High hydrostatic pressure induces immunogenic cell death in human tumor cells

Recent studies have identified molecular events characteristic of immunogenic cell death (ICD), including surface exposure of calreticulin (CRT), the heat shock proteins HSP70 and HSP90, the release of high-mobility group box protein 1 (HMGB1) and the release of ATP from dying cells. We investigated the potential of high hydrostatic pressure (HHP) to induce ICD in human tumor cells. HHP induced the rapid expression of HSP70, HSP90 and CRT on the cell surface. HHP also induced the release of HMGB1 and ATP. The interaction of dendritic cells (DCs) with HHP-treated tumor cells led to a more rapid rate of DC phagocytosis, upregulation of CD83, CD86 and HLA-DR and the release of interleukin IL-6, IL-12p70 and TNF-α. DCs pulsed with tumor cells killed by HHP induced high numbers of tumor-specific T cells. DCs pulsed with HHP-treated tumor cells also induced the lowest number of regulatory T cells. In addition, we found that the key features of the endoplasmic reticulum stress-mediated apoptotic pathway, such as reactive oxygen species production, phosphorylation of the translation initiation factor eIF2α and activation of caspase-8, were activated by HHP treatment. Therefore, HHP acts as a reliable and potent inducer of ICD in human tumor cells.

NF-kappa B activation in tumor necrosis factor alpha-stimulated neutrophils is mediated by protein kinase Cdelta. Correlation to nuclear Ikappa Balpha

The transcription factor NF-kappaB is critical for the expression of multiple genes involved in inflammatory responses and apoptosis. However, the signal transduction pathways regulating NF-kappaB activation in human neutrophils in response to stimulation with tumor necrosis factor-alpha (TNFalpha) are undefined. Since recent studies implicated activation of NF-kappaB as well as protein kinase C-delta (PKCdelta) in neutrophil apoptosis, we investigated involvement of PKCdelta in the activation of NF-kappaB in TNFalpha-stimulated neutrophils. Specific inhibition of PKCdelta by rottlerin prevented IkappaBalpha degradation and NF-kappaB activation in TNFalpha-stimulated neutrophils. This regulation of NF-kappaB activation by PKCdelta was specific only for TNFalpha signaling, since lipopolysaccharide- or interleukin-1beta-induced NF-kappaB activation and IkappaBalpha degradation were not inhibited by rottlerin. In addition, we show that in human neutrophils, but not monocytes, IkappaBalpha localizes in significant amounts in the nucleus of unstimulated cells, and the amount of IkappaBalpha in the nucleus, as well as in the cytoplasm, correlates with the NF-kappaB DNA binding. These results suggest that in human neutrophils, the presence of IkappaBalpha in the nucleus may function as a safeguard against initiation of NF-kappaB dependent transcription of pro-inflammatory and anti-apoptotic genes, and represents a distinct and novel mechanism of NF-kappaB regulation.

Activation of nuclear factor-kappaB and its suppression by dexamethasone in polymorphonuclear leukocytes: newborn versus adult

Polymorphonuclear leukocytes (PMN) of the newborn, to a greater extent than those of the adult, have the ability to amplify PMN recruitment to an inflammatory site by their own release of IL-8, and this process is inhibited by dexamethasone. The aim of the present study was to determine whether the regulation of nuclear factor-kappaB (NF-kappaB) could explain the previous observations. NF-kappaB is a transcription factor pivotal for expression of genes encoding inflammatory cytokines such as IL-8, but NF-kappaB has not been previously studied in the PMN of the newborn. NF-kappaB activation was measured by an electrophoretic mobility shift assay in nuclear extracts prepared from PMN isolated from adults and cord blood from newborns. Two distinct molecular forms of NF-kappaB were identified after tumor necrosis factor-alpha stimulation; this included the previously characterized p50/65 heterodimer and a newly identified p50/50 homodimer. Both NF-kappaB dimers were activated by tumor necrosis factor-alpha to significantly higher levels in the neutrophil of the newborn versus adult. An additional new finding was that pretreatment of PMN with dexamethasone (10(-7) M, therapeutic range) inhibited activation of both NF-kappaB complexes in both the newborn and the adult PMN. We conclude that the increased activation of NF-kappaB by the PMN of the newborn may play an important role in neonatal inflammatory reactions. Eventually, specific targeting of NF-kappaB activation in the neutrophil may be an effective molecular approach for the treatment of neutrophil-mediated disorders in the newborn.

