DLBCL is a common malignant tumor that has a high mortality rate in relapsed or refractory patients. The underlying mechanism of development and progression of DLBCL is complex that is influenced by a variety of genetic and environmental variables. Therefore, it is essential to identify highly accurate indicators and novel molecular targets to improve outcomes for patients with DLBCL.
AS, a sophisticated and pivotal nuclear process, contributes to the development of various diseases including cancer. The SRSF family has 12 members and participates in the regulation of RNA metabolism. In addition to the key regulators of alternative splicing, SRs are important regulators of RNA modification (m6A), export, and translation(Michlewski et al., 2008). The role of the SRSF family as a proto-oncogene crucial for tumor proliferation and maintenance was established by several studies. SRSF5 regulated tumor cell proliferation in lung cancer by affecting the glycolysis process of key target genes such as PKM2(Yan et al., 2019). SRSF3 could also promote tumorigenesis through the repression of the tumor suppressor gene programmed cell death 4 (PDCD4)(Park and Jeong, 2016). Besides, the SRSF family plays a vital role in the regulation of chemoresistance and radioresistance in cancer. Sheng et al.(Sheng et al., 2018) reported that SRSF1 regulates the cancer-related splicing process, which enhances the sensitivity of the cancer cell to radiotherapy. In general, this evidence makes the SRSFs potential prognostic and therapeutic targets for antitumor therapy. Although several studies have investigated the correlations between the SRSF family gene and cancers, the roles of the SRSF family gene in DLBCL and underlying mechanisms have not been explored. In this study, we conducted a comprehensive analysis of the function of the SRSF family gene in DLBCL.
In the current study, we first assessed the expression differences of the SRSF family members between DLBCL and normal tissue by using the TCGA and GTEx databases. Results indicated that almost all SRSF genes were substantially overexpressed in DLBCL compared to normal tissues. We further confirmed the dysregulated protein expression of the SRSF family in DLBCL, which is consistent with the results of gene expression. This suggests that the SRSF family may be oncogenic genes that play a significant role in the early deterioration of lymph nodes, which could be regarded as a diagnostic criterion for DLBCL.
The clinical prognostic significance of SRSF in patients with DLBCL has not been reported, so our study sheds insights into their associations with survival outcomes. The results showed that higher mRNA expressions of SRSF1, SRSF4, SRSF5, SRSF7, SRSF10 and SRSF12 were associated with poorer prognosis. Several studies have demonstrated that the SRSF family could affect the abnormal splicing of tumor-related genes and thereby mediate cancer development and prognosis. SRSF1 has the potential to inhibit apoptosis, which has been linked to a poor prognosis in breast cancer(Anczuków et al., 2012). Yu fu et al.(Fu and Wang, 2018) also discovered that SRSF7 was highly expressed in human colon and lung cancer tissue and involved in the growth of cancer cells. Zhou X et al.(Zhou et al., 2014) reported that SRSF10 could affect the expression of oncogene to promote tumorigenesis in colorectal cancer cells. Our data corroborated that the SRSF family may serve as a prognostic biomarker in DLBCL. These results indicated that the SRSF family plays an important role in the staging, metastasis, and prognosis of DLBCL.
Tumor stemness is characterized by multi-directional differentiation potentials and self-renewal, which has been widely accepted as crucial biological characteristics driving tumor cell invasion and metastatic dissemination(Kreso and Dick, 2014; Yi et al., 2020). Cancer stem cells (CSCs) could be able to resist chemotherapy through a series of progress(Ombrato et al., 2019). Despite the developments in chemotherapy and target therapy research, the prognosis of relapsed or refractory patients remains dismal. This might be explained by the high resistance of CSCs to different chemotherapy drugs. Herein, we first assessed the association between SRSF expression and tumor stemness and found that the expression level of SRSF was positively correlated with tumor stemness, which suggests that increased expression of SRSF can promote tumorigenesis and metastasis of tumor cells. Furthermore, a high level of SRSF could explain the phenomenon of refractory or aggressive DLBCL for which we currently have no effective treatments.
