Overexpression of Spry1 in chondrocytes causes attenuated FGFR ubiquitination and sustained ERK activation resulting in chondrodysplasia

Abstract

The FGF signaling pathway plays essential roles in endochondral ossification by regulating osteoblast proliferation and differentiation, chondrocyte proliferation, hypertrophy, and apoptosis. FGF signaling is controlled by the complementary action of both positive and negative regulators of the signal transduction pathway. The Spry proteins are crucial regulators of receptor tyrosine kinase-mediated MAPK signaling activity. Sprys are expressed in close proximity to FGF signaling centers and regulate FGFR-ERK-mediated organogenesis. During endochondral ossification, Spry genes are expressed in prehypertrophic and hypertrophic chondrocytes. Using a conditional transgenic approach in chondrocytes in vivo, the forced expression of Spry1 resulted in neonatal lethality with accompanying skeletal abnormalities resembling thanatophoric dysplasia II, including increased apoptosis and decreased chondrocyte proliferation in the presumptive reserve and proliferating zones. In vitro chondrocyte cultures recapitulated the inhibitory effect of Spry1 on chondrocyte proliferation. In addition, overexpression of Spry1 resulted in sustained ERK activation and increased expression of p21 and STAT1. Immunoprecipitation experiments revealed that Spry1 expression in chondrocyte cultures resulted in decreased FGFR2 ubiquitination and increased FGFR2 stability. These results suggest that constitutive expression of Spry1 in chondrocytes results in attenuated FGFR2 degradation, sustained ERK activation, and up-regulation of p21Cip and STAT1 causing dysregulated chondrocyte proliferation and terminal differentiation.

Spry1 and Spry4 Differentially Regulate Human Aortic Smooth Muscle Cell Phenotype via Akt/FoxO/Myocardin Signaling

“…This is surprising because loss of Spry1 function in several other contexts results in enhanced signaling downstream of RTKs [25], [26]. However, previous studies have also shown that Spry1 and Spry2 can interfere with ubiquitination and degradation of FGFR1 [27] and EGFR [28], [29], which leads to enhanced RTK signaling. By binding to c-Cbl, Spry2 prevents c-Cbl mediated ubiquitination and degradation of EGFR.…”

Loss of adult skeletal muscle stem cells drives age-related neuromuscular junction degeneration

“…Wild type C57BL/6J mice were obtained from National Institute on Aging; Pax7 CreERT2 (017763), Rosa26 mTmG (007576), Rosa26 nTnG (023035) and Rosa26 DTA (009669) mice were obtained from Jackson Laboratories (Bar Harbor, Maine); mice carrying a transgene encoding a Cre-inducible expression construct for Spry1 controlled by a chicken β-actin gene (CAG) promoter were used for Spry1-overexpression studies (Chakkalakal et al, 2012; Yang et al, 2008). Rosa26 mTmG , Rosa26 nTnG , Rosa26 DTA and CAG Spry1 mice were crossed with Pax7 CreERT2 mice to generate Pax7 CreER/+ ; Rosa26 mTmG/+ (P7mTmG), Pax7 CreER/+ ; Rosa26 nTnG/+ (P7nTnG), Pax7 CreER/+ ; Rosa26 DTA/+ (P7DTA), Pax7 CreER/+ ; CAG Spry1/+ (Spry1OX) mice and control CreER negative (Ctrl) littermates.…”

RECENT RESEARCH ON THE GROWTH PLATE: Advances in fibroblast growth factor signaling in growth plate development and disorders

“…Stability of proteins is essential for the maintenance of protein function. Overexpression of Sprouty 1 in chondrocytes results in decreased FGFR2 ubiquitination, increased FGFR2 stability, and sustained ERK activation (Yang et al 2008). The detailed mechanisms underlying the degradation of FGFRs after ligand binding are poorly known.…”