Identification of novel genetic and prognostic markers in hereditary and sporadic cancer: "two sides of the same coin"

This thesis has focused on the discovery and characterization of novel diagnostic and prognostic markers in various cancer entities, with a special emphasis on colorectal cancer (CRC).
In Switzerland the incidence of colorectal cancer ranks third in males and second in females, with about 4000 new patients diagnosed each year. Incidence trends over the last decades have remained constant in both sexes, whereas mortality rates have been decreasing. Decreasing mortality is thought to be related to improved treatment during the past years as well as generalisation of colorectal cancer screening in the Swiss population. About 80% of colorectal cancers are thought to have occurred by chance (sporadic) with the remainder displaying either familial aggregation (about 15%) or mendelian inheritance (about 5%).
In the first part of this work we identify and characterize a novel target gene locus for microsatellite instability (MSI) consisting of a mononucleotide (T/U)16 tract, EWS16T, located in the 3’ UTR of the Ewing sarcoma break point region 1 (EWSR1) gene in 319 patients with hereditary and sporadic CRC. We show that the EWS16T locus discriminates MMR proficient from deficient cancers with high diagnostic sensitivity (100%) and specificity (100%). It could thus substantially improve and facilitate MSI analysis in routine daily practice. In addition, biochemical analyses indicate that EWS16T contractions alter poly(A) site selection by promoting SFPQ-mediated distal poly(A) site usage in EWSR1 pre-mRNAs and result in decreased mRNA as well as EWS protein expression. Our findings thus directly implicate the RNA-/DNA-binding Ewing sarcoma protein in MSI-associated colorectal tumorigenesis.
In the second part we characterize a new tumour suppressor gene designated SH2D4A located on the short arm of chromosome 8. We demonstrate that SH2D4A physically interacts with the EGFR/STAT3 pathway and controls cell proliferation. Upon EGF signaling, SH2D4A recruits the serine/threonine phosphatase PP1β to the receptor complex and represses activated STAT3 via dephosphorylation. SH2D4A expression reduces anchorage-independent tumour cell growth and its loss promotes the expression of c-Myc, Cyclin D1 and Jun B. In addition we show that SH2D4A expression is partially lost in human colorectal cancers as a result of chromosomal instability, mutations and epigenetic changes. Finally, diminished SH2D4A protein expression was found to correlate with advanced disease stages and was associated with poor prognosis.
In the third part we investigate HGMA1/HGM2 protein expression 210 and 1202 patients with pancreatic and breast cancers, respectively. HMGA1 and HMGA2 over-expression was found in a significant number of breast and pancreatic carcinoma samples, and its over-expression positively correlated with grade and stage of the disease. Conversely, no HMGA1 and HMGA2 expression was observed in cancer-free breast and pancreas tissues. Taken together, our findings show that high expression levels of HMGA1 and HMGA2 are related to an unfavorable histological type and a poor prognosis in both, pancreatic and breast cancer. Moreover, these findings further support the notion that these proteins represent appropriate targets for the therapy of human cancer, as suggested by numerous in vitro and in vivo studies.
In the fourth part of the thesis we evaluate the potential role of the cancer stem cell (CSC) proteins EpCAM, CD44s, CD166 and CD133 in tumors of the ampulla of Vater. CSC expression was determined in 175 carcinoma, 111 adenoma and 152 cancer free-mucosa specimens arranged on a tissue microarray format. The expression of all evaluated marker proteins differed significantly between cancer-free mucosa, adenoma and carcinoma samples. EpCAM expression was significantly correlated with better patient survival. In contrast, increased expression of CD44s, CD166 and CD133 from normal mucosa samples to adenoma and carcinoma was linked to tumor progression but no statistically significant correlation with survival observed. Our findings therefore indicate that in ampullary carcinomas loss of EpCAM expression may be associated with a more aggressive tumor phenotype.
In the fifth part we develop a specific monoclonal antibody for the highly immunogenic member of the MAGE-A family of cancer/testis tumor-associated antigens (C/T TAAs). The antibody was used to stain a multi-tumor tissue microarray comprising more than 2,500 paraffin-embedded specimens of different histological origin. C/T TAA appears to be expressed in a high percentage (>50%) of cancer cells from different tumor types such as lung, skin, gynecological, stomach and gall bladder cancers. The future characterization of MAGE-A10-specific antibodies might set the stage for the development of targeted active immunotherapy by clarifying potential indications and by allowing the selection of patients eligible for treatment and monitoring of its effectiveness.