p300 參與表皮生長因子促進 CTEN 基因表現之調控機制

Abstract

EGFR signaling 是細胞複雜的訊息傳遞途徑之一，而 EGFR 的訊息可透過調控 tensin 家族的 tensin3 及 CTEN 蛋白質含量的消長，使蛋白質含量增加的 CTEN 取代 tensin3，進而拆卸肌動蛋白絲，增強乳癌細胞遷移的能力，但 EGFR 訊息傳導調控 CTEN 表現量上升機制目前仍不清楚。本論文的研究發現，在人類正常前列腺細胞株 RWPE-1 以及人類子宮頸癌細胞株 HeLa 中，若 knockdown p300 時會降低 EGF 誘導 CTEN 之 mRNA 表現量以及蛋白質含量，證實 p300 確實參與了 EGF signaing 調控 CTEN 的途徑。我們進一步證明了 HeLa 細胞受到 EGF 刺激後，透過 MEK/ERK 的訊息傳遞可使 p300 結合上 CTEN 啟動子，並增加 CTEN 啟動子上 histone acetylation 的修飾，以活化 CTEN 基因表現。EGF 也可透過 MEK/ERK pathway 來誘導 HeLa 細胞中 p300 的磷酸化，因此我們推測 EGF signaling 是經由 MEK/ERK 的訊息傳遞促使 p300 磷酸化，進而提升其histone acetyltransferase 的活性，並與 CTEN 啟動子結合而促進 CTEN 基因表現。

Epidermal growth factor receptor (EGFR) signaling is one of the complex signal transduction pathways. Following EGF stimulation, tensin3 expression is downregulated and CTEN is upregulated, to a level that is sufficient for displacement of tensin3 from integrin. Then tensin3 dissociates from focal adhesion, leading to the breakdown of F-actin and initiation of cell migration in breast cancer. However, the mechanism of EGFR-induced CTEN gene expression is still unclear. Our results have shown that knockdown p300 expression could decrease EGF-induced CTEN mRNA and protein levels in a normal human prostate cell lines, RWPE-1, and a human cervical cancer cell line, HeLa. It indicates that p300 participates in the EGF-regulated CTEN expression. We further demonstrate that after EGF stimulation, p300 is recruited to CTEN promoter through MEK/ERK pathway in HeLa cells, and increases histone acetylation on CTEN promoter to activate CTEN gene expression. EGF also induces the phosphorylation of p300 through MEK/ERK pathway in HeLa cells. Therefore, our study suggests that EGF signaling induces the phosphorylation of p300 through MEK/ERK pathway, thereby enhancing its histone acetyltransferase activity, and in turn recruits an increased level of p300 to CTEN promoter to activate CTEN gene expression.