Reg IV regulates normal intestinal and colorectal cancer cell susceptibility to radiation-induced apoptosis.
OBJECTIVE
Regenerating (Reg) gene IV is predominantly expressed in gastrointestinal cells and highly up-regulated in many gastrointestinal malignancies, including colorectal cancer (CRC). Human CRC cells expressing higher levels of Reg IV gene and its protein product (Reg IV) are resistant to conventional therapies, including irradiation (IR). However, the underlying mechanism is not well defined.


METHODS
A murine model of IR-induced intestinal injury and in vitro and in vivo models of human CRC were used to determine the role of Reg IV in regulation of normal intestinal and colorectal cancer cell susceptibility to IR-induced apoptosis.


RESULTS
Treatments of recombinant human Reg IV (rhR4) protein protected normal intestinal crypt cells from IR-induced apoptosis by increasing the expression of antiapoptotic genes Bcl-2, Bcl-XL, and survivin. However, overexpression of Reg IV in human CRC cells was associated with increased resistance to IR-induced apoptosis. Therefore, we used antagonism of Reg IV as a tool to increase CRC cell susceptibility to IR-induced cell death. Two complementary approaches using specific monoclonal antibodies and small interfering RNAs were tested in both in vitro and in vivo models of human CRC. Both approaches resulted in increased apoptosis and decreased cell proliferation, leading to decreased tumor growth and increased animal survival. Furthermore, these approaches increased CRC cell susceptibility to IR-induced apoptosis.


CONCLUSIONS
These results implicate Reg IV as an important modulator of gastrointestinal cell susceptibility to IR; hence, it is a potential target for adjunctive treatments for human CRC and other gastrointestinal malignancies.
Bishnupuri
Kumar S
KS
Division of Gastroenterology, Washington University School of Medicine, St Louis, Missouri 63110, USA.
Luo
Qizhi
Q
Sainathan
Satheesh K
SK
Kikuchi
Kento
K
Sureban
Sripathi M
SM
Sabarinathan
Mekala
M
Gross
Jennifer H
JH
Aden
Konrad
K
May
Randal
R
Houchen
Courtney W
CW
Anant
Shrikant
S
Dieckgraefe
Brian K
BK
D000230:Adenocarcinoma / Q000473:pathology / Q000532:radiotherapy*; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017209:Apoptosis / Q000528:radiation effects*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D003106:Colon / Q000378:metabolism* / Q000473:pathology; D015179:Colorectal Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D004195:Disease Models, Animal; D005260:Female; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D037181:Lectins, C-Type / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008819:Mice, Nude; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000073718:Pancreatitis-Associated Proteins; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011878:Radiotherapy; D012097:Repressor Proteins; D000077022:Survivin; D014183:Transplantation, Heterologous; D016896:Treatment Outcome; D051020:bcl-X Protein / Q000378:metabolism
D000911:Antibodies, Monoclonal; C107489:BIRC5 protein, human; C117749:Birc5 protein, mouse; D051034:Inhibitor of Apoptosis Proteins; D037181:Lectins, C-Type; D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D000073718:Pancreatitis-Associated Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; C428528:REG4 protein, human; C546117:REG4 protein, mouse; D012097:Repressor Proteins; D000077022:Survivin; D051020:bcl-X Protein