Regulation of Gfi1B Expression in K562 Cells During Phorbol Ester-Induced Differentiation

• Main Authors: LI HSIN-YI, 黎欣怡
• Other Authors: Chang Zee-Feng
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/79851100290122395506

碩士 === 國立臺灣大學 === 生化學研究所 === 89 === Gfi1B（growth factor independence 1B） is a cellular proto-oncogene that encodes a transcriptional repressor with an N-terminal SNAG repressor domain and a C-terminal zinc finger domain. Gfi1B expression is restricted to bone marrow and spleen, and is found to be expressed at very high levels in the CML (chronic myelocytic leukemia) line K562. Its biological function in K562 cells is still unclear. The purpose of this study is to investigate the regulation of Gfi1B expression in K562 cells. In this study, we found that the expressed levels of Gfi1B protein decline significantly during TPA-induced differentiation of K562 cells. The results indicated that TPA-induced downregulation of Gfi1B expression is through a mechanism involving ubiquitin-dependent proteasomal degradation. By deletion analysis, it seemed that the region covering amino acid 45 to 137 contains the signal sequence for TPA- induced degradation. Furthermore, the TPA-induced Gfi1B degradation requires the involvement of the MAPK (mitogen-activated protein kinase)-dependent pathway and appears to be a cell type-specific event. Here we also showed that there is a reciprocal relationship between the expression of Gfi1B and cyclin-dependent kinase inhibitor, p21WAF1, in response to the TPA treatment. Gfi1B could repress the transcriptional activity of the p21WAF1 promoter when overexpressed in HeLa cells. However, abrogation of the endogenous Gfi1B expression by RNA interference in K562 cells did not promote the expression of p21WAF1, suggesting that the elevated levels of Gfi1B in K562 cells is not sufficient to suppress the expression of p21WAF1 during proliferation. Overall, the results from this study provide evidences that the expression of Gfi1B is highly regulated and is probably important to the growth control in K562 cells.