Modular Evolution of PGC-1α in Vertebrates

In mammals, the peroxisome proliferator activated receptor (PPAR)γ coactivator-1α (PGC-1α) is a central regulator of mitochondrial gene expression, acting in concert with nuclear respiratory factor-1 (NRF-1) and the PPARs. Its role as a “master regulator” of oxidative capacity is clear in mammals, but its role in other vertebrates is ambiguous. In lower vertebrates, although PGC-1α seems to play a role in coordinating the PPARα axis as in mammals, it does not appear to be involved in NRF-1 regulation of mitochondrial content. To evaluate the evolutionary patterns of this coactivator in fish and mammals, we investigated the evolutionary trajectories of PGC-1α homologs in representative vertebrate lineages. A phylogeny of the PGC-1 paralogs suggested that the family diversified through repeated genome duplication events early in vertebrate evolution. Bayesian and maximum likelihood phylogenetic reconstructions of PGC-1α in representative vertebrate species revealed divergent evolutionary dynamics across the different functional domains of the protein. Specifically, PGC-1α exhibited strong conservation of the activation/PPAR interaction domain across vertebrates, whereas the NRF-1 and MEF2c interaction domains experienced accelerated rates of evolution in actinopterygian (fish lineages) compared to sarcopterygians (tetrapod lineages). Furthermore, analysis of the amino acid sequence of these variable domains revealed successive serine- and glutamine-rich insertions within the teleost lineages, with important ramifications for PGC-1α function in these lineages. Collectively, these results suggest modular evolution of the PGC-1α protein in vertebrates that could allow for lineage-specific divergences in the coactivating capabilities of this regulator.     

Synaptic Function of Cholinergic-Specific Chol-1α Ganglioside

The function of a cholinergic-specific ganglioside, Chol-1alpha, was investigated. The release of acetylcholine from synaptosomes was inhibited by anti-Chol-1alpha monoclonal antibody but not by monoclonal antibodies against other brain gangliosides tested. Chol-1alpha ganglioside stimulated the high-affinity choline uptake by synaptosomes and consequently enhanced acetylcholine synthesis, resulting in an increased release of acetylcholine from synaptosomes. The memory and learning abilities of rats given anti-Chol-1alpha antibody were remarkably suppressed. These in vitro and in vivo studies suggest that Chol-1alpha ganglioside plays a pivotal role in cholinergic synaptic transmission and participates in cognitive function.     

Differential roles of Sirt1 in HIF-1α and HIF-2α mediated hypoxic responses

Hypoxia-inducible factors 1α and 2α (HIF-1α and HIF-2α) determine cancer cell fate under hypoxia. Despite the similarities of their structures, HIF-1α and HIF-2α have distinct roles in cancer growth under hypoxia, that is, HIF-1α induces growth arrest whereas HIF-2α promotes cell growth. Recently, sirtuin 1 (Sirt1) was reported to fine-tune cellular responses to hypoxia by deacetylating HIF-1α and HIF-2α. Yet, the roles of Sirt1 in HIF-1α and HIF-2α functions have been controversial. We here investigated the precise roles of Sirt1 in HIF-1α and HIF-2α regulations. Immunological analyses revealed that HIF-1α K674 and HIF-2α K741 are acetylated by PCAF and CBP, respectively, but are deacetylated commonly by Sirt1. In the Gal4 reporter systems, Sirt1 was found to repress HIF-1α activity constantly in ten cancer cell-lines but to regulate HIF-2α activity cell type-dependently. Moreover, Sirt1 determined cell growth under hypoxia depending on HIF-1α and HIF-2α. Under hypoxia, Sirt1 promoted cell proliferation of HepG2, in which Sirt1 differentially regulates HIF-1α and HIF-2α. In contrast, such an effect of Sirt1 was not shown in HCT116, in which Sirt1 inactivates both HIF-1α and HIF-2α because conflicting actions of HIF-1α and HIF-2α on cell growth may be offset. Our results provide a better understanding of the roles of Sirt1 in HIF-mediated hypoxic responses and also a basic concept for developing anticancer strategy targeting Sirt1.     

Glial localization of interleukin-1α in invertebrate ganglia

1. Mytilus pedal ganglion contains a small population of glial cells that are immunopositive for interleukin-1 alpha. Positively stained fibers can also be seen in the neuropil of these sections. 2. The marine worm Nereis diversicolor also exhibits positive neural immunostaining for interleukin-1 alpha. 3. Both organisms contain hemocytes that contain immunoactivity for interleukin-1 alpha. The study suggests interleukin-1 alpha to be an ancient cytokine given its presence in organisms that evolved significantly earlier than mammals.     

Mechanism of HCV's resistance to IFN-α in cell culture involves expression of functional IFN-α receptor 1

The mechanisms underlying the Hepatitis C virus (HCV) resistance to interferon alpha (IFN-α) are not fully understood. We used IFN-α resistant HCV replicon cell lines and an infectious HCV cell culture system to elucidate the mechanisms of IFN-α resistance in cell culture. The IFN-α resistance mechanism of the replicon cells were addressed by a complementation study that utilized the full-length plasmid clones of IFN-α receptor 1 (IFNAR1), IFN-α receptor 2 (IFNAR2), Jak1, Tyk2, Stat1, Stat2 and the ISRE- luciferase reporter plasmid. We demonstrated that the expression of the full-length IFNAR1 clone alone restored the defective Jak-Stat signaling as well as Stat1, Stat2 and Stat3 phosphorylation, nuclear translocation and antiviral response against HCV in all IFN-α resistant cell lines (R-15, R-17 and R-24) used in this study. Moreover RT-PCR, Southern blotting and DNA sequence analysis revealed that the cells from both R-15 and R-24 series of IFN-α resistant cells have 58 amino acid deletions in the extracellular sub domain 1 (SD1) of IFNAR1. In addition, cells from the R-17 series have 50 amino acids deletion in the sub domain 4 (SD4) of IFNAR1 protein leading to impaired activation of Tyk2 kinase. Using an infectious HCV cell culture model we show here that viral replication in the infected Huh-7 cells is relatively resistant to exogenous IFN-α. HCV infection itself induces defective Jak-Stat signaling and impairs Stat1 and Stat2 phosphorylation by down regulation of the cell surface expression of IFNAR1 through the endoplasmic reticulum (ER) stress mechanisms. The results of this study suggest that expression of cell surface IFNAR1 is critical for the response of HCV to exogenous IFN-α.     

