| Summary: | 碩士 === 國立陽明大學 === 生化暨分子生物研究所 === 98 === Human MMS21 (hMMS21) is a SUMO ligase required for DNA repair in human cells. Our laboratory demonstrated previously that hMMS21 could regulate cell proliferation; whereas knockdown of hMMS21 reduced cell growth, ectopic expression of hMMS21 enhanced the cell proliferation. Analysis of cell cycle profile by flow cytometry showed that G0/G1 and G1/S transition were both delayed in hMMS21-knockdowned MCF-7 stable clone (I15), suggesting that hMMS21 may play a role in cell cycle control. Previous work in our lab showed that cyclin E/CDK2 activity, protein expression of E2F1 and c-Myc were all lower in I15 than MCF-7 cells. Since estrogen plays a major role in supporting MCF-7 cell growth by stimulating c-Myc and cyclin D1 expression, we examined the effect of 17β-estradiol (E2) on growth of both MCF-7 and I15 cells. Our experimental results showed that E2-dependent cell proliferation was significantly decreased in I15 than MCF-7 cells. Similarly, protein and mRNA levels of c-Myc and cyclin D1 were lower in I15 cells. This indicates that hMMS21 is required for proper ER signaling pathway. In addition, we found that E2-stimulated Src and Akt activities were greatly depressed in I15 cells and ectopic expression of v-Src may restore the responses of c-Myc and cyclin D1 expressions to E2. Furthermore, we found that the association of ERα-Src-p85 was affected by knockdown of hMMS21 by siRNA. These findings thus suggest that hMMS21 may regulate ER signaling and consequently cell growth by modulating ERα-Src-p85 complex formation.
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