblast nuclear proteins to the ERE-LS was observed in vitro; however, ER antibodies failed to supershift the complex and in vitro-transcribed/translated ER did not bind. Nonetheless, chromatin immunoprecipitation assays in cultured trophoblasts revealed recruitment of endogenous ER to the –255- to –155-bp region containing the ERE-LS before induction of hCYP19 expression; this was inhibited by ICI 182,780. Chromatin immunoprecipitation also revealed increased acetylated histone H3(K9/14) and decreased methylated histone H3(K9) associated with this region during trophoblast differentiation. These modifications were prevented when trophoblasts were incubated with ICI 182,780, suggesting that ER recruitment to the –255- to –155-bp region promotes histone modifications leading to increased hCYP19 transcription. Thus, during trophoblast differentiation, estrogen/ER exerts a positive feedback role, which promotes permissive histone modifications that are associated with induction of hCYP19 gene transcription.

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