Nuclear actin and myosins in adenovirus infection

Adenovirus serotypes have been shown to cause drastic changes in nuclear organization, including the transcription machinery, during infection. This ability of adenovirus to subvert transcription in the host cell facilitates viral replication. Because nuclear actin and nuclear myosin I, myosin V and myosin VI have been implicated as direct regulators of transcription and important factors in the replication of other viruses, we sought to determine how nuclear actin and myosins are involved in adenovirus infection. We first confirmed reorganization of the host's transcription machinery to viral replication centers. We found that nuclear actin also reorganizes to sites of transcription through the intermediate but not the advanced late phase of viral infection. Furthermore, nuclear myosin I localized with nuclear actin and sites of transcription in viral replication centers. Intriguingly, nuclear myosins V and VI, which also reorganized to viral replication centers, exhibited different localization patterns, suggesting specialized roles for these nuclear myosins. Finally, we assessed the role of actin in adenovirus infection and found both cytoplasmic and nuclear actin likely play roles in adenovirus infection and replication. Together our data suggest the involvement of actin and multiple myosins in the nuclear replication and late viral gene expression of adenovirus.Fil: Fuchsova, Beata. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Biotecnológicas. Instituto de Investigaciones Biotecnológicas ; Argentina. University of Illinois; Estados UnidosFil: Serebryannyy, Leonid A.. University of Illinois; Estados UnidosFil: De Lanerolle, Primal. University of Illinois; Estados Unido

Nuclear actin: to polymerize or not to polymerize

The form and function of actin in the nucleus have been enigmatic for over 30 years. Recently actin has been assigned numerous functional roles in the nucleus, but its form remains a mystery. The intricate relationship between actin form and function in the cytoplasm implies that understanding the structural properties of nuclear actin is elementary to fully understanding its function. In this issue, McDonald et al. (p. 541) use fluorescence recovery after photobleaching (FRAP) to tackle the question of whether nuclear actin exists as monomers or polymers

The impact of membrane protein diffusion on GPCR signaling

This research was carried out as part of the Math-+ excellence cluster (DFG EXC 2046, Project A01-11 [HHB, PA]) and was partially funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through the following grants: Project 421152132 SFB1423 subproject C03 (PA), SFB 1470 subproject A01 (PA) and SFB 1114/2 (SW).Spatiotemporal signal shaping in G protein-coupled receptor (GPCR) signaling is now a well-established and accepted notion to explain how signaling specificity can be achieved by a superfamily sharing only a handful of downstream second messengers. Dozens of Gs-coupled GPCR signals ultimately converge on the production of cAMP, a ubiquitous second messenger. This idea is almost always framed in terms of local concentrations, the differences in which are maintained by means of spatial separation. However, given the dynamic nature of the reaction-diffusion processes at hand, the dynamics, in particular the local diffusional properties of the receptors and their cognate G proteins, are also important. By combining some first principle considerations, simulated data, and experimental data of the receptors diffusing on the membranes of living cells, we offer a short perspective on the modulatory role of local membrane diffusion in regulating GPCR-mediated cell signaling. Our analysis points to a diffusion-limited regime where the effective production rate of activated G protein scales linearly with the receptor–G protein complex’s relative diffusion rate and to an interesting role played by the membrane geometry in modulating the efficiency of coupling.Publisher PDFPeer reviewe

SUMOylation of nuclear actin

Actin, a major component of the cytoplasm, is also abundant in the nucleus. Nuclear actin is involved in a variety of nuclear processes including transcription, chromatin remodeling, and intranuclear transport. Nevertheless, the regulation of nuclear actin by posttranslational modifications has not been investigated. We now show that nuclear actin is modified by SUMO2 and SUMO3 and that computational modeling and site-directed mutagenesis identified K68 and K284 as critical sites for SUMOylating actin. We also present a model for the actin–SUMO complex and show that SUMOylation is required for the nuclear localization of actin

Myosin-I nomenclature

We suggest that the vertebrate myosin-I field adopt a common nomenclature system based on the names adopted by the Human Genome Organization (HUGO). At present, the myosin-I nomenclature is very confusing; not only are several systems in use, but several different genes have been given the same name. Despite their faults, we believe that the names adopted by the HUGO nomenclature group for genome annotation are the best compromise, and we recommend universal adoption

VEGFR2 Translocates to the Nucleus to Regulate Its Own Transcription

Vascular Endothelial Growth Factor Receptor-2 (VEGFR2) is the major mediator of the angiogenic effects of VEGF. In addition to its well known role as a membrane receptor that activates multiple signaling pathways, VEGFR2 also has a nuclear localization. However, what VEGFR2 does in the nucleus is still unknown. In the present report we show that, in endothelial cells, nuclear VEGFR2 interacts with several nuclear proteins, including the Sp1, a transcription factor that has been implicated in the regulation of genes needed for angiogenesis. By in vivo chromatin immunoprecipitation (ChIP) assays, we found that VEGFR2 binds to the Sp1-responsive region of the VEGFR2 proximal promoter. These results were confirmed by EMSA assays, using the same region of the VEGFR2 promoter. Importantly, we show that the VEGFR2 DNA binding is directly linked to the transcriptional activation of the VEGFR2 promoter. By reporter assays, we found that the region between -300/-116 relative to the transcription start site is essential to confer VEGFR2-dependent transcriptional activity. It was previously described that nuclear translocation of the VEGFR2 is dependent on its activation by VEGF. In agreement, we observed that the binding of VEGFR2 to DNA requires VEGF activation, being blocked by Bevacizumab and Sunitinib, two anti-angiogenic agents that inhibit VEGFR2 activation. Our findings demonstrate a new mechanism by which VEGFR2 activates its own promoter that could be involved in amplifying the angiogenic response

Naturally Extended CT · AG Repeats Increase H-DNA Structures and Promoter Activity in the Smooth Muscle Myosin Light Chain Kinase Gene▿

Naturally occurring repeat sequences capable of adopting H-DNA structures are abundant in promoters of disease-related genes. In support of this, we found (CT)22 · (AG)22 repeats in the promoter of smooth muscle myosin light chain kinase (smMLCK), a key regulator of vascular smooth muscle function. We also found an insertion mutation that adds another six pairs of CT · AG repeats and increases smMLCK promoter activity in spontaneously hypertensive rats (SHR). Therefore, we used the smMLCK promoters from normotensive and hypertensive rats as a model system to determine how CT · AG repeats form H-DNA, an intramolecular triplex, and regulate promoter activity. High-resolution mapping with a chemical probe selective for H-DNA showed that the CT · AG repeats adopt H-DNA structures at a neutral pH. Importantly, the SHR promoter forms longer H-DNA structures than the promoter from normotensive rats. Reconstituting nucleosomes on the promoters, in vitro, showed no difference in nucleosome positioning between the two promoters. However, chromatin immunoprecipitation analyses revealed that histone acetylations are greater in the hypertensive promoter. Thus, our findings suggest that the extended CT · AG repeats in the SHR promoter increase H-DNA structures, histone modifications, and promoter activity of the smMLCK, perhaps contributing to vascular disorders in hypertension