A search for miRNAs that regulates the expression of the atypical kinases ERK3, ERK4 and MK5

Abstract

In 2010, there were 2839 women and 13 men diagnosed with breast cancer in Norway, which was equivalent to an increase of almost 50% since 1956. The risk of developing breast cancer increases with age, and will affect one in ten women during their lifetime. Despite a substantial increase in the number of early-stage breast cancers detected due to screening-programs, there is still a need for new and improved prognostic tools and therapies for a disease with such distinctive gene expression signature and cellular composition, essential for both the biological and clinical features of the disease. The deregulation of single-stranded RNA molecules called microRNAs (19-23 nt long) is associated to development and progression of several cancers, including in breast cancer. This has opened up the prospect of a potential role both as biomarkers, markers of cancer progression and prognosis and therapeutic targets. miRNAs regulate the cell’s gene activity and protein synthesis, and their function can be both cancer-repressing and cancer-stimulating. It has been shown that miRNAs regulates the expression of the protein-coding components of many cell signaling pathways, however the complete picture of how these key cell signaling systems are regulated by miRNAs and regulate miRNA biogenesis remains to be described. The extracellular signal-regulated kinase 3 (ERK 3) and -kinase 4 (ERK 4) are members of the atypical subgroup of MAP kinases. There is little knowledge about the upstream regulation of ERK3/4, and also their downstream targets. To this day, MAPK-activated protein kinase 5 (MK5) is the only known substrate of ERK3/4. It is believed that ERK3 is involved in cell differentiation and regulation of the cell cycle. The expression of ERK3 is up-regulated in various cancers, and ERK3 may play an important role in migration and invasive growth of cancer cells. However, the precise molecular mechanism of ERK3, ERK4 and MK5 in cancer and cancer-related signaling pathways remains to be unraveled. In this thesis we aimed to see if we could detect a microRNA that targets and regulates ERK3, ERK 4 or MK5, either post-transcriptionally or at the translational level. By comparing the results from different target expression-experiments we sought to find correlations between the expressions of ERK3/4 or MK5 mRNA or protein and the pertaining expression of putative miRNAs with potential binding sites in the 3’UTR of these atypical kinases. Our experiments revealed the presence of ERK3 and MK5 protein in all breast cancer cell lines tested and a possible miRNA mediated regulation of ERK3 and MK5 expression at the translational level.