Δ‐2 Hexadecenal Generated from S1P by Nuclear S1P Lyase Is a Regulator of HDAC1/2 Activity and Histone Acetylation in Lung Epithelial Cells

Abstract

Sphingosine‐1‐phosphate (S1P), a bioactive lipid mediator, is generated from sphingosine by sphingosine kinases (SPHKs) 1 and 2 and is metabolized to Δ‐2 hexadecenal (Δ2HD) and ethanolamine‐phosphate by S1P lyase (S1PL) in mammalian cells. While the role of S1P as a key regulator of cellular functions in normal and pathological conditions is well established, the physiological role of fatty aldehyde released from S1P by S1PL is still unclear. We have recently demonstrated activation of nuclear SPHK2 and generation of S1P and Δ‐2 Hexadecenal in the nucleus of lung epithelial cells exposed to Pseudomonas aeruginosa (PA). Here, we have investigated the nuclear localization of S1PL and the role of Δ2HD as a modulator of nuclear HDAC activity and histone acetylation.Nuclear extracts, free from cytosolic and ER contamination, prepared by detergent fractionation method, were probed for purity by Western blotting using organelle‐specific markers Lamin B, ERp72, and GAPDH. Nuclear fractions derived from primary lung bronchial epithelial cells and alveolar epithelial MLE‐12 cell line exhibited S1PL activity, as measured by a fluorogenic substrate assay and mass spectrometric analysis and immunostained for S1PL by Western blotting. Activation of lung epithelial cells with heat‐inactivated Pseudomonas aeruginosa (PA) stimulated Δ2HD generation in the nucleus, which was S1PL dependent. Blocking S1PL activity with an inhibitor, compound C1 (5μM), in MLE‐12 cells inhibited PA‐induced nuclear Δ2HD production and H3 and H4 histone acetylation. In vitro, addition of exogenous Δ2HD (100–10000 nM) to lung epithelial cell nuclear preparation inhibited HDAC 1/2 activity, and increased acetylation of Histone H3 and H4. Overexpressing wild‐type Sgpl1 gene into mouse embryonic fibroblasts (MEFs) deficient in Sgpl1 decreased basal and PA‐induced nuclear HDAC activity, underlining the role of S1P degradative products in modulating HDAC activity. Furthermore, in Sgpl1 −/−MEFs, PA‐induced HDAC activity was higher compared to Sgpl1+/+MEFs treated with PA. Additionally, incubation of Δ2HD with HDAC1 generated 5 different amino acid adducts as detected by LC‐MS/MS; the predominant adduct being Δ2HD with lysine residues of HDAC1.These data show nuclear localization of S1PL in lung epithelial cells and indicate a crucial epigenetic role for Δ2HD, released from S1P by S1PL in the nucleus, in regulating HDAC1/2 activity and histone acetylation. Thus, nuclear S1PL and generation Δ2HD may have a physiological and pathophysiological relevance to lung inflammatory injury.Support or Funding InformationThis work was supported by NIH grant HL 098050 to VN.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.