Accelerating Socket Repair via WNT3A Curtails Alveolar Ridge Resorption

Tooth extraction triggers alveolar ridge resorption, and when this resorption is extensive, it can complicate subsequent reconstructive procedures that use dental implants. Clinical data demonstrate that the most significant dimensional changes in the ridge occur soon after tooth extraction. Here, we sought to understand whether a correlation existed between the rate at which an extraction socket heals and the extent of alveolar ridge resorption. Maxillary molars were extracted from young and osteoporotic rodents, and quantitative micro-computed tomographic imaging, histology, and immunohistochemistry were used to simultaneously follow socket repair and alveolar ridge resorption. Extraction sockets rapidly filled with new bone via the proliferation and differentiation of Wnt-responsive osteoprogenitor cells and their progeny. At the same time that new bone was being deposited in the socket, tartrate-resistant acid phosphatase-expressing osteoclasts were resorbing the ridge. Significantly faster socket repair in young animals was associated with significantly more Wnt-responsive osteoprogenitor cells and their progeny as compared with osteoporotic animals. Delivery of WNT3A to the extraction sockets of osteoporotic animals restored the number of Wnt-responsive cells and their progeny back to levels seen in young healthy animals and accelerated socket repair in osteoporotic animals back to rates seen in the young. In cases where the extraction socket was treated with WNT3A, alveolar ridge resorption was significantly reduced. These data demonstrate a causal link between enhancing socket repair via WNT3A and preserving alveolar ridge dimensions following tooth extraction.

Interspecies Comparison of Alveolar Bone Biology, Part I: Morphology and Physiology of Pristine Bone

INTRODUCTION

Few interspecies comparisons of alveolar bone have been documented, and this knowledge gap raises questions about which animal models most accurately represent human dental conditions or responses to surgical interventions.

OBJECTIVES

The objective of this study was to employ state-of-the-art quantitative metrics to directly assess and compare the structural and functional characteristics of alveolar bone among humans, mini pigs, rats, and mice.

METHODS

The same anatomic location (i.e., the posterior maxillae) was analyzed in all species via micro-computed tomographic imaging, followed by quantitative analyses, coupled with histology and immunohistochemistry. Bone remodeling was evaluated with alkaline phosphatase activity and tartrate-resistant acid phosphatase staining to identify osteoblast and osteoclast activities. In vivo fluorochrome labeling was used as a means to assess mineral apposition rates.

RESULTS

Collectively, these analyses demonstrated that bone volume differed among the species, while bone mineral density was equal. All species showed a similar density of alveolar osteocytes, with a highly conserved pattern of collagen organization. Collagen maturation was equal among mouse, rat, and mini pig. Bone remodeling was a shared feature among the species, with morphologically indistinguishable hemiosteonal appearances, osteocytic perilacunar remodeling, and similar mineral apposition rates in alveolar bone.

CONCLUSIONS

Our analyses demonstrated equivalencies among the 4 species in a plurality of the biological features of alveolar bone. Despite contradictory results from older studies, we found no evidence for the superiority of pig models over rodent models in representing human bone biology.

KNOWLEDGE TRANSFER STATEMENT

Animal models are extensively used to evaluate bone tissue engineering strategies, yet there are few state-of-the-art studies that rigorously compare and quantify the factors influencing selection of a given animal model. Consequently, there is an urgent need to assess preclinical animal models for their predictive value to dental research. Our article addresses this knowledge gap and, in doing so, provides a foundation for more effective standardization among animal models commonly used in dentistry.

WNT3A accelerates delayed alveolar bone repair in ovariectomized mice

Our goal was to evaluate alveolar bone healing in OVX mice, and to assess the functional utility of a WNT-based treatment to accelerate healing in mice with an osteoporotic-like bony phenotype.

INTRODUCTION

Is osteoporosis a risk factor for dental procedures? This relatively simple question is exceedingly difficult to answer in a clinical setting, for two reasons. First, as an age-related disease, osteoporosis is frequently accompanied by age-related co-morbidities that can contribute to slower tissue repair. Second, the intervals at which alveolar bone repair are assessed in a clinical study are often measured in months to years. This study aimed to evaluate alveolar bone repair in ovariectomized (OVX) mice and provide preclinical evidence to support a WNT-based treatment to accelerate alveolar bone formation.

METHODS

OVX was performed in young mice to produce an osteoporotic-like bone phenotype. Thereafter, the rate of extraction socket healing and osteotomy repair was assessed. A liposomal WNT3A treatment was tested for its ability to promote alveolar bone formation in this OVX-induced model of bone loss.

