Olfactomedin 4 associates with expression of differentiation markers but not with properties of cancer stemness, EMT nor metastatic spread in colorectal cancer.

Tumor stem cells play a pivotal role in carcinogenesis and metastatic spread in colorectal cancer (CRC). Olfactomedin 4 (OLFM4) is co-expressed with the established stem cell marker leucine-rich repeat-containing G protein-coupled receptor 5 at the bottom of intestinal crypts and has been suggested as a surrogate for cancer stemness and a biomarker in gastrointestinal tumors associated with prognosis. Therefore, it was the aim of the present study to clarify whether OLFM4 is involved in carcinogenesis and metastatic spread in CRC. We used a combined approach of functional assays using forced OLFM4 overexpression in human CRC cell lines, xenograft mice, and an immunohistochemical approach using patient tissues to investigate the impact of OLFM4 on stemness, canonical Wnt signaling, properties of metastasis and differentiation as well as prognosis. OLFM4 expression correlated weakly with tumor grade in one patient cohort (metastasis collection: p = 0.05; pooled analysis of metastasis collection and survival collection: p = 0.19) and paralleled the expression of differentiation markers (FABP2, MUC2, and CK20) (p = 0.002) but did not correlate with stemness-associated markers. Further analyses in CRC cells lines as well as xenograft mice including forced overexpression of OLFM4 revealed that OLFM4 neither altered the expression of markers of stemness nor epithelial-mesenchymal transition, nor did OLFM4 itself drive proliferation, migration, or colony formation, which are all prerequisites of carcinogenesis and tumor progression. In line with this, we found no significant correlation between OLFM4 expression, metastasis, and patient survival. In summary, expression of OLFM4 in human CRC seems to be characteristic of differentiation marker expression in CRC but is not a driver of carcinogenesis nor metastatic spread.

Human telomerase reverse transcriptase (hTERT) is a target gene of ß-catenin in human colorectal tumors.

The majority of colorectal cancers (CRCs) are characterized by a dysregulated canonical Wnt-signaling pathway leading to the stabilization and subsequent cellular increase and accumulation of ß-catenin. After translocation into the nucleus, it acts as a transcription factor resulting in the expression of ß-catenin target genes. These resemble most of the hallmarks of cancer except eternal life. The central mediator of this hallmark is hTERT (human telomerase reverse transcriptase). The hTERT gene is regulated, besides others, by the transcription factor c-Myc and, thus, indirectly via ß-catenin as c-Myc is a ß-catenin target gene. Interestingly, the expression patterns of hTERT and ß-catenin, but not c-Myc are overlapping, probably because c-Myc is not only regulated by ß-catenin, but also by many other transcription factors and pathways. Therefore, we argued that hTERT might be a direct target gene of ß-catenin. In this study, we show evidence that ß-catenin directly regulates the expression of the hTERT gene.

The expression pattern of aldehyde dehydrogenase 1 (ALDH1) is an independent prognostic marker for low survival in colorectal tumors.

BACKGROUND: Aldehyde dehydrogenase-1 (ALDH1) is involved in the regulation of cell proliferation and differentiation. Moreover, it is a marker for cancer stem cells (CSC). As CSCs were shown to be the driving force of tumor progression and metastases we suspected that the expression of ALDH1 correlated with the prognostic 5 year survival of colorectal cancer. METHODS: ALDH1 expression was analyzed in a highly stratified collective of 186 T3 N0 M0 G2 primary colorectal cancer specimens applying immunohistochemistry. For the analysis a scoring system for the expression of ALDH1 was developed that was aided by the pattern of the subcellular expression of beta-catenin which is a well known indicator for colorectal CSCs. RESULTS: First, ALDH1 expression could be assigned to two groups which correlated with the absence or presence of nuclear beta-catenin expression. Second, ALDH1 group 2 expression patterning correlated highly significantly with low long term survival (p=0.010) of patients with T3 N0 M0 G2 colorectal cancer. This correlation was found univariately and when applying the multivariate Cox-model. CONCLUSION: ALDH1 expression pattern is an independent prognostic marker for survival of T3 N0 M0 G2 colorectal cancer patients.