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J. Preston Alexander, Ted S. Acott; Involvement of Protein Kinase C in TNFα Regulation of Trabecular Matrix Metalloproteinases and TIMPs. Invest. Ophthalmol. Vis. Sci. 2001;42(12):2831-2838.
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purpose. The cytokine TNFα is a strong modulator of trabecular meshwork (TM)
matrix metalloproteinase (MMP) and tissue inhibitor (TIMP) expression.
Studies were conducted to identify signal-transduction pathways
methods. Porcine TM cells were treated with TNFα, and MMP and TIMP levels were
evaluated by zymography and Western immunoblot. Inhibitors and
activators of several signal-transduction pathways were used to select
pathways that could be involved. Trabecular protein kinase C (PKC)
isoforms were identified and localized by using Western immunoblots and
confocal immunohistochemistry. Changes in subcellular distribution of
PKC isoforms were evaluated. PKC isoform downregulation and additional
inhibition profiles were used to refine the involvement pattern of
results. TNFα treatment increased MMP-1, -3, and -9 and TIMP-1
expression, whereas MMP-2 expression was not affected and TIMP-2
expression decreased. Agents that modulate protein kinase A (PKA) or
inhibit phosphatidylinositol 3-kinase (PI3K) had minimal effects on
trabecular MMP or TIMP induction by TNFα, whereas several agents that
modulate PKC activity were effective. Trabecular cells expressed
several PKC isoforms, which exhibited distinctive subcellular
localization. TNFα treatment triggered some PKC isoform
translocations. Exposure of trabecular cells to TNFα for 72 hours
differentially downregulated several PKC isoforms. Treatment with a
phorbol mitogen that stimulates most PKC isoforms produced strong
increases in these MMPs. TNFα’s effects on MMP and TIMP expression
were completely blocked by only one PKC inhibitor.
conclusions. The PKA and PI3K pathways appear not to be involved directly in
transducing this TNFα signal, but at least one isoform of PKC seems
to be required. Based on the inhibitor profiles and the downregulation
and translocation studies, PKCμ appears to be critical in transducing
this signal. Unraveling the remaining steps in this and in additional
related TM signal-transduction pathways may provide targets for
developing improved glaucoma treatments.
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