RESULTS

Bone loss was observed throughout the murine skeleton, including the maxilla, and mirrored the pattern of bone loss observed in aged mice. Injuries to the alveolar bone, including tooth extraction and osteotomy site preparation, both healed significantly slower than the same injuries produced in young controls. Given sufficient time, however, all injuries eventually healed. In OVX mice, osteotomies healed significantly faster if they were treated with L-WNT3A.

CONCLUSIONS

Alveolar bone injuries heal slower in OVX mice that exhibit an osteoporotic-like phenotype. The rate of alveolar bone repair in OVX mice can be significantly promoted with local delivery of L-WNT3A.

Osteoporotic Changes in the Periodontium Impair Alveolar Bone Healing

Osteoporosis is associated with decreased bone density and increased bone fragility, but how this disease affects alveolar bone healing is not clear. The objective of this study was to determine the extent to which osteoporosis affects the jaw skeleton and then to evaluate possible mechanisms whereby an osteoporotic phenotype might affect the rate of alveolar bone healing following tooth extraction. Using an ovariectomized mouse model coupled with micro-computed tomographic imaging, histologic, molecular, and cellular assays, we first demonstrated that the appendicular and jaw skeletons both develop osteoporotic phenotypes. Next, we demonstrated that osteoporotic mice exhibit atrophy of the periodontal ligament (PDL) and that this atrophy was accompanied by a reduction in the pool of osteoprogenitor cells in the PDL. The paucity of PDL-derived osteoprogenitor cells in osteoporotic mice was associated with significantly slower extraction socket healing. Collectively, these analyses demonstrate that the jaw skeleton is susceptible to the untoward effects of osteoporosis that manifest as thinner, more porous alveolar bone, PDL thinning, and slower bone repair. These findings have potential clinical significance for older osteopenic patients undergoing reconstructive procedures.

Molecular Basis for Periodontal Ligament Adaptation to In Vivo Loading

A soft food diet leads to changes in the periodontal ligament (PDL). These changes, which have been recognized for more than a century, are ascribed to alterations in mechanical loading. While these adaptive responses have been well characterized, the molecular, cellular, and mechanical mechanisms underlying the changes have not. Here, we implicate Wnt signaling in the pathoetiology of PDL responses to underloading. We show that Wnt-responsive cells and their progeny in the PDL space exhibit a burst in proliferation in response to mastication. If an animal is fed a soft diet from the time of weaning, then this burst in Wnt-responsive cell proliferation is quelled; as a consequence, both the PDL and the surrounding alveolar bone undergo atrophy. Returning these animals to a hard food diet restores the Wnt signaling in PDL. These data provide, for the first time, a molecular mechanism underlying the adaptive response of the PDL to loading.

A Comparative Assessment of Implant Site Viability in Humans and Rats

Our long-term objective is to devise methods to improve osteotomy site preparation and, in doing so, facilitate implant osseointegration. As a first step in this process, we developed a standardized oral osteotomy model in ovariectomized rats. There were 2 unique features to this model: first, the rats exhibited an osteopenic phenotype, reminiscent of the bone health that has been reported for the average dental implant patient population. Second, osteotomies were produced in healed tooth extraction sites and therefore represented the placement of most implants in patients. Commercially available drills were then used to produce osteotomies in a patient cohort and in the rat model. Molecular, cellular, and histologic analyses demonstrated a close alignment between the responses of human and rodent alveolar bone to osteotomy site preparation. Most notably in both patients and rats, all drilling tools created a zone of dead and dying osteocytes around the osteotomy. In rat tissues, which could be collected at multiple time points after osteotomy, the fate of the dead alveolar bone was followed. Over the course of a week, osteoclast activity was responsible for resorbing the necrotic bone, which in turn stimulated the deposition of a new bone matrix by osteoblasts. Collectively, these analyses support the use of an ovariectomy surgery rat model to gain insights into the response of human bone to osteotomy site preparation. The data also suggest that reducing the zone of osteocyte death will improve osteotomy site viability, leading to faster new bone formation around implants.

