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Open Access Publications from the University of California

Scholarly Works (8 results)

  • Thesis
  • Peer Reviewed
UC San Francisco Electronic Theses and Dissertations (2013)

microRNA-1 (miR-1) is an evolutionarily conserved, striated muscle enriched miRNA. Most mammalian genomes contain two copies of miR-1, both of which are transcribed with another myogenic miRNA, miR-133a. Compound miR-1 knockout mice died uniformly before weaning due to severe cardiac dysfunction. miR-1-null cardiomyocytes had abnormal sarcomere organization and decreased phosphorylation of the regulatory myosin light chain-2 (MLC2), a critical cytoskeletal regulator. The smooth muscle-restricted inhibitor of MLC2 phosphorylation, Telokin, was ectopically expressed in the myocardium, along with other smooth-muscle genes. miR-1 repressed Telokin expression through direct targeting and by repressing its transcriptional regulator, Myocardin. Our results reveal that miR-1 is required for postnatal cardiac function and reinforces the striated muscle phenotype by regulating both transcriptional and effector nodes of the smooth-muscle gene-expression network.

miR-133a also represses the smooth muscle gene program in postnatal hearts and thus cooperates with miR-1 in this context. Interestingly, during cardiac precursor differentiation, these miRNAs have opposing regulatory functions suggesting that the relative expression of these miRNAs may be functionally important. The RNA binding protein, LIN28, regulates miR-1 but not miR-133a post-transcriptionally and may provide a mechanism for their differential accumulation in the heart. However, we find LIN28A loss in vivo is insufficient to alter the expression of either miR-1 or miR-133a in embryonic mouse hearts, suggesting that another mechanism may regulate these miRNAs in this context.

Among its many functions, miR-1 generally inhibits cell proliferation and promotes differentiation. In postnatal mouse hearts, miR-1 expression is inversely correlated with cardiomyocyte proliferative and regenerative potential. We find that reduced miR-1 in vivo is sufficient to inhibit the process of neonatal cardiomyocyte binucleation, a process closely linked with cardiomyocyte maturation and the loss of proliferative potential. However, we find that animals with reduced miR-1 display decreased regenerative potential, an increase in scar size and a greater impairment of cardiac function following myocardial infarction. Our results suggest that normal levels of miR-1 may be required for limiting tissue damage and promoting healing in injured hearts. Collectively, our data reveal that miR-1 is an essential cardiac gene that plays a variety of roles in the mammalian heart.

