Protein kinase D promotes activity-dependent AMPA receptor endocytosis in hippocampal neurons.

α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type glutamate receptors (AMPARs) mediate the majority of fast excitatory neurotransmission in the brain. The continuous trafficking of AMPARs into and out of synapses is a core feature of synaptic plasticity, which is considered as the cellular basis of learning and memory. The molecular mechanisms underlying the postsynaptic AMPAR trafficking, however, are still not fully understood. In this work, we demonstrate that the protein kinase D (PKD) family promotes basal and activity-induced AMPAR endocytosis in primary hippocampal neurons. Pharmacological inhibition of PKD increased synaptic levels of GluA1-containing AMPARs, slowed down their endocytic trafficking and increased neuronal network activity. By contrast, ectopic expression of constitutive active PKD decreased the synaptic level of AMPARs, while increasing their colocalization with early endosomes. Our results thus establish an important role for PKD in the regulation of postsynaptic AMPAR trafficking during synaptic plasticity.

Inhibition of Tumor Cell Growth and Cancer Stem Cell Expansion by a Bispecific Antibody Targeting EGFR and HER3.

The frequent activation of HER3 signaling as a resistance mechanism to EGFR-targeted therapy has motivated the development of combination therapies that block more than one receptor tyrosine kinase. Here, we have developed a novel tetravalent, bispecific single-chain diabody-Fc fusion protein targeting EGFR and HER3 (also known as ErbB3) that integrates the antigen-binding sites of a humanized version of cetuximab as well as a recently developed anti-HER3 antibody, IgG 3-43. This bispecific antibody combines the binding and neutralizing properties of the parental antibodies, as observed in biochemical and in vitro two-dimensional and three-dimensional cell culture assays, and gave rise to long-lasting growth suppression in a subcutaneous xenograft head and neck tumor model. In triple-negative breast cancer (TNBC) cell lines, treatment with the bispecific antibody inhibited the proliferation and oncosphere formation efficiency driven by HER3 signaling. In an orthotopic MDA-MB-468 tumor model, this translated into antitumor effects superior to those obtained by the parental antibodies alone or in combination and was associated with a reduced number of cells with stem-like properties. These findings demonstrate that the bispecific antibody efficiently blocks not only TNBC proliferation, but also the survival and expansion of the cancer stem cell population, holding promise for further preclinical development.

The GEF-H1/PKD3 signaling pathway promotes the maintenance of triple-negative breast cancer stem cells.

Protein kinase D3 (PKD3) is upregulated in triple-negative breast cancer (TNBC) and associated with cell proliferation and metastasis development but its precise pro-oncogenic function is unknown. Here we show that PKD3 is required for the maintenance of the TNBC stem cell population. The depletion of PKD3 in MDA-MB-231 cells reduced the cancer stem cell frequency in vitro and tumor initiation potential in vivo. We further provide evidence that the RhoGEF GEF-H1 is upstream of PKD3 activation in TNBC stem cells. Most importantly, pharmacological PKD inhibition in combination with paclitaxel synergistically decreased oncosphere and colony formation efficiency in vitro and tumor recurrence in vivo. Based on our results we propose that targeting the GEF-H1/PKD3 signaling pathway in combination with chemotherapy might provide an effective therapeutic option for TNBC.

The Ability of Nitric Oxide to Lower Intraocular Pressure Is Dependent on Guanylyl Cyclase.

Purpose: While nitric oxide (NO) donors are emerging as treatments for glaucoma, the mechanism by which NO lowers intraocular pressure (IOP) is unclear. NO activates the enzyme guanylyl cyclase (GC) to produce cyclic guanosine monophosphate. We studied the ocular effects of inhaled and topically applied NO gas in mice and lambs, respectively. Methods: IOP and aqueous humor (AqH) outflow were measured in WT and GC-1α subunit null (GC-1-/-) mice. Mice breathed 40 parts per million (ppm) NO in O2 or control gas (N2/O2). We also studied the effect of ocular NO gas exposure (80, 250, 500, and 1000 ppm) on IOP in anesthetized lambs. NO metabolites were measured in AqH and plasma. Results: In awake WT mice, breathing NO for 40 minutes lowered IOP from 14.4 ± 1.9 mm Hg to 10.9 ± 1.0 mm Hg (n = 11, P < 0.001). Comparable results were obtained in anesthetized WT mice (n = 10, P < 0.001). In awake or anesthetized GC-1-/- mice, IOP did not change under similar experimental conditions (P ≥ 0.08, n = 20). Breathing NO increased in vivo outflow facility in WT but not GC-1-/- mice (+13.7 ± 14.6% vs. -12.1 ± 9.4%, n = 4 each, P < 0.05). In lambs, ocular exposure to NO lowered IOP in a dose-dependent manner (-0.43 mm Hg/ppm NO; n = 5 with 40 total measurements; P = 0.04) without producing corneal pathology or altering pulmonary and systemic hemodynamics. After ocular NO exposure, NO metabolites were increased in AqH (n = 8, P < 0.001) but not in plasma. Conclusions: Breathing NO reduced IOP and increased outflow facility in a GC-dependent manner in mice. Exposure of ovine eyes to NO lowers IOP.

