Cytotoxic chemotherapy upregulates pro-apoptotic Bax and Bak in the small intestine of rats and humans.
OBJECTIVE
Small intestinal crypt cells rapidly undergo apoptosis in response to cytotoxic drug treatment that results in gastrointestinal toxicity. The Bcl-2 family have been implicated in both positive and negative regulation of intestinal cell apoptosis. The aim of this study was to examine the effect of cytotoxic treatment on Bcl-2 protein expression in patients and rats with tumours.


METHODS
Four pro- and four anti-apoptotic members of the Bcl-2 family, caspase-3 and p53 were examined in small intestinal crypts before and after treatment in rats and humans. Immunohistochemistry identified changes in protein expression over time, while relative RT-PCR was used to investigate mRNA expression in rat small intestine.


RESULTS
Cytotoxic treatment increased p53 and caspase-3 which coincided with elevated levels of apoptosis. Bax and Bak protein and mRNA expression also significantly increased at 6 hours following treatment in rats. Bax and Bak protein increased at day 1 after treatment in humans. Anti-apoptotic Mcl-1 protein decreased within 24hours. Other Bcl-2 family members showed only modest changes.


CONCLUSIONS
Increased expression of Bax and Bak but not other Bcl-2 family members is associated with apoptosis in small intestinal crypts and may amplify the sensitivity and susceptibility of crypt cells to chemotherapy-induced enteropathy.
Bowen
Joanne M
JM
Department of Medical Oncology, Royal Adelaide Hospital, Adelaide, South Australia. joanne.bowen@adelaide.edu.au
Gibson
Rachel J
RJ
Keefe
Dorothy M
DM
Cummins
Adrian G
AG
D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D053148:Caspase 3; D020169:Caspases / Q000187:drug effects; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000187:drug effects*; D007414:Intestinal Neoplasms / Q000188:drug therapy; D008565:Membrane Proteins / Q000187:drug effects*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000187:drug effects*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein
D000970:Antineoplastic Agents; C494772:BAK1 protein, human; C494826:BAX protein, human; C494774:Bak1 protein, rat; C494828:Bax protein, rat; D008565:Membrane Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; C505407:CASP3 protein, human; C505410:Casp3 protein, rat; D053148:Caspase 3; D020169:Caspases