SspA, an outer membrane protein, is highly induced under salt-stressed conditions and is essential for growth under salt-stressed aerobic conditions in Rhodobacter sphaeroides f. sp. denitrificans

We have previously shown that an outer membrane protein, SspA, is prominently induced by salt stress in a photosynthetic bacterium, Rhodobacter sphaeroides f. sp. denitrificans IL106 (R. sphaeroides). In this study, we investigated the physiological role of SspA under various stress conditions. Using recombinant SspA expressed in Escherichia coli as an antigen, the polyclonal antiserum of SspA was prepared. Western blot analysis demonstrated that SspA was highly induced by salt stress under both anaerobic and aerobic conditions. SspA was also induced, but to a lesser extent, by osmotic and acid stress. It is reduced under heat and cold compared to non-stressed conditions. While sspA-disrupted R. sphaeroides grew normally under anaerobic conditions in either the presence or absence of stress, it displayed significantly retarded growth under aerobic conditions in the dark, especially when osmotic or salt stress were imposed. In addition, the sspA disruptant, but not the wild type, formed cell aggregates when grown under both anaerobic and aerobic conditions, and this phenotype was significantly enhanced under salt-stressed aerobic conditions. Together, our findings suggest that SspA is critical under salt-stressed, aerobic growth conditions.

Molecular cloning, functional expression and characterization of p15, a novel fungal protein with potent neurite-inducing activity in PC12 cells

p15 is a novel fungal protein which induces neurite outgrowth and neuronal differentiation of PC12 cells. In the present study, we report molecular cloning, functional expression and characterization of the gene encoding p15. The deduced amino acid sequence suggested that p15 is synthesized as a precursor with 31 extra amino-terminal amino acids including a putative signal sequence, and 20 carboxy-terminal amino acids, in addition to the 118 amino acids-long mature region with neurite-inducing activity. From the poly(A)(+) RNA prepared from the producing fungal strain, a cDNA fragment encoding the mature region of p15 was amplified and His(6)-tagged recombinant p15 was produced in Escherichia coli. The recombinant protein purified by a single step on Ni(2+) agarose column chromatography exhibited comparable specific activity as native p15 in the PC12 neurite extension assay. The effect of His(6)-p15 was blocked by nicardipine, suggesting that Ca(2+) influx through the L-type Ca(2+) channels is essential for its neurite-inducing activity. In addition, mutational analysis of His(6)-p15 demonstrated that both intramolecular disulfide bonds are essential for its biological activity.

Cloning and sequence analysis of cnaA gene encoding the catalytic subunit of calcineurin from Aspergillus oryzae

Calcineurin has been implicated in ion-homeostasis, stress adaptation in yeast and for hyphal growth in filamentous fungi. Genomic DNA and cDNA encoding the catalytic subunit of calcineurin (cnaA) were isolated from Aspergillus oryzae. The cnaA open reading frame extended to 1727 bp and encoded a putative protein of 514 amino acids. Comparative analysis of the nucleotide sequence of cnaA genomic DNA and cDNA confirmed the presence of three introns and a highly conserved calmodulin binding domain. The deduced amino acid sequence was homologous to calcineurin A from Aspergillus nidulans (92%), Neurospora crassa (84%), human (67%), Saccharomyces cerevisiae (58%) and Schizosaccharomyces pombe (54%). Further, A. oryzae cnaA cDNA complemented S. cerevisiae calcineurin disruptant strain (Deltacmp1 Deltacmp2), which was not viable in the presence of high concentrations of NaCl (1.2 M) and at alkaline pH 8.5.

PIP kinase Igamma is the major PI(4,5)P(2) synthesizing enzyme at the synapse

Disruption of the presynaptically enriched polyphosphoinositide phosphatase synaptojanin 1 leads to an increase of clathrin-coated intermediates and of polymerized actin at endocytic zones of nerve terminals. These changes correlate with elevated levels of PI(4,5)P(2) in neurons. We report that phosphatidylinositol phosphate kinase type Igamma (PIPKIgamma), a major brain PI(4)P 5-kinase, is concentrated at synapses. Synaptojanin 1 and PIPKIgamma antagonize each other in the recruitment of clathrin coats to lipid membranes. Like synaptojanin 1 and other proteins involved in endocytosis, PIPKIgamma undergoes stimulation-dependent dephosphorylation. These results implicate PIPKIgamma in the synthesis of a PI(4,5)P(2) pool that acts as a positive regulator of clathrin coat recruitment and actin function at the synapse.

