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Induction of hsp 70 in HepG2 cells in response to hepatotoxicants
W F Salminen1, R Voellmy, S M Roberts
1Department of Pharmacology and Therapeutics, J. Hillis Miller Health Science Center, University of Florida, Gainesville 32601, USA.
Abstract:
The objective of this study was to determine if a variety of hepatotoxicants could induce the level of heat shock protein 70I, and whether or not elevated levels of heat shock proteins (hsp's) could provide cytoprotection from those hepatotoxicants. Exposure of HepG2 cells to cytotoxic concentrations of bromobenzene, cadmium, cyclophosphamide, or diethylnitrosamine increased the level of hsp 70I protein and mRNA, while carbon tetrachloride and cocaine had no effect on hsp 70I or mRNA levels. To determine if induction of hsp 70I might afford protection against cytotoxicity, HepG2 cells were given a prior sublethal heat shock (sub-LHS) (43 degrees C for 1 hr) to induce hsp's and then challenged 24 hr later with the hepatotoxicants. Sub-LHS pretreatment diminished toxicity from bromobenzene, cadmium, cyclophosphamide, or diethyl-nitrosamine, but not carbon tetrachloride or cocaine. In cells treated with [14C]carbon tetrachloride or [3H]cocaine, no detectable covalent binding to proteins was observed; whereas, [14C]-bromobenzene treatment resulted in substantial covalent binding to cellular protein. The apparent absence of formation of reactive metabolite adducted proteins from cocaine and carbon tetrachloride may explain why no hsp 70I induction was observed with these agents. The correlation between hepatotoxicant induction of hsp 70I and cytoprotection afforded by sub-LHS pretreatment suggests that hsp 70I induction may represent an important cellular defense mechanism in the liver.
Insights
Hepatotoxicants like bromobenzene can induce heat shock protein 70I (hsp 70I) in liver cells. Pre-treating cells with heat shock to elevate hsp 70I levels protected them from certain toxic agents.
Area of Science:
- Hepatology
- Cellular Biology
- Toxicology
Background:
- Hepatotoxicants pose a significant threat to liver health.
- Heat shock proteins (hsp's) are known cellular stress responders.
- The role of hsp 70I in liver cell defense against toxins requires further elucidation.
Purpose of the Study:
- To investigate the induction of heat shock protein 70I (hsp 70I) by various hepatotoxicants.
- To determine if elevated hsp levels confer cytoprotection against these toxins.
- To explore the relationship between hsp 70I induction and cellular defense mechanisms.
Main Methods:
- Exposure of HepG2 liver cells to cytotoxic concentrations of hepatotoxicants (bromobenzene, cadmium, cyclophosphamide, diethylnitrosamine, carbon tetrachloride, cocaine).
- Measurement of hsp 70I protein and mRNA levels.
- Pretreatment with sublethal heat shock (sub-LHS) to induce hsp's before toxic challenge.
- Assessment of cellular toxicity and covalent protein binding.
Main Results:
- Bromobenzene, cadmium, cyclophosphamide, and diethylnitrosamine increased hsp 70I levels.
- Carbon tetrachloride and cocaine did not affect hsp 70I or mRNA.
- Sub-LHS pretreatment reduced toxicity from the inducing agents but not from carbon tetrachloride or cocaine.
- Covalent binding to proteins was observed with bromobenzene but not with carbon tetrachloride or cocaine.
Conclusions:
- Hsp 70I induction correlates with cytoprotection against certain hepatotoxicants.
- The absence of hsp 70I induction by carbon tetrachloride and cocaine may be due to lack of reactive metabolite formation.
- Hsp 70I induction appears to be a crucial cellular defense mechanism in the liver.