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Downregulation of Akt activity contributes to the growth arrest induced by FGF in chondrocytes
Author(s) -
Priore Riccardo,
Dailey Lisa,
Basilico Claudio
Publication year - 2006
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.20620
Subject(s) - protein kinase b , fibroblast growth factor , pi3k/akt/mtor pathway , microbiology and biotechnology , phosphorylation , chondrocyte , signal transduction , downregulation and upregulation , biology , cancer research , chemistry , biochemistry , gene , receptor , in vitro
Unregulated FGF signaling produced by activating FGFR3 mutations causes several forms of dwarfism‐associated chondrodysplasias in humans and mice. FGF signaling inhibits chondrocyte proliferation by activating multiple signal transduction pathways that all contribute to chondrocyte growth arrest and induction of some aspects of differentiation. Previous studies had identified the Stat1 pathway, dephosphorylation of the Rb family proteins p107 and p130, induction of p21 expression and sustained activation of MAP kinases as playing a role in the FGF response of chondrocytes. We have examined the role of Akt (PKB) in the response of chondrocytes to FGF signaling. Differently from what is observed in many other cell types, FGF does not activate Akt in chondrocytes, and Akt phosphorylation is actually downregulated after FGF treatment. By expressing a constitutively activated, myristylated form of Akt (myr‐Akt) in the RCS chondrosarcoma cell line, we show that Akt activation partially counteracts the inhibitory effect of FGF signaling. The response of myr‐Akt expressing cells to FGF is identical to parental RCS in the first few hours after treatment, but then diverges as myr‐Akt cells show decreased p130 phosphorylation, increased cyclin E/cdk2 activity and continue to proliferate at a slow rate. Constitutive Akt activation does not affect p21 expression but appears to influence directly cdk/cyclin activity. On the other hand, the induction of differentiation‐related genes is unchanged in myr‐Akt cells. These results identify Akt downregulation as an important aspect of the response of chondrocytes to FGF that, however, only affects chondrocyte proliferation and not the ability of FGF to induce differentiation genes. J. Cell. Physiol. © 2006 Wiley‐Liss, Inc.