Alternative titles; symbols
HGNC Approved Gene Symbol: CASP8AP2
Cytogenetic location: 6q15 Genomic coordinates (GRCh38) : 6:89,829,880-89,874,436 (from NCBI)
Imai et al. (1999) cloned Casp8ap2, which they called Flash, from a mouse T-cell lymphoma cDNA library. The deduced 1,962-amino acid protein has a calculated molecular mass of 219.1 kD. It contains a motif structurally related to CED4/Apaf1 (602233) and a C-terminal death effector domain (DED)-recruiting domain (DRD). Imai et al. (1999) identified transcripts of 4.7 kb and 7 kb in adult mouse tissues, with highest expression in heart, brain, thymus, lung, testis, and spleen, and much lower expression in liver, kidney, and skeletal muscle. By Western blot analysis of mouse fibroblasts and thymocytes, Imai et al. (1999) observed endogenous Casp8ap2 as a protein band at 220 kD.
Kimura et al. (1999) cloned full-length human FLASH from a KT-cell cDNA library. The deduced 1,982-amino acid protein shares 66% identity with mouse Flash. Human FLASH lacks the CED4 homologous region found in mouse Flash, but it contains the C-terminal DRD.
By sequencing clones obtained from a size-fractionated fetal brain cDNA library, Nagase et al. (2000) cloned CASP8AP2, which they designated KIAA1315. RT-PCR analysis showed significant CASP8AP2 expression in testis and ovary only, with much weaker expression in amygdala. Little to no expression was detected in other tissues examined.
Using immunofluorescence analysis of Drosophila and HeLa cells, Yang et al. (2009) found that FLASH concentrated in nuclear bodies called histone locus bodies (HLBs), which are distinct from Cajal bodies.
Through coimmunoprecipitation and transfection experiments, Imai et al. (1999) determined that the DRD of Flash bound the DEDs of caspase-8 (601763) and Fadd (602457). It also specifically coimmunoprecipitated with activated Fas (134637), suggesting that Casp8ap2 is part of the death-inducing signaling complex (DISC).
Using luciferase reporter analysis, Choi et al. (2001) showed that inhibition of FLASH expression abolished TNF (191160)-induced NFKB (164011) activation in embryonic kidney cells. Expression or overexpression of FLASH activated NFKB through a central oligomerization domain, called the NFKB activation domain (NAD), in a TRAF2 (601895)-NIK (604655)-IKKA (600664)-dependent pathway. Immunoprecipitation analysis indicated that the FLASH NAD interacted with TRAF2. Choi et al. (2001) concluded that FLASH coordinates downstream NFKB activity via a TRAF2-dependent pathway in TNF signaling.
Using a library of endoribonuclease-prepared short interfering RNAs (esiRNAs), Kittler et al. (2004) identified 37 genes required for cell division, one of which was CASP8AP2. These 37 genes included several splicing factors for which knockdown generates mitotic spindle defects. In addition, a putative nuclear-export terminator was found to speed up cell proliferation and mitotic progression after knockdown.
Barcaroli et al. (2006) found that FLASH colocalized with coilin (COIL; 600272) and NPAT (601448) in Cajal bodies in several human cell lines and primary fibroblasts. Knockdown of NPAT by small interfering RNA resulted in FLASH delocalization, and downregulation of FLASH resulted in altered localization of coilin and other Cajal body components.
Barcaroli et al. (2006) stated that Cajal body components such as NPAT and CDK2 (116953) play a role in S-phase regulation and histone precursor mRNA transcription. They found that depletion of FLASH resulted in reduced histone H4 (see 602822) mRNA and protein levels and an S-phase block.
Unlike the majority of pre-mRNAs, replication-dependent histone pre-mRNAs are not processed at the 3-prime end to include a polyA tail. Instead, they are proteolytically cleaved between a conserved stem-loop structure and a purine-rich histone downstream element (HDE), resulting in histone mRNAs that terminate with a stem loop followed by a 5-nucleotide single-stranded tail. Processing of histone pre-mRNAs at the 3-prime end requires the U7 small nucleolar ribonuclear particle (snRNP; see 617876), which binds the HDE and recruits the endonuclease CPSF73 (CPSF3; 606029). Yang et al. (2009) found that FLASH was required for 3-prime end processing of histone pre-mRNA. Truncation analysis showed that the N-terminal domain of FLASH interacted with an N-terminal domain of the U7 snRNP-specific subunit LSM11 (617910). Drosophila Flash also interacted directly with human and Drosophila LSM11. Depletion of Flash in Drosophila cells resulted in polyadenylation of histone mRNAs.
