Regulation of bovine corneal endothelial cell cycle by transforming growth factor-β.

Abstract. Purpose: The transforming growth factor-β (TGF-β) family includes three multifunctional proteins, TGF-β1, TGF-β2 and TGF-β3, expressed in ocular tissue, which are involved in regulating cell differentiation, cell proliferation and other cell functions. TGF-β is present in aqueous humour and regulates corneal endothelial cells. This study explores the mechanism by which TGF-β regulates the cell cycle in cultured corneal endothelial cells. Methods: The expression of specific receptors for the TGF-β family was investigated at the protein level by affinity cross-linking with radio-iodinated TGF-β1 and immunoprecipitation with specific antibodies to TGF-β receptors. Regulation of entry into the S-phase of the cell cycle was determined by 5-bromo-2′ deoxyuridine (BrdU) incorporation into the cells. The signal transduction pathways were investigated using various blocking agents for protein kinase transducers involved in intracytoplasmic signal transduction. Results: Cultured bovine corneal endothelial cells were confirmed to express TGF-β type 1 and type 2 receptors and endoglin. In the confluent state, TGF-β1 and TGF-β2 stimulated the cells to progress to the S-phase of the cell cycle through platelet-derived growth factor-B (PDGF-B) chain production and protein kinase C. Conclusions: TGF-β accelerated cell cycle progression from the G0/G1 phase to the S-phase in cultured corneal endothelial cells, under our experimental conditions, through pathways involving protein kinase C. These pathways are related to the cross-talk between TGF-β and other cytokines. The conditions employed in the present experiments may be useful for investigating the complex cross-talk between various cytokines and growth factors. [ABSTRACT FROM AUTHOR]