title: Phospholipase A/Acyltransferase enzyme activity of H-rev107 inhibits the H-RAS signaling pathway.
abstract: BACKGROUND
  H-rev107, also called HRASLS3 or PLA2G16, is a member of the HREV107 type II tumor suppressor gene family. Previous studies showed that H-rev107 exhibits phospholipase A/acyltransferase (PLA/AT) activity and downregulates H-RAS expression. However, the mode of action and the site of inhibition of H-RAS by H-rev107 are still unknown.
  
  
  RESULTS
  Our results indicate that H-rev107 was co-precipitated with H-RAS and downregulated the levels of activated RAS (RAS-GTP) and ELK1-mediated transactivation in epidermal growth factor-stimulated and H-RAS-cotransfected HtTA cervical cancer cells. Furthermore, an acyl-biotin exchange assay demonstrated that H-rev107 reduced H-RAS palmitoylation. H-rev107 has been shown to be a PLA/AT that is involved in phospholipid metabolism. Treating cells with the PLA/AT inhibitor arachidonyl trifluoromethyl ketone (AACOCF3) or methyl arachidonyl fluorophosphate (MAFP) alleviated H-rev107-induced downregulation of the levels of acylated H-RAS. AACOCF3 and MAFP also increased activated RAS and ELK1-mediated transactivation in H-rev107-expressing HtTA cells following their treatment with epidermal growth factor. In contrast, treating cells with the acyl-protein thioesterase inhibitor palmostatin B enhanced H-rev107-mediated downregulation of acylated H-RAS in H-rev107-expressing cells. Palmostatin B had no effect on H-rev107-induced suppression of RAS-GTP levels or ELK1-mediated transactivation. These results suggest that H-rev107 decreases H-RAS activity through its PLA/AT activity to modulate H-RAS acylation.
  
  
  CONCLUSIONS
  We made the novel observation that H-rev107 decrease in the steady state levels of H-RAS palmitoylation through the phospholipase A/acyltransferase activity. H-rev107 is likely to suppress activation of the RAS signaling pathway by reducing the levels of palmitoylated H-RAS, which decreases the levels of GTP-bound H-RAS and also the activation of downstream molecules. Our study further suggests that the PLA/AT activity of H-rev107 may play an important role in H-rev107-mediated RAS suppression.
authors.forename: Chun-Hua
authors.initials: CH
authors.lastname: Wang
authors.forename: Rong-Yaun
authors.initials: RY
authors.lastname: Shyu
authors.forename: Chang-Chieh
authors.initials: CC
authors.lastname: Wu
authors.forename: Tzung-Chieh
authors.initials: TC
authors.lastname: Tsai
authors.forename: Lu-Kai
authors.initials: LK
authors.lastname: Wang
authors.forename: Mao-Liang
authors.initials: ML
authors.lastname: Chen
authors.forename: Shun-Yuan
authors.initials: SY
authors.lastname: Jiang
authors.affiliation: Department of Research, Taipei Tzuchi Hospital, The Buddhist Tzuchi Medical Foundation, New Taipei City, Taiwan. afu2215@gmail.com.
authors.forename: Fu-Ming
authors.initials: FM
authors.lastname: Tsai
mesh_terms: D000217:Acyltransferases / Q000378:metabolism*; D004815:Epidermal Growth Factor; D005786:Gene Expression Regulation; D011905:Genes, ras / Q000235:genetics*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D054467:Phospholipases A2 / Q000378:metabolism*; D054512:Phospholipases A2, Calcium-Independent / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D025521:Tumor Suppressor Proteins; D004815:Epidermal Growth Factor; D000217:Acyltransferases; C490065:PLAAT3 protein, human; D054467:Phospholipases A2; D054512:Phospholipases A2, Calcium-Independent