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Hahn, Stefanie (2014): Characterization of ZNF281 and its role in colorectal carcinogenesis. Dissertation, LMU München: Medizinische Fakultät



The vast majority of colorectal cancer (CRC)-related deaths is caused by the metastatic spread of tumor cells to distant organs rather than by the growth of the primary tumor. However, until today the mechanisms involved in CRC metastasis are not completely understood. For cancer cells the epithelial-mesenchymal transition (EMT) is thought to represent a prerequisite to invade adjacent tissue and form metastases at distant sites. Transcription factors, cytokines or oncogenic signaling pathways play an important role in the regulation of the EMT program. Recently, the oncoprotein c-MYC was shown to induce EMT, e.g. by enhancing SNAIL expression. Previously an interaction between c-MYC and the transcription factor ZNF281/ZBP-99 has been described. However, so far it remained elusive which upstream signals regulate ZNF281 levels or activity and furthermore, what functions are mediated by ZNF281, which may contribute to the c-MYC-mediated tumor progression. Here, it could be shown that SNAIL and miR-34a/b/c control the expression of ZNF281 in a coherent feed-forward-loop: the EMT-transcription factor SNAIL directly induced ZNF281 transcription and repressed miR-34a/b/c, thereby alleviating ZNF281 from direct down-regulation by miR-34. Moreover, p53 activation led to a miR-34a-dependent down-regulation of ZNF281 expression. Additionally, in CRC cells it could be demonstrated, that ectopic ZNF281 expression induces EMT. This process was mediated by and dependent on the direct induction of SNAIL. Furthermore, ectopic ZNF281 increased migration/invasion, and enhanced β-catenin activity. Expression of the stemness markers LGR5 was directly and CD133 indirectly induced by ectopic ZNF281 expression, which also increased sphere formation. Conversely, in CRC cells the experimental down-regulation of ZNF281 resulted in a mesenchymal-epithelial transition (MET), inhibited migration/invasion and decreased sphere formation. Additionally, repression of ZNF281 led to decreased formation of lung metastases by CRC cells in a xenograft mouse tumor model. Furthermore, ZNF281 protein expression was indirectly elevated by ectopic c-MYC expression. Inactivation of ZNF281 prevented the induction of EMT by c-MYC or SNAIL. The analysis of tumor samples revealed that ZNF281 expression increases during CRC progression and correlates with tumor recurrence. Taken together, the results identify ZNF281 as a new EMT-promoting transcription factor, which contributes to metastasis formation in CRC. In the future, this knowledge may be exploited for therapeutic and diagnostic purposes in cancer therapy.