Negative regulation of mTOR activity by LKB1-AMPK signaling in non-small cell lung cancer cells

Abstract

Aim: To investigate the role of LKB1 in regulation of mTOR signaling in non-small cell lung cancer (NSCLC) cells. Methods: LKB1 protein expression and phosphorylation of AMPK, 4E-BP1 and S6K in the cells were assessed using Western blotting in various NSCLC cell lines (A549, H460, H1792, Calu-1, and H1299). Energy stress was mimicked by treating the cells with 2-deoxyglucose (2-DG). Compound C was used to inhibit AMPK activity. Cell growth was measured using the MTS assay. Results: LKB1 protein was expressed in LKB1 wild-type Calu-1, H1299, and H1792 cells, but it was undetected in LKB1 mutant A549 and H460 cells. Treatment of the LKB1 wild-type cells with 2-DG (5, 10, and 25 mmol/L) augmented the phosphorylation of AMPK in dose-and time-dependent manners. In the LKB1 wild-type cells, 2-DG dramatically suppressed the phosphorylation of two mTOR targets, 4E-BP1 and S6K, whereas the LKB1 mutant A549 and H460 cells were highly resistant to 2-DG-induced inhibition on mTOR activity. In addition, stable knockdown of LKB1 in H1299 cells impaired 2-DG-induced inhibition on mTOR activity. Pretreatment of H1299 and H1792 cells with the AMPK inhibitor compound C (10 µmol/L) blocked 2-DG-induced inhibition on mTOR activity. 2-DG inhibited the growth of H1299 cells more effectively than that of H460 cells; stable knockdown of LKB1 in H1299 cells attenuated the growth inhibition caused by 2-DG. Conclusion: In non-small cell lung cancer cells, LKB1/AMPK signaling negatively regulates mTOR activity and contributes to cell growth inhibition in response to energy stress.

Integrated Analysis of Transcriptomes of Cancer Cell Lines and Patient Samples Reveals STK11/LKB1–Driven Regulation of cAMP Phosphodiesterase-4D

“…It further represents a possible route to therapeutic application for regulating lung cancer progression. In addition, our results are consistent with STK11-mediated activation of AMPK contributing to carcinogenesis (47). We found the knockdown of AMPK and STK11 resulted in similar effects on PDE4D expression.…”

“…cAMP is known to activate protein kinase A (PKA)-an AMP-dependent enzyme, then activate enzymes related to metabolic response and regulate gene expression by the activation of transcription factors (such as CREB) (49). An increased intracellular cAMP has also been shown to increase the activity of AMPK (50), which is the direct downstream target of STK11 (LKB1) (47). Further mechanistic studies will be required to understand the relationship among STK11, AMPK, and PDE4D in cancer progression.…”

Liver kinase B1/adenosine monophosphate‑activated protein kinase signaling axis induces p21/WAF1 expression in a p53‑dependent manner

“…Thus, the present study identified AMPK as a potential downstream molecule of LKB1 involved in the mediation of p21/WAF1 induction. We previously revealed that 2-DG treatment potently inhibits the proliferation of LKB1 wild-type lung cancer cells (8). Given the importance of p21/WAF1 in growth arrest, it has been suggested that 2-DG-mediated p21/WAF1 induction may contribute to the inhibitory effect of the compound.…”

“…AMPK is activated by LKB1 under energy stresses, including adenosine triphosphate (ATP) depletion induced by glycolysis inhibitors. 2-deoxyglucose (2-DG) is a well-characterized glycolysis inhibitor (8). 2-DG is converted by hexokinase to 2-DG-P, which cannot be further metabolized, thus is trapped inside the cell and inhibits hexokinase.…”

The p53 Target Gene SIVA Enables Non–Small Cell Lung Cancer Development

“…SIVA may affect metabolism by stimulating mTOR signaling, which is known to enhance oxidative metabolism at least in part via activation of S6K and 4EBP1 and consequent translation of nuclear-encoded mitochondrial proteins (34, 35), and to dampen autophagy through phosphorylation and inactivation of the autophagy initiating kinase ULK1/ATG1 (36). Moreover, mTOR is known to promote tumorigenesis in mouse hepatocellular, renal and lung cancer models (28, 29, 37, 38). Thus, a role for SIVA in the positive regulation of mTOR could account for the decreased oxidative phosphorylation, increased autophagy, and reduced tumor burden with Siva deficiency (27, 34, 36, 38).…”