The dysregulation of the DNA damage repair gene can drive genomic instability and higher mutation rates, which are common factors in the development of tumorigenesis(Ruiz-Bañobre and Goel, 2019). Correlation analysis revealed that most SRSF family expression is positively associated with MMR gene expression, particularly MLH1, MSH2, and MSH6. MSH2 has been shown to regulate the cancer-associated cell adhesion pathway and contribute to tumor aggressiveness(Nargund et al., 2022). Moreover, variants in MSH6 could lead to disease recurrence and poor survival after treatment for tumor(Zanusso et al., 2017). These findings shed new insights into the understanding of the role of the SRSF family in tumorigenesis and development in DLBCL. DNA methyltransferases are enzymes that promote and maintain DNA methylation, which has been shown to influence tumor pathology, invasion, and progression(Li et al., 2023). The expression of SRSF was found to be significantly related to the levels of DNMT1 and DNMT3B. Therefore, the SRSF family might mediate tumor progression by regulating the expression of DNA methyltransferase.
DLBCL is not only a disease caused by the accumulation of genetic mutations but is also affected by complex interactions and relationships among immune cells, tumor cells, and stromal cells. Emerging evidence highlights that the tumor microenvironment has a strong impact on tumorigenesis and metastasis(Tamma et al., 2020). We analyzed the association between SRSF expression levels and the infiltration of immune cells. High SRSF expression was found to be significantly associated with increased infiltration of B cells naive, T cells follicular helper cells, Tregs, and NK cells resting. Further, we found that the expressions of SRSF1, SRSF5 and SRSF7 were negatively correlated with CD8 + T-cells, T cell CD4 memory activated, which are considered to strengthen the immunotherapy response(Zaitsev et al., 2022) and participate in the process of immunogenic cell death(Catanzaro et al., 2022), which improves treatment efficacy. Further, Merdan et.al(Merdan et al., 2021) provided information for the prediction of favorable prognosis in DLBCL, suggesting that SRSF may play important roles in cancer progression by regulating the composition of the tumor microenvironment.
More importantly, we constructed the upstream and downstream regulatory networks of SRSF, which provided a reference for revealing the mechanism of SRSF in tumorigenesis and development. In this study, GSEA analysis showed that SRSF were mainly associated with oncogenic pathways including galactose metabolism pathway, which leading to alterations in tumor cell metabolism and affecting cancer development, growth, and survival(Liu et al., 2022). Pathway enrichment analysis indicated that the SRSF family was involved in the upregulation of tumor metabolism and metastasis, which provided novel clues for further exploration for the molecular mechanisms of SRSF in DLBCL. Furthermore, we constructed the downstream regulatory network for SRSF in DLBCL. For example, SRSF7 may regulate tumorigenesis and development via interaction with protein serine/threonine kinase activator. Understanding the relationship between SRSF family genes and DLBCL may help identify novel molecules that are involved in the regulation of tumor progression and provide better insights into pathogenesis. Moreover, it may also provide potential target drugs used for DLBCL treatment.
To further confirm the result of our finding, we conducted western blot to analyze the expression level of SRSF7 in DLBCL cell lines. The expressions of SRSF1 and SRSF7 were significant upregulated in DLBCL cells than that in the control cell, which were consistent with our results.
In conclusion, our study has investigated the expression of SRSF family genes in a broader perspective, which has deepened our understanding of the role of SRSF family members in DLBCL. Furthermore, this study may provide a basis for elucidating the molecular mechanisms of SRSF in the tumorigenesis, tumor progression, prognosis, tumor microenvironment, DNA methyltransferase, tumor stemness index of DLBCL, and provide a potential therapeutic target for treating DLBCL. Our findings also shed new insights into the understanding of immunotherapy for cancer.