phosphothreonine and Carcinoma--Non-Small-Cell-Lung

Hypoxic non-small cell lung cancer (NSCLC) is dependent on Notch-1 signaling for survival. Targeting Notch-1 by means of γ-secretase inhibitors (GSI) proved effective in killing hypoxic NSCLC. Post-mortem analysis of GSI-treated, NSCLC-burdened mice suggested enhanced phosphorylation of 4E-BP1 at threonines 37/46 in hypoxic tumor tissues. In vitro dissection of this phenomenon revealed that Amyloid Precursor Protein (APP) inhibition was responsible for a non-canonical 4E-BP1 phosphorylation pattern rearrangement-a process, in part, mediated by APP regulation of the pseudophosphatase Styx. Upon APP depletion we observed modifications of eIF-4F composition indicating increased recruitment of eIF-4A to the mRNA cap. This phenomenon was supported by the observation that cells with depleted APP were partially resistant to silvestrol, an antibiotic that interferes with eIF-4A assembly into eIF-4F complexes. APP downregulation in dividing human cells increased the rate of global protein synthesis, both cap- and IRES-dependent. Such an increase seemed independent of mTOR inhibition. After administration of Torin-1, APP downregulation and Mechanistic Target of Rapamycin Complex 1 (mTORC-1) inhibition affected 4E-BP1 phosphorylation and global protein synthesis in opposite fashions. Additional investigations indicated that APP operates independently of mTORC-1. Key phenomena described in this study were reversed by overexpression of the APP C-terminal domain. The presented data suggest that APP may be a novel regulator of protein synthesis in dividing human cells, both cancerous and primary. Furthermore, APP appears to affect translation initiation using mechanisms seemingly dissimilar to mTORC-1 regulation of cap-dependent protein synthesis.

Topics: Adaptor Proteins, Signal Transducing; Amyloid beta-Protein Precursor; Amyloid Precursor Protein Secretases; Animals; Carcinoma, Non-Small-Cell Lung; Cell Cycle Proteins; Cell Division; Cell Hypoxia; Cell Line, Tumor; Down-Regulation; Eukaryotic Initiation Factor-4A; Extracellular Signal-Regulated MAP Kinases; Gene Expression Regulation, Neoplastic; Humans; Intracellular Signaling Peptides and Proteins; Lung Neoplasms; Mechanistic Target of Rapamycin Complex 1; Mice; Models, Biological; Multiprotein Complexes; Nuclear Proteins; Phosphoproteins; Phosphorylation; Phosphothreonine; Protein Biosynthesis; RNA Caps; RNA, Messenger; Substrate Specificity; TOR Serine-Threonine Kinases

LCRMP-1, a novel isoform of CRMP-1, can promote cancer cell migration, invasion and associate with poor clinical outcome in patients with non-small-cell lung cancer (NSCLC). However, the underlying regulatory mechanisms of LCRMP-1 in cancer cell invasiveness still remain obscure. Here, we report that GSK3β can phosphorylate LCRMP-1 at Thr-628 in consensus sequences and this phosphorylation is crucial for function of LCRMP-1 to promote filopodia formation, migration and invasion in cancer cells. Impediment of Thr-628 phosphorylation attenuates the stimulatory effects of LCRMP-1 on filopodia forming, migration and invasion abilities in cancer cells; simultaneously, kinase-dead GSK3β diminishes regulation of LCRMP-1 on cancer cell invasion. Furthermore, we also found that patients with low-level Ser-9-phosphorylated GSK3β expression and high-level LCRMP-1 expression have worse overall survival than those with high-level inactive GSK3β expressions and low-level LCRMP-1 expressions (P<0.0001). Collectively, these results demonstrate that GSK3β-dependent phosphorylation of LCRMP-1 provides an important mechanism for regulation of LCRMP-1 on cancer cell invasiveness and clinical outcome.

Topics: Amino Acid Sequence; Carcinoma, Non-Small-Cell Lung; Cell Line, Tumor; Cell Movement; Enzyme Activation; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Humans; Kaplan-Meier Estimate; Lung Neoplasms; Male; Middle Aged; Molecular Sequence Data; Neoplasm Invasiveness; Nerve Tissue Proteins; Phosphorylation; Phosphothreonine; Proportional Hazards Models; Protein Isoforms; Pseudopodia; Substrate Specificity

Several non-small cell lung carcinomas (squamous cell carcinomas and adenocarcinomas) were analyzed for protein kinase activity. Soluble protein extracts derived from these tumors and from the lung parenchyma adjacent to the tumors were resolved by Mono Q anion exchange chromatography, and the fractions were assayed for phosphotransferase activity towards in vitro substrates. Myelin basic protein, casein, and a ribosomal S6-1 COOH-terminus peptide were efficient substrates for protein kinases that exhibited elevated phosphotransferase activity in the tumor extracts when compared to extracts derived from the adjacent nonneoplastic lung or from the lung parenchyma from patients with nonneoplastic lung disorders. Casein phosphotransferase activity was resolved into two peaks that eluted at 0.44 M NaCl and 0.56 M NaCl. The second peak was identified as casein kinase 2, based upon immunoreactivity to casein kinase 2-specific antipeptide antibodies and its sensitivity to inhibition by heparin sulfate. Myelin basic protein phosphotransferase activity eluted at 0.44 M NaCl, but Western blot analysis revealed that this could not be ascribed to mitogen-activated protein (MAP) kinases. This tumor associated protein kinase, designated p40TAK, exhibited a molecular mass of approximately 40 kDa upon gel filtration. In addition to myelin basic protein, it phosphorylated S6 peptide analogues and histone H1 on seryl residues. Like casein kinase 2, p40TAK exhibited elevated basal phosphotransferase activity in squamous cell carcinomas and adenocarcinomas of the lung when compared to the nonneoplastic lung parenchyma adjacent to the tumor.

Topics: Adenocarcinoma; Amino Acid Sequence; Antibodies; Blotting, Western; Carcinoma, Non-Small-Cell Lung; Carcinoma, Squamous Cell; Casein Kinases; Caseins; Chromatography, Ion Exchange; Electrophoresis, Polyacrylamide Gel; Enzyme Activation; Humans; Kinetics; Lung; Lung Neoplasms; Molecular Sequence Data; Myelin Basic Protein; Peptides; Phosphoserine; Phosphothreonine; Phosphotyrosine; Protein Kinases; Protein Serine-Threonine Kinases; Ribosomal Protein S6; Ribosomal Proteins; Substrate Specificity; Tyrosine