cGMP-dependent protein kinase II (cGKII; encoded by PRKG2) is a serine/threonine kinase that is critical for skeletal growth in mammals; in mice, cGKII deficiency results in dwarfism. Using radiographic analysis, we determined that this growth defect was a consequence of an elongated growth plate and impaired chondrocyte hypertrophy. To investigate the mechanism of cGKII-mediated chondrocyte hypertrophy, we performed a kinase substrate array and identified glycogen synthase kinase–3β (GSK-3β; encoded by Gsk3b) as a principal phosphorylation target of cGKII. In cultured mouse chondrocytes, phosphorylation-mediated inhibition of GSK-3β was associated with enhanced hypertrophic differentiation. Furthermore, cGKII induction of chondrocyte hypertrophy was suppressed by cotransfection with a phosphorylation-deficient mutant of GSK-3β. Analyses of mice with compound deficiencies in both protein kinases (Prkg2–/–Gsk3b+/–) demonstrated that the growth retardation and elongated growth plate associated with cGKII deficiency were partially rescued by haploinsufficiency of Gsk3b. We found that β-catenin levels decreased in Prkg2–/– mice, while overexpression of cGKII increased the accumulation and transactivation function of β-catenin in mouse chondroprogenitor ATDC5 cells. This effect was blocked by coexpression of phosphorylation-deficient GSK-3β. These data indicate that hypertrophic differentiation of growth plate chondrocytes during skeletal growth is promoted by phosphorylation and inactivation of GSK-3β by cGKII.
Yosuke Kawasaki, Fumitaka Kugimiya, Hirotaka Chikuda, Satoru Kamekura, Toshiyuki Ikeda, Naohiro Kawamura, Taku Saito, Yusuke Shinoda, Akiro Higashikawa, Fumiko Yano, Toru Ogasawara, Naoshi Ogata, Kazuto Hoshi, Franz Hofmann, James R. Woodgett, Kozo Nakamura, Ung-il Chung, Hiroshi Kawaguchi
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