Identification and characterization of SRSF2 as a splicing-relevant factor associated with the distribution of membranous to secreted PD-L1, exemplarily considered on human renal tissue, including renal cell carcinoma

Abstract

Background: The immunomodulatory molecule PD-L1 and its immunological tolerance-mediating interaction with the PD-1 receptor on many immune effector cells represent one of the most important tumor immune checkpoint axes in antibody-based anti-tumor therapies. Furthermore, PD-L1 is subject to alternative splicing, whereby, in addition to the membrane-bound PD-L1, secreted PD-L1 is also formed as an additional splice variant. This also exerts its effects in the tumor microenvironment, even away from the actual tumor cells, and contributes additional benefits to immune evasion of the tumor. Methods: To examine the association of the splicing factor SRSF2 with the PD-L1 splicing pattern, respective SRSF2 overexpression and knockdown experiments were performed. The precise characterization of SRSF2 followed in human kidney tissue samples and RCCs, including immunofluorescence staining. The impact of the known oncogenic SRSF2 on the host cell transcriptome was further analyzed by RNA sequencing analyses in SRSF2 overexpression and knockdown experiments. Results: In this original research article, the trans splicing factor SRSF2 is identified to be associated with the shift in the alternative splicing pattern of PD-L1 towards the secreted splice variant. The impact of SRSF2 on the cellular transcriptome was demonstrated, and its involvement in the process of malignant transformation, which is obviously also directly linked to immune evasion. Discussion: The optimization of anti-tumor therapies based on monoclonal antibodies against immunomodulatory axes such as PD-1 and PD-L1, including necessary cost reductions, requires the detailed characterization of the gene expression and gene regulation of such molecules, as well as comprehensive molecular biological diagnostics of the tumor sample before putative therapy formulations, e.g., antibody panel collection. Conclusion: Thus, both the amount of PD-L1 protein produced and its splicing pattern are crucial for therapy success and for selecting the most effective therapeutic antibodies.