Decoding the Significance of Amino Acid-dependent Signal Recognition Particle 9 Nuclear Translocation: Implications for Pancreatic Cancer Prognosis and Functionality [RIP-seq]
Signal recognition particles (SRPs) are important components in regulating intracellular protein transport and secretion, and tumors with high expression of Signal recognition particle 9 (SRP9) have tended to have poorer overall survival, although no reports have described the relationship between its localization and prognosis in pancreatic cancer. We conducted immunohistochemical staining for SRP9 for excised specimens from pancreatic cancer surgery cases without preoperative chemotherapy or radiotherapy performed. We found that in some cases SRP9 was preferentially expressed in the nucleus of the cancerous regions, which was hardly detected in other cases, suggesting SRP9 was transported to nucleus in the former cases. Therefore, the prognosis of patients with SRP9 nuclear translocation was compared by dividing them into two groups: those with a nuclear translocation rate of >50% and =50%. Patients with a nuclear translocation rate of >50% had significantly better recurrence-free survival compared with nuclear translocation rate of =50% group (p = 0.037). Subsequent in vitro experiments also showed that its nuclear translocation rate is reduced under amino acid deficient conditions. Further, to investigate the mechanism of SRP9 nuclear translocation, we studied in vitro by introducing the genes of SRP9 splicing variants (v1 and v2) and their deletion mutants lacking C-terminal regions into MiaPaCa pancreatic cancer cells. As a result, it was confirmed that both splicing variants showed nuclear translocation regardless of C-terminal deletions. Taking advantage of the fact that SRP9 is an RNA-binding protein, we next decided to sequence RNAs that bind to nuclear translocated v1 and v2 and evaluate their function in nuclear translocation. RNA Immunoprecipitation Sequencing of nuclear translocated v1 and v2 showed that pathways involved in cancer progression and protein translation were downregulated. The further study of nuclear translocation of SRP9 may open an avenue to optimization of precise evaluation and therapeutic control of pancreatic cancer. Overall design: Taking advantage of the RNA-binding nature of SRP9, we transfected MiaPaCa cell lines with SRP9 v1 and v2 with nuclear translocation signals, immunoprecipitated them, and performed RNA immunoprecipitation (RIP) sequencing on them to investigate their functions in the nucleus.