CAPN1 promotes malignant behavior and erlotinib resistance mediated by phosphorylation of c‐Met and PIK3R2 via degrading PTPN1 in lung adenocarcinoma

BACKGROUND: Calpain 1 (CAPN1) has been found to be a promoter of cancer progression. PTPN1 as a physiological target molecule of CAPN1 plays a dephosphorylated role on multiple receptor tyrosine kinases. This study aimed to reveal the effects of CAPN1/PTPN1 on malignant phenotype and EGFR‐TKI resistance of lung adenocarcinoma (LUAD) cells. METHODS: A total of 84 primary LUAD tissues and paired paracancerous normal tissues were collected. Quantitative real‐time PCR (qRT‐PCR) and immunohistochemical (IHC) methods were used to measure the expression of CAPN1 and PTPN1 in tissues. qRT‐PCR and western blot were used to detect the expressions of CAPN1, PTPN1, c‐Met and PIK3R2 in cell lines. Cell counting kit‐8 (CCK‐8), colony formation and transwell assay were carried out to evaluate cell erlotinib resistance, proliferation, migration and invasion. Co‐IP assay was used to verify the interaction between proteins. Cycloheximide (CHX) was applied to block protein synthesis. RESULTS: CAPN1, c‐Met and PIK3R2 were significantly upregulated and the correlation was positive in LUAD, while PTPN1 was decreased. EGFR‐sensitive mutation was related to CAPN1/PTPN1. in vitro studies showed that PTPN1 can mediate dephosphorylation of c‐Met and PIK3R2 by binding with both, thereby weakening cell proliferation, metastasis and erlotinib resistance, while CAPN1 could enhance the degradation of PTPN1 protein as a cancer promoter. CONCLUSIONS: CAPN1 enhances the malignant behavior and erlotinib resistance of LUAD cells via degrading PTPN1 and then activating c‐Met/PIK3R2, which suggests CAPN1/PTPN1 may serve as tumor markers or potential targets for diagnosis and treatment of LUAD. KEY POINTS: Significant findings of the study Superior CAPN1 and inferior PTPN1 were related to activation of c‐Met/PIK3R2 in lung adenocarcinoma. Moreover, regulations of CAPN1 and PTPN1 induced the changes of malignant behavior and erlotinib resistance. What this study adds Our findings confirmed that CAPN1/PTPN1 play crucial roles on proliferation, metastasis and erlotinib resistance of LUAD cells as c‐Met/PIK3R2 regulators, and validated the regulatory mechanism of CAPN1 on PTPN1 in tumor model for the first time.