Actin-membrane interaction in fibroblasts: what proteins are involved in this association?

In this review we discuss some of the proteins for which a role in linking actin to the fibroblast plasma membrane has been suggested. We focus on the family of proteins related to erythrocyte spectrin, proteins that have generally been viewed as having an organization and a function in actin-membrane attachment similar to those of erythrocyte spectrin. Experiments in which we precipitated the nonerythrocyte spectrin within living fibroblasts have led us to question this supposed similarity of organization and function of the nonerythrocyte and erythrocyte spectrins. Intracellular precipitation of fibroblast spectrin does not affect the integrity of the major actin-containing structures, the stress fiber microfilament bundles. Unexpectedly, however, we found that the precipitation of spectrin results in a condensation and altered distribution of the vimentin class of intermediate filaments in most cells examined. Although fibroblast spectrin may have a role in the attachment of some of the cortical, submembranous actin, it is surprising how little the intracellular immunoprecipitation of the spectrin affects the cells. Several proteins have been found concentrated at the ends of stress fibers, where the actin filaments terminate at focal contacts. Two of these proteins, alpha-actinin and fimbrin, have properties that suggest that they are not involved in the attachment of the ends of the bundles to the membrane but are more probably involved in the organization and cross-linking of the filaments within the bundles. On the other hand, vinculin and talin are two proteins that interact with each other and may form part of a chain of attachments between the ends of the microfilament bundles and the focal contact membrane. Their role in this attachment, however, has not been established and further work is needed to examine their interaction with actin and to identify any other components with which they may interact, particularly in the plasma membrane

Study of in vitro phosphorylation of histones H3, H4 and of the non-acetylated and acetylated tetramers (H3–H4)2

Granyer Giralt, JosepPrimer pla de l'obra. Coneguda com el Vedell o el Toro, en actitud de meditar. Mesura 2,42 x 0,62 x 0,76 metres i és de bronze

Inhibition of HIV-1 replication by balsamin, a ribosome inactivating protein of Momordica balsamina

Ribosome-inactivating proteins (RIPs) are endowed with several medicinal properties, including antiviral activity. We demonstrate here that the recently identified type I RIP from Momordica balsamina also possesses antiviral activity, as determined by viral growth curve assays and single-round infection experiments. Importantly, this activity is at play even as doses where the RIP has no cytotoxic effect. In addition, balsamin inhibits HIV-1 replication not only in T cell lines but also in human primary CD4(+) T cells. This antiviral compound exerts its activity at a viral replicative step occurring later than reverse-transcription, most likely on viral protein translation, prior to viral budding and release. Finally, we demonstrate that balsamin antiviral activity is broad since it also impedes influenza virus replication. Altogether our results demonstrate that type I RIP can exert a potent anti-HIV-1 activity which paves the way for new therapeutic avenues for the treatment of viral infections

Immunohistochemical staining of radixin and moesin in prostatic adenocarcinoma

<p>Abstract</p> <p>Background</p> <p>Some members of the Protein 4.1 superfamily are believed to be involved in cell proliferation and growth, or in the regulation of these processes. While the expression levels of two members of this family, radixin and moesin, have been studied in many tumor types, to our knowledge they have not been investigated in prostate cancer.</p> <p>Methods</p> <p>Tissue microarrays were immunohistochemically stained for either radixin or moesin, with the staining intensities subsequently quantified and statistically analyzed using One-Way ANOVA or nonparametric equivalent with subsequent Student-Newman-Keuls tests for multiple comparisons. There were 11 cases of normal donor prostates (NDP), 14 cases of benign prostatic hyperplasia (BPH), 23 cases of high-grade prostatic intraepithelial neoplasia (HGPIN), 88 cases of prostatic adenocarcinoma (PCa), and 25 cases of normal tissue adjacent to adenocarcinoma (NAC) analyzed in the microarrays.</p> <p>Results</p> <p>NDP, BPH, and HGPIN had higher absolute staining scores for radixin than PCa and NAC, but with a significant difference observed between only HGPIN and PCa (p = < 0.001) and HGPIN and NAC (p = 0.001). In the moesin-stained specimens, PCa, NAC, HGPIN, and BPH all received absolute higher staining scores than NDP, but the differences were not significant. Stage 4 moesin-stained PCa had a significantly reduced staining intensity compared to Stage 2 (p = 0.003).</p> <p>Conclusions</p> <p>To our knowledge, these studies represent the first reports on the expression profiles of radixin and moesin in prostatic adenocarcinoma. The current study has shown that there were statistically significant differences observed between HGPIN and PCa and HGPIN and NAC in terms of radixin expression. The differences in the moesin profiles by tissue type were not statistically significant. Additional larger studies with these markers may further elucidate their potential roles in prostatic neoplasia progression.</p

