Homeostatic response under carcinogen withdrawal, heme oxygenase 1 expression and cell cycle association.
BACKGROUND
Chronic injury deregulates cellular homeostasis and induces a number of alterations leading to disruption of cellular processes such as cell cycle checkpoints and apoptosis, driving to carcinogenesis. The stress protein heme oxygenase-1 (HO-1) catalyzes heme degradation producing biliverdin, iron and CO. Induction of HO-1 has been suggested to be essential for a controlled cell growth. The aim of this work was to analyze the in vivo homeostatic response (HR) triggered by the withdrawal of a potent carcinogen, p-dimethylaminoazobenzene (DAB), after preneoplastic lesions were observed. We analyzed HO-1 cellular localization and the expression of HO-1, Bcl-2 and cell cycle related proteins under these conditions comparing them to hepatocellular carcinoma (HC).


METHODS
The intoxication protocol was designed based on previous studies demonstrating that preneoplastic lesions were evident after 89 days of chemical carcinogen administration. Male CF1 mice (n = 18) were used. HR group received DAB (0.5 % w/w) in the diet for 78 days followed by 11 days of carcinogen deprivation. The HC group received the carcinogen and control animals the standard diet during 89 days. The expression of cell cycle related proteins, of Bcl-2 and of HO-1 were analyzed by western blot. The cellular localization and expression of HO-1 were detected by immnunohistochemistry.


RESULTS
Increased expression of cyclin E/CDK2 was observed in HR, thus implicating cyclin E/CDK2 in the liver regenerative process. p21cip1/waf1 and Bcl-2 induction in HC was restituted to basal levels in HR. A similar response profile was found for HO-1 expression levels, showing a lower oxidative status in the carcinogen-deprived liver. The immunohistochemical studies revealed the presence of macrophages surrounding foci of necrosis and nodular lesions in HR indicative of an inflammatory response. Furthermore, regenerative cells displayed changes in type, size and intensity of HO-1 immunostaining.


CONCLUSIONS
These results demonstrate that the regenerative capacity of the liver is still observed in the pre-neoplastic tissue after carcinogen withdrawal suggesting that reversible mechanism/s to compensate necrosis and to restitute homeostasis are involved.
Castronuovo
Cynthia C
CC
Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, CONICET Buenos Aires, Argentina. cynthiac@qb.fcen.uba.ar <cynthiac@qb.fcen.uba.ar>
Sacca
Paula A
PA
Meiss
Roberto
R
Caballero
Fabiana A
FA
Batlle
Alcira
A
Vazquez
Elba S
ES
D000818:Animals; D002273:Carcinogens / Q000008:administration & dosage / Q000633:toxicity*; D006528:Carcinoma, Hepatocellular / Q000201:enzymology; D002453:Cell Cycle / Q000187:drug effects*; D018797:Cell Cycle Proteins / Q000235:genetics*; D004334:Drug Administration Schedule; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D051547:Heme Oxygenase-1 / Q000235:genetics*; D006706:Homeostasis; D008113:Liver Neoplasms / Q000201:enzymology; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D004124:p-Dimethylaminoazobenzene / Q000008:administration & dosage / Q000633:toxicity*
D002273:Carcinogens; D018797:Cell Cycle Proteins; D004124:p-Dimethylaminoazobenzene; D051547:Heme Oxygenase-1