title: beta-Phenylethyl isothiocyanate mediated apoptosis: a proteomic investigation of early apoptotic protein changes.
abstract: beta-Phenylethyl isothiocyanate (PEITC) is a promising chemopreventative agent found in abundance in watercress (Rorripa nasturtium aquaticum) as its glucosinolate precursor. In the present investigation, we sought to determine the early changes in protein expression that contribute to the mechanism(s) of PEITC-mediated apoptosis in the human hepatoma HepG2 cell line. Such data may invariably identify new molecular targets of PEITC, contributing to a greater understanding of the mechanism(s) by which isothiocyanates mediate apoptotic cascades. Using two-dimensional difference gel electrophoresis we determined the changes in global protein expression between control (0.01% dimethyl sulfoxide) and PEITC (IC50 approximately 20 microM) treated cells after 3 and 6 h, such time points being used to circumvent the effects of caspase mediate proteolysis. Comparison between PEITC treated cells with their respective controls showed that 17 protein spots were differentially expressed. Fourteen of these spots, representing 9 unique proteins, were successfully identified using matrix-assisted laser desorption / ionization-time of flight (MALDI-TOF) and MALDI tandem time of flight (TOF/TOF) mass spectrometry. We observed significant shifts in isoelectric points on two-dimensional electrophoresis gels in heat shock 27 kDa protein (HSP27), macrophage migration inhibition factor and heterogeneous nuclear ribonucleoprotein K (hnRNP K) indicating that these proteins are probably involved in protein phosphorylation. Indeed, hnRNP K was determined to be phosphorylated on key tyrosine residues as assessed by using antiphosphotyrosine antibodies. In separate experiments we also showed that c-myc is up-regulated in PEITC treated cells, and since hnRNP K is reported to induce overexpression of c-myc, we proposed that PEITC-induced apoptosis may involve a c-myc dependent apoptotic pathway in HepG2 cells.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, National University of Singapore.
authors.forename: Jason Chun Hong
authors.initials: JC
authors.lastname: Neo
authors.forename: Peter
authors.initials: P
authors.lastname: Rose
authors.forename: Choon Nam
authors.initials: CN
authors.lastname: Ong
authors.forename: Maxey C M
authors.initials: MC
authors.lastname: Chung
mesh_terms: D017209:Apoptosis; D015153:Blotting, Western; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D045744:Cell Line, Tumor; D030562:Databases, Protein; D015180:Electrophoresis, Gel, Two-Dimensional; D005786:Gene Expression Regulation; D055551:HSP27 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000737:chemistry; D034641:Heterogeneous-Nuclear Ribonucleoprotein K / Q000737:chemistry; D006801:Humans; D007091:Image Processing, Computer-Assisted; D020128:Inhibitory Concentration 50; D007525:Isoelectric Focusing; D017879:Isothiocyanates / Q000494:pharmacology*; D008263:Macrophage Migration-Inhibitory Factors / Q000737:chemistry; D013058:Mass Spectrometry; D018832:Molecular Chaperones; D009363:Neoplasm Proteins / Q000737:chemistry; D019000:Phosphotyrosine / Q000737:chemistry; D010940:Plant Proteins / Q000737:chemistry*; D040901:Proteomics / Q000379:methods*; D016271:Proto-Oncogene Proteins c-myc / Q000737:chemistry; D015398:Signal Transduction; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013997:Time Factors; D014357:Trypsin / Q000494:pharmacology; D014443:Tyrosine / Q000737:chemistry; D015854:Up-Regulation
chemical_list: D055551:HSP27 Heat-Shock Proteins; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; D034641:Heterogeneous-Nuclear Ribonucleoprotein K; D017879:Isothiocyanates; D008263:Macrophage Migration-Inhibitory Factors; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D010940:Plant Proteins; D016271:Proto-Oncogene Proteins c-myc; D019000:Phosphotyrosine; D014443:Tyrosine; C058305:phenethyl isothiocyanate; D014357:Trypsin; D020169:Caspases