A constitutive NADPH oxidase-like system containing gp91phox homologs in human keratinocytes.
In non-phagocytic cells, superoxide has been implicated in physiological and pathological cellular functions in the skin and mucosa, such as, host defense, mitogenic responses, and malignant conversion. Here, we identify a constitutively expressed heme-flavoprotein NADPH oxidase (Nox) system as a source of superoxide in human skin (HaCaT) and gingival mucosal (GM16) keratinocyte cell lines. Western blot analysis showed that both cell lines expressed the phagocyte oxidase (phox) cytosolic proteins Rac1, p40phox, and p67phox. With respect to the catalytic flavoheme protein subunit, HaCaT membranes, which expressed p22phox, showed an absorbance peak at 558 nm indicative of a b-type cytochrome. At mRNA levels, both GM16 and HaCaT cells expressed gp91phox homologs Nox1, Nox2, and Nox4, however, HaCaT cells expressed very low levels of Nox1 mRNA. At protein levels, Nox1 was readily detected in HaCaT but was nearly undetectable in GM16 cells. Consistently, Nox activity of HaCaT membranes was demonstrated by electron paramagnetic resonance spin-trapping and cytochrome c reduction, and the activity was sensitive to the flavoprotein inhibitor diphenylene iodonium. V(max) values were 20-fold lower than those reported for phagocytic oxidase. In conclusion, keratinocytes expressed a Nox distinct from the phox isoform of phagocytes providing molecular evidence for a source of superoxide that may regulate cell proliferation and host defense in skin and oral mucosa.
Chamulitrat
Walee
W
Department of Internal Medicine IV, University of Heidelberg, Heidelberg, Germany. Walee_Chamulitrat@med.uni-heidelberg.de
Stremmel
Wolfgang
W
Kawahara
Tsukasa
T
Rokutan
Kazuhito
K
Fujii
Hirotada
H
Wingler
Kirstin
K
Schmidt
Harald H H W
HH
Schmidt
Rainer
R
D002460:Cell Line; D002474:Cell-Free System / Q000378:metabolism; D005881:Gingiva / Q000166:cytology; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D009061:Mouth Mucosa / Q000166:cytology; D000074624:NADPH Oxidase 1; D000074662:NADPH Oxidase 2; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D012867:Skin / Q000166:cytology; D013481:Superoxides / Q000378:metabolism
D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D013481:Superoxides; C056558:CYBB protein, human; D000074624:NADPH Oxidase 1; D000074662:NADPH Oxidase 2; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases; C402799:NOX1 protein, human; C498910:NOX4 protein, human