Regulation of bovine corneal endothelial cell cycle by transforming growth factor-beta.
OBJECTIVE
The transforming growth factor-beta (TGF-beta) family includes three multifunctional proteins, TGF-beta1, TGF-beta2 and TGF-beta3, expressed in ocular tissue, which are involved in regulating cell differentiation, cell proliferation and other cell functions. TGF-beta is present in aqueous humour and regulates corneal endothelial cells. This study explores the mechanism by which TGF-beta regulates the cell cycle in cultured corneal endothelial cells.


METHODS
The expression of specific receptors for the TGF-beta family was investigated at the protein level by affinity cross-linking with radio-iodinated TGF-beta1 and immunoprecipitation with specific antibodies to TGF-beta 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-beta type 1 and type 2 receptors and endoglin. In the confluent state, TGF-beta1 and TGF-beta2 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-beta 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-beta 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.
D000818:Animals; D015703:Antigens, CD; D002417:Cattle; D002453:Cell Cycle / Q000187:drug effects* / Q000502:physiology; D002478:Cells, Cultured; D000071063:Endoglin; D004728:Endothelium, Corneal / Q000166:cytology* / Q000378:metabolism; D016193:G1 Phase; D006801:Humans; D011493:Protein Kinase C / Q000378:metabolism; D020574:Proto-Oncogene Proteins c-sis / Q000096:biosynthesis; D011956:Receptors, Cell Surface; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D016192:Resting Phase, Cell Cycle; D016196:S Phase; D015398:Signal Transduction / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000378:metabolism / Q000494:pharmacology*; D053773:Transforming Growth Factor beta1; D053781:Transforming Growth Factor beta2; D019010:Vascular Cell Adhesion Molecule-1 / Q000378:metabolism
D015703:Antigens, CD; C064206:ENG protein, human; D000071063:Endoglin; D020574:Proto-Oncogene Proteins c-sis; D011956:Receptors, Cell Surface; D018125:Receptors, Transforming Growth Factor beta; C508960:TGFB1 protein, human; C509041:TGFB2 protein, human; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D053781:Transforming Growth Factor beta2; D019010:Vascular Cell Adhesion Molecule-1; D011493:Protein Kinase C