title: Geranylgeranyl transferase 1 modulates autophagy and apoptosis in human airway smooth muscle.
abstract: Geranylgeranyl transferase 1 (GGT1) is involved in the posttranslational prenylation of signaling proteins, such as small GTPases. We have shown that blocking the formation of isoprenoids with statins regulates survival of human lung mesenchymal cells; thus, we tested the hypothesis that GGT1 may specifically modulate programmed cell death pathways in these cells. To this end, human airway smooth muscle (HASM) cells were treated with the selective GGT1 inhibitor GGTi-298. Apoptosis was seen using assays for cellular DNA content and caspase activation. Induction of autophagy was observed using transmission electron microscopy, immunoblotting for LC3 lipidation and Atg5-12 complex content, and confocal microscopy to detect formation of lysosome-localized LC3 punctae. Notably, GGT1 inhibition induced expression of p53-dependent proteins, p53 upregulated modulator of apoptosis (Noxa), and damage-regulated autophagy modulator (DRAM), this was inhibited by the p53 transcriptional activation inhibitor cyclic-pifithrin-α. Inhibition of autophagy with bafilomycin-A1 or short-hairpin RNA silencing of Atg7 substantially augmented GGTi-298-induced apoptosis. Overall, we demonstrate for the first time that pharmacological inhibition of GGT1 induces simultaneous p53-dependent apoptosis and autophagy in HASM. Moreover, autophagy regulates apoptosis induction. Thus, our findings identify GGT1 as a key regulator of HASM cell viability.
authors.affiliation: Department of Physiology, University of Manitoba, Winnipeg, Canada.
authors.forename: Saeid
authors.initials: S
authors.lastname: Ghavami
authors.forename: Mark M
authors.initials: MM
authors.lastname: Mutawe
authors.forename: Dedmer
authors.initials: D
authors.lastname: Schaafsma
authors.forename: Behzad
authors.initials: B
authors.lastname: Yeganeh
authors.forename: Helmut
authors.initials: H
authors.lastname: Unruh
authors.forename: Thomas
authors.initials: T
authors.lastname: Klonisch
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Halayko
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D017209:Apoptosis; D001343:Autophagy; D001549:Benzamides / Q000494:pharmacology; D052160:Benzothiazoles / Q000494:pharmacology; D001980:Bronchi / Q000166:cytology*; D002470:Cell Survival; D002478:Cells, Cultured; D051231:Farnesyltranstransferase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D032389:Myocytes, Smooth Muscle / Q000201:enzymology* / Q000502:physiology; D061251:Primary Cell Culture; D015398:Signal Transduction; D014050:Toluene / Q000031:analogs & derivatives / Q000494:pharmacology; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: D001549:Benzamides; D052160:Benzothiazoles; C102521:GGTI 298; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D014050:Toluene; C121565:pifithrin; D019883:Alkyl and Aryl Transferases; C083291:geranylgeranyltransferase type-I; D051231:Farnesyltranstransferase