Glutathione (GSH) is an abundant cellular non-protein sulfhydryl that functions as an important protectant against reactive oxygen species and electrophiles, is involved in the detoxification of xenobiotics, and contributes to the maintenance of cellular redox balance. The rate-limiting enzyme in the de novo synthesis of glutathione is ␥-glutamylcysteine synthetase (GCS), a heterodimer consisting of heavy and light subunits expressing catalytic and regulatory functions, respectively. Exposure of HepG2 cells to ␤-naphthoflavone (␤-NF) resulted in a time-and dose-dependent increase in the steady-state mRNA levels for both subunits. In order to identify sequences mediating the constitutive and induced expression of the heavy subunit gene, a series of deletion mutants created from the 5 -flanking region (؊3802 to ؉465) were cloned into a luciferase reporter vector (pGL3-Basic) and transfected into HepG2 cells. Constitutive expression was maximally directed by sequences between ؊202 and ؉22 as well as by elements between ؊3802 to ؊2752. Glutathione (L-␥-glutamyl-L-cysteinyl-glycine, GSH), 1 a nonprotein sulfhydryl compound present in millimolar concentrations in virtually all cells, serves a myriad of cellular functions and plays a prominent role as an intracellular protectant (1, 2). GSH is an effective oxygen radical scavenger and serves as a critical co-factor in peroxide detoxification via a reaction catalyzed by glutathione peroxidase. Furthermore, conjugation with GSH is an integral step in the detoxification and elimination of diverse classes of toxic chemical compounds. The formation of hydrophilic glutathionyl conjugates is catalyzed by glutathione S-transferases, a family of isozymes that mediate the conjugation reaction in a substrate-dependent fashion (3). Long the object of interest from a toxicology perspective, the protective properties of GSH have assumed even further significance since GSH not only plays a critical role in protection of normal cells, but it has recently been implicated in protection of neoplastic cells from a number of chemotherapeutic agents that exert their cytotoxic effects via generation of reactive oxygen species or production of electrophilic intermediates (4, 5). The augmentation of GSH and GSH-related detoxification systems has also engendered considerable interest as a possible approach for the chemoprevention of cancer. Many chemical chemopreventive agents have been shown to exert an effect on GSH homeostasis or on other elements of GSH detoxification pathways (6 -8).Exposure of cells to a number of xenobiotic agents has been demonstrated to result in an increase in the total intracellular GSH content. In several cases (9 -16) where it has been examined, the increase in GSH has been attributed to an

Chronic exposure to UV radiation (UVR), especially in the UVA (315-400 nm) and UVB (280 -315 nm) spectrum of sunlight, is the major risk factor for the development of nonmelanoma skin cancer. UVR is a complete carcinogen, which both initiates and promotes carcinogenesis. We found that protein kinase C ⑀ (PKC⑀), a member of the phospholipiddependent threonine/serine kinase family, is an endogenous photosensitizer, the overexpression of which in the epidermis increases the susceptibility of mice to UVR-induced cutaneous damage and development of squamous cell carcinoma. The PKC⑀ transgenic mouse (FVB/N) lines 224 and 215 overexpressed 8-and 18-fold PKC⑀ protein, respectively, over endogenous levels in basal epidermal cells. UVR exposure (1 kJ/m 2 three times weekly) induced irreparable skin damage in high PKC⑀-overexpressing mouse line 215. However, the PKC⑀ transgenic mouse line 224, when exposed to UVR (2 kJ/m 2 three times weekly), exhibited minimum cutaneous damage but increased squamous cell carcinoma multiplicity by 3-fold and decreased tumor latency by 12 weeks. UVR exposure of PKC⑀ transgenic mice compared with wild-type littermates (1) elevated the levels of neither cyclobutane pyrimidine dimer nor pyrimidine (6-4) pyrimidone dimer, (2) reduced the appearance of sunburn cells, (3) induced extensive hyperplasia and increased the levels of mouse skin tumor promoter marker ornithine decarboxylase, and (4) elevated the levels of tumor necrosis factor ␣ (TNF␣) and other growth stimulatory cytokines, granulocyte colony-stimulating factor, and granulocyte macrophage colony-stimulating factor. The role of TNF␣ in UVR-induced cutaneous damage was evaluated using PKC⑀ transgenic mice deficient in TNF␣. UVR treatment three times weekly for 13 weeks at 2 kJ/m 2 induced severe cutaneous damage in PKC⑀ transgenic mice (line 215), which was partially prevented in PKC⑀-transgenic TNF␣-knockout mice. Taken together, the results indicate that PKC⑀ signals UVR-induced TNF␣ release that is linked, at least in part, to the photosensitivity of PKC⑀ transgenic mice.