Apoptotic properties of the type 1 interferon induced family of human mitochondrial membrane ISG12 proteins.
BACKGROUND
Interferons are a family of cytokines with growth inhibitory and antiviral functions, which exert their biological actions through the expression of interferon-stimulated genes (ISGs). The human ISG12 family of proteins comprises ISG12A, ISG12B, ISG12C and ISG6-16. Due to differential splicing and a gene variation, the human ISG12A protein exists as a full-length ISG12A form and three ISG12A variants. ISG12 genes have been found transcriptionally dysregulated in many disorders. High levels of ISG12A mRNA have been found in breast and ovarian cancers. Loss of heterozygosity at the position of the ISG12 genes often occurs in ovarian carcinomas and lymphoblastic leukemias. Both ISG12A and ISG6-16 are up-regulated in psoriasis.


RESULTS
We demonstrate here that expression of the human full-length ISG12A protein sensitises cells for TNFα and the BH3 mimetic gossypol induced apoptosis, and the other ISG12A variants as well as ISG12B and ISG12C can induce apoptosis directly in HEK293 cells. Also ISG6-16 sensitises HEK293 cells for gossypol-induced apoptosis. In the ISG12 motif, two putative Bcl-2 homology (BH)3 like motifs were found, which may be decisive for the apoptotic properties of the ISG12 proteins. A series of BH3 mutants was made in ISG12AΔ-S, the smallest apoptosis-inducing ISG12A variant and our results indicate that ISG12AΔ-S indeed possesses features resembling those of BH3-only proteins. Supporting this notion are our findings that the full-length ISG12A co-immunoprecipitates with the Bcl-2 protein, and the apoptotic properties of the ISG12A variants are reduced in Bcl-2 expressing HEK293 cells. In addition, full-length ISG12A is able to form homodimers, which suggests a possible involvement in pore formation during apoptosis. The full-length ISG12A, the three ISG12A variants and the ISG12B proteins were found to be localised in the mitochondria.


CONCLUSIONS
Our results suggest that the ISG12 family of proteins has an important role for the apoptotic properties induced by type 1 interferon.


CONCLUSIONS
The ISG12 family constitute small hydrophic proteins involved in apoptosis. This is the first comparison of the apoptotic potentials of the full-length ISG12A protein and the three ISG12A variants. The differential apoptotic potentials of these proteins might have an impact on the strategies to monitor and interpret their dysregulation associated with many disorders.
Department of Molecular Biology and Genetics, Aarhus University, Aarhus, 8000, Denmark.
Heidi
H
Gytz
Department of Molecular Biology and Genetics, Aarhus University, Aarhus, 8000, Denmark.
Mariann F
MF
Hansen
Department of Molecular Biology and Genetics, Aarhus University, Aarhus, 8000, Denmark.
Signe
S
Skovbjerg
Department of Molecular Biology and Genetics, Aarhus University, Aarhus, 8000, Denmark.
Anders C M
AC
Kristensen
Department of Molecular Biology and Genetics, Aarhus University, Aarhus, 8000, Denmark.
Sofie
S
Hørlyck
Department of Molecular Biology and Genetics, Aarhus University, Aarhus, 8000, Denmark.
Mette B
MB
Jensen
Department of Molecular Biology and Genetics, Aarhus University, Aarhus, 8000, Denmark.
Marlene
M
Fredborg
Department of Molecular Biology and Genetics, Aarhus University, Aarhus, 8000, Denmark.
Lotte D
LD
Markert
Centre of Immunological and Cancer Research, Queensland University, Brisbane, Australia.
Nigel A
NA
McMillan
Department of Biomedicine, Aarhus University, Aarhus, 8000, Denmark.
Erik I
EI
Christensen
Department of Molecular Biology and Genetics, Aarhus University, Aarhus, 8000, Denmark.|Centre of Immunological and Cancer Research, Queensland University, Brisbane, Australia.
Pia M
PM
Martensen
D000595:Amino Acid Sequence; D017209:Apoptosis; D017124:Conserved Sequence; D006072:Gossypol / Q000494:pharmacology; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000502:physiology*; D008928:Mitochondria / Q000378:metabolism; D051336:Mitochondrial Membranes / Q000378:metabolism; D020125:Mutation, Missense; D011485:Protein Binding; D020033:Protein Isoforms / Q000502:physiology; D021381:Protein Transport; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
C000595707:BCL2 protein, human; C406887:IFI27 protein, human; D008565:Membrane Proteins; D020033:Protein Isoforms; D019253:Proto-Oncogene Proteins c-bcl-2; C439524:TNF protein, human; D014409:Tumor Necrosis Factor-alpha; D006072:Gossypol
6-16 (G1P3); Apoptosis; Gossypol; ISG12A(IFI27); ISG12B(IFI27L2)