Identification and functional characterization of splicing factors implicated in mantle cell lymphoma aggressiveness

Mantle cell lymphoma (MCL) is a clinically aggressive and incurable form of non-Hodgkin lymphoma with very heterogeneous clinical and biological behaviors. Dysregulation of RNA splicing machinery is common in various types of cancer, including hematologic malignancies, and is associated with cancer progression. However, whether and how splicing factors, the spliceosome components responsible for pre-mRNA splicing, regulate MCL aggressive behaviors remain largely unknown. Bioinformatics analyses were employed to profile the mRNA expression of two key families of splicing factors, that are serine/arginine-rich (SR) and heterogenous nuclear ribonucleoprotein (hnRNP) families, in clinical specimens of MCL patients in comparison to normal B cells. Functional roles of splicing factors in MCL aggressive phenotypes defined as hallmarks of cancer were investigated in MCL cell lines. Kaplan-Meier survival analyses were performed to determine the clinical significance of splicing factors according to their gene expression level. Depletion of SRSF1, hnRNP F, and PTBP1, which are highly expressed in MCL clinical specimens, by CRISPR/Cas9 system significantly inhibit cell growth and proliferation, motility, and angiogenesis of MCL cells. SRSF1, hnRNP F (for Z-138 cells), and PTBP1 were found to mediate BTZ sensitivity in MCL cells, in agreement with an increase in caspase-3 activation and the occurrence of splicing events that favor the expression of pro-apoptotic isoforms of apoptosis regulatory genes. We also found that depletion of SRSF1, hnRNP F, and PTBP1 induces the expression of autophagy-related genes and the accumulation of autophagic vacuoles, which may act as one of the tumor-suppressive mechanisms. Survival analyses revealed that co-high expression of SRSF1, HNRNPF, or PTBP1 and oncogenic MYC predicts poor clinical outcomes in MCL patients. Our data describe the clinical significance of aberrant SRSF1, hnRNP F, and PTBP1 in MCL and their tumor-promoting roles via the regulation of cancer hallmarks, which could be important in understanding MCL pathogenesis and therapeutic development.