Xylosylated-proteoglycan-induced Golgi alterations

Synthesis, Antimicrobial and Mutagenic Activity of a New Class of d-Xylopyranosides

Eight N-[2-(2',3',4'-tri-O-acetyl-α/β-d-xylopyranosyloxy)ethyl]ammonium bromides, a new class of d-xylopyranosides containing a quaternary ammonium aglycone, were obtained. Their complete structure was confirmed using NMR spectroscopy (¹H, ¹³C, COSY and HSQC) and high-resolution mass spectrometry (HRMS). An antimicrobial activity against fungi (Candida albicans, Candida glabrata) and bacteria (Staphylococcus aureus, Escherichia coli) and a mutagenic Ames test with Salmonella typhimurium TA 98 strain were performed for the obtained compounds. The greatest activity against the tested microorganisms was shown by glycosides with the longest (octyl) hydrocarbon chain in ammonium salt. None of the tested compounds exhibited mutagenic activity in the Ames test.

Endoplasmic reticulum and Golgi stress in microcephaly

Microcephaly is a neurodevelopmental condition characterized by a small brain size associated with intellectual deficiency in most cases and is one of the most frequent clinical sign encountered in neurodevelopmental disorders. It can result from a wide range of environmental insults occurring during pregnancy or postnatally, as well as from various genetic causes and represents a highly heterogeneous condition. However, several lines of evidence highlight a compromised mode of division of the cortical precursor cells during neurogenesis, affecting neural commitment or survival as one of the common mechanisms leading to a limited production of neurons and associated with the most severe forms of congenital microcephaly. In this context, the emergence of the endoplasmic reticulum (ER) and the Golgi apparatus as key guardians of cellular homeostasis, especially through the regulation of proteostasis, has raised the hypothesis that pathological ER and/or Golgi stress could contribute significantly to cortical impairments eliciting microcephaly. In this review, we discuss recent findings implicating ER and Golgi stress responses in early brain development and provide an overview of microcephaly-associated genes involved in these pathways.

PGSE Is a Novel Enhancer Regulating the Proteoglycan Pathway of the Mammalian Golgi Stress Response

The Golgi stress response is a homeostatic mechanism that augments the functional capacity of the Golgi apparatus when Golgi function becomes insufficient (Golgi stress). Three response pathways of the Golgi stress response have been identified in mammalian cells, the TFE3, HSP47 and CREB3 pathways, which augment the capacity of specific Golgi functions such as N-glycosylation, anti-apoptotic activity and pro-apoptotic activity, respectively. On the contrary, glycosylation of proteoglycans (PGs) is another important function of the Golgi, although the response pathway upregulating expression of glycosylation enzymes for PGs in response to Golgi stress remains unknown. Here, we found that expression of glycosylation enzymes for PGs was induced upon insufficiency of PG glycosylation capacity in the Golgi (PG-Golgi stress), and that transcriptional induction of genes encoding glycosylation enzymes for PGs was independent of the known Golgi stress response pathways and ER stress response. Promoter analyses of genes encoding these glycosylation enzymes revealed the novel enhancer elements PGSE-A and PGSE-B (the consensus sequences are CCGGGGCGGGGCG and TTTTACAATTGGTC, respectively), which regulate their transcriptional induction upon PG-Golgi stress. From these observations, the response pathway we discovered is a novel Golgi stress response pathway, which we have named the PG pathway.Key words: Golgi stress, proteoglycan, ER stress, organelle zone, organelle autoregulation.

TFE3, HSP47, and CREB3 Pathways of the Mammalian Golgi Stress Response

The capacity of each organelle in eukaryotic cells is tightly regulated in accordance with cellular demands by specific regulatory systems, which are generically termed organelle autoregulation. The Golgi stress response is one of the systems of organelle autoregulation and it augments the capacity of Golgi function if this becomes insufficient (Golgi stress). Recently, several pathways of the mammalian Golgi stress response have been identified, specifically the TFE3, HSP47, and CREB3 pathways. This review summarizes the essential parts of the Golgi stress response from the perspective of the organelle autoregulation.

