UV induced bystander signaling leading to apoptosis.
Human keratinocytes (HaCaT) were exposed to UV (A+B) (UVA-350-400 mJ/cm2 and UVB-30 mJ/cm2) which induces apoptosis as evidenced by MTT assay, DNA laddering, Bax and Fas up-regulation. UV induced apoptotic conditioned media (6 h or earlier) did not cause apoptosis in unexposed cells. However, treatment with conditioned medium collected post UV exposure (1 h) induced Bax in unexposed cells as observed by RT-PCR. The induction of cell death was initiated by conditioned medium collected 12 h after UV exposure and the extent of death was increased progressively when conditioned medium collected 24 or 72 h post UV exposure was used. Medium collected 24 h after UV exposure also increased mitochondrial membrane permeability as determined by rhodamine uptake. Conditioned medium induced apoptosis did not involve reactive oxygen species (ROS) unlike UV induced apoptosis indicating that the apoptosis pathway could be different. Interestingly, at high dilution apototic conditioned medium did not induce apoptosis but actually protected cells from UV insult. The role of nerve growth factor (NGF) in UV induced bystander effects are also discussed.
Banerjee
Gautam
G
Cell and Molecular Biology, Environmental Safety Laboratory, Hindustan Lever Research Centre, Mumbai, India. gautam.banerjee@unilever.com
Gupta
Nishma
N
Kapoor
Arun
A
Raman
Govindarajan
G
D017209:Apoptosis; D024201:Bystander Effect; D002463:Cell Membrane Permeability; D017077:Culture Media, Conditioned; D004249:DNA Damage; D005562:Formazans / Q000494:pharmacology; D005786:Gene Expression Regulation; D006801:Humans; D015603:Keratinocytes / Q000502:physiology*; D008928:Mitochondria; D017382:Reactive Oxygen Species; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013778:Tetrazolium Salts / Q000494:pharmacology; D014466:Ultraviolet Rays; D015854:Up-Regulation
D017077:Culture Media, Conditioned; D005562:Formazans; D017382:Reactive Oxygen Species; D013778:Tetrazolium Salts; C079782:MTT formazan