Deciphering the role of MSI2 as a regulator of stem‐like properties in mantle cell lymphoma

Abstract

Introduction: Mantle cell lymphoma (MCL) is one of the most aggressive mature B-cell neoplasms. MCL frequently responds to initial treatments although later the development of resistance is common, relapsing with a more aggressive disease. Several groups have isolated MCL-cancer stem cells (CSC), presenting self-renewal, clonogenic growth, tumorigenic capabilities, and resistance to standard therapies. SRY-related HMG-box gene 11 (SOX11) is expressed in progenitors and embryonic stem cells (ESC). Its overexpression has been observed in undifferentiated tumor cell populations with CSC features. In MCL, its overexpression has been associated with more aggresive behavior and worse patient’s outcome. SOX11 is regulating several oncogenic mechanisms in MCL. However, nothing is known about its possible stemness role in MCL. Methods: To search for stem-cell related genes regulated by SOX11 that may contribute to MCL biological and clinical evolution, we compared SOX11+ and SOX11- MCL primary cases differential gene expression profiling (GEP). We analyzed the prognostic value of stem-cell related genes directly regulated by SOX11 and their involvement in stemness features in MCL, using several cellular and molecular approaches. Results: We observed a significant enrichment of leukemic- and hematopoietic stem cells (HSC)-related genes in the SOX11+ compared to SOX11- MCCL subtype. The RNA-binding protein Musashi-2 (MSI2), that maintains self-renewal and prevents differentiation in ESC and HSC, emerged as one of the most significant stem cell-related gene upregulated in SOX11+ MCL primary cases. Moreover, we have demonstrated that SOX11 binds to MSI2 promoter and activates its expression. However, MSI2 intronic superenhancers might be also responsible for MSI2 upregulation in MCL. Moreover, we found that higher expression of MSI2 is significantly associated with poor overall survival, independently of other knows high-risk features in MCL. MSI2 knockdown (KD) or MSI2 function inhibition with Ro 08-2750 (Ro) changed the GEP, downregulating genes involved in CSC-related pathways whereas upregulating pro-apoptotic genes in MCL cells. MSI2KD or MSI2 Ro-inhibition led to suppress stemness phenotypic features, such as clonogenic growth, chemoresistance and cell survival. Moreover, MSI2KD MCL cells have reduced tumorigenic engraftment into mice bone marrow and spleen compared to control cell lines in vivo, suggesting that MSI2 is an important tumorigenic factor in MCL. Conclusions: Our findings suggest that MSI2 expression in MCL is upregulated by SOX11 binding to its promoter and to several active MSI2 intronic superenhancers. MSI2 upregulation might contribute to sustain stemness and chemoresistance to MCL cells, through the post-transcriptional regulation of stem cell-related genes, representing a novel target for therapeutic interventions in aggressive MCL. Keywords: Genomics, Epigenomics, and Other -Omics, Tumor Biology and Heterogeneity No conflicts of interests pertinent to the abstract.