title: Molecular mechanism(s) for UV-B irradiation-induced glutathione depletion in cultured human keratinocytes.
abstract: Glutathione (GSH) plays a central role in maintenance of cellular redox homeostasis and protection against oxidative injury. Ultraviolet B (UV-B) irradiation-induced GSH depletion is believed to be involved in the pathogenesis of several cutaneous disorders. In this study, the molecular mechanism(s) of UV-B-induced GSH depletion was investigated in cultured human keratinocytes, HaCaT cells. We found that UV-B irradiation caused GSH depletion in a dose- and time-dependent manner in HaCaT cells. The mechanistic studies showed that UV-B-induced GSH depletion did not result from the GSH efflux. UV-B irradiation appeared to cause a slight decrease in enzymatic activity of gamma-glutamate cysteine ligase (GCL), a rate-limiting enzyme in GSH biosynthesis. UV-B irradiation resulted in the GCL cleavage through the activation of a caspase cascade. Inhibition of total caspase activity by the general caspase inhibitor, zVAD-fmk, partially reversed the UV-B-induced GSH depletion. More importantly, we found that UV-B irradiation could dramatically decrease the cystine uptake through the functional inhibition of the system Xc(-), a cystine transporter on the cell membrane. The results suggest that the inactivation of cystine transporter system Xc(-) was a major contributor to the UV-B-mediated decrease of GSH levels in human keratinocytes.
authors.affiliation: Arizona Cancer Center, University of Arizona, Tucson, AZ 85724, USA.
authors.forename: Ming
authors.initials: M
authors.lastname: Zhu
authors.forename: G Tim
authors.initials: GT
authors.lastname: Bowden
mesh_terms: D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D003545:Cysteine / Q000494:pharmacology; D004789:Enzyme Activation / Q000528:radiation effects; D005721:Glutamate-Cysteine Ligase / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism*; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects*; D014466:Ultraviolet Rays
chemical_list: D020169:Caspases; D005721:Glutamate-Cysteine Ligase; D005978:Glutathione; D003545:Cysteine