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Cooperation between Shh and IGF‐I in promoting myogenic proliferation and differentiation via the MAPK/ERK and PI3K/Akt pathways requires smo activity
Author(s) -
MadhalaLevy D.,
Williams V.C.,
Hughes S.M.,
Reshef R.,
Halevy O.
Publication year - 2012
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.22861
Subject(s) - smoothened , cyclopamine , sonic hedgehog , phosphorylation , protein kinase b , mapk/erk pathway , microbiology and biotechnology , pi3k/akt/mtor pathway , hedgehog signaling pathway , biology , chemistry , signal transduction , growth factor , endocrinology , medicine , biochemistry , receptor
Abstract Sonic Hedgehog (Shh) has been shown to promote adult myoblast proliferation and differentiation and affect Akt phosphorylation via its effector Smoothened (Smo). Here, the relationship between Shh and insulin‐like growth factor I (IGF‐I) was examined with regard to myogenic differentiation via signaling pathways which regulate this process. Each factor enhanced Akt and MAPK/ERK (p42/44) phosphorylation and myogenic factor expression levels in a dose‐responsive manner, while combinations of Shh and IGF‐I showed additive effects. Blockage of the IGF‐I effects by neutralizing antibody partially reduced Shh's effects on signaling pathways, suggesting that IGF‐I enhances, but is not essential for Shh effects. Addition of cyclopamine, a Smo inhibitor, reduced Shh‐ and IGF‐I‐induced Akt phosphorylation in a similar manner, implying that Shh affects gain of the IGF‐I signaling pathway. This implication was also examined via a genetic approach. In cultures derived from Smo mut ( MCre;Smo flox/flox ) mice lacking Smo expression specifically in hindlimb muscles, IGF‐I‐induced Akt and p42/44 phosphorylation was significantly reduced compared to IGF‐I's effect on Smo cont cells. Moreover, remarkable inhibition of the stimulatory effect of IGF‐I on myogenic differentiation was observed in Smo mut cultures, implying that intact Smo is required for IGF‐I effects in myoblasts. Immunoprecipitation assays revealed that tyrosine‐phosphorylated proteins, including the regulatory unit of PI3K (p85), are recruited to Smo in response to Shh. Moreover, IGF‐IR was found to associate with Smo in response to Shh and to IGF‐I, suggesting that Shh and IGF‐I are already integrated at the receptor level, a mechanism by which their signaling pathways interact in augmenting their effects on adult myoblasts. J. Cell. Physiol. 227: 1455–1464, 2012. © 2011 Wiley Periodicals, Inc.