Increase of integrin α6+p63+ cells after ultraviolet B irradiation in normal human keratinocytes

Epidermal stem cells (SC) are believed to be resistant to environmental damage for the purpose of self renewal. Most promising SC markers include integrin α6 and p63. The aim of our study was to determine whether the integrin α6+p63+ cell fraction representative of the epidermal progenitor or SC is increased after ultraviolet B (UVB) irradiation and to clarify the hypothesis that epidermal SC are resistant to high-dose UVB damage. We irradiated early passage normal human keratinocytes (NHK) with 0, 25, 50, and 100 mJ/cm(2) UVB. The percentage of cell death was calculated. Real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and western blotting analyses were performed to identify integrin α6 and p63, and flow cytometry analysis with integrin α6 and p63 antibodies was done. After 50 and 100 mJ/cm(2) UVB, integrin α6+p63+ cells were found to be much increased by fluorescence-activated cell sorting. Expression of integrin α6 and p63 was increased in NHK after UVB irradiation, which was shown with real-time RT-PCR and western blotting analyses. We concluded that an increase of integrin α6+p63+ cells after high-dose UVB may suggest that the putative progenitor or SC are resistant to UVB irradiation.