Tyrosinase biosynthesis in adult mammalian retinal pigment epithelial cells.
Tyrosinase (EC 1.14.18.1) is the rate limiting enzyme of melanogenesis and it is unclear whether it is synthesized in postnatal retinal pigment epithelium (RPE). Cultured RPE cells from cattle were fed with isolated rod outer segments (ROS). After phagocytosis, RPE cells were tested for tyrosinase presence and activity with three independent methods: (1) ultrastructural DOPA (l-3,4-dihydroxyphenylalanine) histochemistry (2) immunocytochemistry with anti-tyrosinase antibodies (3) measuring tyrosine hydroxylase activity using [(3)H]tyrosine. With all three methods tyrosinase was found in RPE cells after ROS-feeding but was absent without feeding. In contrast to the classical hypothesis, we demonstrated with three independent methods that the expression of tyrosinase and its enzymatic activity are induced in cultured adult RPE by phagocytosis of rod outer segments (ROS) in vitro.
Section for Experimental Vitreoretinal Surgery, University Eye Hospital Tubingen, Schleichstr. 12/1, D-72076 Tubingen, Germany. ulrich.schraermeyer@med.uni-tuebingen.de
Ulrich
U
Schraermeyer
Jürgen
J
Kopitz
Swaantje
S
Peters
Sigrid
S
Henke-Fahle
Petra
P
Blitgen-Heinecke
Despina
D
Kokkinou
Tobias
T
Schwarz
Karl-Ulrich
KU
Bartz-Schmidt
D000818:Animals; D000906:Antibodies / Q000276:immunology; D002417:Cattle; D002478:Cells, Cultured; D004295:Dihydroxyphenylalanine / Q000378:metabolism; D011992:Endosomes / Q000201:enzymology / Q000648:ultrastructure; D004847:Epithelial Cells / Q000201:enzymology / Q000648:ultrastructure; D007150:Immunohistochemistry / Q000379:methods; D020460:Melanosomes / Q000201:enzymology / Q000648:ultrastructure; D008854:Microscopy, Electron / Q000379:methods; D014442:Monophenol Monooxygenase / Q000096:biosynthesis* / Q000276:immunology; D018384:Oxidative Stress / Q000502:physiology; D010587:Phagocytosis / Q000502:physiology; D010857:Pigment Epithelium of Eye / Q000201:enzymology* / Q000648:ultrastructure; D012374:Rod Cell Outer Segment / Q000502:physiology; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
D000906:Antibodies; D004295:Dihydroxyphenylalanine; D014446:Tyrosine 3-Monooxygenase; D014442:Monophenol Monooxygenase