Downregulation of the α1- and β1-subunit of sGC in Arterial Smooth Muscle Cells of OPSCC Is HPV-Independent

The nitric oxide (NO)-sensitive soluble guanylyl cyclase (sGC) is a heterodimeric enzyme with an α and β subunit. NO binds to heme of the β₁-subunit of sGC, activates the enzyme in the reduced heme iron state in vascular smooth muscle cells (VSMCs), and generates cGMP-inducing vasodilatation and suppression of VSMC proliferation. In the complex tumor milieu with higher levels of reactive oxygen species (ROS), sGC heme iron may become oxidized and insensitive to NO. To change sGC from an NO-insensitive to NO-sensitive state or NO-independent manner, protein expression of sGC in VSMC is required. Whether sGCα₁β₁ exists at the protein level in arterial VSMCs of oropharyngeal squamous cell carcinoma (OPSCC) is unknown. In addition, whether differences in the genetic profile between human papillomavirus (HPV)-positive and HPV-negative OPSCC contributes to the regulation of sGCα₁β₁ is unclear. Therefore, we compared the effects of HPV-positive and HPV-negative OPSCC on the expression of sGCα₁β₁ in arterial VSMCs from tumor-free and tumor-containing regions of human tissue sections using quantitative immunohistochemistry. In comparison to the tumor-free region, we found a decrease in expression of both α₁- and β₁-subunits in the arterial VSMC layer of the tumor-containing areas. The OPSCC-induced significant downregulation of the α₁- and β₁-subunits of sGC in arterial VSMC was HPV-independent. We conclude that the response of sGC to NO in tumor arterial VSMCs may be impaired by oxidation of the heme of the β₁-subunit, and thus, α₁- and β₁-subunits of sGC could be targeted to degradation under oxidative stress in OPSCC in an HPV-independent manner. The degradation of sGCα₁β₁ in VSMCs may result in increased proliferation of VSMCs, promoting tumor arteriogenesis in OPSCC. This can be interrupted by preserving the active heterodimer sGCα₁β₁ in arterial VSMCs.

Evaluating the suitability of nicotinic acetylcholine receptor antibodies for standard immunodetection procedures

Nicotinic acetylcholine receptors play important roles in numerous cognitive processes as well as in several debilitating central nervous system (CNS) disorders. In order to fully elucidate the diverse roles of nicotinic acetylcholine receptors in CNS function and dysfunction, a detailed knowledge of their cellular and subcellular localizations is essential. To date, methods to precisely localize nicotinic acetylcholine receptors in the CNS have predominantly relied on the use of anti-receptor subunit antibodies. Although data obtained by immunohistology and immunoblotting are generally in accordance with ligand binding studies, some discrepancies remain, in particular with electrophysiological findings. In this context, nicotinic acetylcholine receptor subunit-deficient mice should be ideal tools for testing the specificity of subunit-directed antibodies. Here, we used standard protocols for immunohistochemistry and western blotting to examine the antibodies raised against the alpha3-, alpha4-, alpha7-, beta2-, and beta4-nicotinic acetylcholine receptor subunits on brain tissues of the respective knock-out mice. Unexpectedly, for each of the antibodies tested, immunoreactivity was the same in wild-type and knock-out mice. These data imply that, under commonly used conditions, these antibodies are not suited for immunolocalization. Thus, particular caution should be exerted with regards to the experimental approach used to visualize nicotinic acetylcholine receptors in the brain.

Fibroblasts in mechanically stressed collagen lattices assume a "synthetic" phenotype

Fibroblasts are subjected to changes of the mechanical force balance during physiological as well as pathological situations, such as wound healing, development of hypertrophic scars, and fibrogenesis. However, the molecular response and the changes in fibroblast gene expression upon mechanical stimulation remain poorly understood. As an in vitro model, human dermal fibroblasts were cultured within a three-dimensional network of fibrillar collagen either under high (stressed) or low tension (relaxed). cDNA microarray technology in combination with Northern blot analysis led to identification of mechano-responsive genes coding for extracellular matrix proteins, fibrogenic growth factors, protease inhibitors, components of focal adhesions, and the cytoskeleton. Application of biaxial strain to fibroblasts cultured on flexible silicone membranes revealed that the type of strain as well as the properties of the substrate induced different patterns of gene regulation. The transcriptional profile of mechanically induced genes in collagen lattices suggests that mechanical stimuli lead to a "synthetic" fibroblast phenotype characterized by induction of connective tissue synthesis while simultaneously inhibiting matrix degradation.

