Alternative titles; symbols
HGNC Approved Gene Symbol: DIABLO
Cytogenetic location: 12q24.31 Genomic coordinates (GRCh38): 12:122,207,662-122,227,456 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 12q24.31 | Deafness, autosomal dominant 64 | 614152 | Autosomal dominant | 3 |
Caspase activation is a key regulatory step for apoptosis. Cytochrome c (123970) released from the mitochondrial intermembrane space triggers 1 major caspase activation cascade. Upon its release to the cytosol, cytochrome c binds to APAF1 (602233) in the presence of dATP or ATP. The cytochrome c/APAF1 complex then recruits procaspase-9 (CASP9; 602234), inducing its autoactivation and leading to the activation of downstream caspases. Proteins of the BCL2 (see 603167) and inhibitor-of-apoptosis, or IAP (see API3; 300079), families are major regulators of the cytochrome c/APAF1/CASP9 pathway. SMAC promotes caspase activation in this pathway.
Du et al. (2000) identified and purified a protein, which they termed SMAC (second mitochondria-derived activator of caspase), that promotes caspase activation in the cytochrome c/APAF1/CASP9 pathway. By microsequence analysis, searching an EST database, and screening a HeLa cell cDNA library, they isolated a cDNA encoding SMAC. The predicted SMAC polypeptide contains 239 amino acids. Northern blot analysis detected a 1.5-kb SMAC transcript in all tissues tested, with highest expression in adult testis, high expression in heart, liver, kidney, spleen, prostate, and ovary, and low expression in brain, lung, thymus, and peripheral blood leukocytes.
Cheng et al. (2011) noted that the N-terminal 55 residues serve as a mitochondrial-targeting sequence, which is removed after the Diablo protein is imported into mitochondria intermembrane space. They found broad expression of DIABLO in human embryonic tissue at 17 weeks' gestation. The highest expression was in the testis, adrenal gland, and ears, with moderate expression in the brain, eyes, liver, kidney, lung, and spinal cord. Low expression was seen in the spleen. In the developing mouse cochlea, Diablo was significantly upregulated in hair cells from E18.5 to P0, but was subsequently downregulated. The extended distribution of Diablo at different stages of development in the mouse inner ear and the particular enrichment in hair cells suggested that Diablo functions in the development and homeostasis of the inner ear and in hair cells in particular.
Cheng et al. (2011) noted that the DIABLO gene contains 7 exons.
Scott (2000) mapped the DIABLO gene to chromosome 12 based on sequence similarity between the DIABLO sequence (GenBank AF262240) and the chromosome 12 clone RP11-512M8 (GenBank AC048338).
Cheng et al. (2011) noted that the DIABLO gene maps to chromosome 12q24.31.
Du et al. (2000) showed that SMAC promotes CASP9 activation by binding to IAPs and removing their inhibitory activity. SMAC is normally a mitochondrial protein, but it is released into the cytosol when cells undergo apoptosis. Mitochondrial import and cleavage of its signal peptide are required for SMAC to gain its apoptotic activity. Overexpression of SMAC increases cell sensitivity to apoptotic stimuli. SMAC was the second mitochondrial protein identified (the first being cytochrome c) that promotes apoptosis by activating caspases.
Verhagen et al. (2000) identified the murine homolog of SMAC, which they called DIABLO (direct IAP-binding protein with low pI). They showed that DIABLO can bind mammalian IAP homolog A (MIHA, or API3) and can also interact with MIHB (API1; 601712), MIHC (API2; 601721), and OpIAP, the baculoviral IAP. Immunoprecipitation and Western blot analysis indicated that the N-terminally processed, IAP-interacting form of DIABLO is concentrated in membrane fractions in healthy cells but is released into the MIHA-containing cytosolic fractions upon ultraviolet (UV) irradiation. Since transfection of cells with DIABLO was able to counter the protection afforded by MIHA against UV irradiation, the authors suggested that DIABLO may promote apoptosis by binding to IAPs and preventing them from inhibiting caspases.
Chai et al. (2000) showed that SMAC/DIABLO promotes not only the proteolytic activation of procaspase-3, but also the enzymatic activity of mature caspase-3, both of which depend upon its ability to interact physically with IAPs.
Nonsteroidal antiinflammatory drugs (NSAIDs) can prevent colonic tumor progression in both experimental animals and humans. Kohli et al. (2004) found that NSAID-induced apoptosis in a human colorectal cancer cell line was accompanied by release of SMAC from mitochondria into the cytosol. When SMAC was disrupted by homologous recombination and RNA interference, the NSAID-induced apoptosis was abrogated. SMAC release was dependent on BAX (600040), since SMAC release was not found in BAX knockout cells.
Burri et al. (2005) identified mouse Imp1 (IMMP1L; 612323) and Imp2 (IMMP2L; 605977) as the catalytic subunits of the mitochondrial inner membrane peptidase (IMP) complex. Imp1 and Imp2 activated Diablo by removing its presequence, resulting in sequestration of Diablo in the intermembrane space prior to activation by an apoptotic signal.