    Cover page: The Role of microRNA-1 in the Mammalian Heart
    • Article
    • Peer Reviewed
    UC San Francisco Previously Published Works (2013)
    Heart disease is a major cause of morbidity and mortality in the developed world. Patient recovery after cardiac injury is hampered by the extremely limited regenerative capacity of the adult mammalian heart. In addition to cell-based approaches and in situ cardiac reprogramming, significant interest has been focused on genetic and small molecule–based strategies to enhance endogenous cardiomyocyte proliferative potential. A recent study in Nature suggests, for the first time, that microRNAs may have the ability to induce cardiomyocyte proliferation and cardiac regeneration in adult mice.
      • Article
      • Peer Reviewed
      UC San Francisco Previously Published Works (2013)
      microRNA-1 (miR-1) is an evolutionarily conserved, striated muscle-enriched miRNA. Most mammalian genomes contain two copies of miR-1, and in mice, deletion of a single locus, miR-1-2, causes incompletely penetrant lethality and subtle cardiac defects. Here, we report that deletion of miR-1-1 resulted in a phenotype similar to that of the miR-1-2 mutant. Compound miR-1 knockout mice died uniformly before weaning due to severe cardiac dysfunction. miR-1-null cardiomyocytes had abnormal sarcomere organization and decreased phosphorylation of the regulatory myosin light chain-2 (MLC2), a critical cytoskeletal regulator. The smooth muscle-restricted inhibitor of MLC2 phosphorylation, Telokin, was ectopically expressed in the myocardium, along with other smooth muscle genes. miR-1 repressed Telokin expression through direct targeting and by repressing its transcriptional regulator, Myocardin. Our results reveal that miR-1 is required for postnatal cardiac function and reinforces the striated muscle phenotype by regulating both transcriptional and effector nodes of the smooth muscle gene expression network. DOI: http://dx.doi.org/10.7554/eLife.01323.001.
        • Article
        • Peer Reviewed
        UC San Francisco Previously Published Works (2015)
        The presence of a small number of infected but transcriptionally dormant cells currently thwarts a cure for the more than 35 million individuals infected with HIV. Reactivation of these latently infected cells may result in three fates: 1) cell death due to a viral cytopathic effect, 2) cell death due to immune clearance, or 3) a retreat into latency. Uncovering the dynamics of HIV gene expression and silencing in the latent reservoir will be crucial for developing an HIV-1 cure. Here we identify and characterize an intracellular circuit involving TRIM32, an HIV activator, and miR-155, a microRNA that may promote a return to latency in these transiently activated reservoir cells. Notably, we demonstrate that TRIM32, an E3 ubiquitin ligase, promotes reactivation from latency by directly modifying IκBα, leading to a novel mechanism of NF-κB induction not involving IκB kinase activation.
          Cover page: MicroRNA-155 Reinforces HIV Latency*
          • Article
          • Peer Reviewed
          UC San Francisco Previously Published Works (2017)
            • Article
            • Peer Reviewed
            UC San Francisco Previously Published Works (2017)
            miR-1 is a small noncoding RNA molecule that modulates gene expression in heart and skeletal muscle. Loss of Drosophila miR-1 produces defects in somatic muscle and embryonic heart development, which have been partly attributed to miR-1 directly targeting Delta to decrease Notch signaling. Here, we show that overexpression of miR-1 in the fly wing can paradoxically increase Notch activity independently of its effects on Delta. Analyses of potential miR-1 targets revealed that miR-1 directly regulates the 3'UTR of the E3 ubiquitin ligase Nedd4 Analysis of embryonic and adult fly heart revealed that the Nedd4 protein regulates heart development in Drosophila Larval fly hearts overexpressing miR-1 have profound defects in actin filament organization that are partially rescued by concurrent overexpression of Nedd4. These results indicate that miR-1 and Nedd4 act together in the formation and actin-dependent patterning of the fly heart. Importantly, we have found that the biochemical and genetic relationship between miR-1 and the mammalian ortholog Nedd4-like (Nedd4l) is evolutionarily conserved in the mammalian heart, potentially indicating a role for Nedd4L in mammalian postnatal maturation. Thus, miR-1-mediated regulation of Nedd4/Nedd4L expression may serve to broadly modulate the trafficking or degradation of Nedd4/Nedd4L substrates in the heart.
              • Article
              • Peer Reviewed
              UC San Francisco Previously Published Works (2014)
              MicroRNA (miRNA) maturation is regulated by interaction of particular miRNA precursors with specific RNA-binding proteins. Following their biogenesis, mature miRNAs are incorporated into the RNA-induced silencing complex (RISC) where they interact with mRNAs to negatively regulate protein production. However, little is known about how mature miRNAs are regulated at the level of their activity. To address this, we screened for proteins differentially bound to the mature form of the miR-1 or miR-133 miRNA families. These muscle-enriched, co-transcribed miRNA pairs cooperate to suppress smooth muscle gene expression in the heart. However, they also have opposing roles, with the miR-1 family, composed of miR-1 and miR-206, promoting myogenic differentiation, whereas miR-133 maintains the progenitor state. Here, we describe a physical interaction between TDP-43, an RNA-binding protein that forms aggregates in the neuromuscular disease, amyotrophic lateral sclerosis, and the miR-1, but not miR-133, family. Deficiency of the TDP-43 Drosophila ortholog enhanced dmiR-1 activity in vivo. In mammalian cells, TDP-43 limited the activity of both miR-1 and miR-206, but not the miR-133 family, by disrupting their RISC association. Consistent with TDP-43 dampening miR-1/206 activity, protein levels of the miR-1/206 targets, IGF-1 and HDAC4, were elevated in TDP-43 transgenic mouse muscle. This occurred without corresponding Igf-1 or Hdac4 mRNA increases and despite higher miR-1 and miR-206 expression. Our findings reveal that TDP-43 negatively regulates the activity of the miR-1 family of miRNAs by limiting their bioavailability for RISC loading and suggest a processing-independent mechanism for differential regulation of miRNA activity.
                • Article
                • Peer Reviewed
                UC San Francisco Previously Published Works (2019)
                Multiple myeloma (MM) arises from malignant immunoglobulin (Ig)-secreting plasma cells and remains an incurable, often lethal disease despite therapeutic advances. The unfolded-protein response sensor IRE1α supports protein secretion by deploying a kinase-endoribonuclease module to activate the transcription factor XBP1s. MM cells may co-opt the IRE1α-XBP1s pathway; however, the validity of IRE1α as a potential MM therapeutic target is controversial. Genetic disruption of IRE1α or XBP1s, or pharmacologic IRE1α kinase inhibition, attenuated subcutaneous or orthometastatic growth of MM tumors in mice and augmented efficacy of two established frontline antimyeloma agents, bortezomib and lenalidomide. Mechanistically, IRE1α perturbation inhibited expression of key components of the endoplasmic reticulum-associated degradation machinery, as well as secretion of Ig light chains and of cytokines and chemokines known to promote MM growth. Selective IRE1α kinase inhibition reduced viability of CD138+ plasma cells while sparing CD138- cells derived from bone marrows of newly diagnosed or posttreatment-relapsed MM patients, in both US- and European Union-based cohorts. Effective IRE1α inhibition preserved glucose-induced insulin secretion by pancreatic microislets and viability of primary hepatocytes in vitro, as well as normal tissue homeostasis in mice. These results establish a strong rationale for developing kinase-directed inhibitors of IRE1α for MM therapy.
                  Cover page: Disruption of IRE1α through its kinase domain attenuates multiple myeloma
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