Intracellular Sphingosine-1-Phosphate Receptor 3 Contributes to Lung Tumor Cell Proliferation

Abstract

Background/Aims: The pleiotropic lipid mediator sphingosine-1-phosphate (S1P) exerts a multitude of effects on respiratory cell physiology and pathology through five S1P receptors (S1PR1-5). Epidemiological studies proved high levels of circulating S1P in non-small cell lung cancer (NSCLC) patients. Studies in literature suggest that high levels of S1P support carcinogenesis but the exact mechanism is still elusive. The aim of this study was to understand the mechanism/s underlying S1P-mediated lung tumor cell proliferation. Methods: We used human samples of NSCLC, a mouse model of first-hand smoking and of Benzo(a)pyrene (BaP)-induced tumor-bearing mice and A549 lung adenocarcinoma cells. Results: We found that the expression of S1PR3 was also into the nucleus of lung cells in vitro, data that were confirmed in lung tissues of NSCLC patients, smoking and tumor bearing BaP-exposed mice. The intranuclear, but not the membrane, localization of S1PR3 was associated to S1P-mediated proliferation of lung adenocarcinoma cells. Indeed, the inhibition of the membrane S1PR3 did not alter tumor cell proliferation after Toll Like Receptor (TLR) 9 activation. Instead, according to the nuclear localization of sphingosine kinase (SPHK) II, the inhibition of the kinase completely blocked the endogenous S1P-induced tumor cell proliferation. Conclusion: These results prove that the nuclear S1PR3/SPHK II axis is involved in lung tumor cell proliferation, highlighting a novel molecular mechanism which could provide differential therapeutic approaches especially in non-responsive lung cancer patients.

S1P-Induced TNF-α and IL-6 Release from PBMCs Exacerbates Lung Cancer-Associated Inflammation

“…Because S1P carries out its biological effect by interacting with its surface receptors (S1PRs) [ 1 ], we went on to evaluate their expression on H- and LK-derived PBMCs. S1PR3 was the most expressed receptor ( Figure 2 A), likewise previously observed on structural cells [ 5 ]. Whereas S1PR1 and S1PR2 were not detected on PBMCs (data not shown).…”

“…In another set of experiments, PBMCs were also treated with ceramidase inhibitor (D-NMAPPD, 5 µM; #SML2358; Sigma-Aldrich, Merck Life Science S.r.l., Milan, Italy), TY52156, a S1PR3 antagonist (αS1PR3, #5328; 10 µM; Tocris Bioscience, Ellisville, MO, USA), SKI II, a selective inhibitor of sphingosine kinases (SKI II, 10 µM; #2097; Tocris Bioscience, Ellisville, MO, USA), PF-543, a sphingosine-competitive inhibitor of sphingosine kinase I, SPHK I (PF543, 2 µM; #57177; Selleck Chemical, Houston, TX, USA), ABC294640 (Opaganib), a selective inhibitor of sphingosine kinase II, SPHK II (Opa, 60 µM; #915385-81-8; RedHill Biopharma, Tel-Aviv, Israel), FTI-276, a K-Ras inhibitor (FTI, 2 µg/mL; #F9553; Sigma-Aldrich, Merck Life Science S.r.l., Milan, Italy), Rapamycin, a potent and specific mTOR inhibitor (Rap, 100 ng/mL; #553210; Calbiochem, Sigma-Aldrich, Merck Life Science S.r.l., Milan, Italy), MG132, a proteasome inhibitor (MG132, 10 µM; #M8699; Sigma-Aldrich, Merck Life Science S.r.l., Milan, Italy). The concentration of all substances was chosen on the basis of the existing literature and on our previous experiments/data [ 4 , 5 ].…”

“…The endogenous S1P induced by TLR9 boosted the release of pro-inflammatory cytokines that, in the context of the lung tumor microenvironment, foster tumor proliferation. Indeed, the activation of cell surface receptors and the nuclear S1P receptor 3/sphingosine kinase II (S1PR3/SPHK II) axis facilitated tumor cell proliferation [ 5 ], leading us to suppose that S1P could be at the basis of lung carcinogenesis associated with inflammatory patterns, as in the case of smoking exposure. Smoking mice as well as smoking patients with non-small cell lung cancer (NSCLC) and murine lungs of carcinogen-induced tumors were characterized by high levels of S1P associated with both an inflammatory pattern and tumor growth [ 5 ].…”

“…Indeed, the activation of cell surface receptors and the nuclear S1P receptor 3/sphingosine kinase II (S1PR3/SPHK II) axis facilitated tumor cell proliferation [ 5 ], leading us to suppose that S1P could be at the basis of lung carcinogenesis associated with inflammatory patterns, as in the case of smoking exposure. Smoking mice as well as smoking patients with non-small cell lung cancer (NSCLC) and murine lungs of carcinogen-induced tumors were characterized by high levels of S1P associated with both an inflammatory pattern and tumor growth [ 5 ]. In support of this, others have demonstrated the S1P pro-survival role in cancer [ 6 , 7 ], leading them to suggest it as a biomarker and therapeutic target for various types of solid tumors [ 8 , 9 ].…”

Keep a Little Fire Burning—The Delicate Balance of Targeting Sphingosine-1-Phosphate in Cancer Immunity

“…Similar to S1PR2, as mentioned above, so far most studies addressing the function of S1PR3 in cancer concentrated on its role in tumor cells. There, it was shown that S1P/S1PR3 signaling is a potent driver for tumor cell migration, proliferation, angiogenesis, and metastasis in different tumor entities such as lung and breast cancer [161][162][163][164]. However, little is known about the immune cell specific function of S1PR3.…”