IEX-1, an immediate early gene, increases the rate of apoptosis in keratinocytes.
IEX-1, an immediate early gene, is widely expressed in epithelial and endothelial tissues, and is altered by a variety of growth regulatory factors. We have shown that expression of IEX-1 in keratinocytes increases the growth rate of these cells. The effects of IEX-1 on apoptosis, however, are unclear. To clarify the effects of IEX-1 on apoptosis, we investigated the effects of IEX-1 expression in keratinocytes (HaCaT cells) in the basal state and after the induction of cellular stress. Under normal, non-stressed conditions, both control (HaCaT) and IEX-1-transfected (IEX-HaCaT) cell lines showed no significant differences in the activity of a key apoptotic enzyme, caspase 3 despite significantly higher levels of IEX-1 expression. IEX-HaCaT cells grew faster than HaCaT cells. When both cell lines were irradiated with ultraviolet B radiation, caspase 3 activity increased to a greater extent in the IEX-HaCaT cells than in HaCaT cells. Camptothecin increased caspase 3 activity twice as much in the IEX-HaCaT cells when compared to HaCaT cells. When histone-complex DNA fragments were measured in IEX-HaCaT or HaCaT cells following UVB irradiation or treatment with camptothecin, significantly higher amounts of nucleosomes were seen in the IEX-HaCaT transfected cells. Likewise, serum deprivation induced higher degrees of apoptosis in IEX-HaCaT cells than in HaCaT cells. We conclude that overexpression of IEX-1 in HaCaT keratinocytes increases the growth rate of cells under basal conditions; in the basal state the rate of apoptosis is unchanged. However, the rate of apoptosis increases in IEX-1 overexpressing HaCaT keratinocytes after cells are subjected to stress.
Schilling
D
D
Department of Medicine, Mayo Clinic and Foundation, Rochester, Minnesota, MN 55905, USA.
Pittelkow
M R
MR
Kumar
R
R
D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D051017:Apoptosis Regulatory Proteins; D002166:Camptothecin / Q000494:pharmacology; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002448:Cell Adhesion; D002455:Cell Division / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects / Q000528:radiation effects; D017781:Genes, Immediate-Early / Q000235:genetics*; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism*; D015603:Keratinocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured; D014466:Ultraviolet Rays
D051017:Apoptosis Regulatory Proteins; C099815:IER3 protein, human; D017874:Immediate-Early Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D012333:RNA, Messenger; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D002166:Camptothecin