Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A complementary DNA (cDNA) for rat hepatic aryl sulfotransferase IV (AST IV) was isolated, characterized, and used as a hybridization probe to evaluate the molecular basis for the differential expression of AST IV during 2-acetylaminofluorine (2AAF)-induced hepatocarcinogensis. The AST IV cDNA clone was obtained by immunochemical screening of a male Sprague-Dawley rat liver cDNA library. The AST IV cDNA was found to be 1.3 kilobases long and to encode a fusion protein which was reactive with an antibody to AST IV and enzymatically able to generate the sulfuric acid ester of N-hydroxy-2AAF. Sequence analysis of the AST IV cDNA showed it to be 1127 residues in length and to have essentially complete homology with PST-I cDNA, a previously reported (S. Ozawa, et al., Nucleic Acids Res., 18: 4001, 1990), 1028-base cDNA for an uncharacterized rat liver aryl sulfotransferase. Comparison of the PST-I/AST IV cDNA-deduced amino acid sequence with data from a partial (51%) amino acid sequence analysis of purified AST IV showed complete amino acid homology, confirming the identity of the cDNA and establishing that AST IV was an N-blocked, 291-amino acid protein with a molecular mass of 33,909 daltons. The AST IV cDNA sequence differed from the PST-I cDNA in two principal ways: the 5' end lacked 18 coding bases, and the 3' end contained a 190-base extention in the untranslated region, including a consensus sequence for signalling polyadenylation. Studies of AST IV gene transcript levels showed that the livers of rats fed 2AAF for 3 wk (early stage hepatocarcinogenesis) and hyperplastic nodules from the livers of rats fed 2AAF for 19 wk (intermediate stage hepatocarcinogenesis) displayed transcript levels similar to those of livers from normal rats. This contrasted with the 60 to 70% lower than normal capacity of the mRNA fractions to express AST IV observed during in vitro translation. These results indicated that modulation of AST IV expression at early and intermediate stages of hepatocarcinogenesis involved regulatory mechanisms at the translational level. In contrast, mRNA fractions isolated from some 2AAF-induced liver tumors or from known chemical carcinogen-derived rat hepatoma cell lines showed losses of both AST IV transcript level and in vitro translation capacity, suggesting that regulation at the transcriptional level may become important at late stages of 2AAF-induced hepatocarcinogenesis. These results indicated that the molecular mechanisms for the 2AAF-mediated down regulation of AST IV expression during 2AAF-induced hepatocarcinogenesis involved alterations in regulation at both translational and transcriptional levels.
 ...
PMID:Characterization of a complementary DNA for rat liver aryl sulfotransferase IV and use in evaluating the hepatic gene transcript levels of rats at various stages of 2-acetylaminofluorene-induced hepatocarcinogenesis. 151 41

Rat liver cytosolic sulfotransferase activity forms the highly reactive sulfuric acid ester of N-hydroxy-2-acetylaminofluorene (N-OH-2AAF), an ultimate carcinogen in 2-acetylaminofluorene (2AAF) hepatocarcinogenesis. A previous report demonstrated that 2AAF-induced liver hyperplastic nodules displayed a persistent loss of cytosolic N-OH-2AAF sulfotransferase activity following a hepatocarcinogenesis-producing regimen of 2AAF administration. As an initial step in examining the mechanism responsible for lowering N-OH-2AAF sulfotransferase activity, a monospecific polyclonal antibody to aryl sulfotransferase IV (AST IV) was produced and used in the assessment of AST IV as a candidate enzyme for liver cytosolic N-OH-2AAF sulfotransferase activity. Studies comparing the levels of N-OH-2AAF sulfotransferase activity of highly purified AST IV and rat liver cytosols with corresponding immunochemical analysis of AST IV contents demonstrated that there was sufficient AST IV activity in liver cytosols to indicate that it was the primary enzyme catalyzing cytosolic N-OH-2AAF sulfation. A subsequent immunochemical survey of nine extrahepatic tissues showed no detectable AST IV content and indicated that AST IV expression may be tissue specific. An immunochemical comparison of AST IV levels in control liver cytosols (high in sulfotransferase activity) with cytosols from 2AAF-derived hyperplastic nodules (low in sulfotransferase activity) or liver tumors (no sulfotransferase activity) showed low or no detectable levels, respectively, of AST IV. In addition, an immunochemical analysis of four rat hepatoma cell lines showed they contained no detectable levels of AST IV. These results suggested a strong correlation existed between a decrease in AST IV expression and tumor development. When the liver cytosols of rats taken from early, intermediate, and late stages of 2AAF carcinogenesis were analyzed for the development of a persistent loss of N-OH-2AAF sulfotransferase activity, a parallel loss of cytosolic N-OH-2AAF sulfotransferase activity and AST IV content was observed in rats which had proceeded from a stage of low risk to high risk for liver cancer. These findings indicated that (a) AST IV, a liver-specific enzyme, was the principle enzyme comprising cytosolic N-OH-2AAF sulfotransferase activity and (b) the decrease in sulfotransferase activity in nodules and tumors resulted from a decrease in the level of AST IV expression. Furthermore, it is suggested that a persistent decrease in AST IV expression may reflect a role for AST IV as part of a resistance phenotype in which transforming liver cells are able to escape the cytotoxic effects of highly reactive 2AAF metabolites and progress to cancer.
 ...
PMID:2-Acetylaminofluorene-mediated alteration in the level of liver arylsulfotransferase IV during rat hepatocarcinogenesis. 238 38

Rat hepatic aryl sulfotransferase IV (AST IV), which catalyses sulfuric acid esterification of N-hydroxy-2-acetylaminofluorene to its ultimate carcinogenic form, is differentially expressed during multistep 2-acetylaminofluorene (AAF) hepatocarcinogenesis. Two molecular mechanisms associated with this effect involve modulation of mRNA translational capacity at the early stages, and gene transcription at the late stages of the carcinogenic process. To characterize further the molecular mechanisms that may be involved in the transient regulation of the enzyme expression, an AST IV cDNA was used to assess the change in methylation profile and restriction fragment length polymorphism (RFLP) in the gene domain of genomic DNA derived from rats at different stages of carcinogenesis. The onset of hypomethylation of the AST IV gene domain and amplification of a 5.3-kb DNA sequence was found to correlate with the stage in AAF hepatocarcinogenesis, where rats begin to exhibit irreversible loss in hepatic enzyme expression and the liver becomes committed to hepatoma formation. This represents the first observation of both altered methylation status of AST IV gene domain and amplification of a DNA sequence whose expression may play a role in the genesis and/or progression of neoplastic transformation of initiated cells during AAF hepatocarcinogenesis.
 ...
PMID:Hypomethylation of the rat aryl sulfotransferase IV gene and amplification of a DNA sequence during multistage 2-acetylaminofluorene hepatocarcinogenesis. 791 17