The actin and intermediate filament cytoskeletons contribute to numerous cellular processes, including morphogenesis, cytokinesis and migration. These two cytoskeletal systems associate with each other, but the underlying mechanisms of this interaction are incompletely understood. Here, we show that inactivation of vimentin leads to increased actin stress fiber assembly and contractility, and consequent elevation of myosin light chain phosphorylation and stabilization of tropomyosin-4.2 (see Geeves et al., 2015). The vimentin-knockout phenotypes can be rescued by re-expression of wild-type vimentin, but not by the non-filamentous ‘unit length form’ vimentin, demonstrating that intact vimentin intermediate filaments are required to facilitate the effects on the actin cytoskeleton. Finally, we provide evidence that the effects of vimentin on stress fibers are mediated by activation of RhoA through its guanine nucleotide exchange factor GEF-H1 (also known as ARHGEF2). Vimentin depletion induces phosphorylation of the microtubule-associated GEF-H1 on Ser886, and thereby promotes RhoA activity and actin stress fiber assembly. Taken together, these data reveal a new mechanism by which intermediate filaments regulate contractile actomyosin bundles, and may explain why elevated vimentin expression levels correlate with increased migration and invasion of cancer cells.

Previous reports have shown that in avian and rodent isolated skeletal muscle cells and cultured myoblast cell lines, vitamin D 3 metabolites, such as 25-hydroxyvitamin D 3 (25(OH)D 3 ) and 1␣,25(OH) 2 D 3 , influence cellular calcium and phosphorus uptake, cellular growth, differentiation, and the expression of a limited number of genes (14 -19). Many reports suggest that the vitamin D receptor (VDR) is expressed in skeletal muscle (20 -24), and VDR deletion in mice results in alterations in muscle function and strength (25,26). Treatment of vitamin D-deficient humans with cholecalciferol improves muscle phosphocreatine recovery after exercise (27), suggesting that vitamin D 3 or its metabolites alter skeletal muscle oxidative capacity.To assess the mechanism of action of the active metabolite of vitamin D 3 , 1␣,25(OH) 2 D 3 , in human skeletal muscle cells, we examined changes in mitochondrial oxygen consumption (OCR), mitochondrial dynamics, mitochondrial OXPHOS proteins, pyruvate dehydrogenase phosphorylation, and nuclear gene expression using whole transcriptome shotgun sequencing (WTSS, RNA-seq) of messenger RNAs and micro-RNAs Tables 1 and 2

BackgroundChromosomal complement, including that provided by the sex chromosomes, influences expression of proteins and molecular signaling in every cell. However, less than 50% of the scientific studies published in 2009 using experimental animals reported sex as a biological variable. Because every cell has a sex, we conducted a literature review to determine the extent to which sex is reported as a variable in cardiovascular studies on cultured cells.MethodsArticles from 10 cardiovascular journals with high impact factors (Circulation, J Am Coll Cardiol, Eur Heart J, Circ Res, Arterioscler Thromb Vasc Biol, Cardiovasc Res, J Mol Cell Cardiol, Am J Physiol Heart Circ Physiol, J Heart Lung Transplant and J Cardiovasc Pharmacol) and published in 2010 were searched using terms 'cultured' and 'cells' in any order to determine if the sex of those cells was reported. Studies using established cell lines were excluded.ResultsUsing two separate search strategies, we found that only 25 of 90 articles (28%) and 20 of 101 articles (19.8%) reported the sex of cells. Of those reporting the sex of cells, most (68.9%; n = 31) used only male cells and none used exclusively female cells. In studies reporting the sex of cells of cardiovascular origin, 40% used vascular smooth-muscle cells, and 30% used stem/progenitor cells. In studies using cells of human origin, 35% did not report the sex of those cells. None of the studies using neonatal cardiac myocytes reported the sex of those cells.ConclusionsThe complement of sex chromosomes in cells studied in culture has the potential to affect expression of proteins and 'mechanistic' signaling pathways. Therefore, consistent with scientific excellence, editorial policies should require reporting sex of cells used in in vitro experiments.

SUMMARY Cell adhesion, morphogenesis, mechanosensing, and muscle contraction rely on contractile actomyosin bundles, where the force is produced through sliding of bipolar myosin II filaments along actin filaments. The assembly of contractile actomyosin bundles involves registered alignment of myosin II filaments and their subsequent fusion into large stacks. However, mechanisms underlying the assembly of myosin II stacks, and their physiological functions have remained elusive. Here we identified myosin-18B, an unconventional myosin, as a stable component of contractile stress fibers. Myosin-18B co-localized with myosin II motor domains in stress fibers, and was enriched at the ends of myosin II stacks. Importantly, myosin-18B deletion resulted in drastic defects in the concatenation and persistent association of myosin II filaments with each other, and thus led to severely impaired assembly of myosin II stacks. Consequently, lack of myosin-18B resulted in defective maturation of actomyosin bundles from their precursors in osteosarcoma cells. Moreover, myosin-18B knockout cells displayed abnormal morphogenesis, migration, and ability to exert forces to the environment. These results reveal a critical role for myosin-18B in myosin II stack assembly, and provide evidence that myosin II stacks are important for a variety of vital processes in cells.