Steady-State Levels of Phosphorylated Mitogen-Activated Protein Kinase Kinase 1/2 Determined by Mortalin/HSPA9 and Protein Phosphatase 1 Alpha in KRAS and BRAF Tumor Cells

Abstract

Although deregulation of MEK/extracellular signal-regulated kinase (ERK) activity is a key feature in cancer, high-magnitude MEK/ERK activity can paradoxically induce growth inhibition. Therefore, additional mechanisms may exist to modulate MEK/ERK activity in favor of tumor cell proliferation. We previously reported that mortalin/HSPA9 can facilitate proliferation of certain KRAS and BRAF tumor cells by modulating MEK/ERK activity. In this study, we demonstrated that mortalin can regulate MEK/ERK activity via protein phosphatase 1␣ (PP1␣). We found that PP1␣ inhibition increases steady-state levels of phosphorylated MEK1/2 in various tumor cells expressing B-Raf V600E or K-Ras G12C/D . Intriguingly, coimmunoprecipitation and in vitro binding assays revealed that mortalin facilitates PP1␣-mediated MEK1/2 dephosphorylation by promoting PP1␣-MEK1/2 interaction in an ATP-sensitive manner. The region spanning Val482 to Glu491 in the substrate-binding cavity and the substrate lid of mortalin were necessary for these physical interactions, which is consistent with conventional heat shock protein 70 (HSP70)-client interaction mechanisms. Nevertheless, mortalin depletion did not affect cellular PP1␣ levels or its regulatory phosphorylation, suggesting a nonconventional role for mortalin in promoting PP1␣-MEK1/2 interaction. Of note, PP1␣ was upregulated in human melanoma and pancreatic cancer biopsy specimens in correlation with mortalin upregulation. PP1␣ may therefore have a role in tumorigenesis in concert with mortalin, which affects MEK/ERK activity in tumor cells. KEYWORDS MEK1/2, ERK1/2, protein phosphatase 1, heat shock protein, mortalin T he Raf/MEK/extracellular signal-regulated kinase (ERK) pathway is a highly specific three-layer kinase cascade that consists of the Ser/Thr kinases, Raf (i.e., A-, B-, and C-Raf), the highly homologous dual-specificity kinases MEK1 and MEK2 (collectively referred to as MEK1/2), and the ubiquitously expressed Ser/Thr kinases ERK1/2 (1). Upon activation, Raf phosphorylates two Ser residues in the activation segment of MEK1/2, which in turn activate ERK1/2 by sequentially phosphorylating Tyr and Thr in their activation loop (2). ERK1/2 then activate/inactivate various targets, including transcription factors, other kinases, phosphatases, cytoskeletal proteins, scaffolds, receptors, and signaling components (1). The Raf/MEK/ERK pathway has pivotal roles in regulating cell survival, cell cycle progression, and differentiation (3), and its deregulation often leads to the onset of cancer, including malignancies of skin, thyroid, pancreas, and colon, wherein mutations in BRAF and its upstream activator, RAS, are prevalent (4).Diverse physiological outputs of Raf/MEK/ERK signaling are determined by the duration and strength of signals, physical interactions with specific scaffolds, subcellular compartmentalization, cross talk with other signaling pathways, and distinct functions

Bioinformatics and Molecular Insights to Anti-Metastasis Activity of Triethylene Glycol Derivatives

“…Pancreatic cancer (Panc-1) cells have previously been shown to (i) abundantly express mortalin, VEGF and MMP [49][50][51]; (ii) harbor a high number of oncogenic mutations in KRAS, TP53, CDKN2A/p16 and SMAD4/DPC4 [52]; (iii) possess strong migratory and adhesive abilities [53] and (iv) easily cluster and difficultly differentiate into their functional phenotypes [54]. Thus, we chose to examine the regulation of EMT by the TEG derivatives in these cells.…”

Mortalin (GRP75/HSPA9) Promotes Survival and Proliferation of Thyroid Carcinoma Cells

“…Mortalin also affected Ras activity through its interaction with mevalonate pyrophosphate decarboxylase, an enzyme that biochemically modifies Ras [24]. Although the exact location for the regulation is yet unclear, we have recently demonstrated that mortalin negatively regulates the activity of the Raf/MEK/ERK pathway by promoting the physical interaction between protein phosphatase 1 alpha and MEK1/2 [25]. Of note, this ability of mortalin to modulate the Raf/MEK/ERK pathway was important for B-Raf V600E melanoma and K-Ras G12V colon carcinoma cells to bypass the cytostatic effects associated with high MEK/ERK activity [12].…”

Treatment of Cells and Tissues with Chromate Maximizes Mitochondrial 2Fe2S EPR Signals

“…A375 cells were infected with the lentiviral pLKO.1-shACO2 (TRCN0000056561, Dharmacon, Lafayette, CO, USA) to suppress aconitase-2 or the control pLKO.1 for 3 or 6 days prior to EPR. Lentivirus production and infection procedures were previously described [ 27 , 28 , 29 ]. Cells were treated with 10 µM chromate (Sigma, St. Louis, MO, USA) in HBSS (Invitrogen) in a CO 2 incubator at 37 °C for 30 min and were harvested using cell scrapers.…”