探討RPS20在核糖體轉譯中的功能及其對癌細胞增殖的影響

核糖體是在轉譯過程中相當重要的胞器，是由大次單元與小次單元組成。核糖體蛋白S20是組成核糖體小次單元的一部分，對於蛋白質合成至關重要。本研究主要探討RPS20過度表現對KB細胞的影響，使用過度表達RPS20蛋白的KB細胞株及其對照組KB C1細胞作為研究對象。在軟瓊膠脂生長分析 (soft agar assay) 與細胞生長曲線分析的結果顯示，RPS20的過度表現顯著抑制KB細胞的增殖及群落形成能力。由細胞週期分析進一步表明，這一現象與細胞週期停滯在G1期有關，並且觀察到cyclin D蛋白表現量的上升，cyclin E、A、B蛋白表現量下降。此外，後續蛋白質分析中發現，RPS20過表達會降低許多訊號蛋白的表現量，像是MAPK家族的ERK、JNK、P38，以及β-actin、MDM2、p53、eIF2α等。多核糖體分析 (polysome profiling) 顯示，這種多種訊號途徑蛋白表現量下降的原因是由於RPS20導致蛋白質合成的效率降低。多核糖體分析及共同免疫沉澱分析 (co-immunoprecipitation analysis) 進一步揭示RPS20的泛素化修飾狀況，表明RPS20的過度表現會影響核糖體在泛素化調控的動態平衡。因此，我們發現RPS20會影響蛋白質合成進而影響細胞增殖，並對於核糖體泛素化調控的潛在機制提供一個新的見解，這對於核糖體的品質管制 (Ribosome-associated quality control, RQC) 機制具有重要意義。

The ribosome, a crucial component in the translation process, is composed of large and small subunits. Ribosomal protein S20 (RPS20) is a vital part of the small subunit and plays an essential role in protein synthesis. In this study, we investigated the effects of RPS20 overexpression in KB cells by comparing KB cells overexpressing RPS20 with control KB C1 cells. Results from the soft agar assay and cell growth curve analysis indicated that RPS20 overexpression significantly inhibited the proliferation and colony formation of KB cells. Cell cycle analysis further revealed that these effects were associated with G1 phase arrest, characterized by an increase in cyclin D expression and a decrease in cyclins E, A, and B. Additionally, subsequent protein analyses demonstrated that RPS20 overexpression led to a reduction in the expression of multiple signaling pathway proteins. Polysome profiling suggested that this reduction in protein expression is due to decreased protein synthesis efficiency caused by RPS20. Furthermore, polysome profiling and co-immunoprecipitation analysis revealed the ubiquitination status of RPS20, showing that its overexpression disrupts the dynamic balance of ubiquitination regulation in the ribosome. Overall, our findings suggest that RPS20 impacts protein synthesis and cell growth and provide new insights into the potential regulation of ribosomal ubiquitination, offering a better understanding of ribosome-associated quality control (RQC) mechanisms.