Pak2對於上皮細胞極化與功能的角色

Abstract

腎臟上皮細胞的極性對於進行方向性的物質運輸至關重要，而這個過程仰賴正確的細胞接合結構與動態穩定的肌動蛋白骨架。Pak2是一種 p21活化型激酶，已知在多種細胞中參與細胞骨架與極性的調控，但其在腎臟集尿管細胞中的功能尚未明確。本研究顯示，在腎臟集尿管細胞mpkCCD中降低Pak2表現會使跨上皮電阻下降以及接合蛋白 ZO-1 和 E-cadherin 的錯誤定位，代表細胞極化受損。此外，我們觀察到降低Pak2表現會使細胞質中單體肌動蛋白（G-actin）顯著升高，顯示肌動蛋白聚合受阻。更重要的是，Pak2表現下降也導致腦下垂體加壓素第二型受體（Avpr2）和水通道蛋白2（Aqp2）基因的 mRNA表現量降低，而這兩者皆是血管加壓素（vasopressin）訊號傳導的重要組成。使用細胞骨架聚合抑制劑 cytochalasin D處理細胞，模擬細胞Pak2降低的狀況，同樣可以觀察到提升G-actin水平、破壞細胞極性並抑制Avpr2和Aqp2基因表現，進一步證實G-actin升高對這些效應具有關鍵影響。整體而言，本研究發現 Pak2在維持腎臟集尿管細胞的細胞骨架動態、細胞極性，以及血管加壓素相關基因表達中扮演關鍵角色，並揭示了細胞骨架與基因轉錄之間新的調控連結。

Cell polarization is essential for vectorial transport in renal epithelial cells and relies on proper junctional organization and actin cytoskeletal dynamics. Pak2, a p21-activated kinase, is known to regulate cytoskeletal organization and polarity in various cell types, but its role in kidney collecting duct cells remains unclear. In this study, we show that Pak2 knockdown in kidney collecting duct cells (mpkCCD) disrupts epithelial polarization, as indicated by reduced transepithelial electrical resistance and mis-localization of junctional proteins ZO-1 and E-cadherin. This effect was accompanied by elevated cytoplasmic G-actin levels, suggesting impaired actin polymerization. Notably, Pak2 knockdown also led to decreased mRNA expression of Avpr2 and Aqp2, key components for the vasopressin response. Treatment with cytochalasin D, an actin polymerization inhibitor that increases G-actin, phenocopied the effects of Pak2 knockdown, indicating that elevated G-actin impairs both polarity and gene transcription. These findings identify Pak2 as a critical regulator of actin dynamics, cell polarity, and vasopressin-responsive gene expression in renal collecting duct cells.