Attenuated LKB1-SIK1 signaling promotes epithelial-mesenchymal transition and radioresistance of non–small cell lung cancer cells

Abstract

BackgroundRadiotherapy is one of the main therapeutic approaches for non–small cell lung cancer (NSCLC). However, radioresistant cancer cells can eventually cause tumor relapse and even fatal metastasis. It is thought that radioresistance and metastasis could be potentially linked by epithelial-mesenchymal transition (EMT). In this study, we established radioresistant NSCLC cells to investigate the potential relationship among radioresistance, EMT, and enhanced metastatic potential and the underlying mechanism involving liver kinase B1 (LKB1)-Salt-inducible kinase 1 (SIK1) signaling.MethodsThe radioresistant cell lines A549R and H1299R were generated by dose-gradient irradiation of the parental A549 and H1299 cells. The radioresistance/sensitivity was evaluated by Cell Counting Kit-8 assay, apoptosis analysis, and/or clonogenic cell survival assay. The EMT phenotype and the signaling change were assessed by Western blotting. The abilities of invasion and migration were evaluated by transwell assays and wound healing assays.ResultsThe radioresistant cell lines A549R and H1299R displayed mesenchymal features with enhanced invasion and migration. Mechanistically, A549R and H1299R cells had attenuated LKB1-SIK1 signaling, which leaded to the up-regulation of Zinc-finger E-box-binding homeobox factor 1 (ZEB1)—a transcription factor that drives EMT. Re-expression of LKB1 in A549R cells reversed the EMT phenotype, whereas knockdown of LKB1 in H1299R cells further promoted the EMT phenotype. Moreover, re-expression of LKB1 in A549 cells increased the radiosensitivity, whereas knockdown of LKB1 in H1299 cells decreased the radiosensitivity.ConclusionsOur findings suggest that attenuated LKB1-SIK1 signaling promotes EMT and radioresistance of NSCLC cells, which subsequently contributes to the enhanced metastatic potential. Targeting the LKB1-SIK1-ZEB1 pathway to suppress EMT might provide therapeutic benefits.

Functional characterization of AMP-activated protein kinase signaling in tumorigenesis

“…The CCL2-mediated macrophage recruitment is enhanced in part due to the loss-of-function mutation on LKB1 , which partially explains the development of endometrial cancer [49]. Besides, LKB1 could likewise affect epithelial mesenchymal transition [50], Hippo/YAP signaling [51], proinflammatory transduction [52] as well as TGF-β pathway [53] to function as a tumor suppressor in multiple neoplasms.…”

LKB1 pro‐oncogenic activity triggers cell survival in circulating tumor cells

“…LKB1 displays tumor-suppressing characteristics; its upregulation inhibits metastasis (Zhuang et al, 2006), while its downregulation or deletion promotes EMT and cancer progression (Li et al, 2014a). Moreover, a correlation between LKB1 downregulation and ZEB1 upregulation with concomitant induction of EMT in tumor cells has been described (Yao et al, 2016). However, LKB1 is also a potent sensor of metabolic low energy.…”

Liver kinase B1 suppresses growth of lung cancer cells through sonic hedgehog signaling pathway

“…All these results suggest that LKB1 contributes to apoptosis of lung cancer cells. Due to its effects on apoptosis of lung cancer cells, LKB1 may also sensitize lung cancer to radiotherapy and chemotherapy (Ou and Ye, 2012;Whang et al, 2016;Yao and Cui, 2016) and contribute to the poor prognosis of lung cancer . Thus, LKB1 may become a potential target for lung cancer treatment.…”

“…LKB1 can induce growth suppression and apoptosis in various cancer cells and inhibit metastasis and angiogenesis of cancers (Zhuang et al, 2006;Ji et al, 2007;Wang et al, 2014). LKB1 is also associated with resistance to chemotherapy and radiotherapy (Ou et al, 2012;Xia et al, 2014;Yao et al, 2016), as well as poor prognosis of cancers (Huang et al, 2013;Yang et al, 2015). Somatic mutation of LKB1 often occurs in lung cancer.…”

“…Mutation or deletion of LKB1 often results in loss of partial functions, thus may contribute to the initiation and aggravation of lung cancer. LKB1 is reported to alter cell growth, metastasis, and resistance of lung cancer (Jimenez et al, 2003;Ji and Ramsey, 2007;Ou and Ye, 2012;Yao and Cui, 2016); however, the underlying mechanism remains unclear.…”