By immunoprecipitation analysis, Kiriyama et al. (2009) found that FLASH interacted with ARS2 (SRRT; 614469) in human cell lines. Both proteins colocalized at nuclear foci. Knockdown of either FLASH or ARS2 inhibited cell growth and reduced mRNA levels of replication-dependent histones. Mutation analysis revealed that the N-terminal coiled-coil domain of FLASH was required for both self-association and for S-phase progression. A central region of FLASH, which the authors called the FLASH-ARS2-binding (FARB) region, was required and sufficient for interaction with the conserved C-terminal domain of ARS2. Interaction of FLASH with ARS2 was also required for FLASH-dependent S-phase progression.
Hartz (2012) mapped the CASP8AP2 gene to chromosome 6q15 based on an alignment of the CASP8AP2 sequence (GenBank AF154415) with the genomic sequence (GRCh37).
Barcaroli, D., Bongiorno-Borbone, L., Terrinoni, A., Hofmann, T. G., Rossi, M., Knight, R. A., Matera, A. G., Melino, G., De Laurenzi, V. FLASH is required for histone transcription and S-phase progression. Proc. Nat. Acad. Sci. 103: 14808-14812, 2006. [PubMed: 17003125] [Full Text: https://doi.org/10.1073/pnas.0604227103]
Barcaroli, D., Dinsdale, D., Neale, M. H., Bongiorno-Borbone, L., Ranalli, M., Munarriz, E., Sayan, A. E., McWilliam, J. M., Smith, T. M., Fava, E., Knight, R. A., Melino, G., De Laurenzi, V. FLASH is an essential component of Cajal bodies. Proc. Nat. Acad. Sci. 103: 14802-14807, 2006. [PubMed: 17003126] [Full Text: https://doi.org/10.1073/pnas.0604225103]
Choi, Y.-H., Kim, K.-B., Kim, H.-H., Hong, G.-S., Kwon, Y.-K., Chung, C.-W., Park, Y.-M., Shen, Z.-J., Kim, B. J., Lee, S.-Y., Jung, Y.-K. FLASH coordinates NF-kappa-B activity via TRAF2. J. Biol. Chem. 276: 25073-25077, 2001. [PubMed: 11340079] [Full Text: https://doi.org/10.1074/jbc.M102941200]
Hartz, P. A. Personal Communication. Baltimore, Md. 2/1/2012.
Imai, Y., Kimura, T., Murakami, A., Yajima, N., Sakamaki, K., Yonehara, S. The CED-4-homologous protein FLASH is involved in Fas-mediated activation of caspase-8 during apoptosis. Nature 398: 777-785, 1999. Note: Erratum: Nature 400: 89 only, 1999. [PubMed: 10235259] [Full Text: https://doi.org/10.1038/19709]
Kimura, T., Imai, Y., Yonehara, S. Reply to Koonin et al. (Letter) Nature 401: 662-663, 1999. [PubMed: 10537104] [Full Text: https://doi.org/10.1038/44317]
Kiriyama, M., Kobayashi, Y., Saito, M., Ishikawa, F., Yonehara, S. Interaction of FLASH with arsenite resistance protein 2 is involved in cell cycle progression at S phase. Molec. Cell. Biol. 29: 4729-4741, 2009. [PubMed: 19546234] [Full Text: https://doi.org/10.1128/MCB.00289-09]
Kittler, R., Putz, G., Pelletier, L., Poser, I., Heninger, A.-K., Drechsel, D., Fischer, S., Konstantinova, I., Habermann, B., Grabner, H., Yaspo, M.-L., Himmelbauer, H., Korn, B., Neugebauer, K., Pisabarro, M. T., Buchholz, F. An endoribonuclease-prepared siRNA screen in human cells identifies genes essential for cell division. Nature 432: 1036-1040, 2004. [PubMed: 15616564] [Full Text: https://doi.org/10.1038/nature03159]
Nagase, T., Kikuno, R., Ishikawa, K., Hirosawa, M., Ohara, O. Prediction of the coding sequences of unidentified human genes. XVI. The complete sequences of 150 new cDNA clones from brain which code for large proteins in vitro. DNA Res. 7: 65-73, 2000. [PubMed: 10718198] [Full Text: https://doi.org/10.1093/dnares/7.1.65]
Yang, X., Burch, B. D., Yan, Y., Marzluff, W. F., Dominski, Z. FLASH, a proapoptotic protein involved in activation of caspase-8, is essential for 3-prime end processing of histone pre-mRNAs. Molec. Cell 36: 267-278, 2009. [PubMed: 19854135] [Full Text: https://doi.org/10.1016/j.molcel.2009.08.016]