[Expression of SIPA1 in colorectal cancer and its impact on its biological behavior]

Objectives: To investigate the expression of signal-induced proliferation-associated 1 (SIPA1) in colorectal cancer tissues and its relationship with patient prognosis. To explore the effects of SIPA1 on proliferation and migration abilities, as well as the possible molecular mechanisms. Methods: Using The Cancer Genome Atlas (TCGA) database to analyze the differential expression of SIPA1 and conduct survival analysis. Then, plotting receiver operating characteristic curve (ROC) and prognosis calibration curve analysis to assess the predictive capability and accuracy of SIPA1 for patient prognosis. Subsequently, verifying the expression levels of SIPA1 in tumor tissues and adjacent normal tissues using immunohistochemistry (IHC) and western blot (WB) assays(from March 1, 2023, to May 1, 2024, pathological specimens of five colorectal cancer patients were selected from the tissue bank of affiliated hospital of Nantong University. tissue microarrays were constructed using both cancerous tissues and adjacent normal tissues), and exploring the correlation between SIPA1 and clinical pathological parameters. Next, establishing SIPA1 stable knockdown cell lines in colorectal cancer cell lines DLD1 and HCT116, and assessing the biological behavior changes of tumor cells after SIPA1 knockdown through cell proliferation, invasion, and migration experiments. Validating the impact of SIPA1 on colorectal cancer cell proliferation in vivo through subcutaneous xenograft experiments in nude mice. Exploring the potential pro-tumor mechanisms of SIPA1 through pathway enrichment analysis, and confirming these using WB experiments. The proliferation, invasion and migration of tumor cells were detected after adding PI3K activator. Lastly, conducting correlation analysis between SIPA1 and immune checkpoint, as well as the association with immune cells in the tumor microenvironment. Results: Differential analysis showed that mRNA expression of SIPA1 in colorectal cancer tissues was significantly higher than that in adjacent normal tissues (P＜0.05). Prognostic analysis indicated that patients with high expression of SIPA1 had poor overall survival (P＜0.001), and the expression level of SIPA1was correlated with lymph node invasion (P＜0.001) and N stage (P＜0.05). ROC curve and prognosis calibration curve suggest that SIPA1 can effectively predict five-year survival rate of patients (AUC=0.7), and the predictive performance of the model is relatively accurate (P＜0.001). WB experiments showed a significant increase in the expression level of SIPA1 protein in colorectal cancer specimens (P＜0.001). Immunohistochemistry results indicated higher staining scores of SIPA1 in tumor tissues. In vitro experiments demonstrated that SIPA1 knockdown significantly inhibited the proliferation, invasion, and migration capabilities of colorectal cancer cells. In DLD1 and HCT116 cells, the SIPA1-knockdown group exhibited significantly lower absorbance compared to the control group (0.89±0.01 vs. 1.57±0.02 and 0.72±0.01 vs. 1.31±0.03, respectively, both P＜0.001). The SIPA1-knockdown group also demonstrated a reduced number of migrated cells relative to the control group (197.93±16.64 vs. 518.48±29.15 and 171.83±12.49 vs. 446.00±21.81, respectively, both P＜0.001). Furthermore, the cell wound-healing rate was significantly lower in the SIPA1-knockdown group than that in the control group [(0.32±0.01)% vs. (0.61±0.01)% and (0.28±0.01)% vs. (0.75±0.01)%, respectively, both P＜0.001]. In vivo animal experiments suggested that SIPA1 knockdown could inhibit tumor growth [(460.35±57.47) mm³ vs (1 177.55±208.24)mm³, (0.76±0.11)g vs (1.43±0.08)g, P＜0.05]. Pathway enrichment analysis revealed significant enrichment of the receptor tyrosine kinase signaling pathway, and SIPA1 knockdown could inhibit the activation of the phosphatidylinositide 3-kinases (PI3K)/protein kinase B (PKB)/glycogen synthase kinase-3β (GSK3β) signaling pathway. The PI3K activator reversed the inhibitory effect of SIPA1 silencing on tumor cell proliferation, invasion and migration. Correlation analysis indicated that high expression of SIPA1 was associated with immune checkpoints and various immunosuppressive cells (all P＜0.05). Conclusions: SIPA1 is highly expressed in colorectal cancer and associated with poor prognosis. SIPA1 may affect the proliferation and migration abilities of tumor cells by regulating the PI3K/AKT/GSK3β signaling pathway.