Developmental regulation of the mouse IGF-I exon 1 promoter region by calcineurin activation of NFAT in skeletal muscle

Abstract

Skeletal muscle development and growth are regulated through multiple signaling pathways that include insulin-like growth factor I (IGF-I) and calcineurin activation of nuclear factor of activated T cell (NFAT) transcription factors. The developmental regulation and molecular mechanisms that control IGF-I gene expression in murine embryos and in differentiating C2C12 skeletal myocytes were examined. IGF-I is expressed in developing skeletal muscle, and its embryonic expression is significantly reduced in embryos lacking both NFATc3 and NFATc4. During development, the IGF-I exon 1 promoter is active in multiple organ systems, including skeletal muscle, whereas the alternative exon 2 promoter is expressed predominantly in the liver. The IGF-I exon 1 promoter flanking sequence includes two highly conserved regions that contain NFAT consensus binding sequences. One of these conserved regions contains a calcineurin/NFAT-responsive regulatory region that is preferentially activated by NFATc3 in C2C12 skeletal muscle cells and NIH3T3 fibroblasts. This NFAT-responsive region contains three clustered NFAT consensus binding sequences, and mutagenesis experiments demonstrated the requirement for two of these in calcineurin or NFATc3 responsiveness. Chromatin immunoprecipitation analyses demonstrated that endogenous IGF-I genomic sequences containing these conserved NFAT binding sequences interact preferentially with NFATc3 in C2C12 cells. Together, these experiments demonstrated that a NFAT-rich regulatory element in the IGF-I exon 1 promoter flanking region is responsive to calcineurin signaling and NFAT activation in skeletal muscle cells. The identification of a calcineurin/NFAT-responsive element in the IGF-I gene represents a potential mechanism of intersection of these signaling pathways in the control of muscle development and homeostasis.

Calcineurin in Reactive Astrocytes Plays a Key Role in the Interplay between Proinflammatory and Anti-Inflammatory Signals

“…2 F), we concluded that calcineurin activity in AIC astrocytes was regulated by Dox in vivo and in vitro. That calcineurin activity is regulated by Dox was indirectly confirmed by the observation that Dox regulated the release by AIC astrocytes of humoral neuroprotective signals such as Cu/Zn SOD or IGF-I that are known to be functionally associated with calcineurin (Tokheim and Martin, 2006;Alfieri et al, 2007). Thus, in response to proinflammatory challenge with LPS, AIC astrocytes secreted larger amounts of SOD and IGF-I when cultured without Dox (Fig.…”

Deregulated NFATc1 activity transforms murine fibroblasts via an autocrine growth factor‐mediated Stat3‐dependent pathway

“…Indeed, there is a striking parallel between the observed effects of caNFATc1 in promoting the autocrine growth factor-mediated transforming pathway in murine fibroblasts that we describe here, and the well-established functional role of endogenous NFAT proteins in promoting T lymphocyte growth during the immune response via the autocrine production of the primary T lymphocyte growth factor, interleukin-2 [Rao et al, 1997;Macian, 2005]. Moreover, NFAT binding sites are present in the promoter regions of numerous cytokines and growth factor genes and the activation of the NFAT signaling pathway has been implicated in the expression of an array of secreted factors, many of which are known to act in an autocrine fashion [Rao et al, 1997;Boss et al, 1998;Abbott et al, 2000;Hogan et al, 2003;Yang and Chow, 2003;Reinhold et al, 2004;Alfieri et al, 2007]. Hence, it is tempting to speculate that the increased expression and subsequent autocrine action of growth promoting cytokines and growth factors maybe a common mechanism by which deregulated NFAT activity is able to contribute towards initial tumor growth and malignant transformation.…”

Stimulation of calcineurin Aα activity attenuates muscle pathophysiology inmdxdystrophic mice

“…Calcineurin can regulate myoblast differentiation (1), transcription and/or activation of myoregulatory and growth factors [e.g., myocyte enhancer factor 2A (MEF-2A), MyoD, myogenin, and insulinlike growth factor I] (2,13,60), fusion of myoblasts to nascent myofibers (8), and expression of the developmental MyHC isoform (39). In hindlimb muscles of young mdx mice, pharmacological inhibition of calcineurin increased degeneration, impaired regeneration, and compromised muscle force-producing capacity, effects that appear to be dose dependent (49).…”