Systematische RNA-Expressions-Analyse verschiedener Mitglieder der WNT- und Frizzled-Genfamilien beim Mamma- und Ovarialkarzinom (2012)

Cancer is the second most common cause of death in Germany. So far, the exact molecular processes of tumorigenesis for many cancer entities are still unrevealed and have to be deciphered in more detail. In a mice model it was demonstrated that an overexpression of WNT1, a ligand of the WNT signaling pathway, contributes to breast cancer development. In 60% of human mamma carcinomas ß catenin, a key molecule of the WNT signaling pathway, was shown to be stabilized, indicating a role of the WNT signaling pathway in human breast carcinogenesis. The ß catenin stabilization occurs due to WNT pathway activation triggered by the binding of WNT ligands to frizzled receptors. Previous studies our group "molecular oncology" demonstrated that an aberrant promoter methylation of SFRP1, a WNT antagonist, causes functional loss during breast cancer progression and correlated further with an unfavorable prognosis. For these reasons, the first step of this work was to study the mRNA expression of WNT ligands and frizzled receptors in normal breast tissue. In the second step the expression status of the most abundant frizzled and WNT molecules as found in normal breast epithelium was examined in a collective of normal and tumorous breast tissues using RT PCR. None of the four analyzed frizzled receptors (FZD1, FZD4, FZD6 and FZD10) showed differential expression on mRNA level. The WNT ligands exhibit a wide range of expression levels in the analyzed collective. Especially WNT2, WNT4, WNT5a, WNT7b, WNT9a and WNT11 were overexpressed on mRNA level in malignant tumors compared to normal tissue served as control. Beyond tumorigenesis, WNT signaling has been highlighted to be involved in the organogenesis of organs such as ovaries. Furthermore unpublished results of our group indicate differential expression of several WNT molecules in ovarian cancer. For these reasons the expression of WNT2b and WNT7a on mRNA level was examined with real time RT PCR in a collective of normal and tumorous ovarian tissues. In case of WNT2b a significant (p=0.0024) downregulation in ovarian cancer compared to normal ovarian tissue could be shown. In a further step, MSP (methylation specific PCR) was used to study whether this differential expression was influenced by hypermethylation of the promoter region of WNT2b in cancer. In this current study a ubiquitous methylation pattern was found within the analyzed locus of the WNT2b promoter in normal as well as in tumorous tissue. Furthermore, WNT7a was significantly (p=0.025) upregulated on mRNA level in course of ovarian carcinogenesis. This confirms the published data of Zhan et al., which demonstrated an overexpression on protein level of WNT7a in the epithelium of ovarian tumors compared to normal ovarian epithelium. Finally, the results of the ovarian cancer determination revealed a complex regulation of WNT-signaling as various WNT ligands exhibit opposite expression configurations within the canonical WNT pathway. According to the defined valid model of the canonical WNT pathway an upregulation of the WNT ligands during tumorigenesis would be expected. In this work WNT2b unexpectedly showed a significant downregulation on mRNA level in ovarian cancer. For further research it is instructive to analyze the WNT2b expression on protein level to ascertain if the differential mRNA expression leads to a differential protein expression. Further studies on the WNT signaling pathway should be performed in order to gain a detailed understanding of the specific impact of different WNT ligands of the WNT Pathway on tumorigenesis.