Quantitative Multicolor Super-Resolution Microscopy Reveals Tetherin HIV-1 Interaction

Virus assembly and interaction with host-cell proteins occur at length scales below the diffraction limit of visible light. Novel super-resolution microscopy techniques achieve nanometer resolution of fluorescently labeled molecules. The cellular restriction factor tetherin (also known as CD317, BST-2 or HM1.24) inhibits the release of human immunodeficiency virus 1 (HIV-1) through direct incorporation into viral membranes and is counteracted by the HIV-1 protein Vpu. For super-resolution analysis of HIV-1 and tetherin interactions, we established fluorescence labeling of HIV-1 proteins and tetherin that preserved HIV-1 particle formation and Vpu-dependent restriction, respectively. Multicolor super-resolution microscopy revealed important structural features of individual HIV-1 virions, virus assembly sites and their interaction with tetherin at the plasma membrane. Tetherin localization to micro-domains was dependent on both tetherin membrane anchors. Tetherin clusters containing on average 4 to 7 tetherin dimers were visualized at HIV-1 assembly sites. Combined biochemical and super-resolution analysis revealed that extended tetherin dimers incorporate both N-termini into assembling virus particles and restrict HIV-1 release. Neither tetherin domains nor HIV-1 assembly sites showed enrichment of the raft marker GM1. Together, our super-resolution microscopy analysis of HIV-1 interactions with tetherin provides new insights into the mechanism of tetherin-mediated HIV-1 restriction and paves the way for future studies of virus-host interactions

Likely Role of APOBEC3G-Mediated G-to-A Mutations in HIV-1 Evolution and Drug Resistance

The role of APOBEC3 (A3) protein family members in inhibiting retrovirus infection and mobile element retrotransposition is well established. However, the evolutionary effects these restriction factors may have had on active retroviruses such as HIV-1 are less well understood. An HIV-1 variant that has been highly G-to-A mutated is unlikely to be transmitted due to accumulation of deleterious mutations. However, G-to-A mutated hA3G target sequences within which the mutations are the least deleterious are more likely to survive selection pressure. Thus, among hA3G targets in HIV-1, the ratio of nonsynonymous to synonymous changes will increase with virus generations, leaving a footprint of past activity. To study such footprints in HIV-1 evolution, we developed an in silico model based on calculated hA3G target probabilities derived from G-to-A mutation sequence contexts in the literature. We simulated G-to-A changes iteratively in independent sequential HIV-1 infections until a stop codon was introduced into any gene. In addition to our simulation results, we observed higher ratios of nonsynonymous to synonymous mutation at hA3G targets in extant HIV-1 genomes than in their putative ancestral genomes, compared to random controls, implying that moderate levels of A3G-mediated G-to-A mutation have been a factor in HIV-1 evolution. Results from in vitro passaging experiments of HIV-1 modified to be highly susceptible to hA3G mutagenesis verified our simulation accuracy. We also used our simulation to examine the possible role of A3G-induced mutations in the origin of drug resistance. We found that hA3G activity could have been responsible for only a small increase in mutations at known drug resistance sites and propose that concerns for increased resistance to other antiviral drugs should not prevent Vif from being considered a suitable target for development of new drugs