PT  - JOURNAL ARTICLE
AU  - Rong-Sen Yang
AU  - Chih-Hsin Tang
AU  - Qing-Dong Ling
AU  - Shing-Hwa Liu
AU  - Wen-Mei Fu
TI  - Regulation of Fibronectin Fibrillogenesis by Protein Kinases in Cultured Rat Osteoblasts
AID  - 10.1124/mol.61.5.1163
DP  - 2002 May 01
TA  - Molecular Pharmacology
PG  - 1163--1173
VI  - 61
IP  - 5
4099  - http://molpharm.aspetjournals.org/content/61/5/1163.short
4100  - http://molpharm.aspetjournals.org/content/61/5/1163.full
SO  - Mol Pharmacol2002 May 01; 61
AB  - Fibronectin (Fn) plays an important role in the regulation of adhesion, migration, and maturation of osteoblasts. Fn fibrillogenesis is involved in the process of bone mineralization. To elucidate the regulatory role of protein kinases in the formation of fibrillar Fn matrix, Fn synthesis and assembly were examined in cultured osteoblasts. Osteoblasts assembled the endogenously released soluble Fn into immobilized form on the substratum in a time-dependent manner. Both 12-O-tetradecanoylphorbol-13 acetate (TPA) and forskolin increased the synthesis of Fn. However, the extracellular assembly of Fn fibril from both endogenously released and exogenously applied soluble Fn was increased by TPA but decreased by forskolin. Protein kinase C (PKC) inhibitors, such as H7, Ro 318220, and Gö6976, inhibited Fn fibrillogenesis. These results suggest that the dynamic of Fn fibrillogenesis is differentially regulated by the activation of PKC and protein kinase A (PKA). Both classic and novel isoforms of PKC are involved in the action of TPA in osteoblasts. It has been reported that α5β1 integrin is related to Fn fibrillogenesis. Immunocytochemistry and flow cytometry showed that TPA and forskolin increased and inhibited, respectively, the clustering and surface expression of α5 integrins. TPA and forskolin did not affect protein levels of α5 integrins. The Western blot and reverse transcriptase-polymerase chain reaction showed that protein and mRNA levels of β1 integrins also were not affected by TPA and forskolin. These results suggest that TPA and forskolin may affect the surface expression of α5β1 integrins. cAMP response element-binding protein phosphorylation is involved in the action of forskolin but not that of TPA. Our results suggest that PKC activation enhanced Fn fibrillogenesis, whereas PKA activation inhibited extracellular Fn fibrillogenesis in primary cultured osteoblasts. Cytosolic Fn synthesis and extracellular Fn assembly may be differentially regulated by the activation of PKA.