Chai et al. (2000) determined the crystal structure of SMAC/DIABLO at 2.2-angstrom resolution, which revealed that it homodimerizes through an extensive hydrophobic interface. Missense mutations inactivating this dimeric interface significantly compromised the function of SMAC/DIABLO. The N-terminal amino acids of SMAC/DIABLO are indispensable for its function, and a 7-residue peptide derived from the N terminus promotes procaspase-3 activation in vitro.
To understand the structural basis of molecular recognition between SMAC and the IAPs, Liu et al. (2000) determined the solution structure of the BIR3 domain of XIAP (300079) complexed with a functionally active 9-residue peptide derived from the N terminus of SMAC. Wu et al. (2000) performed the same experiment. They found that the N-terminal 4 residues (ala-val-pro-ile) in SMAC/DIABLO recognize a surface groove on BIR3, with the first residue ala binding a hydrophobic pocket and making 5 hydrogen bonds to neighboring residues on BIR3. These observations provided a structural explanation for the roles of the SMAC N terminus as well as for the conserved N-terminal sequences in the Drosophila proteins Hid/Grim/Reaper. In conjunction with other observations, Wu et al. (2000) concluded that their results reveal how SMAC may relieve IAP inhibition of caspase-9 activity. In addition to explaining a number of biologic observations, both Liu et al. (2000) and Wu et al. (2000) suggested that their structural analyses identified potential targets for drug screening that may be used for the treatment of cancers that overexpress IAPs.
XIAP interacts with caspase-9 and inhibits its activity, whereas SMAC (also known as DIABLO) relieves this inhibition through interaction with XIAP. Srinivasula et al. (2001) demonstrated that XIAP associates with the active caspase-9-APAF1 holoenzyme complex through binding to the amino terminus of the linker peptide on the small subunit of caspase-9, which becomes exposed after proteolytic processing of procaspase-9 at asp315. Supporting this observation, point mutations that abrogate the proteolytic processing but not the catalytic activity of caspase-9, or deletion of the linker peptide, prevented caspase-9 association with XIAP and its concomitant inhibition. Srinivasula et al. (2001) noted that the N-terminal 4 residues of caspase-9 linker peptide share significant homology with the N-terminal tetrapeptide in mature SMAC and in the Drosophila proteins Hid/Grim/Reaper, defining a conserved class of IAP-binding motifs. Consistent with this finding, binding of the caspase-9 linker peptide and SMAC to the BIR3 domain of XIAP is mutually exclusive, suggesting that SMAC potentiates caspase-9 activity by disrupting the interaction of the linker peptide of caspase-9 with BIR3. Srinivasula et al. (2001) concluded that their studies reveal a mechanism in which binding to the BIR3 domain of XIAP by 2 conserved peptides, one from SMAC and the other from caspase-9, has opposing effects on caspase activity and apoptosis.
In affected members of a large Chinese family with young-adult onset of autosomal dominant nonsyndromic deafness-64 (DFNA64; 614152), Cheng et al. (2011) identified a heterozygous mutation in the DIABLO gene (S126L; 605219.0001). In vitro functional expression studies in E. coli and HeLa cells showed that the mutant protein did not increase apoptotic activity compared to wildtype. However, transfection of HeLa cells with the mutant protein enhanced the degradation of mutant and wildtype DIABLO via heterodimerization. Cells expressing the mutant protein showed increased susceptibility to calcium-induced loss of mitochondrial potential compared to wildtype, indicating increased sensitivity to mitochondrial stress and suggestive of mitochondrial dysfunction. A decrease in wildtype protein did not yield similar findings, suggesting that the existence of mutant DIABLO leads to activation of a degradation machinery for constant clearance of aberrant proteins.
Okada et al. (2002) generated Diablo-deficient mice by homologous recombination. Western blot analysis confirmed the null mutation. The mice were fertile and appeared grossly normal at more than 1 year of age, and histologic analysis failed to detect any abnormalities. In vitro analysis indicated an inhibition of procaspase-3 (CASP3; 600636) cleavage in Diablo -/- cell lysates, but all types of Diablo -/- cells tested responded normally to a number of apoptotic stimuli. Fas (134637)-mediated apoptosis in liver was also normal in vivo in these mice. The authors concluded that a redundant molecule, possibly Omi (HTRA2; 606441), or molecules are capable of compensating for the loss of Diablo function. Alternatively, they suggested that Diablo may only regulate programmed cell death in specific situations or tissues not yet identified.