Cloning and characterization of Aspergillus nidulans vpsA gene which is involved in vacuolar biogenesis

In Saccharomyces cerevisiae, vacuoles play very important roles in pH and osmotic regulation, protein degradation and storage of amino acids, small ions as well as polyphosphates. In filamentous fungi, however, little is known about vacuolar functions at a molecular level. In this paper, we report the isolation of the vpsA gene from the filamentous fungus Aspergillus nidulans as a homologue of the VPS1 gene of S. cerevisiae which encodes a dynamin-related protein. The vpsA gene encodes a polypeptide consisting of 696 amino acids that is nearly 60% homologous to the S. cerevisiae Vps1. Similar to Vps1, VpsA contains a highly conserved tripartite GTPase domain but lacks the pleckstrin homology domain and proline-rich region. The vpsA disruptant shows poor growth and contains highly fragmented vacuoles. These results suggest that A. nidulans VpsA functions in the vacuolar biogenesis.

Characterization of a novel fungal protein, p15, which induces neuronal differentiation of PC12 cells

In our previous paper, we reported that a 15 kDa protein (p15) produced by a fungus, genus Helicosporium, enhanced NGF-induced neurite outgrowth from PC12 cells. Here we further characterized the actions of p15. The complete amino acid sequence of p15 was determined and it was shown to be a hydrophilic protein composed of 118 amino acid residues with two intramolecular disulfide bridges. p15-induced neurite outgrowth was blocked by the depletion of extracellular Ca(2+) in the culture medium and was significantly inhibited by L-type Ca(2+) channel inhibitor nicardipine. p15 stimulated Src kinase and MAPK activities, and neurite outgrowth was not observed in srcDN2, a dominant negative c-src(K295R)-expressing cell line, and was significantly reduced in RasN17-expressing cells. These results suggest that p15 stimulates neurite outgrowth through the potentiation of L-type Ca(2+) channels, thereby activating the Src-Ras-MAPK cascade.

S19159, a modulator of neurite outgrowth produced by the ascomycete Preussia aemulans. I. Producing strain, fermentation, isolation and biological activity

A modulator of neurite outgrowth, designated S19159, was isolated from the fermentation broth of fungal strain 19159. This fungus was identified as the loculoascomycete, Preussia aemulans (Rehm) von Arx. In the presence of S19159, the number of neurites extending from the cell bodies of cerebral cortical neurons was markedly reduced. The effect of S19159 was observed specifically in neurons from the central nervous system. The compound exhibited similar activities on cultured cortical, hippocampal and cerebeller neurons but was without detectable effect on dorsal root ganglion neurons and PC12 cells.

Multidrug resistance phenotype conferred by overexpressing bfr2+/pad1+/sks1+ or pap1+ genes and mediated by bfr1+ gene product, a structural and functional homologue of P-glycoprotein in Schizosaccharomyces pombe

We investigated the mechanism of multidrug resistance conferred by overexpression of bfr2+/pad1+/sks1+ or pap1+ genes of Schizosaccharomyces pombe. Overexpression of bfr2+ did not confer multidrug resistance on a pap1-disrupted strain. In a mutant with bfr1+ (a putative membrane transporter which belongs to the ATP-binding cassette superfamily) disrupted, overexpression of either bfr2+ or pap1+ did not confer multidrug resistance. These findings suggest that bfr1+ acts as the most downstream effector of the multidrug resistance conferred by bfr2+ and pap1+ genes.

Identification and characterization of porcine NP-190, a novel protein that is specifically expressed in the axonal membrane during the embryonic period

To identify and analyze the function of proteins expressed in the growth cones, we have screened monoclonal antibodies raised against the preparation of the growth cone particles derived from fetal porcine brains and found a novel neuronal antigen, termed NP-190. Biochemical characterization of NP-190 demonstrated that it was an integral membrane protein with an apparent molecular weight of 190 kDa and that it was mainly expressed in fetal brains. Homologous antigens with molecular weights of 200 and 170 kDa were also identified in the fetal brain extracts of chickens and rats, respectively. Immunoblot experiments of brain extracts from chickens and rats in various stages of development indicated that the expression of NP-190 homologs was developmentally regulated; it began to appear and increased in the embryonic stage, then decreased to very low level in the adult brains. Immunostaining of cultured primary of neurons from the embryonic day 18 rat cerebral cortex demonstrated that rat NP-190 homolog localized in the cell bodies, axons and growth cones, but not in dendrites. Partial amino acid sequence analysis of affinity-purified NP-190 from fetal porcine brains demonstrated that it was a novel protein. These results suggest that NP-190 plays a distinct role in brain development.

