Characterization of ZNF281 and its role in colorectal carcinogenesis

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.