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Skeletal muscle atrophy can result from a range of physiological conditions, including denervation, immobilization, hindlimb unweighting, and aging. To better characterize the molecular genetic events of atrophy, a microarray analysis revealed that FGGY carbohydrate kinase domain containing (Fggy) is expressed in skeletal muscle and is induced in response to denervation. Bioinformatic analysis of the Fggy gene locus revealed two validated isoforms with alternative transcription initiation sites that we have designated Fggy-L-552 and Fggy-S-387. Additionally, we cloned two novel alternative splice variants, designated Fggy-L-482 and Fggy-S-344, from cultured muscle cells suggesting that at least four Fggy splice variants are expressed in skeletal muscle. Quantitative RT-PCR was performed using RNA isolated from muscle cells and primers designed to distinguish the four alternative Fggy transcripts and found that the Fggy-L transcripts are more highly expressed during myoblast differentiation, while the Fggy-S transcripts show relatively stable expression in proliferating myoblasts and differentiated myotubes. Confocal fluorescent microscopy revealed that the Fggy-L variants appear to localize evenly throughout the cytoplasm, while the Fggy-S variants produce a more punctuate cytoplasmic localization pattern in proliferating muscle cells. Finally, ectopic expression of Fggy-L-552 and Fggy-S-387 resulted in inhibition of muscle cell differentiation and attenuation of the MAP kinase and Akt signaling pathways. The identification and characterization of novel genes such as Fggy helps to improve our understanding of the molecular and cellular events that lead to atrophy and may eventually result in the identification of new therapeutic targets for the treatment of muscle wasting., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Protein phosphatase methylesterase 1 has been identified as a novel gene in skeletal muscle that is upregulated in response to neurogenic atrophy in mice. Western blot analysis confirms that Ppme1 is expressed during both muscle cell proliferation and differentiation. Additionally, the Ppme1 promoter is active in muscle cells, while mutation of a conserved E-box element prevents full induction of the Ppme1 reporter gene, suggesting that Ppme1 is transcriptionally regulated by myogenic regulatory factors. Interestingly, immunofluorescence analysis indicates that Ppme1 is localized to both the cytoplasm and the nucleus, while cell fractionation shows that Ppme1 is found only in the cytoplasm. Functional studies reveal that inhibition of Ppme1 using ABL127 or AMZ30 attenuates muscle cell differentiation. Interestingly, inhibition of Ppme1 by ABL127 led to a significant increase in AP-1 reporter activity, as well as, increases in ERK1/2, c-Jun, Ppme1, and PP2A protein levels in differentiating muscle cells. In contrast, AMZ30 treated cells showed a significant decrease in AP-1 reporter activity and a decrease in ERK1/2 and p38 phosphorylation levels. Finally, co-immunoprecipitation studies show that ABL127, but not AMZ30, causes disruption of the endogenous interaction between Ppme1 and PP2A. The data in this study show for the first time that Ppme1 is expressed in skeletal muscle and is upregulated in response to neurogenic atrophy. Furthermore, these findings suggest that Ppme1 may act as a sentinel of the MAP kinase signaling pathway and may indirectly regulate the ERK1/2 and p38 branches via a non-canonical mechanism leading to inhibition of muscle cell differentiation., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Muscle atrophy results from a range of physiological conditions, including immobilization, spinal cord damage, inflammation and aging. In this study we describe two genes, NEFA-interacting nuclear protein 30 (Nip30) and RING Finger and SPRY domain containing 1 (Rspry1), which have not previously been characterized or shown to be expressed in skeletal muscle. Furthermore, Nip30 and Rspry1 were transcriptionally induced in response to neurogenic muscle wasting in mice and were also found to be expressed endogenously at the RNA and protein level in C2C12 mouse muscle cells. Interestingly, during analysis of Nip30 and Rspry1 it was observed that these genes share a 230 base pair common regulatory region that contains several putative transcription regulatory elements. In order to assess the transcriptional activity of the Nip30 and Rspry1 regulatory regions, a fragment of the promoter of each gene was cloned, fused to a reporter gene, and transfected into cells. The Nip30 and Rspry1 reporters were both found to have significant transcriptional activity in cultured cells. Furthermore, the Nip30-Rspry1 common regulatory region contains a conserved E-box enhancer, which is an element bound by myogenic regulatory factors that function in the regulation of muscle-specific gene expression. Therefore, in order to determine if the predicted E-box was functional, Nip30 and Rspry1 reporters were transfected into cells ectopically expressing the myogenic regulatory factor, MyoD1, resulting in significant induction of both reporter genes. In addition, mutation of the conserved E-box element eliminated MyoD1 activation of the Nip30 and Rspry1 reporters. Finally, GFP-tagged Nip30 was found to localize to the nucleus, while GFP-tagged Rspry1 was found to localize to the cytoplasm of muscle cells., (Copyright © 2015 Elsevier B.V. All rights reserved.)