Glucocorticoids are beneficial in many muscular dystrophies but they are ineffective in treating dysferlinopathy, a rare muscular dystrophy caused by loss of dysferlin. We sought to understand the molecular basis for this disparity by studying the effects of a glucocorticoid on differentiation of the myoblast cell line, C2C12, and dysferlin-deficient C2C12s. We found that pharmacologic doses of dexamethasone enhanced the myogenic fusion efficiency of C2C12s and increased the induction of dysferlin, along with specific myogenic transcription factors, sarcolemmal and structural proteins. In contrast, the dysferlin-deficient C2C12 cell line demonstrated a reduction in long myotubes and early induction of particular muscle differentiation proteins, most notably, myosin heavy chain. Dexamethasone partially reversed the defect in myogenic fusion in the dysferlin-deficient C2C12 cells. We hypothesize that a key therapeutic benefit of glucocorticoids may be the up-regulation of dysferlin as an important component of glucocorticoid-enhanced myogenic differentiation.

The laboratory mouse gene encodes a retroviral restriction factor that mediates resistance to murine leukemia viruses (MLVs). Sequence similarity between and the protein of the murine endogenous retrovirus-L (MuERV-L) family of ERVs suggests that was co-opted from an ancient provirus. Previous evolutionary studies found orthologs only in the genus. Here, we describe identification of orthologous sequences in several species belonging to multiple families of rodents outside of the genus We show that these orthologs are in the same region of conserved synteny, between the genes and , suggesting a minimum insertion time of 45 million years for the ancient progenitor of Our analysis also reveals that was not detectable or heavily mutated in some lineages in the superfamily while, in concert with previous findings in the genus, we found strong evidence of positive selection of in the African clade in the subfamily Residues identified as evolving under positive selection include those that have been previously found to be important for restriction of multiple retroviral lineages. Taken together these findings suggest that the evolutionary origin of substantially predates evolution, that the rodent has been shaped by lineage-specific differential selection pressures, and that has long been evolving under positive selection in the rodent family supporting a defensive role that significantly antedates exposure to MLVs. Retroviruses have adapted to living in concert with their hosts throughout vertebrate evolution. Over the years, the study of these relationships revealed the presence of host proteins called restriction factors that inhibit retroviral replication in host cells. The first of these restriction factors to be identified, the gene found in mice, was thought to have originated in the genus In this study, we utilized genome database searches and DNA sequencing to identify copies in multiple rodent lineages. Our findings suggest a minimum insertion time of 45 million years into the genome of rodents for the ancestral progenitor of While is not detectable in some lineages, we also identified full-length orthologs showing signatures of a molecular "arms race" in a family of rodent species indigenous to Africa. This finding suggests that in these species has been co-evolving with unidentified retroviruses for millions of years.

SUMMARY Accessory proteins of lentiviruses, such as HIV-1, target cellular restriction factors to enhance viral replication. Systematic analyses of proteins that are targeted for degradation by HIV-1 accessory proteins may provide a better understanding of viral immune evasion strategies. Here, we describe a high-throughput platform developed to study cellular protein stability in a highly parallelized matrix format. We used this approach to identify cellular targets of the HIV-1 accessory protein Vpu through arrayed coexpression with 433 interferon-stimulated genes, followed by differential fluorescent labeling and automated image analysis. Among the previously unreported Vpu targets identified by this approach, we find that the E2 ligase mediating ISG15 conjugation, UBE2L6, and the transmembrane protein PLP2 are targeted by Vpu during HIV-1 infection to facilitate late-stage replication. This study provides a framework for the systematic and high-throughput evaluation of protein stability and establishes a more comprehensive portrait of cellular Vpu targets.

The evolutionary conflict between retroviruses and their vertebrate hosts over millions of years has led to the emergence of cellular innate immune proteins termed restriction factors as well as their viral antagonists. Evidence accumulated in the last two decades has substantially increased our understanding of the elaborate mechanisms utilized by these restriction factors to inhibit retroviral replication, mechanisms that either directly block viral proteins or interfere with the cellular pathways hijacked by the viruses. Analyses of these complex interactions describe patterns of accelerated evolution for these restriction factors as well as the acquisition and evolution of their virus-encoded antagonists. Evidence is also mounting that many restriction factors identified for their inhibition of specific retroviruses have broader antiviral activity against additional retroviruses as well as against other viruses, and that exposure to these multiple virus challenges has shaped their adaptive evolution. In this review, we provide an overview of the restriction factors that interfere with different steps of the retroviral life cycle, describing their mechanisms of action, adaptive evolution, viral targets and the viral antagonists that evolved to counter these factors.