The Ras/Rac Guanine Nucleotide Exchange Factor Mammalian Son-of-sevenless Interacts with PACSIN 1/Syndapin I, a Regulator of Endocytosis and the Actin Cytoskeleton

Mammalian Son-of-sevenless (mSos) functions as a guanine nucleotide exchange factor for Ras and Rac, thus regulating signaling to mitogen-activated protein kinases and actin dynamics. In the current study, we have identified a new mSos-binding protein of 50 kDa (p50) that interacts with the mSos1 proline-rich domain. Mass spectrometry analysis and immunodepletion studies reveal p50 as PACSIN 1/syndapin I, a Src homology 3 domain-containing protein functioning in endocytosis and regulation of actin dynamics. In addition to PACSIN 1, which is neuron-specific, mSos also interacts with PACSIN 2, which is expressed in neuronal and nonneuronal tissues. PACSIN 2 shows enhanced binding to the mSos proline-rich domain in pull-down assays from brain extracts as compared with lung extracts, suggesting a tissue-specific regulation of the interaction. Proline to leucine mutations within the Src homology 3 domains of PACSIN 1 and 2 abolish their binding to mSos, demonstrating the specificity of the interactions. In situ, PACSIN 1 and mSos1 are co-expressed in growth cones and actin-rich filopodia in hippocampal and dorsal root ganglion neurons, and the two proteins co-immunoprecipitate from brain extracts. Moreover, epidermal growth factor treatment of COS-7 cells causes co-localization of PACSIN 1 and mSos1 in actin-rich membrane ruffles, and their interaction is regulated through epidermal growth factor-stimulated mSos1 phosphorylation. These data suggest that PACSINs may function with mSos1 in regulation of actin dynamics.

Phosphorylation of a synaptic vesicle-associated protein by an inositol hexakisphosphate-regulated protein kinase

Despite the fact that inositol hexakisphosphate (InsP(6)) is the most abundant inositol metabolite in cells, its cellular function has remained an enigma. In the present study, we present the first evidence of a protein kinase identified in rat cerebral cortex/hippocampus that is activated by InsP(6). The substrate for the InsP(6)-regulated protein kinase was found to be the synaptic vesicle-associated protein, pacsin/syndapin I. This brain-specific protein, which is highly enriched at nerve terminals, is proposed to act as a molecular link coupling components of the synaptic vesicle endocytic machinery to the cytoskeleton. We show here that the association between pacsin/syndapin I and dynamin I can be increased by InsP(6)-dependent phosphorylation of pacsin/syndapin I. These data provide a model by which InsP(6)-dependent phosphorylation regulates synaptic vesicle recycling by increasing the interaction between endocytic proteins at the synapse.

All three PACSIN isoforms bind to endocytic proteins and inhibit endocytosis

The PACSINs are a family of cytoplasmic phosphoproteins that play a role in vesicle formation and transport. We report the cloning and cDNA sequencing of PACSIN 3 and the analysis of all three PACSIN isoforms with regard to tissue distribution, ligand binding properties and influence on endocytosis. PACSIN 3 differs from the other family members in having a short proline-rich region and lacking asparagine-proline-phenylalanine motifs. In contrast to the neurospecific PACSIN 1 and the ubiquitously expressed PACSIN 2, PACSIN 3 is mainly detected in lung and muscle tissues. All isoforms potentially oligomerize and bind to dynamin, synaptojanin 1 and N-WASP via their Src homology 3 domains. The PACSIN proteins colocalize with dynamin, but not with clathrin, implying a specific role with a distinct subpopulation of dynamin at defined cellular sites. Transferrin endocytosis is blocked in a dose-dependent manner in cells overexpressing the PACSIN variants, but the inhibitory effect can be abolished by mutating specific amino acid residues in the Src homology 3 domains. These characteristics of the PACSIN protein family suggest a general function in recruitment of the interacting proteins to sites of endocytosis.

PACSIN 2, a novel member of the PACSIN family of cytoplasmic adapter proteins

The PACSIN-related proteins are cytoplasmic adapter proteins with a common arrangement of domains and conserved regions. Here we report the cloning, sequencing, and expression of PACSIN 2, a novel member of the PACSIN protein family and accordingly rename the original PACSIN to PACSIN 1. The sequences of the murine and human cDNAs reveal an open reading frame encoding a putative protein of 486 residues. Despite its high sequence similarity to PACSIN 1, PACSIN 2 is encoded by distinct transcripts in human and mouse, in particular displaying a ubiquitous expression pattern. Immunofluorescence microscopy of PACSIN 2-transfected NIH3T3 fibroblasts reveal a broad, vesicle-like cytoplasmic staining. In contrast to FAP52, another PACSIN-related protein derived from chicken brain, PACSIN 2 could not be detected at focal contacts. Taken together, these findings suggest that PACSIN 2 is a novel PACSIN isoform with similar domain and motif arrangement, but an unrestricted expression pattern, which may participate in the organization of the actin cytoskeleton and the regulation of vesicular traffic.

