Epigenetic therapy of novel tumour suppressor ZAR1 and its cancer biomarker function

Background: Cancer still is one of the leading causes of death and its death toll is predicted to rise further. We identified earlier the potential tumour suppressor zygote arrest 1 (ZAR1) to play a role in lung carcinogenesis through its epigenetic inactivation. Results: We are the first to report that ZAR1 is epigenetically inactivated not only in lung cancer but also across cancer types, and ZAR1 methylation occurs across its complete CpG island. ZAR1 hypermethylation significantly correlates with its expression reduction in cancers. We are also the first to report that ZAR1 methylation and expression reduction are of clinical importance as a prognostic marker for lung cancer and kidney cancer. We further established that the carboxy (C)-terminally present zinc-finger of ZAR1 is relevant for its tumour suppression function and its protein partner binding associated with the mRNA/ribosomal network. Global gene expression profiling supported ZAR1's role in cell cycle arrest and p53 signalling pathway, and we could show that ZAR1 growth suppression was in part p53 dependent. Using the CRISPR-dCas9 tools, we were able to prove that epigenetic editing and reactivation of ZAR1 is possible in cancer cell lines. Conclusion: ZAR1 is a novel cancer biomarker for lung and kidney, which is epigenetically silenced in various cancers by DNA hypermethylation. ZAR1 exerts its tumour suppressive function in part through p53 and through its zinc-finger domain. Epigenetic therapy can reactivate the ZAR1 tumour suppressor in cancer.