title: Expression of heavy subunit of gamma-glutamylcysteine synthetase (gamma-GCSh) in human colorectal carcinoma.
abstract: Gamma-glutamylcysteine synthetase (gamma-GCS) is a heterodimer consisting of heavy (gamma-GCSh) and light (gamma-GCSl) subunits. gamma-GCS catalyzes the rate-limiting de novo biosynthesis of glutathione (GSH), an abundant physiological antioxidant that plays important roles for regulating oxidative stress. Expression of gamma-GCSh and gamma-GCSl are sensitive to oxidative stress. To investigate whether expression of gamma-GCS is correlated with tumor progression, we used immunohistochemical approaches to examine 16 human colorectal adenomas and resected 57 carcinomas from untreated patients. In adjacent normal colorectal epithelium, levels of gamma-GCSh expression were low. Strong cytoplasmic staining for gamma-GCSh was detected in 3 (18.8%) adenoma and 48 (84.2%) carcinomas. The frequency of gamma-GCSh expression in carcinoma was significantly higher than in adenoma (p<0.0001). We used RNase protation assay and Western blot to determine levels of gamma-GCSh mRNA and protein from 10 pairs of matched carcinomas with adjacent normal controls. Elevated expression of both gamma-GCSh mRNA and protein were found in 6 cases, suggesting that transcriptional and/or posttranscriptional regulation play an important role in the upregulation of gamma-GCS during colorectal carcinogenesis. We also examined the expression of another redox-regulated gene, multidrug resistance protein 1 (MRP1). Strong staining for MRP1 was detected in 1 (6.3%) adenoma and 40 (70.2%) carcinomas. The frequency of MRP1 expression in carcinoma was significantly higher than in adenoma ( p<0.0001). Nuclear p53 expression was detected in 30 (52.6%) of carcinomas. There is a significant correlation between gamma-GCSh and MRP1 expression (p=0.013) but not between gamma-GCSh and p53. Since gamma-GCS is a sensor of oxidative stress, these results are consistent with the notion that oxidative stress is associated with colorectal tumor progression.
authors.affiliation: Department of Molecular Pathology, The University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Shigeru
authors.initials: S
authors.lastname: Tatebe
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Unate
authors.forename: Frank A
authors.initials: FA
authors.lastname: Sinicrope
authors.forename: Takashi
authors.initials: T
authors.lastname: Sakatani
authors.forename: Kenji
authors.initials: K
authors.lastname: Sugamura
authors.forename: Masato
authors.initials: M
authors.lastname: Makino
authors.forename: Hisao
authors.initials: H
authors.lastname: Ito
authors.forename: Niramol
authors.initials: N
authors.lastname: Savaraj
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Kaibara
authors.forename: M Tien
authors.initials: MT
authors.lastname: Kuo
mesh_terms: D000236:Adenoma / Q000201:enzymology* / Q000473:pathology; D015153:Blotting, Western; D015179:Colorectal Neoplasms / Q000201:enzymology* / Q000473:pathology; D004268:DNA-Binding Proteins / Q000378:metabolism; D004790:Enzyme Induction; D005260:Female; D005721:Glutamate-Cysteine Ligase / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D008875:Middle Aged; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D000074081:MutS Homolog 3 Protein; D016612:Paraffin Embedding; D012333:RNA, Messenger / Q000378:metabolism; D012260:Ribonucleases / Q000378:metabolism; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D005721:Glutamate-Cysteine Ligase; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D000074081:MutS Homolog 3 Protein; D012333:RNA, Messenger; D012260:Ribonucleases; D016159:Tumor Suppressor Protein p53; C078444:MSH3 protein, human; C421109:multidrug resistance-associated protein 1