Unraveling the role of Musashi2 in c-MYC regulation and its implications for Chronic Lymphocytic Leukemia therapy

Abstract

The regulation of gene expression sustains the cellular homeostasis, and its dysregulation is associated with various types of cancers. Therefore, understanding its role in cancer could give us tools for identifying new therapeutic targets. At the post-transcriptional level, RNA-binding proteins are crucial in controlling gene expression by regulating the temporal, spatial, and functional dynamics of messengers RNAs (mRNA). Among these proteins, the oncoprotein Musashi2 (MSI2) plays a significant role in these regulatory processes. MSI2 binds to consensus sequences on target mRNAs, blocking protein translation, and in some cases, contributes to mRNA stability, positively regulating translation. Interestingly, elevated MSI2 levels have been reported in various cancers, including chronic lymphocytic leukemia (CLL). Our group has identified high MSI2 levels in CLL patients with poor prognosis. Notably, reducing MSI2 levels or inhibiting its function with Ro082750 eliminates both human and murine CLL cells. Given that MSI2 regulates cancer-associated biological processes, MSI2 and its target mRNAs represent promising therapeutic targets. Although MSI2 binds to consensus sequences in mRNAs, its binding and regulation of different mRNA molecules vary across tissues, affecting distinct cellular functions. Currently, the specific mRNAs that MSI2 binds in B-lymphocytes from CLL patients remains unknown. Interestingly, the MSI2 regulatory pathway is linked to the oncogene c-MYC in acute myeloid leukemia, an oncoprotein with higher mRNA expression in B-cells from CLL patients with poor prognosis. Additionally, it has been shown that MSI2 can bind to c-MYC mRNA in hepatocellular carcinoma. Based on this, we aimed to determine whether MSI2 regulates c-MYC expression in the tumor clones of CLL patients. To investigate this, B-cells from 13 CLL patients were treated in-vitro with either the MSI2 inhibitor Ro082750 (5 µM) or a vehicle for 24 hours, and c-MYC expression levels were assessed by flow cytometry. Results showed that inhibiting MSI2 reduced c-MYC expression in 11 out of 13 samples (p=0.0042). Furthermore, we examined the effect of the MSI2 inhibitor on c-MYC levels in TCL1 mice. Animals treated with the MSI2 inhibitor showed reduced c-MYC expression in B220 + CD5 + cells, reinforcing the role of MSI2 in positively regulating c-MYC. These data suggest that MSI2 directly or indirectly regulates c-MYC expression. To determine if MSI2 indeed binds to c-MYC mRNA, we immunoprecipitated MSI2 from CLL patient cells and amplified c-MYC by PCR, confirming that c-MYC mRNA directly binds to MSI2. Our results provide insights into post-transcriptional regulation in CLL. Since it has been proposed that inhibiting translation could be an effective strategy for controlling CLL development by blocking the translation of several oncogenic pathways, including MYC, we are curious whether disrupting the MSI2–c-MYC mRNA axis might offer a more targeted therapeutic strategy for certain patients. Further studies will be done to confirm the idea.