Loss of SMYD5 downregulates proliferative signaling pathways in B cell acute lymphoblasticleukemia

Acute lymphoblastic leukemia (ALL) is characterized by the uncontrolled proliferation of immature lymphoblasts, leading to impaired normal hematopoiesis and potential infiltration of extramedullary tissues. B-cell acute lymphoblastic leukemia (B-ALL) predominantly affects children aged 1 to 4 years, with a progressive decline in incidence in older age groups. Histone methyltransferases (HMTs) act as key epigenetic regulators, and their dysregulation has been associated with tumor initiation and progression. The SMYD5 gene, a member of the HMT family, is found to be overexpressed in ALL patients and has been linked to hematopoietic, inflammatory processes, genomic stability and regulation of protein synthesis. However, its specific role in ALL remains poorly understood. Therefore, investigating the function of SMYD5 in this context may provide insights that contribute to the development of more effective diagnostic and therapeutic strategies. We performed a combination of in silico and in vitro analyses. In silico analyses using public databases were conducted to evaluate SMYD5 mRNA expression in B-cell acute lymphoblastic leukemia (B-ALL). Subsequently, in vitro experiments were performed using a CRISPR-Cas9-mediated knockout (KO) approach in the REH leukemic cell line. Following confirmation of SMYD5 loss at the protein level, transcriptomic profiling was carried out to identify differentially expressed genes and to investigate their involvement in relevant biological pathways. In silico analysis revealed that SMYD5 mRNA expression was significantly higher in B-ALL samples compared with healthy bone marrow samples (p = 0.0022). In the in vitro analysis , SMYD5 mRNA expression was compared across B-ALL cell lines, and the REH cell line was selected because it displayed the highest expression level. Subsequently, gene knockout (KO) was performed, resulting in the generation of two clones with reduced SMYD5 protein levels. RNA sequencing revealed substantial transcriptional changes in the KO clones compared with the wild-type cell line. GSEA analysis revealed positive enrichment in clones C52 and C78 for the E2F Targets (NES = 3.08, FDR < 0.001; NES = 2.93, FDR < 0.001), Myc Targets V1 (NES = 2.88, FDR < 0.001; NES = 2.86, FDR < 0.001), and Myc Targets V2 (NES = 2.31, FDR < 0.001; NES = 2.33, FDR < 0.001). The reduction of SMYD5 in knockout clones was associated with downregulation of key proliferative pathways, suggesting its involvement in maintaining proliferative capacity and leukemogenesis. Literature evidence indicates that the E2F and Myc Targets (V1 and V2) pathways regulate pro-proliferative transcriptional programs in B-ALL. Accordingly, our findings suggest that SMYD5 loss dampens these transcriptional programs, potentially reducing the proliferative rate of leukemic cells and highlighting this gene as a potential therapeutic target.