XPNPEP3 is a novel transcriptional target of canonical Wnt/ß-catenin signaling.

Canonical Wnt/ß-catenin signaling plays important roles in embryonic development and adult tissue regeneration while aberrant Wnt activation is the major driver of sporadic colorectal cancer (CRC). Thus, it is important to characterize the complete ß-catenin target transcriptome. We previously performed microarray-based mRNA profiling of rectal cancer samples stratified for Wnt status. In addition to AXIN2 and EPHB2, XPNPEP3 transcripts were significantly elevated in tumors exhibiting activated Wnt/ß-catenin signaling, validated by Q-PCR. Three different cell lines supported elevated XPNPEP3 transcript levels upon activation of Wnt signaling, confirmed using promoter-luciferase assays. Ectopic expression of XPNPEP3 promoted tumorigenic properties in CRC cells. Immunohistochemistry on a CRC tissue microarray revealed significant correlation between ß-catenin nuclear localization and XPNPEP3 levels. More importantly, XPNPEP3 expression was upregulated compared to normal samples in published expression data sets from several cancers including CRC. Finally, XPNPEP3 expression correlated with poor survival in many cancers. Our results therefore suggest XPNPEP3 to be a transcriptional target of Wnt/ß-catenin pathway with particular significance for CRC.

The Yin and Yang of cancer genes.

Cancer is caused by malfunctioning of genes that normally regulate cardinal processes including various nuclear functions, cell division and survival, cell surface to nucleus signaling cascades, etc. Cancer associated genes are often classified as oncogenes (OCGs) or tumor suppressor genes (TSGs) depending on whether they promote or suppress tumorigenesis, respectively. Such strict classification of cancer genes may however be an over-simplification. Several studies have highlighted a dual role for cancer genes, often impacting the same facet of tumorigenesis. Knowledge of a possible dichotomy of a cancer gene (particularly an OCG) is imperative when evaluating its possible utility as a therapeutic target. Though previous studies have extensively evaluated specific examples of cancer genes exhibiting a dual nature, efforts to unravel the molecular basis for such contrasting functions have been fewer. The current review is an attempt to delineate molecular events underlying the functional dichotomy of cancer genes at the DNA (mutations, gene fusions, etc.), RNA (alternative splicing, regulation through non-coding RNAs, etc.) and protein (isoforms, mis-localisation, post-translational modifications, proteolytic cleavage, etc.) levels.