Release of Interleukin-1α or Interleukin-1β Depends on Mechanism of Cell Death

The cytokine interleukin-1 (IL-1) has two main pro-inflammatory forms, IL-1α and IL-1β, which are central to host responses to infection and to damaging sterile inflammation. Processing of IL-1 precursor proteins to active cytokines commonly occurs through activation of proteases, notably caspases and calpains. These proteases are instrumental in cell death, and inflammation and cell death are closely associated, hence we sought to determine the impact of cell death pathways on IL-1 processing and release. We discovered that apoptotic regulation of caspase-8 specifically induced the processing and release of IL-1β. Conversely, necroptosis caused the processing and release of IL-1α, and this was independent of IL-1β processing and release. These data suggest that the mechanism through which an IL-1-expressing cell dies dictates the nature of the inflammatory mechanism that follows. These insights may allow modification of inflammation through the selective targeting of cell death mechanisms during disease.     

N-terminal phosphorylation of HP1α increases its nucleosome-binding specificity

Heterochromatin protein 1 (HP1) is an evolutionarily conserved chromosomal protein that binds to lysine 9-methylated histone H3 (H3K9me), a hallmark of heterochromatin. Although HP1 phosphorylation has been described in several organisms, the biological implications of this modification remain largely elusive. Here we show that HP1''s phosphorylation has a critical effect on its nucleosome binding properties. By in vitro phosphorylation assays and conventional chromatography, we demonstrated that casein kinase II (CK2) is the kinase primarily responsible for phosphorylating the N-terminus of human HP1α. Pull-down assays using in vitro-reconstituted nucleosomes showed that unmodified HP1α bound H3K9-methylated and H3K9-unmethylated nucleosomes with comparable affinity, whereas CK2-phosphorylated HP1α showed a high specificity for H3K9me3-modified nucleosomes. Electrophoretic mobility shift assays showed that CK2-mediated phosphorylation diminished HP1α''s intrinsic DNA binding, which contributed to its H3K9me-independent nucleosome binding. CK2-mediated phosphorylation had a similar effect on the nucleosome-binding specificity of fly HP1a and S. pombe Swi6. These results suggested that HP1 phosphorylation has an evolutionarily conserved role in HP1''s recognition of H3K9me-marked nucleosomes.     

Tissue-Specific Expression of Neurexin-1α Isoforms in Rat Organs

Russian Journal of Bioorganic Chemistry - Neurexins are a family of synaptic adhesion proteins that play a key role in synapse formation and maintenance. Neurexins undergo extensive alternative...     

The role of PGC-1α in the regulation of skeletal muscle metabolism

The purpose of this review was to provide an understanding of the role of PGC-1α in the regulation of skeletal muscle metabolism and to describe the results of studies on the association of the polymorphism gene PPARGC1A with human muscle performance.     

Interaction of ZPR1 with Translation Elongation Factor-1α in Proliferating Cells

The zinc finger protein ZPR1 is present in the cytoplasm of quiescent mammalian cells and translocates to the nucleus upon treatment with mitogens, including epidermal growth factor (EGF). Homologues of ZPR1 were identified in yeast and mammals. These ZPR1 proteins bind to eukaryotic translation elongation factor-1α (eEF-1α). Studies of mammalian cells demonstrated that EGF treatment induces the interaction of ZPR1 with eEF-1α and the redistribution of both proteins to the nucleus. In the yeast Saccharomyces cerevisiae, genetic analysis demonstrated that ZPR1 is an essential gene. Deletion analysis demonstrated that the NH₂-terminal region of ZPR1 is required for normal growth and that the COOH-terminal region was essential for viability in S. cerevisiae. The yeast ZPR1 protein redistributes from the cytoplasm to the nucleus in response to nutrient stimulation. Disruption of the binding of ZPR1 to eEF-1α by mutational analysis resulted in an accumulation of cells in the G2/M phase of cell cycle and defective growth. Reconstitution of the ZPR1 interaction with eEF-1α restored normal growth. We conclude that ZPR1 is essential for cell viability and that its interaction with eEF-1α contributes to normal cellular proliferation.     

Mapping of the regulatory type Iα and catalytic β subunits of cAMP-dependent protein kinase and interleukin 1α and 1β in the pig

The genes coding for the regulatory type I subunit (PRKAR1A) and the catalytic subunit (PRKACB) of cAMP-dependent protein kinase and the genes for interleukin 1 (IL1A) and interleukin 1 (IL1B) were localized in the pig by means of radioactive in situ hybridization. PRKAR1A was mapped to 12p1.4 and PRKARB to 6q3.1 q3.3. The genes for IL1A and IL1B were both assigned to Chromosome (Chr) 3, in the region q1.2 q1.3 and q1.1 q1.4, respectively. The cDNA nucleotide sequences of these porcine genes were compared with those of human, mouse, and cattle. The location of the genes was discussed in relation to the position of their homologous loci in these mammalian species.