During radiotherapy of cancer, neighboring normal cells may receive sub-lethal doses of radiation. To investigate whether such low levels of radiation modulate normal cell responses to death stimuli, primary cultured human fibroblasts were exposed to various doses of gamma-rays. Analysis of cell viability using an exclusion dye propidium iodide revealed that the irradiation up to 10 Gy killed the fibroblasts only to a minimal extent. In contrast, the cells efficiently lost their viability when exposed to 0.5-0.65 mM H2O2. This type of cell death was accompanied by JNK activation, and was reversed by the use of a JNK-specific inhibitor SP600125. Interestingly, H2O2 failed to kill the fibroblasts when these cells were pre-irradiated, 24 h before H2O2 treatment, with 0.25-0.5 Gy of gamma-rays. These cytoprotective doses of gamma-rays did not enhance cellular capacity to degrade H2O2, but elevated cellular levels of p21Cip/WAF1, a p53 target that can suppress H2O2-induced cell death by blocking JNK activation. Consistently, H2O2-induced JNK activation was dramatically suppressed in the pre-irradiated cells. The overall data suggests that ionizing radiation can impart normal fibroblasts with a survival advantage against oxidative stress by blocking the process leading to JNK activation.
Antioxidants/pharmacology ; Cell Death ; Cells, Cultured ; Enzyme Activation/radiation effects ; Fibroblasts/enzymology/radiation effects ; *Gamma Rays ; Heat-Shock Proteins/metabolism ; Humans ; JNK Mitogen-Activated Protein Kinases/*antagonists & inhibitors ; Oxidative Stress/*radiation effects ; Research Support, Non-U.S. Gov't ; Water/pharmacology

BACKGROUNDSolar ultraviolet (UV) irradiation induces the production of matrix metalloproteinases (MMPs) by activating cellular signalling transduction pathways. MMPs are responsible for the degradation and/or inhibition of synthesis of collagenous extracellular matrix in connective tissues. We mimicked the action of environmental ultraviolet on skin and investigated the effects of UVB-irradiated human keratinocytes HaCaT and IL-1alpha on mitogen activated protein (MAP) kinase activation, c-Jun and c-Fos (AP-1 is composed of Jun and Fos proteins) mRNA expression and MMP-1 production in UVA-irradiated dermal fibroblasts.

METHODSFollowing UVA irradiation, the culture medium of fibroblasts was replaced by culture medium from UVB-irradiated HaCaT, or replaced by the complete culture medium with interleukin (IL)-1alpha. MAP kinase activity expression in fibroblasts was detected by Western blot. c-Jun and c-Fos mRNA expressions were determined by reverse transcriptional polymerase chain reaction (RT-PCR); MMP-1 production in culture medium was detected by enzyme-linked immunosorbent assay (ELISA).

RESULTSCulture medium from UVB-irradiated keratinocytes increased MAP kinase activity and c-Jun mRNA expression in UVA-irradiated fibroblasts. IL-1alpha increased MAP kinase activity and c-Jun mRNA expression, IL-1alpha also increased c-Fos mRNA expression. Both culture media from UVB-irradiated human keratinocytes and externally applied IL-1alpha increased MMP-1 production in UVA-irradiated fibroblasts.

CONCLUSIONSUVB-irradiated keratinocytes and IL-1alpha indirectly promote MMP-1 production in UVA-irradiated fibroblasts by increasing MAP kinase/AP-1 activity. IL-1 may play an important role in the paracrine activation and dermal collagen excessive degradation leading to skin photoaging.

Cell Line ; Enzyme Activation ; Fibroblasts ; enzymology ; radiation effects ; Humans ; Interleukin-1 ; pharmacology ; Keratinocytes ; physiology ; radiation effects ; Matrix Metalloproteinase 1 ; biosynthesis ; Mitogen-Activated Protein Kinases ; metabolism ; Proto-Oncogene Proteins c-fos ; genetics ; Proto-Oncogene Proteins c-jun ; genetics ; RNA, Messenger ; analysis ; Skin ; radiation effects ; Skin Aging ; Transcription Factor AP-1 ; metabolism ; Ultraviolet Rays