Development of the intestinal SGLT1 transporter in rats

Glucose absorption from the small intestine is largely mediated via the sodium-coupled glucose transporter (SGLT1). The goal of this study was to investigate the ontogenesis of the SGLT1, using the rat as an animal model at three stages of development: during lactation, at weaning, and at physiologic maturity. The techniques involved upper small intestinal perfusions with solutions containing 200 mM glucose and 50 mM NaCl, with or without 1 mM phloridzin (Phl), as an inhibitor of SGLT1. Molecular expression of the SGLT1 was also investigated via Western blot analysis from intestinal specimens of the three growth periods. Glucose absorption in weanling rats, in the absence of Phl, was several times higher than in sucklings and approximately double that of mature animals, and the effects of Phl were the greatest in weanlings. Furthermore, the physiologic data correlate to the molecular analysis of the SGLT1 which showed an increase in expression of the SGLT1 in both the weanlings and the adults compared to the sucklings. At all three stages of development Phl abolished Na absorption, and in sucklings there was a net outflow of Na. Due to the coupling between Na and water transport, net water absorption and the influx/efflux ratio, a more sensitive indicator of changes in unidirectional fluid movement, were similarly affected by Phl at the three stages of development. Net water absorption was highest in weanling animals. These findings are consistent with an early development of SGLT1 in rat small intestine and an apparent burst of activity at weaning. Less than complete maturity of other absorptive mechansims is occurring at this time.

Regulation of phosphatidylinositol 4-phosphate 5-kinase from Schizosaccharomyces pombe by casein kinase I

Phosphatidylinositol ()P 5-kinase (PtdIns(4)P 5-kinase) catalyzes the last step in the synthesis of phosphatidylinositol 4, 5-bisphosphate (PtdIns(4,5)P2). PtdIns(4,5)P2 is a precursor of diacylglycerol and inositol 1,4,5-trisphosphate and is also involved in regulation of actin cytoskeleton remodeling and membrane traffic. To satisfy such varied demands in several aspects of cell physiology, synthesis of PtdIns(4,5)P2 must be stringently regulated. In this paper we describe extraction, purification, and characterization of PtdIns(4)P 5-kinase from the plasma membranes of Schizosaccharomyces pombe. We also provide evidence that PtdIns(4)P 5-kinase is phosphorylated and inactivated by Cki1, the S. pombe homolog of casein kinase I. Phosphorylation by Cki1 in vitro decreases the activity of PtdIns(4)P 5-kinase. In addition, and most importantly, overexpression of Cki1 in S. pombe results in a reduced synthesis of PtdIns(4,5)P2 and in a lower activity of PtdIns(4)P 5-kinase associated with the plasma membrane. These results suggest that PtdIns(4)P 5-kinase is a target of Cki1 in S. pombe and that Cki1 is involved in regulation of PtdIns(4, 5)P2 synthesis by phosphorylating and inactivating PtdIns(4)P 5-kinase.

A domain distinct from nucleoplasmin's nuclear localization sequence influences its transport

We constructed mutants of the prototypical, nuclear-accumulating protein nucleoplasmin and used them in both in vivo and in vitro nuclear transport assays to search for transport-influencing domains distinct from this protein's recognized nuclear localization sequence. We identified the polyglutamic acid tract on the amino flank of the nuclear localization sequence as being involved in two stages of nuclear transport. This poly-glu tract is required for the facilitated translocation of nucleoplasmin through the nuclear pore complex, and it also enhances the subsequent binding of nucleoplasmin within the nucleus.

Distinct phosphorylation sites differentially influence facilitated transport of an NLS-protein and its subsequent intranuclear binding

We measured the nuclear transport of radiolabeled fusion proteins consisting of variants of the Simian Virus 40 large T antigen's nuclear localization sequence region linked to beta-galactosidase, itself a cytoplasmic protein. We microinjected the fusion protein variants into the cytoplasm of living Xenopus oocytes or supplied them to the surface of oil-isolated oocyte nuclei via paired beads or cytoplasm. Presence of the cdc2 kinase site (124T) on the amino flank of the nuclear localization sequence (126PKKKRKV132) greatly enhances facilitated transport through the nuclear pore complex; additional presence of the casein kinase II site (112S) enhances subsequent intranuclear binding.