Neonatal hypoxia-ischemia in rat increases doublecortin concentration in the cerebrospinal fluid.

Doublecortin (DCX) is a microtubule-associated protein widely used as an indicator of neurogenesis in immunohistochemical analyses of the postmortem adult brain. A recent study reported that DCX can be quantified in the cerebrospinal fluid (CSF) from healthy rats between postnatal day 0 (P0) and P30. However, it is currently unclear whether the concentration of DCX in the CSF (CSF-DCX) may represent a measure of endogenous neurogenesis. To address this question, this study examined the impact of a neonatal hypoxic-ischemic (HI) brain injury, known to induce neurogenesis, on CSF-DCX. HI was elicited at P7 in Sprague-Dawley rat neonates, and CSF was collected serially from the cisterna magna at P5 and P10, or at P10 and P15. A sandwich immunoassay was used to measure CSF-DCX. Brains from P10 neonates were analyzed immunohistochemically for neurogenesis and cell death markers. Mean CSF-DCX was significantly higher in HI- than in sham-exposed animals, at both P10 and P15. In the HI group at P10, CSF-DCX and stroke severity correlated positively. DCX immunoreactivity was increased in the ipsilateral neurogenic niches from the P10 HI brains in comparison with that of shams. The number of proliferative DCX-positive cells was higher in the ipsilateral hippocampal subgranular zone (SGZ) than in the HI contralateral or sham SGZ. Thus, neonatal HI brain injury disrupts the developmental time-course of DCX levels in the CSF. Our data suggest that the increased concentration of DCX in the CSF after neonatal HI is the result of both cellular injury and increased neurogenesis.

Androgen-sensitive hypertension associated with soluble guanylate cyclase-α1 deficiency is mediated by 20-HETE.

Dysregulated nitric oxide (NO) signaling contributes to the pathogenesis of hypertension, a prevalent and often sex-specific risk factor for cardiovascular disease. We previously reported that mice deficient in the α1-subunit of the NO receptor soluble guanylate cyclase (sGCα1 (-/-) mice) display sex- and strain-specific hypertension: male but not female sGCα1 (-/-) mice are hypertensive on an 129S6 (S6) but not a C57BL6/J (B6) background. We aimed to uncover the genetic and molecular basis of the observed sex- and strain-specific blood pressure phenotype. Via linkage analysis, we identified a suggestive quantitative trait locus associated with elevated blood pressure in male sGCα1 (-/-)S6 mice. This locus encompasses Cyp4a12a, encoding the predominant murine synthase of the vasoconstrictor 20-hydroxy-5,8,11,14-eicosatetraenoic acid (20-HETE). Renal expression of Cyp4a12a in mice was associated with genetic background, sex, and testosterone levels. In addition, 20-HETE levels were higher in renal preglomerular microvessels of male sGCα1 (-/-)S6 than of male sGCα1 (-/-)B6 mice. Furthermore, treating male sGCα1 (-/-)S6 mice with the 20-HETE antagonist 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (20-HEDE) lowered blood pressure. Finally, 20-HEDE rescued the genetic background- and testosterone-dependent impairment of acetylcholine-induced relaxation in renal interlobar arteries associated with sGCα1 deficiency. Elevated Cyp4a12a expression and 20-HETE levels render mice susceptible to hypertension and vascular dysfunction in a setting of sGCα1 deficiency. Our data identify Cyp4a12a as a candidate sex-specific blood pressure-modifying gene in the context of deficient NO-sGC signaling.

The Atypical Inhibitor of NF-κB, IκBζ, Controls Macrophage Interleukin-10 Expression.

Macrophages constitute a first line of pathogen defense by triggering a number of inflammatory responses and the secretion of various pro-inflammatory cytokines. Recently, we and others found that IκBζ, an atypical IκB family member and transcriptional coactivator of selected NF-κB target genes, is essential for macrophage expression of a subset of pro-inflammatory cytokines, such as IL-6, IL-12, and CCL2. Despite defective pro-inflammatory cytokine expression, however, IκBζ-deficient mice develop symptoms of chronic inflammation. To elucidate this discrepancy, we analyzed a regulatory role of IκBζ for the expression of anti-inflammatory cytokines and identified IκBζ as an essential activator of IL-10 expression. LPS-challenged peritoneal and bone marrow-derived macrophages from IκBζ-deficient mice revealed strongly decreased transcription and secretion of IL-10 compared with wild-type mice. Moreover, ectopic expression of IκBζ was sufficient to stimulate Il10 transcription. On the molecular level, IκBζ directly activated the Il10 promoter at a proximal κB site and was required for the transcription-enhancing trimethylation of histone 3 at lysine 4. Together, our findings show for the first time the IκBζ-dependent expression of an anti-inflammatory cytokine that is crucial in controlling immune responses.