Apoptotic properties of the type 1 interferon induced family of human mitochondrial membrane ISG12 proteins. (26th October 2016)

• Record Type: Journal Article
• Authors: Gytz, Heidi; Hansen, Mariann F.; Skovbjerg, Signe; Kristensen, Anders C. M.; Hørlyck, Sofie; Jensen, Mette B.; Fredborg, Marlene; Markert, Lotte D.; McMillan, Nigel A.; Christensen, Erik I.; Martensen, Pia M.
• Is Part Of: Biology of the cell. Volume 109:Number 2(2017)
• Page Start: 94
• Page End: 112
• Publication Date: 2016-10-26
• Subjects: 6–16 (G1P3) -- Apoptosis -- Gossypol -- ISG12B(IFI27L2) -- ISG12A(IFI27); Cytology -- Periodicals; Electron microscopy -- Periodicals; 571.6
• DOI: 10.1111/boc.201600034
• Languages: English
• ISSNs: 0248-4900

Abstract

Abstract : Research article : The ISG12 family of proteins constitute small hydrophobic proteins found to be dysregulated in many disorders. Our study presents the first comparison of the ISG12‐induced apoptotic potentials, both in between the ISG12 family members and in between the full‐length ISG12A protein and the three ISG12A variants. Importantly, the three ISG12A variants as well as ISG12B and ISG12C induce apoptosis directly. All ISG12 family members are localised in the mitochondria, and the full‐length ISG12A and the ISG12A variants prime cells for TNFα‐ and gossypol‐induced apoptosis. Exerting their actions via the intrinsic pathway of apoptosis, we found that expression of the anti‐apoptotic Bcl‐2 protein reduces the apoptotic potential of the ISG12A variants. Through analyses of mutant forms, we concluded that the ISG12AΔ‐S variant possesses BH3‐only like features pointing to a new mechanistic action. Abstract : Background information: 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. Significance: 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.