Progastrin stimulates murine colonic epithelial mitosis after DNA damage.
OBJECTIVE
Transgenic mice that overexpress progastrin are more susceptible than either wild-type mice or mice that overexpress amidated gastrin to chemical carcinogen-induced colonic adenomas. We have investigated whether alterations in the regulation of apoptosis or mitosis after DNA damage contribute to the effects of progastrin on murine colonic epithelium.


METHODS
Apoptosis and mitosis were assessed on a cell positional basis in murine intestinal epithelium after gamma-irradiation. Mice analyzed were progastrin overexpressing, gastrin overexpressing, gastrin knockout, and their wild-type counterparts. The expression of cell cycle regulators was analyzed by gene array and Western blotting.


RESULTS
Apoptosis was induced to similar levels in the small intestinal and colonic crypts of all mice 4.5 hours after 8 Gy gamma-radiation. Colonic mitosis was inhibited to almost undetectable levels by 8Gy gamma-radiation in wild-type, gastrin-knockout, and gastrin-overexpressing mice. However, significant colonic mitosis persisted in progastrin-overexpressing mice up to 24 hours after 8Gy gamma-radiation. Increased levels of cdk4 and cyclin D1 proteins were found in the colonic epithelium of progastrin-overexpressing mice relative to wild-type animals after gamma-radiation.


CONCLUSIONS
After DNA damage by gamma-radiation, mice with elevated progastrin exhibit significantly higher levels of colonic mitosis than wild-type or gastrin-overexpressing mice. Persistently elevated cdk4 and cyclin D1 in progastrin overexpressing mice accounts for the capacity of colon cells to continue with the cell cycle after DNA damage.
Department of Medicine, University of Liverpool, England.
Penelope D
PD
Ottewell
Alastair J M
AJ
Watson
Timothy C
TC
Wang
Andrea
A
Varro
Graham J
GJ
Dockray
D Mark
DM
Pritchard
D000818:Animals; D017209:Apoptosis / Q000502:physiology; D003106:Colon / Q000166:cytology*; D019938:Cyclin D1 / Q000235:genetics; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases / Q000235:genetics; D004249:DNA Damage / Q000187:drug effects*; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology / Q000528:radiation effects; D005720:Gamma Rays; D005755:Gastrins / Q000235:genetics*; D015870:Gene Expression; D007413:Intestinal Mucosa / Q000166:cytology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008938:Mitosis / Q000502:physiology / Q000528:radiation effects; D011498:Protein Precursors / Q000235:genetics*; D011518:Proto-Oncogene Proteins
D005755:Gastrins; D011498:Protein Precursors; D011518:Proto-Oncogene Proteins; D019938:Cyclin D1; C013706:big gastrin; C495902:Cdk4 protein, mouse; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases