Protein kinase C-alpha regulates insulin action and degradation by interacting with insulin receptor substrate-1 and 14-3-3 epsilon

Protein kinase C (PKC)-alpha exerts a regulatory function on insulin action. We showed by overlay blot that PKCalpha directly binds a 180-kDa protein, corresponding to IRS-1, and a 30-kDa molecular species, identified as 14-3-3epsilon. In intact NIH-3T3 cells overexpressing insulin receptors (3T3-hIR), insulin selectively increased PKCalpha co-precipitation with IRS-1, but not with IRS-2, and with 14-3-3epsilon, but not with other 14-3-3 isoforms. Overexpression of 14-3-3epsilon in 3T3-hIR cells significantly reduced IRS-1-bound PKCalpha activity, without altering IRS-1/PKCalpha co-precipitation. 14-3-3epsilon overexpression also increased insulin-stimulated insulin receptor and IRS-1 tyrosine phosphorylation, followed by increased activation of Raf1, ERK1/2, and Akt/protein kinase B. Insulin-induced glycogen synthase activity and thymidine incorporation were also augmented. Consistently, selective depletion of 14-3-3epsilon by antisense oligonucleotides caused a 3-fold increase of IRS-1-bound PKCalpha activity and a similarly sized reduction of insulin receptor and IRS-1 tyrosine phosphorylation and signaling. In turn, selective inhibition of PKCalpha expression by antisense oligonucleotides reverted the negative effect of 14-3-3epsilon depletion on insulin signaling. Moreover, PKCalpha inhibition was accompanied by a >2-fold decrease of insulin degradation. Similar results were also obtained by overexpressing 14-3-3epsilon. Thus, in NIH-3T3 cells, insulin induces the formation of multimolecular complexes, including IRS-1, PKCalpha, and 14-3-3epsilon. The presence of 14-3-3epsilon in the complex is not necessary for IRS-1/PKCalpha interaction but modulates PKCalpha activity, thereby regulating insulin signaling and degradation.     

Exploring cellular activity of locked nucleic acid-modified triplex-forming oligonucleotides and defining its molecular basis

Triplex-forming oligonucleotides (TFOs), as DNA-binding molecules that recognize specific sequences, offer unique potential for the understanding of processes occurring on DNA and associated functions. They are also powerful DNA recognition elements for the positioning of ubiquitous molecules acting on DNA, such as anticancer drugs. A prerequisite for further development of DNA code-reading molecules including TFOs is their ability to form a complex in a cellular context: their binding affinities must be comparable to those of DNA-associated proteins. To reach this goal, chemically modified TFOs must be developed. In this work, we present triplex-forming properties (kinetics and thermodynamics) and cellular activity of G-containing locked nucleic acid-modified TFOs (TFO/LNAs). In conditions simulating physiological ones, these TFO/LNAs strongly enhanced triplex stability compared with the non-modified TFO or with the pyrimidine TFO/LNA directed against the same oligopyrimidine.oligopurine sequence, mainly by decreasing the dissociation rate constant and conferring an entropic gain. We provide evidence of their biological activity by a triplex-based mechanism, in vitro and in a cellular context, under conditions in which the parent phosphodiester oligonucleotide did not exhibit any inhibitory effect.     

Giant sperm cells with accessory macrotubules in a neuropteran insect

The flagellar axoneme of the atypical spermatozoa (paraspermatozoa) of Mantispa perla (Neuroptera, Planipennia) contains accessory microtubules or rather macrotubules that are 55 nm in diameter and that has a wall consisting of about 40 protofilaments. The sperm tail further contains two giant mitochondrial derivatives, which during spermiogenesis store an electron dense material. The mature spermatozoon has a flattened acrosome and a elliptical nucleus. These giant spermatozoa may furnish nutrients to the functional spermatozoa (euspermatozoa) when they reach the female genital tracts or/and they function in sperm competition filling the spermatheca.     

Histone modifications affect timing of oligodendrocyte progenitor differentiation in the developing rat brain

Timely differentiation of progenitor cells is critical for development. In this study we asked whether global epigenetic mechanisms regulate timing of progenitor cell differentiation into myelin-forming oligodendrocytes in vivo. Histone deacetylation was essential during a specific temporal window of development and was dependent on the enzymatic activity of histone deacetylases, whose expression was detected in the developing corpus callosum. During the first 10 postnatal days, administration of valproic acid (VPA), the specific inhibitor for histone deacetylase activity, resulted in significant hypomyelination with delayed expression of late differentiation markers and retained expression of progenitor markers. Differentiation resumed in VPA-injected rats if a recovery period was allowed. Administration of VPA after myelination onset had no effect on myelin gene expression and was consistent with changes of nucleosomal histones from reversible deacetylation to more stable methylation and chromatin compaction. Together, these data identify global modifications of nucleosomal histones critical for timing of oligodendrocyte differentiation and myelination in the developing corpus callosum.     

{beta}1 Integrin and IL-3R coordinately regulate STAT5 activation and anchorage-dependent proliferation

We previously demonstrated that integrin-dependent adhesion activates STAT5A, a well known target of IL-3-mediated signaling. Here, we show that in endothelial cells the active beta1 integrin constitutively associates with the unphosphorylated IL-3 receptor (IL-3R) beta common subunit. This association is not sufficient for activating downstream signals. Indeed, only upon fibronectin adhesion is Janus Kinase 2 (JAK2) recruited to the beta1 integrin-IL-3R complex and triggers IL-3R beta common phosphorylation, leading to the formation of docking sites for activated STAT5A. These events are IL-3 independent but require the integrity of the IL-3R beta common. IL-3 treatment increases JAK2 activation and STAT5A and STAT5B tyrosine and serine phosphorylation and leads to cell cycle progression in adherent cells. Expression of an inactive STAT5A inhibits cell cycle progression upon IL-3 treatment, identifying integrin-dependent STAT5A activation as a priming event for IL-3-mediated S phase entry. Consistently, overexpression of a constitutive active STAT5A leads to anchorage-independent cell cycle progression. Therefore, these data provide strong evidence that integrin-dependent STAT5A activation controls IL-3-mediated proliferation.     

Clustering of T cell ligands on artificial APC membranes influences T cell activation and protein kinase C theta translocation to the T cell plasma membrane

T cell activation is associated with active clustering of relevant molecules in membrane microdomains defined as the supramolecular activation cluster. The contact area between these regions on the surface of T cells and APC is defined as the immunological synapse. It has been recently shown that preclustering of MHC-peptide complexes in membrane microdomains on the APC surface affects the efficiency of immune synapse formation and the related T cell activation. Disruption of such clusters may reduce the efficiency of stimulation. We describe here an entirely artificial system for Ag-specific, ex vivo stimulation of human polyclonal T cells (artificial APC (aAPC)). aAPC are based on artificial membrane bilayers containing discrete membrane microdomains encompassing T cell ligands (i.e., appropriate MHC-peptide complexes in association with costimulatory molecules). We show here that preclustering of T cell ligands triggered a degree of T cell activation significantly higher than the one achieved when we used either soluble tetramers or aAPC in which MHC-peptide complexes were uniformly distributed within artificial bilayer membranes. This increased efficiency in stimulation was mirrored by increased translocation from the cytoplasm to the membrane of protein kinase theta, a T cell signaling molecule that colocalizes with the TCR within the supramolecular activation cluster, thus indicating efficient engagement of T cell activation pathways. Engineered aAPC may have immediate application for basic and clinical immunology studies pertaining to modulation of T cells ex vivo.     

A His-155 to Tyr polymorphism confers gain-of-function to the human P2X7 receptor of human leukemic lymphocytes

The P2X(7)R is an ATP-gated cation channel expressed in hemopoietic cells that participates in both cell proliferation and apoptosis. Expression and function of the P2X(7)R have been associated with the clinical course of patients affected by chronic lymphocytic leukemia (CLL). Functional variants causing loss-of-function of the P2X(7)R have been identified, namely, polymorphisms 1513A>C (E496A), 1729T>A (I568N), and 946G>A (R307Q). Here we investigated other nonsynonymous polymorphisms located either in the extracellular portion of the receptor, such as the 489C>T (H155Y) variant, or in the long cytoplasmic tail of the receptor, such as the 1068G>A (A348T), 1096C>G (T357S), and 1405A>G (Q460R) variants. P2X(7)R function was monitored by measuring ATP-induced Ca(2+) influx in PBL of patients affected by CLL and in recombinant human embryonic kidney (HEK) 293 cells stably transfected with each single P2X(7) allelic variant. Ca(2+) influx was markedly reduced in association with the 1513C allele, whereas variants located in the same intracellular domain, such as the 1068A, 1096G, or 1405G variants, were associated with a minor functional decrease. Significant Ca(2+) flux increase was observed in lymphocytes from CLL patients bearing the 489C/T and 489T/T genotypes in association with the 1513A/A genotype. Functional analysis in recombinant HEK293 cells expressing P2X(7)R confirmed an increased ATP-dependent activation of the P2X(7) 489T mutant with respect to the wild type receptor, as assessed by both by [Ca(2+)](i) influx and ethidium uptake experiments. These data identify the 489C>T as a gain-of-function polymorphism of the P2X(7)R.     

Neutrophil apoptosis in autoimmune Fas-defective MRL lpr/lpr mice

The apoptosis-defective lpr (fas) mutation in MRL mice causes the early onset of a lupus-like autoimmune disease with concomitant inflammation. In order to analyse the consequences of the impaired Fas-dependent apoptosis on inflammation, the susceptibility to apoptosis of polymorphonuclear leukocytes (PMN), obtained from MRL lpr/lpr mice, has been studied. Peritoneal PMN from lpr/lpr and control (+/+) mice were recruited with a mild inflammatory stimulus. The number of cells collected from the peritoneal cavity of young lpr/lpr mice was comparable to that obtained from age-matched control mice, indicating that PMN homeostasis is maintained regardless of the loss-of-function Fas mutation. Recruited neutrophils were exposed in culture to apoptosis-inducing stimuli. Treatment with agonist anti-Fas antibody increased apoptosis of +/+ PMN, but did not affect lpr/lpr PMN which do not express Fas on their surface. However, lpr/lpr PMN could undergo both spontaneous and stimulus-induced apoptosis in a fashion comparable to or higher than that of control +/+ mice. Analysis of mRNA expression revealed that lpr/lpr PMN have reduced expression of IL-18, whereas IL-1beta, IFNgamma, caspase 1 and caspase 3 are expressed at levels comparable to those of +/+ cells. However, caspase-3-like activity was higher in PMN from lpr/lpr mice than in +/+ cells, and correlated with enhanced apoptosis. It could be concluded that in young, uncompromised lpr/lpr mice, PMN homeostasis is still fully regulated through the involvement of Fas-independent, compensatory, apoptotic mechanisms. This could include an increased participation of caspase 3 in the apoptotic pathway, consequent to enhanced activation of the enzyme and to the decreased production of IL-18, which acts as a competitive caspase 3 substrate.