TFE3 is a bHLH-ZIP-type transcription factor that regulates the mammalian Golgi stress response

The Golgi stress response is a mechanism by which, under conditions of insufficient Golgi function (Golgi stress), the transcription of Golgi-related genes is upregulated through an enhancer, the Golgi apparatus stress response element (GASE), in order to maintain homeostasis in the Golgi. The molecular mechanisms associated with GASE remain to be clarified. Here, we identified TFE3 as a GASE-binding transcription factor. TFE3 was phosphorylated and retained in the cytoplasm in normal growth conditions, whereas it was dephosphorylated, translocated to the nucleus and activated Golgi-related genes through GASE under conditions of Golgi stress, e.g. in response to inhibition of oligosaccharide processing in the Golgi apparatus. From these observations, we concluded that the TFE3-GASE pathway is one of the regulatory pathways of the mammalian Golgi stress response, which regulates the expression of glycosylation-related proteins in response to insufficiency of glycosylation in the Golgi apparatus.

Hepatocyte extracellular matrix modulates expression of growth factors and growth factor receptors in human colon cancer cells

We investigated the role of hepatocyte extracellular matrix (ECM) on the growth of human colon cancer cell lines. We cultured four cell lines with different liver-colonizing potential on ECM derived from primary rat hepatocyte cultures. We investigated the effect of ECM on cell proliferation, clonal growth, and expression of growth factors and growth factor receptors. The highly metastatic cells showed better clonal growth and produced larger colonies on ECM. The proliferation of all colon cancer cell lines was enhanced on hepatocyte ECM, yet inhibited on fibroblast ECM. Screening of autocrine growth factors and receptors showed that the cells expressed growth factors and receptors of the EGF family: EGF receptor, erb-B2, amphiregulin, and cripto. The expression of cripto mRNA, but not of amphiregulin, was induced in KM12SM cells grown on ECM. All colon cancer cell lines grown on ECM showed increased expression of erb-B2. The effect of ECM on erb-B2 expression was mediated by the heparin chains of heparin proteoglycan. ECM from hepatocytes grown in the presence of nitrophenyl-beta-D-xylopyrannoside or sodium chlorate, which prevent formation of heparin proteoglycan, as well as ECM treated with heparinase, had no effect on erb-B2 expression. Our studies suggest a role for liver ECM as a determinant of colon cancer metastasis. Liver ECM acts, in part, via induction of members of the EGF family of growth factors and their receptors.

Mechanisms of proteinuria in noninflammatory glomerular diseases

Neither the initiating factors nor the proximate causes of injury that produce proteinuria in nephrotic syndrome have been clearly defined. Immune mechanisms have been postulated in minimal-change nephrotic syndrome (MCNS), focal segmental glomerular sclerosis (FSGS), and glomerular sclerosis associated with human immunodeficiency virus (HIV) infection. Circulating factors have been proposed in MCNS and FSGS, although no specific mediator has been identified. Prompt remission of proteinuria following steroid treatment and the presence of altered immune responsiveness in patients with MCNS have been used to support the participation of an immune mechanism in the pathogenesis of MCNS. Both FSGS and HIV-related nephropathy are usually steroid-resistant. Immune mechanisms are postulated in FSGS because of early recurrence after transplantation, and in HIV-related nephropathy because of the numerous associated immune abnormalities. Experimental models of nephrotic syndrome based on neutralization of glomerular charge, toxic injury to podocytes, injection of antibodies to glomerular components, or abnormalities in transgenic mice have been used to define mechanisms of glomerular injury. This review summarizes physiologic and immunologic abnormalities in MCNS, FSGS, and HIV-associated nephropathy and in several experimental models of nephrotic syndrome, and outlines the immunologic mechanisms and cellular reactions that may be responsible for glomerular dysfunction in these entities.