Isolation and characterization of a 230 kDa protein (p230) specifically expressed in fetal brains: its involvement in neurite outgrowth from rat cerebral cortex neurons grown on monolayer of astrocytes

By screening with monoclonal antibodies (mAbs) raised against growth cone membrane fraction from fetal porcine brains, we have identified a 230 kDa antigen, termed p230. Western blot analysis of extracts from various tissues demonstrated that p230 is specifically expressed in brains, in which its expression is temporally restricted; it was especially prominent in the embryonic and the early postnatal stage, and decreased to subdetectable levels in the adult brain. Further characterization of p230 revealed that it is a peripherally-membrane associated, cell surface protein produced by astrocytes. Neurite outgrowth of E18 rat cerebral cortex neurons cultured on a monolayer of astrocytes was significantly reduced in the presence of anti-p230 polyclonal antibody. Partial amino acid sequences of p230 purified from fetal porcine brains were highly homologous to an extracellular matrix protein, tenascin-C. These lines of evidence suggest that p230, a tenascin-C-like molecule present in fetal porcine brains, plays important roles during early brain development, particularly in growth cone guidance.

Purification and characterization of a 15 kDa protein (p15) produced by Helicosporium that exhibits distinct effects on neurite outgrowth from cortical neurons and PC12 cells

We have found that a 15 kDa protein (p15) produced by a fungus of Helicosporium genus induced characteristic morphological changes on neurites extending from rat cerebral cortex neurons in culture. In the presence of p15, neurite elongation from cortical neurons was markedly inhibited, and they extended short, slender, and less branched neurites. Laminin-induced promotion of neurite outgrowth was also dramatically suppressed. In contrast, p15 promoted nerve growth factor (NGF)-induced neurite outgrowth from PC12 cells, although treatment of cells with p15 alone had little effect. Partial amino acid sequence analysis of p15 revealed that it had limited homology to plant lectins. These results suggest that the mechanism of neurite outgrowth was considerably different between cortical neurons and PC12 cells and that p15 modulated neurite outgrowth in cell type-specific manners.

bfr1+, a novel gene of Schizosaccharomyces pombe which confers brefeldin A resistance, is structurally related to the ATP-binding cassette superfamily

We have isolated a Schizosaccharomyces pombe gene, bfr1+, which on a multicopy plasmid vector, pDB248', confers resistance to brefeldin A (BFA), an inhibitor of intracellular protein transport. This gene encodes a novel protein of 1,531 amino acids with an intramolecular duplicated structure, each half containing a single ATP-binding consensus sequence and a set of six transmembrane sequences. This structural characteristic of bfr1+ protein resembles that of mammalian P-glycoprotein, which, by exporting a variety of anticancer drugs, has been shown to be responsible for multidrug resistance in tumor cells. Consistent with this is that S. pombe cells harboring bfr1+ on pDB248' are resistant to actinomycin D, cerulenin, and cytochalasin B, as well as to BFA. The relative positions of the ATP-binding sequences and the clusters of transmembrane sequences within the bfr1+ protein are, however, transposed in comparison with those in P-glycoprotein; the bfr1+ protein has N-terminal ATP-binding sequence followed by transmembrane segments in each half of the molecule. The bfr1+ protein exhibited significant homology in primary and secondary structures with two recently identified multidrug resistance gene products of Saccharomyces cerevisiae, Snq2 and Sts1/Pdr5/Ydr1. The bfr1+ gene is not essential for cell growth or mating, but a delta bfr1 mutant exhibited hypersensitivity to BFA. We propose that the bfr1+ protein is another member of the ATP-binding cassette superfamily and serves as an efflux pump of various antibiotics.

A cdc2-related kinase PSSALRE/cdk5 is homologous with the 30 kDa subunit of tau protein kinase II, a proline-directed protein kinase associated with microtubule

We previously reported that tau protein kinase II (TPKII) from bovine brain was composed of 30 kDa and 23 kDa subunits. The 30 kDa subunit of TPKII can be regarded as a catalytic subunit because of its ATP-binding activity. Antibodies directed against TPKII-phosphorylated tau also reacted with tau phosphorylated by cdc2 kinase obtained from starfish oocytes, indicating that TPKII and cdc2 kinase phosphorylate the same sites. We determined the amino acid sequence of the 30 kDa subunit and found it to be homologous with a cdc2-related kinase, PSSALRE/cdk5. Moreover, an antibody against PSSALRE/cdk5 reacted with the 30 kDa subunit. These results indicate that the 30 kDa subunit of TPKII is bovine homologue of PSSALRE/cdk5. Expression of the 30 kDa subunit mRNA was enhanced in juvenile rat brain. This result supports our previous hypothesis that the kinase works actively in juvenile brain.