In affected members of a large Chinese family with young-adult onset of autosomal dominant nonsyndromic deafness-64 (DFNA64; 614152), Cheng et al. (2011) identified a heterozygous 377C-T transition in exon 5 of the DIABLO gene, resulting in a ser126-to-leu (S126L) substitution in a highly conserved residue. The S126L mutation corresponds to a ser71-to-leu (S71L) mutation in the mature protein. The mutation was not found in 1,000 Chinese control chromosomes. In vitro functional expression studies in E. coli and HeLa cells showed that the mutant protein did not increase apoptotic activity compared to wildtype. However, transfection of HeLa cells with the mutant protein enhanced the degradation of mutant and wildtype DIABLO via heterodimerization. Cells expressing the mutant protein showed increased susceptibility to calcium-induced loss of mitochondrial potential compared to wildtype, indicating increased sensitivity to mitochondrial stress and suggestive of mitochondrial dysfunction. A decrease in wildtype protein did not yield similar findings, suggesting that the existence of mutant DIABLO leads to activation of a degradation machinery for constant clearance of aberrant proteins.
Burri, L., Strahm, Y., Hawkins, C. J., Gentle, I. E., Puryer, M. A., Verhagen, A., Callus, B., Vaux, D., Lithgow, T. Mature DIABLO/Smac is produced by the IMP protease complex on the mitochondrial inner membrane. Molec. Biol. Cell 16: 2926-2933, 2005. [PubMed: 15814844] [Full Text: https://doi.org/10.1091/mbc.e04-12-1086]
Chai, J., Du, C., Wu, J.-W., Kyin, S., Wang, X., Shi, Y. Structural and biochemical basis of apoptotic activation by Smac/DIABLO. Nature 406: 855-862, 2000. [PubMed: 10972280] [Full Text: https://doi.org/10.1038/35022514]
Cheng, J., Zhu, Y., He, S., Lu, Y., Chen, J., Han, B., Petrillo, M., Wrzeszczynski, K. O., Yang, S., Dai, P., Zhai, S., Han, D., Zhang, M. Q., Li, W., Liu, X., Li, H., Chen, Z. Y., Yuan, H. Functional mutation of SMAC/DIABLO, encoding a mitochondrial proapoptotic protein, causes human progressive hearing loss DFNA64. Am. J. Hum. Genet. 89: 56-66, 2011. [PubMed: 21722859] [Full Text: https://doi.org/10.1016/j.ajhg.2011.05.027]
Du, C., Fang, M., Li, Y., Li, L., Wang, X. Smac, a mitochondrial protein that promotes cytochrome c-dependent caspase activation by eliminating IAP inhibition. Cell 102: 33-42, 2000. [PubMed: 10929711] [Full Text: https://doi.org/10.1016/s0092-8674(00)00008-8]
Kohli, M., Yu, J., Seaman, C., Bardelli, A., Kinzler, K. W., Vogelstein, B., Lengauer, C., Zhang, L. SMAC/Diablo-dependent apoptosis induced by nonsteroidal antiinflammatory drugs (NSAIDs) in colon cancer cells. Proc. Nat. Acad. Sci. 101: 16897-16902, 2004. [PubMed: 15557007] [Full Text: https://doi.org/10.1073/pnas.0403405101]
Liu, Z., Sun, C., Olejniczak, E. T., Meadows, R. P., Betz, S. F., Oost, T., Herrmann, J., Wu, J. C., Fesik, S. W. Structural basis for binding of Smac/DIABLO to the XIAP BIR3 domain. Nature 408: 1004-1008, 2000. [PubMed: 11140637] [Full Text: https://doi.org/10.1038/35050006]
Okada, H., Suh, W.-K., Jin, J., Woo, M., Du, C., Elia, A., Duncan, G. S., Wakeham, A., Itie, A., Lowe, S. W., Wang, X., Mak, T. W. Generation and characterization of Smac/DIABLO-deficient mice. Molec. Cell. Biol. 22: 3509-3517, 2002. [PubMed: 11971981] [Full Text: https://doi.org/10.1128/MCB.22.10.3509-3517.2002]
Scott, A. F. Personal Communication. Baltimore, Md. 8/18/2000.
Srinivasula, S. M., Hegde, R., Saleh, A., Datta, P., Shiozaki, E., Chai, J., Lee, R.-A., Robbins, P. D., Fernandes-Alnemri, T., Shi, Y., Alnemri, E. S. A conserved XIAP-interaction motif in caspase-9 and Smac/DIABLO regulates caspase activity and apoptosis. Nature 410: 112-116, 2001. Note: Erratum: Nature 114: 1081 only, 2001. [PubMed: 11242052] [Full Text: https://doi.org/10.1038/35065125]
Verhagen, A. M., Ekert, P. G., Pakusch, M., Silke, J., Connolly, L. M., Reid, G. E., Moritz, R. L., Simpson, R. J., Vaux, D. L. Identification of DIABLO, a mammalian protein that promotes apoptosis by binding to and antagonizing IAP proteins. Cell 102: 43-53, 2000. [PubMed: 10929712] [Full Text: https://doi.org/10.1016/s0092-8674(00)00009-x]
Wu, G., Chai, J., Suber, T. L., Wu, J.-W., Du, C., Wang, X., Shi, Y. Structural basis of IAP recognition by Smac/DIABLO. Nature 408: 1008-1012, 2000. [PubMed: 11140638] [Full Text: https://doi.org/10.1038/35050012]