Effects of p-nitrophenyl-beta-D-xylopyranoside (beta-D-xyloside) on the androgen-induced growth of the lateral prostate of the prepubertally castrated guinea pig

The aim of this study was to examine the effects of beta-D-xyloside (XYL), a compound which interferes with stromal proteoglycan (PG) synthesis, on androgen induced growth of the lateral prostate (LP). Young male guinea pigs were castrated at 3 weeks of age and divided into three groups 6 weeks after castration. In group one, the animals were injected subcutaneously daily with 80 mg/kg of XYL, followed 3 days later by a daily dose of 10 mg/kg of dihydrotestosterone (DHT) for 2 more weeks. The second group served as control and received DHT only. In the third group, animals were treated first with XYL, like those in group one, and then followed by DHT alone for 2 weeks to check reversibility of the XYL effect. At the end of the experiment, the lateral prostate was removed and processed for morphological and cytochemical examination. The results showed that XYL inhibited the DHT stimulated growth of the lateral prostate. The fibroblasts showed a dilated granular endoplasmic reticulum filled with granular substances. In the interstitial spaces, there was a drastic increase in Cuprolinic Blue (CB) positive filaments and polygonal granules believed to be PGs or glycosaminoglycans (GAGs). Their number was much greater than the control. The distribution and density of the collagen fibers appeared similar to the control. The secretory alveoli were lined by epithelium with few secretory granules of low electron density and a larger number of clear vesicles. There was a slight reduction in glycoconjugate reactivities in the epithelial cells. The lectin binding patterns and the structural features were comparable between the control and recovery groups, indicating the XYL effects were reversible. The results suggest that stromal PG biosynthesis may play a role in epithelial function and an altered stromal matrix would hamper the effects of DHT on the target organ.

Morphological differentiation and proteoglycan synthesis regulate Alzheimer amyloid precursor protein processing in PC-12 and human astrocyte cultures

A morphologically differentiated strain of rat pheochromocytoma (PC-12H) metabolically labeled with [35S]methionine and incubated with a phorbol ester displayed reduced 140-kDa and increased 15 kDa bands relative to cells incubated without phorbol ester after immunoprecipitation with antisera elicited by the C-terminal peptide of the Alzheimer amyloid precursor protein (APP). These bands correspond to glycosylated full length APP and a C-terminal fragment previously reported by Anderson et al. (Neurosci. Lett. 120:126-128, 1991) to result from a cleavage within the amyloidotic A4 region of APP, which releases a 120 kDa extracellular fragment. The 15 kDa fragment, not immunoprecipitated with an antisera elicited by the N-terminal portion of A4 amyloid, is nonamyloidogenic. Incubation of these cells with p-nitrophenylxyloside, known to inhibit proteoglycan formation, also increased this nonamyloidogenic cleavage of APP. In contrast to these results, an undifferentiated low passage PC-12-L strain constitutively displayed rapid nonamyloidogenic APP cleavage. Incubation of PC-12-L with phorbol ester did not affect the relative abundance of 140 or 15 kDa bands. Growth of PC-12-L with 7 S NGF or dibutyryl cAMP resulted in increased morphological differentiation and decreased APP cleavage which was now phorbol-inducible. Similar analyses of dividing and senescent human astrocytes and normal and F-AD fibroblasts indicate 5-fold lower rates of mid-A4 APP cleavage. Phorbol esters decreased the 140 kDa APP band without affecting the intensity of the 15 kDa band in these cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Decreased de novo synthesis of proteoglycans in drug-induced renal cystic disease

