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MicroRNA (miR) are important regulators of gene expression, and aberrant miR expression has been linked to oncogenesis; however, little is understood about their contribution to lung tumorigenesis. Here, we determined that miR-31 is overexpressed in human lung adenocarcinoma and this overexpression independently correlates with decreased patient survival. We developed a transgenic mouse model that allows for lung-specific expression of miR-31 to test the oncogenic potential of miR-31 in the lung. Using this model, we observed that miR-31 induction results in lung hyperplasia, followed by adenoma formation and later adenocarcinoma development. Moreover, induced expression of miR-31 in mice cooperated with mutant KRAS to accelerate lung tumorigenesis. We determined that miR-31 regulates lung epithelial cell growth and identified 6 negative regulators of RAS/MAPK signaling as direct targets of miR-31. Our study distinguishes miR-31 as a driver of lung tumorigenesis that promotes mutant KRAS-mediated oncogenesis and reveals that miR-31 directly targets and reduces expression of negative regulators of RAS/MAPK signaling. [ABSTRACT FROM AUTHOR]

Polarized activation of adipose tissue macrophages (ATMs) is crucial for maintaining adipose tissue function and mediating obesity-associated cardiovascular risk and metabolic abnormalities; however, the regulatory network of this key process is not well defined. Here, we identified a PPARγ/microRNA-223 (miR-223) regulatory axis that controls macrophage polarization by targeting distinct downstream genes to shift the cellular response to various stimuli. In BM-derived macrophages, PPARγ directly enhanced miR-223 expression upon exposure to Th2 stimuli. ChIP analysis, followed by enhancer reporter assays, revealed that this effect was mediated by PPARγ binding 3 PPARγ regulatory elements (PPREs) upstream of the pre-miR-223 coding region. Moreover, deletion of miR-223 impaired PPARγ-dependent macrophage alternative activation in cells cultured ex vivo and in mice fed a high-fat diet. We identified Rasa1 and Nfat5 as genuine miR-223 targets that are critical for PPARγ-dependent macrophage alternative activation, whereas the proinflammatory regulator Pknox1, which we reported previously, mediated miR-223-regulated macrophage classical activation. In summary, this study provides evidence to support the crucial role of a PPARγ/miR-223 regulatory axis in controlling macrophage polarization via distinct downstream target genes. [ABSTRACT FROM AUTHOR]

MicroRNAs modulate cellular phenotypes by inhibiting expression of mRNA targets. In this study, we have shown that the muscle-specific microRNAs miR-133a-1 and miR-133a-2 are essential for multiple facets of skeletal muscle function and homeostasis in mice. Mice with genetic deletions of miR-133a-1 and miR-133a-2 developed adult-onset centronuclear myopathy in type II (fast-twitch) myofibers, accompanied by impaired mitochondrial function, fast-to-slow myofiber conversion, and disarray of muscle triads (sites of excitation- contraction coupling). These abnormalities mimicked human centronuclear myopathies and could be ascribed, at least in part, to dysregulation of the miR-133a target mRNA that encodes dynamin 2, a GTPase implicated in human centronuclear myopathy. Our findings reveal an essential role for miR-133a in the maintenance of adult skeletal muscle structure, function, bioenergetics, and myofiber identity; they also identify a potential modulator of centronuclear myopathies. [ABSTRACT FROM AUTHOR]

Platinum-based chemotherapies such as cisplatin are used as first-line treatment for many cancers. Although there is often a high initial responsiveness, the majority of patients eventually relapse with platinum-resistant disease. For example, a subset of testicular cancer patients still die even though testicular cancer is considered a paradigm of cisplatin-sensitive solid tumors, but the mechanisms of chemoresistance remain elusive. Here, we have shown that one key determinant of cisplatin-resistance in testicular embryonal carcinoma (EC) is high cytoplasmic expression of the cyclin-dependent kinase (CDK) inhibitor p21. The EC component of the majority of refractory testicular cancer patients exhibited high cytoplasmic p21 expression, which protected EC cell lines against cisplatin-induced apoptosis via CDK2 inhibition. Localization of p21 in the cytoplasm was critical for cisplatin resistance, since relocalization of p21 to the nucleus by Akt inhibition sensitized EC cell lines to cisplatin. We also demonstrated in EC cell lines and human tumor tissue that high cytoplasmic p21 expression and cisplatin resistance of EC were inversely associated with the expression of Oct4 and miR-106b seed family members. Thus, targeting cytoplasmic p21, including by modulation of the Oct4/miR-106b/p21 pathway, may offer new strategies for the treatment of chemoresistant testicular and other types of cancer. [ABSTRACT FROM AUTHOR]

Previous work showed that calmodulin (CaM) and Ca2+-CaM-dependent protein kinase II (CaMKII) are somehow involved in cardiac hypertrophic signaling, that inositol 1,4,5-trisphosphate receptors (InsP3Rs) in ventricular myocytes are mainly in the nuclear envelope, where they associate with CaMKII, and that class II histone deacetylases (e.g., HDAC5) suppress hypertrophic gene transcription. Furthermore, HDAC phosphorylation in response to neurohumoral stimuli that induce hypertrophy, such as endothelin-1 (ET-1), activates HDAC nuclear export, thereby regulating cardiac myocyte transcription. Here we demonstrate a detailed mechanistic convergence of these 3 issues in adult ventricular myocytes. We show that ET-1, which activates plasmalemmal G protein-coupled receptors and InsP3 production, elicits local nuclear envelope Ca2+ release via InsP3R. This local Ca2+ release activates nuclear CaMKII, which triggers HDAC5 phosphorylation and nuclear export (derepressing transcription). Remarkably, this Ca2+-dependent pathway cannot be activated by the global Ca2+ transients that cause contraction at each heartbeat. This novel local Ca2+ signaling in excitation-transcription coupling is analogous to but separate (and insulated) from that involved in excitation-contraction coupling. Thus, myocytes can distinguish simultaneous local and global Ca2+ signals involved in contractile activation from those targeting gene expression. [ABSTRACT FROM AUTHOR]

Macrophages are critical effectors of bacterial clearance and must retain viability, despite exposure to toxic bacterial products, until key antimicrobial functions are performed. Subsequently, host-mediated macrophage apoptosis aids resolution of infection. The ability of macrophages to make this transition from resistance to susceptibility to apoptosis is important for effective host innate immune responses. We investigated the role of Mcl-1, an essential regulator of macrophage lifespan, in this switch from viability to apoptosis, using the model of pneumococcal-associated macrophage apoptosis. Upon exposure to pneumococci, macrophages initially upregulate Mcl-1 protein and maintain viability for up to 14 hours. Subsequently, macrophages reduce expression of full-length Mcl-1 and upregulate a 34-kDa isoform of Mcl-1 corresponding to a novel BH3-only splice variant, Mcl-1(Exon-1). Change in expression of Mcl-1 protein is associated with mitochondrial membrane permeabilization, which is characterized by loss of mitochondrial inner transmembrane potential and translocation of cytochrome c and apoptosis-inducing factor. Following pneumococcal infection, macrophages expressing full-length human Mcl-1 as a transgene exhibit a delay in apoptosis and in bacterial killing. Mcl-1 transgenic mice clear pneumococci from the lung less efficiently than nontransgenic mice. Dynamic changes in Mcl-1 expression determine macrophage viability as well as antibacterial host defense. [ABSTRACT FROM AUTHOR]