TGF-β-stimulated aberrant expression of class III β-tubulin via the ERK signaling pathway in cultured retinal pigment epithelial cells

The class III beta-tubulin isotype (beta(III)) is expressed exclusively by neurons within the normal human retina and is not present in normal retinal pigment epithelial (RPE) cells in situ or in the early phase of primary cultures. However, aberrant expression of class III beta-tubulin has been observed in passaged RPE cells and RPE cells with dedifferentiated morphology in pathologic epiretinal membranes from idiopathic macular pucker, proliferative vitreoretinopathy (PVR) and proliferative diabetic retinopathy (PDR). Transforming growth factor-beta(TGF-beta) has been implicated in dedifferentiation of RPE cells and has a critical role in the development of proliferative vitreoretinal diseases. Here, we investigated the potential effects of TGF-beta on the aberrant expression of class III beta-tubulin and the intracellular signaling pathway mediating these changes. TGF-beta-induced aberrant expression and O-linked-beta-N-acetylglucosamine (O-GIcNac) modification of class III beta-tubulin in cultured RPE cells as determined using Western blotting, RT-PCR and immunocytochemistry. TGF-beta also stimulated phosphorylation of ERK. TGF-beta-induced aberrant expression of class III beta-tubulin was significantly reduced by pretreatment with U0126, an inhibitor of ERK phosphorylation. Our findings indicate that TGF-beta stimulated aberrant expression of class III beta-tubulin via activation of the ERK signaling pathway. These data demonstrate that mature RPE cells have the capacity to express a neuron-associated gene in response to TGF-beta stimulation and provide useful information towards understanding the pathogenesis of proliferative vitreoretinal diseases. (C) 2011 Elsevier Inc. All rights reserved.