Cellular and extracellular (tubular basement membrane, TBM) alterations in the proteoglycans (PGs) of the rat renal tubules in diphenylthiazole-induced cystic disease were investigated. The PGs of normal and cystic kidneys were labeled with [35S]sulfate in an organ-perfusion system. Extracted cellular and TBM PGs were characterized by Sepharose CL-6B chromatography before or after treatment with heparitinase (degrades heparan sulfate) or chondroitinase ABC (degrades chondroitin sulfate). Total radioactivities in cellular, TBM, and medium fractions of cystic kidneys were reduced by factors of 9, 7, and 3, respectively. The PGs obtained from cystic and normal kidneys had similar profiles, namely, two peaks of radioactivity with Kav values of 0.26 (Mr = 130,000-150,000) and 0.40 (Mr = 50,000-55,000). The peaks had variable proportions of radioactivity for cellular and TBM fractions. Besides heparan sulfate, an additional 15-20% of chondroitin sulfate was synthesized in all three fractions obtained from cystic kidneys. The PGs synthesized by cystic kidneys had lower charge-density characteristics as compared to controls by DEAE-Sephacel chromatography. The medium fractions contained mostly glycosaminoglycan chains (Kav = 0.47, Mr = 24,000-26,000) of heparan sulfate. Autoradiograms of tissue samples revealed approximately 50% and approximately 60% decreases of grain densities over the cellular and TBM compartments, respectively. This decrease in de novo PG synthesis may have some relationship in the pathogenesis of polycystic kidney disease.

Nephritogenicity of proteoglycans. II. A model of immune complex nephritis

Antibodies to glomerular basement membrane, heparan sulfate-proteoglycans are nephrotoxic but possess a weak nephritogenic potential. In order to enhance the nephritogenic potential, the antibodies were intravenously administered into rats presensitized with heterologous rabbit IgG. This resulted in the integration of heterologous and autologous phases, the two phases characteristic of the traditional model of nephrotoxic serum nephritis. The presensitization caused a dramatic shift in the binding characteristics of the heterologous antibodies between the kidney and lymphoid tissues. A proliferative form of immune complex glomerulonephritis associated with a remarkable proteinuric response was observed. In addition, a moderate degree of hematuria was noted as well. The proteinuria was largely complement-dependent and may possibly be cell-mediated as well. The proteinuria became severe with increasing production of host IgG antibodies and with their subsequent sequestration in the glomeruli. The predominant glomerular lesions were in the form of epimembranous/subepithelial immune deposits, which became more frequent with timely increasing titer of host autologous IgG antibodies. These findings indicate that antibodies to heparan sulfate-proteoglycan, an authentic component of the basement membrane, are capable of mediating a glomerular injury with acquisition of nephritogenic potential in an appropriate environment of the host. At present, it seems that this is the sole constituent of the basement membrane whose antibodies are capable of inducing an immune complex nephritis.

Changes in heparan sulfate correlate with increased glomerular permeability

The glomerular capillary wall functions as both a size-selective and charge-selective barrier. Heparan sulfate is known to be an important component of the charge-selective barrier to filtration of polyanions. We studied the alterations in both the charge and size selectivity barriers in a model of experimental membranous nephropathy in the rabbit. The fractional clearance of both charged and uncharged dextrans compared to inulin was measured. Sulfate incorporation into glycosaminoglycans was measured and the glomerular heparan sulfate was isolated and biochemically characterized. Membranous nephropathy in the rabbit was induced with daily injections of cationic bovine serum albumin. After three weeks of injection animals had 735 +/- 196 mg/24 hours of protein excretion. There was no change in [35S] incorporation in 24 hours by experimental animals, 440 +/- 91 DPM/mg dry weight of glomeruli, N = 9 versus 410 +/- 98, N = 11 in controls. The percentage of [35S] incorporated into heparan sulfate versus chondroitin sulfate was decreased, 60% +/- 3 versus 79% +/- 2, P less than 0.001. Heparan sulfate from membranous nephropathy eluted from ion exchange chromatography in a lower molarity salt, indicating a lower effective charge. Fractional clearance of neutral dextrans was significantly increased in membranous nephropathy for dextrans greater than 48 A, while fractional clearance of dextran sulfates was significantly increased compared to controls for dextrans greater than 32 A. Thus, in membranous nephropathy there is loss of both charge selectivity and size selectivity. The loss of charge selectivity correlated with a change in the structure of the glomerular heparan sulfate.(ABSTRACT TRUNCATED AT 250 WORDS)

