Involvement of Ubc9 in tumor growth in nude mice

Abstract

1685

Post-translational modifications play an important role in regulating cellular functions because vast majority of critical proteins such as transcription factors and nuclear receptors are subject to such modifications. Small ubiquitin-related modifier (SUMO) conjugations or sumoylation has been recently identified and implicated in regulating a variety of cellular pathways. Although it is well demonstrated that alterations of ubiquitination pathways can lead to development of cancer, the role for sumoylation in this aspect is unclear. Since Ubc9 is an E2 conjugating enzyme essential for sumoylation, we overexpressed a wild type Ubc9 (Ubc9-WT) and a dominant negative mutant Ubc9 (Ubc9-DN) in MCF7 cells to determine the effect of alteration of Ubc9 on tumor growth in nude mice. While overexpression of Ubc9-WT in MCF7 cells enhances tumor growth, the cells overexpressing Ubc9-DN are less tumorigenic, suggesting a role of Ubc9 in tumor growth. To understand molecular mechanisms underlying this observation, we examined cell cycle profiles and growth rate of these cells. Although no significant alteration of cell cycle profile was detected in these cells, we found that MCF7 cells overexpressing Ubc9-WT grow faster; those cells overexpressing Ubc9-DN grow more slowly than the vector-transfected cells. Of considerable interest, we found that cells expressing Ubc9-DN reveal a higher apoptotic rate, which is associated with down-regulation of anti-apoptotic genes such as Bcl-2. Finally, we also found that up-regulation of Ubc9 is associated with human malignancy in ovarian cancer patient specimens. Together, these results suggest that alteration of Ubc9 could be a potential factor contributing to tumorigenesis (Supported in part by CA40570, CA30103 and CA102630 from NCI, BC980585 from DOD and in part by UIC).