PACSIN, a brain protein that is upregulated upon differentiation into neuronal cells

To identify genes that are differentially expressed during self-repair processes in mouse brain, we screened a subtracted cDNA library enriched for brain-specific clones. One of these clones, H74, detected a 4.4-kb mRNA predominantly expressed in brain and dorsal root ganglia neurons. Expression increased continuously during the lifespan and the state of differentiation, but decreased after entorhinal-cortex lesion. A full-length cDNA clone was isolated from a cerebellum cDNA library and characterized. Sequence analysis and database search revealed high sequence similarity to FAP52, a protein expressed in focal-adhesion contacts, and uncharacterized Echinococcus and Caenorhabditis elegans gene products. Furthermore, peptide sequences derived from human cDNA fragments showed up to 65% sequence identity at the amino acid level. The presence of a C-terminal src homology 3 (SH3) domain and its phosphorylation by casein kinase 2 (CK2) and protein kinase C (PKC) imply a role in signaling. Here we demonstrate that the gene encodes a phosphoprotein, referred to as PACSIN, with a restricted spatial and temporal expression pattern.

Developmentally regulated mouse gene NK10 encodes a zinc finger repressor protein with differential DNA-binding domains

Using oligonucleotides complementary to the conserved inter-finger region of a variety of previously described zinc finger-encoding genes, a novel mouse gene was cloned and characterized. The gene is localized on chromosome 8 and comprises five exons. Its corresponding mRNA is developmentally regulated in various tissues and includes an open reading frame encoding a protein of 72,422 daltons. It shares amino-terminal homologies with human KRAB (or FPB) boxes, and contains 13 zinc fingers of the C2-H2 type. The NK10 KRAB domains exhibit repressing activity when tested in GAL4 fusion protein assays. Cloning of putative target sequences revealed that the individual domains differentially contribute to zinc-dependent target DNA binding.

Inactivation of the N-CAM gene in mice results in size reduction of the olfactory bulb and deficits in spatial learning

Neural-cell adhesion molecules (N-CAMs) are members of the immunoglobulin superfamily mediating homo- and heterophilic cell-cell interactions. N-CAM exists in various isoforms which are generated by alternative splicing. During embryonic development, N-CAMs are expressed in derivatives of all three germ layers, whereas in the adult animal they are predominantly present in neural tissue. Processes like neurulation, axonal outgrowth, histogenesis of the retina and development of the olfactory system are correlated with the regulated expression of N-CAMs. We show here that N-CAM-deficient mice generated by gene targeting appear healthy and fertile, but adult mutants show a 10% reduction in overall brain weight and a 36% decline in size of the olfactory bulb. N-CAM deficiency coincides with almost total loss of protein-bound alpha-(2,8)-linked polysialic acid, a carbohydrate structure thought to be correlated with neural development and plasticity. The animals showed deficits in spatial learning when tested in the Morris water maze, whereas activity and motor abilities appeared normal.

Ankylosing spondylitis: an autoimmune disease?

Identification of several autoantibodies in serum samples from patients with ankylosing spondylitis or suspected ankylosing spondylitis is reported. Five antibodies associated with ankylosing spondylitis were identified by applying cytoimmunofluorescence and immunoblotting techniques to antigen pools from insect tissue. At least one of these antibodies was found in 82% of serum samples from patients with ankylosing spondylitis. A 36 kD drosophila antigen, which showed the most common and most dominant reaction, was further purified and isolated. Thirty two (34%) of the serum samples from 95 patients with definite ankylosing spondylitis and 12 (28%) of the serum samples from 43 patients with suspected ankylosing spondylitis reacted with this antigen. Antibodies purified from the 36 kD antigen reacted specifically with a 69 kD antigen present in separations of total protein preparations from human lymphocytes and HeLa cells. The 36 kD antibody was not found in 29 patients with rheumatoid arthritis nor in 38 apparently healthy controls. The prevalence of the 36 kD antibody was comparable in HLA-B27 positive and negative patients. In addition, the same immunoreaction was found in patients with so called 'seronegative' spondylarthropathies, particularly of the ankylosing spondylitis-type, suggesting that this antibody is specific for ankylosing spondylitis or other 'seronegative' spondylarthropathies with the typical clinical and radiological changes of ankylosing spondylitis.