Status of glomerular proteoglycans in aminonucleoside nephrosis

Status of glomerular proteoglycans (PGs) in puromycin aminonucleoside nephrosis was investigated. Rats were made nephrotic and sacrificed 0, 7, 14, and 21 days later. Maximal proteinuric response was observed between 7 and 14 days. Prior to sacrifice, they received injections of conjugated or unconjugated anti-heparan-sulfate-proteoglycan antibody, directed against its core protein (Mr = 18,000). Their kidneys were processed for direct and indirect immunofluorescence, immunoperoxidase, tannic-acid staining, and tissue autoradiography (ARG). By tannic-acid staining, antibody binding sites identical to the anionic sites described previously were discovered. No qualitative differences were observed by these immunohistochemical techniques. Quantitative tissue ARG did not reveal any statistical differences in the binding of antibody between the control and nephrotic groups. For de novo biosynthetic studies, rats were sacrificed on day 10. Their kidneys were utilized for labeling of basement membrane PGs by employing [35S]-sulfate as the precursor product. Tissue ARG, as well as biochemical studies, were performed on the radiolabeled glomeruli. PGs were extracted with 4 M GuCl and characterized by Sepharose CL-6B and DEAE-Sephacel chromatography. There was an overall increase in the total incorporated radioactivities in the glomerular and media fractions. No differences were observed in the macromolecular size characteristics of intact PGs and glycosaminoglycan chains of either glomerular or media fractions. However, an increase in the charge-density characteristics was observed in PGs of the nephrotic group. By tissue ARG, an increase in the grain densities over the basement membrane and mesangial matrices of the glomerulus was noted. These data indicate that the intact PGs, their chains and core protein do not undergo significant biochemical alterations; however, de novo synthesized PGs have higher charge-density characteristics which may be related to a higher degree of sulfation that occurs during the course of aminonucleoside nephrosis.

The subcellular sites of sulfation of mouse thyrotropin and free alpha subunits: studies employing subcellular fractionation and inhibitors of the intracellular translocation of proteins

To determine the subcellular sites of sulfation of thyrotropin (TSH) and free alpha-subunits, mouse thyrotropic tumor minces were incubated simultaneously with [3H]Met and [35S]SO4 for 1 or 3h, homogenized, and fractionated by discontinuous sucrose gradient ultracentrifugation. Dual-labeled TSH or free alpha-subunits were immunoprecipitated, and analyzed by SDS-gel electrophoresis. Endoglycosidase F released all [35S], but little [3H], from the dual-labeled species, indicating that [35S]SO4 was incorporated into oligosaccharides of TSH and free alpha-subunits. Both [35S]TSH and [35S] free alpha-subunits were predominantly in Golgi fractions at 1 and 3 h, but small amounts were also detected in fractions enriched in rough endoplasmic reticulum (RER). Similar distributions of [35S]SO4-labeled species were noted in cell fractions prepared from mouse pituitaries. Pituitaries from hypothyroid mice were incubated with [3H]Met and [35S]SO4 for 2 h, then chased for 4 or 16 h in the absence or presence of 2 uM monensin (Mon) or 10 uM carboxyl cyanide m-chlorophenylhydrazone (CCCP). At 4h, release into the medium of [3H]TSH was inhibited 59% and 86% by Mon and CCCP, respectively; release of [35S]TSH was inhibited 28% and 46%. At 4h, release of [3H]free alpha-subunits was inhibited 58% and 81% by these drugs, respectively; release of [35S]free alpha-subunits was inhibited 6% and 50%. Thus, Mon and CCCP inhibited the release of each [3H] species more than the [35S] species, indicating that most sulfation occurred in Golgi.