Uncoupling of the LKB1-AMPKα Energy Sensor Pathway by Growth Factors and Oncogenic BRAFV600E

Abstract

BackgroundUnderstanding the biochemical mechanisms contributing to melanoma development and progression is critical for therapeutical intervention. LKB1 is a multi-task Ser/Thr kinase that phosphorylates AMPK controlling cell growth and apoptosis under metabolic stress conditions. Additionally, LKB1Ser428 becomes phosphorylated in a RAS-Erk1/2-p90RSK pathway dependent manner. However, the connection between the RAS pathway and LKB1 is mostly unknown.Methodology/Principal FindingsUsing the UV induced HGF transgenic mouse melanoma model to investigate the interplay among HGF signaling, RAS pathway and PI3K pathway in melanoma, we identified LKB1 as a protein directly modified by HGF induced signaling. A variety of molecular techniques and tissue culture revealed that LKB1Ser428 (Ser431 in the mouse) is constitutively phosphorylated in BRAFV600E mutant melanoma cell lines and spontaneous mouse tumors with high RAS pathway activity. Interestingly, BRAFV600E mutant melanoma cells showed a very limited response to metabolic stress mediated by the LKB1-AMPK-mTOR pathway. Here we show for the first time that RAS pathway activation including BRAFV600E mutation promotes the uncoupling of AMPK from LKB1 by a mechanism that appears to be independent of LKB1Ser428 phosphorylation. Notably, the inhibition of the RAS pathway in BRAFV600E mutant melanoma cells recovered the complex formation and rescued the LKB1-AMPKα metabolic stress-induced response, increasing apoptosis in cooperation with the pro-apoptotic proteins Bad and Bim, and the down-regulation of Mcl-1.Conclusions/SignificanceThese data demonstrate that growth factor treatment and in particular oncogenic BRAFV600E induces the uncoupling of LKB1-AMPKα complexes providing at the same time a possible mechanism in cell proliferation that engages cell growth and cell division in response to mitogenic stimuli and resistance to low energy conditions in tumor cells. Importantly, this mechanism reveals a new level for therapeutical intervention particularly relevant in tumors harboring a deregulated RAS-Erk1/2 pathway.

Bile acid stimulates hepatocyte polarization through a cAMP-Epac-MEK-LKB1-AMPK pathway

“…In contrast, MEK activation in human cancer cell lines inhibited LKB1 phosphorylation by ERK-p90RSK (42). Whether phosphorylation of LKB1 by ERK and p90Rsk is activating or inhbitory is controversial (39)(40)(41)(42). In hepatocyte sandwich cultures, MEK activation correlated directly with LKB1 and AMPK activation and canalicular network formation.…”

“…In mouse melanoma cells and rat embryonic fibroblasts, MEK activated LKB1 via ERK and p90 ribosomal S6 kinase (p90RSK) (39-41), and HGF-induced phosphorylation of p90RSK and LKB1 (Ser-431) was abolished by MEK-ERK inhibitor, U0126, suggesting that LKB1 phosphorylation is MEK-ERK-and p90RSK-dependent (41). In contrast, MEK activation in human cancer cell lines inhibited LKB1 phosphorylation by ERK-p90RSK (42).…”

Epilepsy Related to Developmental Tumors and Malformations of Cortical Development

“…Accordingly, the BRAF V600E mutation has been linked to enhanced mTOR signaling via regulation of the protein kinase B (Akt) pathway [41]. In addtion, other studies indicate that BRAF V600E mutant cells have a dysfunctional tumor suppressor liver kinase B1 (LKB1)-adenosine monophosphate-activated protein kinase-mTOR signaling [42,43], and a positive association between the BRAF V600E mutation and mTOR pathway activation has been reported in BRAF-associated papillary thyroid carcinoma [44]. Thus, BRAF-induced phosphorylation of LKB1 may represent a possible additional mechanism contributing to mTOR activation in BRAF V600E-mutated GNTs, possibly mTOR Signaling Pathway and Malformations Overactivation of the mTOR signaling in glioneuronal tumors (GNT), focal cortical dysplasia (FCD) IIb, and hemimegalencephaly (HME), as well as tubers in tuberous sclerosis complex (TSC), suggests a pathogenic link between these malformations and reflects a spectrum of disorders of mTOR signaling (mTORopathies; see text).…”

Dysembryoplastic neuroepithelial tumour: insight into the pathology and pathogenesis

“…LKB1 with its downstream effector AMPK may act as a tumour suppressor by downregulation of mTOR activity [26]. The crosstalk LKB1/AMPK with RAS/ERK/p90RSK pathway was previously described in melanoma cell cultures [25]. BRAF copy number gain was reported for the first time in DNT tumours by Kakkar et al [32].…”