Glycogen synthase kinase 3 beta is identical to tau protein kinase I generating several epitopes of paired helical filaments

We previously reported that tau protein kinase I (TPKI) induced normal tau protein into a state of paired helical filaments (PHF); this is further confirmed here by immunoblot analysis using several antibodies. We also present the amino acid sequence of TPKI, which is identical to glycogen synthase kinase 3 beta (GSK3 beta). Moreover, we found that TPKI activity was inseparable from GSK3 activity throughout the purification procedure. These results indicate that TPKI is identical to GSK3 beta.

Tau protein kinase II is involved in the regulation of the normal phosphorylation state of tau protein

To study the phosphorylation state of tau in vivo, we have prepared antisera by immunizing rabbits with synthetic phosphopeptides containing phosphoamino acids at specific sites that are potential targets for tau protein kinase II. Immunoblot experiments using these antisera demonstrated that tau in microtubule-associated proteins is phosphorylated at Ser144 and at Ser315. Almost all tau variants separated on two-dimensional gel electrophoresis were phosphorylated at Ser144 and nearly one-half of them at Ser315. Phosphorylation at Ser144 and at Thr147 of tau isolated from heat-stable brain extracts was shown to be developmentally regulated, with the highest level of phosphorylation found at postnatal week 1. In vitro phosphorylation of tau by tau protein kinase I, a kinase responsible for abnormal phosphorylation of tau found in paired helical filaments of patients with Alzheimer's disease, was enhanced by prior phosphorylation of tau by tau protein kinase II. Thus, we suggest that tau protein kinase II is indirectly involved, at least in part, in the regulation of the phosphorylation state of tau in neuronal cells.

Phosphorylation sites on tau by tau protein kinase I, a bovine derived kinase generating an epitope of paired helical filaments

Tau protein kinase I (TPKI) isolated from bovine brain has been determined to phosphorylate tau at four distinct sites by detecting modified Ser and Thr residues with protein sequencer. Ser199, Thr231, Ser396 and Ser413 were all found to have been phosphorylated by TPKI (numbering of amino acids was done in relation to the longest human tau [Neuron, 3 (1989) 519-526]). These phosphorylations generate an epitope of PHF (paired helical filaments) and eliminate the recognition of tau by the monoclonal antibody, tau-1. These results suggested that TPKI might be responsible for at least some of the phosphorylation of tau to induce PHF formation.

Tau protein kinase I converts normal tau protein into A68-like component of paired helical filaments

From bovine brain microtubules we purified tau protein kinase I (TPKI, Mr 45,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and tau protein kinase II (TPKII) whose activity was attributed to a 30-kDa protein on SDS-PAGE by affinity-labeling using an ATP analog. Both kinases were activated by tubulin. TPKII, but not TPKI, phosphorylated tau fragment peptides previously used for detection of a Ser/ThrPro kinase activity. Therefore, TPKII was considered to be the Ser/ThrPro kinase. TPKI was more effective than TPKII for producing the decrease of tau-1 immunoreactivity and mobility shift of tau on SDS-PAGE. Moreover, TPKI, but not TPKII nor other well-known protein kinases, generated an epitope present on paired helical filaments. These findings suggested that tau phosphorylated by TPKI resembled A-68, a component of paired helical filaments.

Brefeldin A blocks an early stage of protein transport in Candida albicans

Brefeldin A (BFA) inhibited in a dose-dependent manner secretion of the cell-surface enzyme acid phosphatase (APase) into the periplasm of Candida albicans and caused intracellular accumulation of enzyme protein. Cells grown in the presence of BFA became more dense, implying that cell-surface growth was also blocked by BFA treatment. The APase that was accumulated intracellularly migrated faster on SDS-PAGE, suggesting less N-linked glycosylation compared with the mature, periplasmic APase produced in the absence of BFA. Pulse-chase experiments and gel-filtration of oligosaccharides released by Endo H treatment suggested that the core-glycosylated precursor form of APase accumulated in the presence of BFA. These results strongly suggested that endoplasmic reticulum (ER)-to-Golgi transport in C. albicans was inhibited by BFA. Aberrant membrane structures were observed in BFA-treated cells. Within 1 h of BFA removal these structures were replaced with rough ER membranes, suggesting that the accumulated membranes were derived from the ER.