The mechanism by which TCERG1 inhibits the growth arrest activity of C/EBPa
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Transcription elongation regulator 1 (TCERG1) is a nuclear protein involved in transcriptional elongation and splicing events, suggesting these two activities may be connected. Moreover, TCERG1 was recently identified as a novel interactor and co-repressor of CCAAT/Enhancer Binding Protein α (C/EBPα) transcriptional activity, suggesting TCERG1 has additional biological roles. Interestingly, TCERG1 also inhibits the growth arrest activity of C/EBPα. Additionally, the original clone found to interact with C/EBPα consisted of only the amino-terminal domain of TCERG1 and functional analysis of this clone indicated that it retained the ability to repress both C/EBPα mediated growth arrest and transcriptional activity. Furthermore, a TCERG1 mutant whose amino-terminal region was deleted was unable to interact with or repress the transcriptional and growth arrest activities of C/EBPα, suggesting the functional domain(s) lie elsewhere. In this study, domains of TCERG1 were examined for the ability to inhibit C/EBPα-mediated growth arrest and the mechanism whereby this effect occurs. By exploiting fluorescent properties of expressed proteins fused with green fluorescent protein, the extent to which each TCERG1 mutant was able to reverse C/EBPα-mediated growth arrest of cultured cells was assessed. Our analyses suggest that the inhibitory activity of TCERG1 lies within the amino-terminal region and may involve WWI and WWII domains within this region. Additionally, laser scanning confocal microscopy (LCSM) was used to visualize the subnuclear localization of fluorescent proteins fused to TCERG1 and C/EBPα. When expressed alone, TCERG1 localized to splicing factor-rich nuclear speckles while C/EBPα was found to reside in discrete punctate foci, both localization patterns being distinct and different from each other. Results from co-localization studies after co-expressing both proteins indicate an alteration in the subnuclear distribution of TCERG1. Furthermore, TCERG1 co-localizes with C/EBPα, suggesting a possible mechanism whereby TCERG1 inhibits the growth arrest and transcriptional activities mediated by C/EBPα.
DegreeMaster of Science (M.Sc.)
CommitteeLaferte, Suzanne; Khandelwal, Ramji; Warrington, Rob; Mousseau, Darrell
Copyright DateMarch 2010
laser scanning confocal microscope