探討Rheb-RACK1的交互作用在BALB/3T3細胞株之生理意義

Abstract

Rheb (Ras homologue enriched in brain) 屬於 ras家族中的一員，可以辨識並水解鳥苷三磷酸 (GTP)。Rheb近年來逐漸的備受重視，是因為許多細胞的生理功能，包括養分吸收，細胞週期的進行，尤其是細胞生長。Rheb主要調控細胞生長的機制是藉由 PI3K/Akt/mTOR (mammalian target of rapamycin) 的訊息傳遞途徑，來調控細胞內轉譯的進行。而最近的研究指出Rheb會藉由抑制B-Raf的磷酸化進而抑制ras調控的NIH3T3細胞株的轉型。 RACK1 (receptor for activated C-kinase 1) 屬於WD40家族，具有七個葉片狀的螺旋槳構造，每一個葉片都可以負責和多種不同的蛋白質作用，像是蛋白激酶C (protein kinase C, PKC), Src, 數種生長因子的接受器，少數 ras家族成員等等。先前的研究指出 RACK1二聚體會參與 ras的訊息傳遞而且可能有參與 ras調控的細胞轉型的機制中。 在我們的實驗中，我們首先建立了Rheb和RhebS16H的質體並轉染到 BALB/3T3細胞株。暫時性轉染的細胞我們用流式細胞儀及細胞分選儀來得到均質具有轉染的細胞族群。與 BALB/3T3細胞株比較起來，Rheb和RhebS16H轉染過的細胞明顯的降低期細胞分裂的速率。我們也利用了免疫沈澱法來證明 Rheb-RACK1間的交互作用。之後我們給予細胞株rapamycin (mTOR抑制劑)，但是我們並沒有發現對於 Rheb-RACK1間的交互作用有顯著的干擾。而未來的實驗將會著重在 Rheb-RACK1間的交互作用與ras 調控細胞轉型之間的探討。

Rheb (Ras homologue enriched in brain) is a small G protein belonged to the ras family, which bind and hydrolyze GTP. Rheb has recently attracted more attentions because of its multiple functions in regulating nutrient sensing and uptake, cell cycle progression, and especially cell growth. The critical role of Rheb in regulating cell growth is due to its involvement in PI3K/Akt/mTOR (mammalian target of rapamycin) signaling pathway in translational modulation. Recent studies also showed that Rheb inhibits ras-mediated transformation in NIH3T3 cells through inhibiting B-Raf phosphorylation. RACK1 (receptor for activated C-kinase 1) belongs to WD40 family, having seven-blade propeller structure, which is responsible for molecular interactions with various proteins, including, PKC, Src, several growth factor receptors, few ras family members etc. Previous study has showed that RACK1 dimer participates in ras signaling pathway and might play a role in ras transformation. In our study, we constructed Rheb and RhebS16H plasmid to transfect BALB/3T3 cells. We transiently over-expressed Rheb and RhebS16H in cells and utilized flowcytometry and cell sorter to achieve homogeneous population. Both Rheb and RhebS16H transfectants decelerated their cell division compared with BALB/3T3 cell. We performed immunoprecipitation to prove Rheb-RACK1 interaction. Then we challenged the cell with Rapamycin (mTOR inhibitor), but we did not find significant disturbance in Rheb-RACK1 interaction. Proceeding study is focused on the role of Rheb-RACK1 interaction in ras-mediated transformation.