title: Inhibition of nuclear factor-kappaB DNA binding by organoselenocyanates through covalent modification of the p50 subunit.
abstract: Most known chemopreventive agents including certain selenium compounds suppress the activation of the nuclear factor kappaB (NF-kappaB), but the mechanisms remain largely elusive. Toward this end, we initially showed that the inhibition of NF-kappaB DNA binding by benzyl selenocyanate (BSC) and 1,4-phenylenebis(methylene)selenocyanate (p-XSC) was reversed by the addition of DTT; this suggests the formation of DTT-reducible selenium-sulfur bonds between selenocyanate moieties and cysteine residues in NF-kappaB (p50) protein. Furthermore, the inhibitory effect of selenocyanates on NF-kappaB was not altered in the presence of physiologic level of reduced glutathione (1 mmol/L), suggesting that selenocyanates can also inhibit NF-kappaB in vivo. Using both matrix-assisted laser desorption/ionization-time of flight and tandem mass spectrometry fragmentation, we showed for the first time that the Cys(62) residue in the active site of NF-kappaB (p50) protein was modified by BSC through the formation of a selenium-sulfur bond. In addition, p-XSC-bound NF-kappaB (p50) protein was also detected by a radiotracer method. To provide further support, molecular models of both BSC and p-XSC positioned in the DNA binding pocket of the p50 were constructed through the covalent modification of Cys(62); the models reveal that DNA substrate could be hindered to enter its DNA binding region. This study shows for the first time that BSC and p-XSC may exert their chemopreventive activity, at least in part, by inhibiting NF-kappaB through covalent modification of Cys(62) of the p50 subunit of NF-kappaB.
authors.affiliation: Department of Biochemistry and Molecular Biology, Penn State College of Medicine, Hershey, PA 17033, USA.
authors.forename: Kun-Ming
authors.initials: KM
authors.lastname: Chen
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Spratt
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Stanley
authors.forename: Dan A
authors.initials: DA
authors.lastname: De Cotiis
authors.forename: Maria C
authors.initials: MC
authors.lastname: Bewley
authors.forename: John M
authors.initials: JM
authors.lastname: Flanagan
authors.forename: Dhimant
authors.initials: D
authors.lastname: Desai
authors.forename: Arunangshu
authors.initials: A
authors.lastname: Das
authors.forename: Emerich S
authors.initials: ES
authors.lastname: Fiala
authors.forename: Shantu
authors.initials: S
authors.lastname: Amin
authors.forename: Karam
authors.initials: K
authors.lastname: El-Bayoumy
mesh_terms: D000595:Amino Acid Sequence; D016588:Anticarcinogenic Agents / Q000494:pharmacology*; D003485:Cyanates / Q000494:pharmacology*; D004247:DNA / Q000378:metabolism*; D004229:Dithiothreitol / Q000494:pharmacology; D006801:Humans; D013058:Mass Spectrometry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D052002:NF-kappa B p50 Subunit / Q000737:chemistry*; D016566:Organoselenium Compounds / Q000494:pharmacology*
chemical_list: D016588:Anticarcinogenic Agents; D003485:Cyanates; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; D016566:Organoselenium Compounds; C054108:benzyl selenocyanate; C074153:1,4-phenylenebis(methylene)selenocyanate; D004247:DNA; D004229:Dithiothreitol