sphingosine-1-phosphate and Carcinoma--Lewis-Lung

During DNA replication, the enzyme telomerase maintains the ends of chromosomes, called telomeres. Shortened telomeres trigger cell senescence, and cancer cells often have increased telomerase activity to promote their ability to proliferate indefinitely. The catalytic subunit, human telomerase reverse transcriptase (hTERT), is stabilized by phosphorylation. We found that the lysophospholipid sphingosine 1-phosphate (S1P), generated by sphingosine kinase 2 (SK2), bound hTERT at the nuclear periphery in human and mouse fibroblasts. Docking predictions and mutational analyses revealed that binding occurred between a hydroxyl group (C'3-OH) in S1P and Asp(684) in hTERT. Inhibiting or depleting SK2 or mutating the S1P binding site decreased the stability of hTERT in cultured cells and promoted senescence and loss of telomere integrity. S1P binding inhibited the interaction of hTERT with makorin ring finger protein 1 (MKRN1), an E3 ubiquitin ligase that tags hTERT for degradation. Murine Lewis lung carcinoma (LLC) cells formed smaller tumors in mice lacking SK2 than in wild-type mice, and knocking down SK2 in LLC cells before implantation into mice suppressed their growth. Pharmacologically inhibiting SK2 decreased the growth of subcutaneous A549 lung cancer cell-derived xenografts in mice, and expression of wild-type hTERT, but not an S1P-binding mutant, restored tumor growth. Thus, our data suggest that S1P binding to hTERT allosterically mimicks phosphorylation, promoting telomerase stability and hence telomere maintenance, cell proliferation, and tumor growth.

Topics: Allosteric Regulation; Animals; Carcinoma, Lewis Lung; Cell Line, Tumor; Cell Nucleus; Humans; Lysophospholipids; Mice; Mice, Knockout; Mice, SCID; Molecular Docking Simulation; Neoplasm Proteins; Phosphorylation; Protein Binding; Sphingosine; Telomerase

Sphingosine-1-phosphate (S1P) regulates a wide array of biological functions. However, the role of S1P signaling in tumorigenesis remains to be elucidated. In this study, we show that S1P receptor subtype 3 (S1P₃) is markedly up-regulated in a subset of lung adenocarcinoma cells compared to normal lung epithelial cells. Specific knockdown of S1P₃ receptors inhibits proliferation and anchorage-independent growth of lung adenocarcinoma cells. Mechanistically, we demonstrate that S1P₃ signaling increases epidermal growth factor receptor (EGFR) expression via the Rho kinase (ROCK) pathway in lung adenocarcinoma cells. Nuclear run-off analysis indicates that S1P/S1P₃ signaling transcriptionally increases EGFR expression. Knockdown of S1P₃ receptors diminishes the S1P-stimulated EGFR expression in lung adenocarcinoma cells. Moreover, S1P treatment greatly enhances EGF-stimulated colony formation, proliferation and invasion of lung adenocarcinoma cells. Together, these results suggest that the enhanced S1P₃-EGFR signaling axis may contribute to the tumorigenesis or progression of lung adenocarcinomas.

Topics: Adenocarcinoma; Adenocarcinoma of Lung; Animals; Carcinoma, Lewis Lung; Cell Line, Tumor; Cell Movement; Cell Proliferation; Epidermal Growth Factor; ErbB Receptors; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Neoplastic; Humans; Lung Neoplasms; Lysophospholipids; Mice; Neoplasm Invasiveness; Receptors, Lysosphingolipid; rho-Associated Kinases; RNA Interference; RNA, Messenger; Signal Transduction; Sphingosine; Sphingosine-1-Phosphate Receptors; Time Factors; Transcriptional Activation; Transfection; Up-Regulation

Sprouty proteins have been shown to negatively regulate a variety of receptor tyrosine kinase (RTK) signaling pathways and are considered to be tumor suppressor proteins. The pathophysiological functions of Sproutys in vivo remain to be investigated. In this study, we examined the physiological function of Sprouty4 as an angiogenic regulator, using Sprouty4 knockout (KO) mice and cells. We found that transplanted tumor cells grow much faster in Sprouty4 KO mice than in wild type (WT) mice, which we associate with enhanced neovascularization in the tumors transplanted into Sprouty4 KO mice. Moreover, vascular endothelial growth factor (VEGF)-A-induced angiogenesis and vascular permeability in vivo were enhanced in Sprouty4 KO mice compared with WT mice. Ex vivo angiogenesis, which we induced by VEGF-A, basic fibroblast growth factor (bFGF), and sphingosine-1-phosphate (S1P), was also enhanced in the aortas of Sprouty4 KO mice. We demonstrated that Sprouty4 suppresses Ras-independent VEGF-A and S1P signaling, while it does not affect Ras-dependent VEGF-C signaling. These data indicate that Sprouty4 selectively suppresses Ras-independent angiogenic factor signals and is an important negative regulator of pathophysiological angiogenesis.

Topics: Animals; Aorta, Thoracic; Blotting, Western; Carcinoma, Lewis Lung; Cells, Cultured; Embryo, Mammalian; Fibroblast Growth Factor 2; Fibroblasts; Luciferases; Lysophospholipids; Male; Melanoma, Experimental; Mice; Mice, Inbred C57BL; Mice, Knockout; Neovascularization, Pathologic; Nerve Tissue Proteins; ras Proteins; Sphingosine; Vascular Endothelial Growth Factor A; Xenograft Model Antitumor Assays

Topics: Animals; Carcinoma, Lewis Lung; Collagen; Drug Combinations; Endothelium, Vascular; Female; Fibroblast Growth Factor 2; Gene Silencing; Genetic Vectors; Humans; Laminin; Lysophospholipids; Mice; Mice, Nude; Proteoglycans; Receptors, Lysosphingolipid; Recombinant Proteins; RNA, Small Interfering; Sphingosine; Transplantation, Heterologous