title: Regulation of ceramide synthase-mediated crypt epithelium apoptosis by DNA damage repair enzymes.
abstract: Acute endothelial cell apoptosis and microvascular compromise couple gastrointestinal tract irradiation to reproductive death of intestinal crypt stem cell clonogens (SCCs) following high-dose radiation. Genetic or pharmacologic inhibition of endothelial apoptosis prevents intestinal damage, but as the radiation dose is escalated, SCCs become directly susceptible to an alternate cell death mechanism, mediated via ceramide synthase (CS)-stimulated de novo synthesis of the proapoptotic sphingolipid ceramide, and p53-independent apoptosis of crypt SCCs. We previously reported that ataxia-telangiectasia mutated deficiency resets the primary radiation lethal pathway, allowing CS-mediated apoptosis at the low-dose range of radiation. The mechanism for this event, termed target reordering, remains unknown. Here, we show that inactivation of DNA damage repair pathways signals CS-mediated apoptosis in crypt SCCs, presumably via persistent unrepaired DNA double-strand breaks (DSBs). Genetic loss of function of sensors and transducers of DNA DSB repair confers the CS-mediated lethal pathway in intestines of sv129/B6Mre11(ATLD1/ATLD1) and C57BL/6(Prkdc/SCID) (severe combined immunodeficient) mice exposed to low-dose radiation. In contrast, CS-mediated SCC lethality was mitigated in irradiated gain-of-function Rad50(s/s) mice, and epistasis studies order Rad50 upstream of Mre11. These studies suggest unrepaired DNA DSBs as causative in target reordering in intestinal SCCs. As such, we provide an in vivo model of DNA damage repair that is standardized, can be exploited to understand allele-specific regulation in intact tissue, and is pharmacologically tractable.
authors.affiliation: Laboratory of Signal Transduction, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
authors.forename: Jimmy A
authors.initials: JA
authors.lastname: Rotolo
authors.forename: Judith
authors.initials: J
authors.lastname: Mesicek
authors.forename: Jerzy
authors.initials: J
authors.lastname: Maj
authors.forename: Jean-Philip
authors.initials: JP
authors.lastname: Truman
authors.forename: Adriana
authors.initials: A
authors.lastname: Haimovitz-Friedman
authors.forename: Richard
authors.initials: R
authors.lastname: Kolesnick
authors.forename: Zvi
authors.initials: Z
authors.lastname: Fuks
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D017766:Acid Anhydride Hydrolases; D000818:Animals; D017209:Apoptosis; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002518:Ceramides / Q000378:metabolism; D064447:Checkpoint Kinase 2; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000473:pathology / Q000528:radiation effects; D007583:Jejunum / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects; D000076228:MRE11 Homologue Protein; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D016513:Mice, SCID; D010088:Oxidoreductases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D013234:Stem Cells / Q000378:metabolism* / Q000473:pathology / Q000528:radiation effects; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D018797:Cell Cycle Proteins; D002518:Ceramides; D004268:DNA-Binding Proteins; C512689:Mre11a protein, mouse; D025521:Tumor Suppressor Proteins; D010088:Oxidoreductases; C108138:dihydroceramide desaturase; D064447:Checkpoint Kinase 2; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; C578633:Chek2 protein, mouse; D017346:Protein Serine-Threonine Kinases; D000076228:MRE11 Homologue Protein; D017766:Acid Anhydride Hydrolases; C495198:Rad50 protein, mouse; D045643:DNA Repair Enzymes