TGF-β induced hyaluronan synthesis in orbital fibroblasts involves protein kinase C βII activation in vitro

Graves' ophthalmopathy is accompanied by hyaluronan (HA) accumulation in the orbital space and infiltration of immunocompetent cells and cytokines, including IFN‐γ, IL‐1β, and TGF‐β. We examined the signal transduction pathways by which TGF‐β induces HA synthesis in normal orbital fibroblasts, orbital fibroblasts from patients with Graves' ophthalmopathy, and abdominal fibroblasts. Calphostin C inhibited the stimulation of HA synthesis by TGF‐β. Phorbol 12‐myristate 13‐acetate (PMA) activation of PKC stimulated HA production. The effects of TGF‐β and PMA were not synergistic. Stimulation by TGF‐β and PMA were dependent on protein synthesis and their effects were inhibited by cycloheximide. Since TGF‐β‐induced HA synthesis was inhibited by BAPTA or by PKC inhibitors, a calcium‐dependent PKC was most likely involved. The PKA inhibitor H‐89 enhanced TGF‐β‐ and PMA‐induced HA synthesis, thus showing that communication between the PKA and PKC pathways was evident. TGF‐β stimulated the translocation of PKCβII to the cell membrane. PKCβII, a key enzyme in the regulation of HA synthesis by TGF‐β, might be an appropriate target for therapeutic compounds to be used to treat Graves' ophthalmopathy accompanied by inflammation. © 2005 Wiley‐Liss, Inc.