The role of large tumor suppressor 2 gene in non-small cell lung cancer

Abstract

Adenocarcinoma (AD) is the predominant subtype of non-small cell lung cancer (NSCLC). Due to the high mortality rate, extensive efforts have been devoted to unravel driver mutations and targetable biomarkers in attempt to improve diagnosis and treatment of lung AD. Being first identified in the Hippo pathway, large tumor suppressor 2 (LATS2) kinase has been shown to play critical roles in multiple biological processes known to be important in carcinogenesis, including cell proliferation, cell differentiation, apoptosis, cell migration and invasion. Aberrant expression of LATS2 has been reported in primary cancer from lung and other solid organ tumors. The expression status and the functional roles of LATS2 kinase in lung AD have not been explored.

In the first part of this study, the expression levels of LATS2 in primary lung AD samples were assessed. LATS2 mRNA level was found to be an independent predictor for progression free survival (DFS) as well as overall survival (OS) in patients with resected pulmonary AD. Furthermore, down-regulation of LATS2 in some lung AD cell lines promoted the phosphorylation status of Erk1/2 and Akt, and it also modulated the expression of p53.

In the second part, in vitro silencing of LATS2 by specific siRNA duplexes altered the levels of apoptosis in response to serum deprivation. The magnitude of this regulation depended on cancer cell characteristics: LATS2 kinase could play a role in facilitating apoptosis in cells sensitive to low serum condition; however, this kinase suppressed apoptosis in cancer cells that were tolerant to serum depletion. The expression levels of Bcl-2 and IAP protein members, including Bcl-xL and survivin, appeared to be modulated by LATS2 knockdown during serum starvation-induced apoptosis.

In the third part, stable knockdown of LATS2 via infection of viral particles with LATS2-specific shRNA could regulate the invasiveness of lung AD cells. This regulation was also cell context dependent: in lung AD cells with low basal LATS2 expression, down-regulation of LATS2 significantly promoted the invasive phenotypes, including enhancing epithelial-to-mesenchymal transition (EMT) and MMP-2 production; on the other hand, in lung AD cell lines with high basal LATS2 expression, depletion of LATS2 led to decreased invading cells across Matrigel together with suppression of EMT and reduction in MMP-2 expression.

In summary, this study provided novel findings that low LATS2 mRNA expression was an independent and significant prognostic factor for inferior DFS and OS in resected lung AD patients. Further in vitro experiments suggested that LATS2 kinase could exert both tumor suppressive and tumor promoting effects depending on the characteristics of lung AD cells, such as basal LATS2 expression level and EGFR mutation status. In EGFR wild-type and low basal LATS2 expression cells, LATS2 kinase promoted apoptosis and suppressed cancer cell invasion; in EGFR wild-type cells with high LATS2 expression at baseline as well as low LATS2-expressed cancer cells bearing EGFR mutations, LATS2 kinase inhibited apoptosis and facilitated the invasive capacities.