title: Expression and function of the leucine zipper protein Par-4 in apoptosis.
abstract: The prostate apoptosis response-4 (par-4) gene was identified by differential screening for genes that are upregulated when prostate cancer cells are induced to undergo apoptosis. The par-4 gene is induced by apoptotic signals but not by growth-arresting, necrotic, or growth-stimulatory signals. The deduced amino acid sequence of par-4 predicts a protein with a leucine zipper domain at its carboxy terminus. We have recently shown that the Par-4 protein binds, via its leucine zipper domain, to the zinc finger domain of Wilms' tumor protein WT1 (R. W. Johnstone et al., Mol. Cell. Biol. 16:6945-6956, 1996). In experiments aimed at determining the functional role of par-4 in apoptosis, an antisense par-4 oligomer abrogated par-4 expression and activator-driven apoptosis in rat prostate cancer cell line AT-3, suggesting that par-4 is required for apoptosis in these cells. Consistent with a functional role for par-4 in apoptosis, ectopic overexpression of par-4 in prostate cancer cell line PC-3 and melanoma cell line A375-C6 conferred supersensitivity to apoptotic stimuli. Transfection studies with deletion mutants of Par-4 revealed that full-length Par-4, but not mutants that lacked the leucine zipper domain of Par-4, conferred enhanced sensitivity to apoptotic stimuli. Most importantly, ectopic coexpression of the leucine zipper domain of Par-4 inhibited the ability of Par-4 to enhance apoptosis. Finally, ectopic expression of WT1 attenuated apoptosis, and coexpression of Par-4 but not a leucine zipperless mutant of Par-4 rescued the cells from the antiapoptotic effect of WT1. These findings suggest that the leucine zipper domain is required for the Par-4 protein to function in apoptosis.
authors.affiliation: Department of Surgery, University of Kentucky, Lexington 40536, USA.
authors.forename: S F
authors.initials: SF
authors.lastname: Sells
authors.forename: S S
authors.initials: SS
authors.lastname: Han
authors.forename: S
authors.initials: S
authors.lastname: Muthukkumar
authors.forename: N
authors.initials: N
authors.lastname: Maddiwar
authors.forename: R
authors.initials: R
authors.lastname: Johnstone
authors.forename: E
authors.initials: E
authors.lastname: Boghaert
authors.forename: D
authors.initials: D
authors.lastname: Gillis
authors.forename: G
authors.initials: G
authors.lastname: Liu
authors.forename: P
authors.initials: P
authors.lastname: Nair
authors.forename: S
authors.initials: S
authors.lastname: Monnig
authors.forename: P
authors.initials: P
authors.lastname: Collini
authors.forename: M P
authors.initials: MP
authors.lastname: Mattson
authors.forename: V P
authors.initials: VP
authors.lastname: Sukhatme
authors.forename: S G
authors.initials: SG
authors.lastname: Zimmer
authors.forename: D P
authors.initials: DP
authors.lastname: Wood
authors.forename: J W
authors.initials: JW
authors.lastname: McRoberts
authors.forename: Y
authors.initials: Y
authors.lastname: Shi
authors.forename: V M
authors.initials: VM
authors.lastname: Rangnekar
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism; D006801:Humans; D016350:Leucine Zippers; D008297:Male; D008969:Molecular Sequence Data; D011467:Prostate / Q000166:cytology; D051381:Rats; D011994:Recombinant Proteins; D013329:Structure-Activity Relationship; D019284:Thapsigargin / Q000494:pharmacology; D014157:Transcription Factors / Q000378:metabolism; D025721:WT1 Proteins
chemical_list: D004268:DNA-Binding Proteins; D011994:Recombinant Proteins; D014157:Transcription Factors; D025721:WT1 Proteins; D019284:Thapsigargin