Transforming growth factor-beta regulates human retinal pigment epithelial cell phagocytosis by influencing a protein kinase C-dependent pathway.
BACKGROUND
Transforming growth factor-beta (TGF-beta) plays an important role in the pathogenesis of many ocular diseases, including proliferative vitreoretinopathy. We examined the effect of TGF-beta on the phagocytosis of rod outer segments by retinal pigment epithelium (RPE), which is a major function of RPE, and investigated the dependence of this effect on the protein kinase C (PKC) pathway.


METHODS
Phagocytotic uptake of fluoresceinated bovine rod outer segments was determined by flow cytometry. RPE cells were treated with TGF-beta 1 or TGF-beta 2 and their effects on phagocytosis were examined. The effects of various PKC inhibitors (calphostin C, staurosporine, and extended exposure to phorbol 12-myristate 13-acetate, PMA) and a stimulator (brief exposure to PMA) on RPE phagocytosis was evaluated.


RESULTS
Both TGF-beta 1 and TGF-beta 2 up-regulated RPE phagocytosis and PMA abolished the up-regulating effect of TGF-beta. In contrast, PKC inhibition by staurosporine and calphostin C resulted in increased phagocytosis. A combination of TGF-beta and PKC inhibitor treatment did not produced any additive effect on phagocytosis.


CONCLUSIONS
We concluded that TGF-beta up-regulates human RPE phagocytosis, but that this effect is counteracted by PKC activation. It is possible that this TGF-beta-induced effect is due, in part, to a negative modulation of the PKC-dependent pathway.
Sheu
S J
SJ
Department of Ophthalmology, University of Southern California, School of Medicine, Los Angeles 90033.
Sakamoto
T
T
Osusky
R
R
Wang
H M
HM
Ogden
T E
TE
Ryan
S J
SJ
Hinton
D R
DR
Gopalakrishna
R
R
D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D005434:Flow Cytometry; D006801:Humans; D009281:Naphthalenes; D010587:Phagocytosis / Q000187:drug effects / Q000502:physiology*; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011083:Polycyclic Compounds / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012374:Rod Cell Outer Segment / Q000502:physiology; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects
D000470:Alkaloids; D009281:Naphthalenes; D011083:Polycyclic Compounds; D016212:Transforming Growth Factor beta; C061465:calphostin complex; D011493:Protein Kinase C; D019311:Staurosporine; D013755:Tetradecanoylphorbol Acetate