SIPA1 as a modulator of HGF/MET induced tumour metastasis via the regulation of tight junction based cell to cell barrier

Lung cancer is the leading cause of cancer-related death in the UK and worldwide. The development and metastasis of lung cancer is regarded as a complex process involving a number of mechanisms. Deep understanding of lung cancer metastasis is necessary to aid clinical diagnosis and management of the disease. SIPA1 (Signal Induced Proliferation Associated 1) is a mitogen induced GTPase activating protein (GAP). This protein may also hamper mitogen-induced cell cycle progression when abnormally or prematurely expressed. Some evidence suggests SIPA1 may be involved in the MET signalling pathway. There is also evidence showing that SIPA1 may be involved in the regulation of tight junctions, which are key components in the prevention of metastasis. The role of SIPA1 in lung cancer remains largely unknown. This study aimed to evaluate the importance of SIPA1 in the development of and progression lung cancer, showing the cellular function of SIPA1 and the molecular mechanism/s involved. Expression of SIPA1 was found to be significantly higher in human lung cancer tissues compared to normal lung tissue. Lung cancer patients with higher SIPA1 levels had a poorer prognosis compared to patients with low SIPA1 level, especially in lung adenocarcinoma. In vitro cell models showed knockdown SIPA1 in A549 cells and SK MES1 cells decreased the aggressive behaviour in invasion and proliferation, and the SIPA1 knockdown cells demonstrated leaky cell to cell barriers. SIPA1 related gene expression correlation assays using our own lung cancer patient cohort and TCGA cohort demonstrated that SIPA1 had high correlation with cell signalling by receptor tyrosine kinases (RTKs), especially HGF/MET signalling pathways and TJ components. KinexusTM protein kinase array analysis also revealed SIPA1 is involved in the regulation on the RTKs signalling and HGF/MET signalling. Co-culture of in vitro cell models with HGF showed that the regulation of HGF on cell barrier and invasion required the present of SIPA1. At the molecular level, knockdown of SIPA1 decreased tight junction based barrier function by downregulating MET. Knockdown of SIPA1 reduced the protein expression level of MET but not the transcript level, and XII regulation was attained through silencing of Grb2, SCOS, and PKCμ, reducing the internalization and recycling of MET. SIPA1 may act as a targeting molecule in cancer. Knockdown of SIPA1 reduced the growth and invasion potential of lung cancer cells in vitro. SIPA1 influences the tight junction proteins in cancer cell lines and further work may reveal the mechanism by which SIPA1 mediates the HGF influenced development and metastasis of tumours. In conclusion, SIPA1 plays an essential role in tumorigenesis and metastasis of lung cancer. SIPA1 could be used as a biomarker for diagnosis and prediction of patients’ prognosis. Moreover, the interaction of SIPA1 with MET showed SIPA1 can be a potential therapeutic target for patients with aberrant MET derived non-small cell lung cancer and drug resistance