Intranuclear binding of nucleoplasmin

Many proteins--including not only structural proteins, but also enzymes, hormone receptors, and other transcription factors--accumulate to much higher nuclear than cytoplasmic concentrations. Nuclear localization sequences or signals (NLSs) within their primary structures entrain specific transport of these proteins through the nuclear pore complexes. This transport process is energy-dependent, but evidence for a true active transport mechanism is not conclusive. An alternative mechanism--facilitated transport of NLS proteins followed by their intranuclear binding--has been implicated by experiments with oil-isolated nuclei. However, there has been no agreement as to a role for binding in the in vivo nuclear accumulation of NLS-containing proteins. We demonstrate herein that a prototypical NLS protein, nucleoplasmin (Np), binds within the nucleus of the living Xenopus oocyte and that this binding accounts for its nuclear accumulation.

Nucleoplasmin associates with and is phosphorylated by casein kinase II

Nucleoplasmin is a phosphorylated nuclear-accumulating protein. We report herein that the kinetics of its cytoplasm-->nucleus transport are affected by its degree of phosphorylation. Therefore, we sought to identify any protein kinase which specifically associates with nucleoplasmin. We discovered that nucleoplasmin co-isolates by two independent methods (immunoabsorption and chromatography) in a complex including a kinase which phosphorylates nucleoplasmin. The co-purifying kinase is casein kinase II-like because: (i) it phosphorylates casein; (ii) its phospho-transferase activity can be competed out by GTP; (iii) it is stimulated by polylysine; and (iv) it is inhibited by heparin. Moreover, a polyclonal antibody to the alpha (38 kDa) and alpha' (36 kDa) catalytic subunits of casein kinase II specifically recognizes 38 and 36 kDa polypeptides in the nucleoplasmin-complex, and a specific inhibitor of casein kinase II inhibits nucleoplasmin's nuclear transport. Additionally, we found that phosphorylation of nucleoplasmin by its associated casein kinase II is strongly inhibited by histones and that, in addition to nucleoplasmin, another protein (p100) in the nucleoplasmin-complex is phosphorylated by casein kinase II.

An NLS is sufficient to engage facilitated translocation by the nuclear pore complex and subsequent intranuclear binding

We investigated the nuclear transport of a fusion protein consisting of a nuclear localization signal linked to beta-galactosidase, normally a cytoplasmic protein. We microinjected the radiolabeled fusion protein into the cytoplasm of living Xenopus oocytes or supplied it directly to the surface of the oil-isolated oocyte nucleus and measured its transport into the nucleus. Our data confirm that a nuclear localization signal is sufficient to entrain a protein's facilitated transport through the nuclear pore complex and its subsequent nuclear accumulation. Moreover, nuclear envelope micropuncture experiments determine that the fusion protein's accumulation results from its intranuclear binding, demonstrating that no specific region of a transported protein--other than the nuclear localization signal itself--is required for facilitated transport and intranuclear binding. Finally, we present evidence that the intranuclear binding of a transported protein requires not only its nuclear localization signal, but also its prior facilitated transport through the nuclear pore complex.

Nucleoplasmin uptake by facilitated transport and intranuclear binding

Specific proteins are selectively translocated into the cell nucleus and accumulated therein, but the molecular mechanisms underlying this fundamental eukaryotic transport process remain obscure. We have employed a new experimental system with notable advantages for resolving protein translocation and accumulation mechanisms. Individual nuclei are isolated from oocytes under mineral oil and conjoined under the oil with either an aqueous bead or a similar volume of oocyte cytoplasm to form closed transport pairs. Using these pairs one can (i) present transportant proteins via the bead or cytoplasm to a minimally disturbed nucleus, (ii) monitor the intactness of the nuclear envelope, and (iii) separate pairs at various times after formation and measure the amount of transportant in each compartment. In addition, it is uniquely possible with these pairs to determine whether or not a transportant's concentration gradient constitutes a chemical activity gradient. This is done by puncturing the envelope, thus eliminating its normal sieving restrictions on diffusion, and measuring the effect on the transportant distributions. We demonstrate that a prototypical nuclear-accumulating protein, nucleoplasmin (Np), is translocated through the nuclear pore complex by a mechanism of facilitated transport, rather than active transport. We further show that Np's high accumulation results from subsequent intranuclear binding. Np's facilitated transport and intranuclear binding are both ATP-dependent, and the latter requires cytoplasmic protein(s).