Activators of apoptosis
The major focus of my research program exploits a genetic model, Drosophila, to understand how apoptotic physiology is regulated during normal development and after cell injury. In this animal, deletion of a complex genomic interval prevents all programmed cell death (PCD). Three genes mapping to this region (Reaper, Grim and Hid) function as potent activators of the apoptotic pathway. In germ line transformation experiments each locus partially "rescues" the cell death defective mutation and, in development, these death activators are expressed in patterns that precede the onset of PCD. In cultured cells and in transgenic animals, each gene is sufficient to provoke apoptosis that can be suppressed by caspase inhibitors. Reaper, Grim and Hid are therefore pivotal apoptosis activators that function through parallel circuits to engage a common set of effectors including caspases.
In efforts directed towards understanding the mechanisms through which these death activators exert their function, we identified a new Drosophila caspase, referred to as Dredd. Dredd is highly related to the nematode gene CED-3 and mammalian Caspase 8/ FLICE and at least one isoform is sufficient to elicit apoptosis. Dredd is unique among the Drosophila caspases because of features found in its long prodomain and a novel residue found at its active site. Cell killing by the death activators Reaper, Grim or Hid is suppressed by deletions of the Dredd locus. Furthermore, these same apoptosis activators promote both activational processing of Dredd protein and the accumulation of Dredd RNA in cells that were specified to die. Together, these observations implicate a novel mechanism that promotes "feed-forward" amplification of caspase function during programmed cell death. Current studies are focused toward understanding how the apoptotic activators engage this and other caspases.
Control of caspase activation
Very recently we discovered an important regulator of caspase activation in flies, referred to as Dark. This is a newly identified Drosophila gene, homologous to both human Apaf-1 and nematode CED-4. Like its mammalian counterpart, Dark evidently constitutes a regulated "bridge" between mitochondrial signals and the apical caspases. Mutations at Dark exhibit profound failures in programmed cell death and, in related genetic studies, we established that Dark is an important effector of apoptosis signaling by Reaper, Grim and Hid. Current studies are directed towards understanding how these activators promote Dark-induced caspase activation. As part of this effort, we are testing the role of two Drosophila bcl2 family members as potential regulators in this process.
Damage-inducible apoptotic responses
One of the PCD-activators, Reaper, also contributes important functions during "unscheduled" apoptosis provoked either by radiation or during aberrant development. Using reporter transgenes, we established that the Reaper promoter contains separate modular elements that are distinctly responsive to cues that elicit unscheduled apoptosis. Transactivation of the Reaper locus evidently functions as an integrating switch to specify cell death during normal PCD and as an adaptive response to injury. Current efforts are devoted to studies of radiation-induced determinants that engage this cell death regulator.
Noncanonical Genomic Transcription
New technologies in genomic sciences offer opportunities to explore the informational content of genomes in ways never before possible. Over the last few years, genome-wide expression analyses at the RNA level have become feasible, if not routine. While these methods have vastly improved our analytical power, the junk DNA paradox is still unresolved. We remain largely ignorant regarding vast portions of the genome that dont encode protein protein products and the extent of transcription though this genomic dark matter is not known. By adapting existing methodologies, we are attempting to advance the operational definition of gene activity and extract more complete informational content from sequenced genomes. This objective can be achieved through systematic and unbiased determinations of transcriptional activity at high resolution. Toward this end, we have initiated a saturation tiling approach, capable of profiling all transcriptional activity (on both strands) spanning more than half a megabase of chromosomal DNA. Transcribed sequences corresponding to unpredicted, noncanonical activity are being tested for authentic biologic function.
F., Christich, A., Sogame, N., Chapo, J., and Abrams, J.M.
p53 Directs Focused Genomic Responses in Drosophila (2007). Oncogene 26: 5184-93
Link, N., Chen, P., Lu, WJ, Pogue, K., Chuong, A., Mata, M., Checketts, J., Abrams, J.M.
A Collective Form of Cell Death Requires Homeodomain Interacting Protein Kinase.(2007) J. Cell Biology 178:567-74
Akdemir, F., Farkas, R., Chen, P., Juhasz, G., Medvedova, L., Sass, M., Wang, L., Wang,X., Chittaranjan, S., Gorski,S.,M., Rodriguez, A., Abrams, J.M. Autophagy Occurs Upstream or Parrallel to the Apoptosome During Histolytic Cell Death. (2006) Development (133) 1457-1465
Chew, S., Akdemir, F.,Chen, P., Lu, W., Mills, K.,Daish, T.,Kumar, S., Rodriguez,, A. and Abrams, J.M. (2004). The Apical Caspase, dronc, Governs Programmed and Unprogrammed Cell Death in Drosophila. Developmental Cell (7): 897-907
Sogame, N., Kim, M. and Abrams, J.M. (2003) Drosophila p53 preserves genomic stability by regulating cell death. Proc. Natl Acad. Sci, USA 100 (8): 4696-4701
Abrams, J.M. (2002) Competition and Compensation: Coupled to Death in Development and Cancer. Cell 110, 403-406
Rodriguez, A., Oliver, H. and Abrams, J. M. (2002) Unrestrained caspase-dependent cell death caused by loss of Diap1 function requires the Drosophila Apaf-1 homolog Dark. EMBO J 21(9): 2189-2197
Christich, A. Kauppila, S., Chen, P., Sogame, N., Ho, S., and Abrams, J. M. (2002) The damage- responsive Drosophila gene, sickle, encodes a novel IAP binding protein similar to, but distinct from, reaper, grim and hid. Current Biology 12: 137-140
Brodsky, M. H., Nordstrom, W., Tsang, G., Kwan, E., Rubin, G. M., and Abrams, J. M. (2000) Drosophila p53 binds a damage response element at the reaper locus. Cell 101: 103-113
Abrams, J. M. (1999) An emerging blueprint for apoptosis in Drosophila. Trends in Cell Biology 9: 435-440
Rodriguez, A., Oliver, H., Zou, H., Chen, P., Wang, X. and Abrams, J. M. (1999) Dark, is a Drosophila Homologue of Apaf-1/Ced-4 and Functions in an Evolutionarily Conserved Death Pathway. Nature Cell Biology 1: 272-279
Varkey, J., Chen, P., Jemmerson, R. and Abrams, J. M. (1999) Altered cytochrome c display precedes apoptosis in Drosophila. J Cell Biol 144: 701-710
Chen, P., Rodriguez, A., Erskine, R., Thach, T. and Abrams J. M. (1998) Dredd, a novel Drosophila caspase, is an effector of the apoptosis activators Reaper, Grim and Hid. Dev Biol 201: 202-216
Rodriguez, A., Chen, P., and Abrams, J. M. (1998) Molecular Prophets of Death in the Fly. Am J Hum Genet 62: 514-519
Chen, P., Lee, P., Otto, L, and Abrams, J. M. (1996) The apoptotic function of REAPER is distinct from signaling by the TNFR1 Death Domain. J Biol Chem 271: 25735-25737
Nordstrom, W., Chen, P., Steller, H. and Abrams, J. M. (1996) Activation of the reaper gene during ectopic cell killing in Drosophila. Dev Biol 180: 213-226
Chen, P., Nordstrom, W., Stuart, B. and Abrams, J. M. (1996) Grim, a novel cell death gene in Drosophila. Genes & Development 10: 1773-1782