Neonatal rat submandibular gland protein SMG-A and parotid secretory protein are alternatively regulated members of a salivary protein multigene family

The parotid secretory protein BPIFA2 is a salivary surfactant that affects lipopolysaccharide action

NEW FINDINGS

What is the central question of this study? The salivary protein BPIFA2 binds lipopolysaccharide, but its physiological function is not known. This study uses a new knockout mouse model to explore the physiological role of BPIFA2 in the oral cavity and systemic physiology. What is the main finding and its importance? BPIFA2 is a crucial surfactant in mouse saliva. In its absence, saliva exhibits the surface tension of water. Depletion of BPIFA2 affects salivary and ingested lipopolysaccharide and leads to systemic sequelae that include increased insulin secretion and metabolomic changes. These results suggest that the lipopolysaccharide-binding activity of BPIFA2 affects the activity of ingested lipopolysaccharide in the intestine and that BPIFA2 depletion causes mild metabolic endotoxaemia.

ABSTRACT

Saliva plays important roles in the mastication, swallowing and digestion of food, speech and lubrication of the oral mucosa, antimicrobial and anti-inflammatory activities, and the control of body temperature in grooming animals. The salivary protein BPIFA [BPI fold containing family A member 2; former names: parotid secretory protein (PSP), SPLUN2 and C20orf70] is related to lipid-binding and lipopolysaccharide (LPS)-binding proteins expressed in the mucosa. Indeed, BPIFA2 binds LPS, but the physiological role of BPIFA2 remains to be determined. To address this question, Bpifa2 knockout (Bpifa2^{tm1(KOMP)Vlcg} ) (KO) mice were phenotyped, with emphasis on the saliva and salivary glands. Stimulated whole saliva collected from KO mice was less able to spread on a hydrophobic surface than wild-type saliva, and the surface tension of KO saliva was close to that of water. These data suggest that BPIFA2 is a salivary surfactant that is mainly responsible for the low surface tension of mouse saliva. The reduced surfactant activity of KO saliva did not affect consumption of dry food or grooming, but saliva from KO mice contained less LPS than wild-type saliva. Indeed, mice lacking BPIFA2 responded to ingested LPS with an increased stool frequency, suggesting that BPIFA2 plays a role in the solubilization and activity of ingested LPS. Consistent with these findings, BPIFA2-depleted mice also showed increased insulin secretion and metabolomic changes that were consistent with a mild endotoxaemia. These results support the distal physiological function of a salivary protein and reinforce the connection between oral biology and systemic disease.

Design and Validation of Anti-inflammatory Peptides from Human Parotid Secretory Protein

Parotid secretory protein (PSP) and palate-lung-nasal epithelium clone (PLUNC) are novel secretory proteins that are expressed in the oral cavity and upper airways. Both proteins are related to bactericidal/permeability increasing protein (BPI). Cationic peptides derived from BPI exhibit anti-inflammatory activity. To test if PSP (C20orf70 gene product) also contains anti-inflammatory peptides, we designed 3 cationic peptides based on the predicted structure of PSP and known active regions of BPI. Each peptide inhibited the lipopolysaccharide (LPS)-stimulated secretion of TNFα from RAW 264.7 macrophage cells. At 200 μg/mL, the peptide GK-7 exhibited inhibition similar to that achieved with 10 μg/mL of polymyxin B. PSP peptides directly inhibited the binding of LPS to LPS-binding protein. The cationic peptide Substance P had no inhibitory effect in these assays, confirming the specificity of the PSP peptides. These findings suggest that PSP peptides can serve as templates for the design of novel anti-inflammatory peptides.

Isolation, biochemical characterization and anti-bacterial activity of BPIFA2 protein

OBJECTIVE

Human BPIFA2 (parotid secretory protein) is a ubiquitous soluble salivary protein, which belongs to the PLUNC family of proteins. Having sequence similarity to bactericidal/permeability-increasing protein and lipopolysaccharide-binding protein, PLUNC proteins are probably involved in local antibacterial response at mucosal sites, such as oral cavity. The aim of the study was to isolate and characterize human BPIFA2.

DESIGN

In this paper, we report one-step affinity chromatography method for BPIFA2 purification from whole human saliva. The isolated BPIFA2 was identified by trypsin mass fingerprinting and characterized by electrophoretic methods. Antibacterial activity of BPIFA2 against model microorganism Pseudomonas aeruginosa was shown in minimum inhibitory concentration and time kill study assays.

RESULTS

The protein showed microheterogeneity, both in molecular weight and pI value. BPIFA2 inhibited the growth of P. aeruginosa in microgram concentration range determined by minimum inhibitory concentration assay. In the time kill study, 32μg/mL BPIFA2 showed clear bactericidal activity and did not cause any aggregation of bacteria.

CONCLUSION

Affinity chromatography is well suited for isolation of functional BPIFA2 with a potent bactericidal activity against P. aeruginosa.

Systematic nomenclature for the PLUNC/PSP/BSP30/SMGB proteins as a subfamily of the BPI fold-containing superfamily

We present the BPIFAn/BPIFBn systematic nomenclature for the PLUNC (palate lung and nasal epithelium clone)/PSP (parotid secretory protein)/BSP30 (bovine salivary protein 30)/SMGB (submandibular gland protein B) family of proteins, based on an adaptation of the SPLUNCn (short PLUNCn)/LPLUNCn (large PLUNCn) nomenclature. The nomenclature is applied to a set of 102 sequences which we believe represent the current reliable data for BPIFA/BPIFB proteins across all species, including marsupials and birds. The nomenclature will be implemented by the HGNC (HUGO Gene Nomenclature Committee).

Dual host-defence functions of SPLUNC2/PSP and synthetic peptides derived from the protein

PSP (parotid secretory protein)/SPLUNC2 (short palate, lung and nasal epithelium clone 2) is expressed in human salivary glands and saliva. The protein exists as an N-glycosylated and non-glycosylated form and both appear to induce agglutination of bacteria, a major antibacterial function for salivary proteins. Both forms of PSP/SPLUNC2 bind LPS (lipopolysaccharide), suggesting that the protein may also play an anti-inflammatory role. Based on the predicted structure of PSP/SPLUNC2 and the location of known antibacterial and anti-inflammatory peptides in BPI (bactericidal/permeability-increasing protein) and LBP (LPS-binding protein), we designed GL13NH2 and GL13K, synthetic peptides that capture these proposed functions of PSP/SPLUNC2. GL13NH3 agglutinates bacteria, leading to increased clearance by macrophages and reduced spread of infection in a plant model. GL13K kills bacteria with a minimal inhibitory concentration of 5-10 μg/ml, kills bacteria in biofilm and retains activity in 150 mM NaCl and 50% saliva. Both peptides block endotoxin action, but only GL13K appears to bind endotoxin. The peptides do not cause haemolysis, haemagglutination in serum, inhibit mammalian cell proliferation or induce an inflammatory response in macrophages. These results suggest that the GL13NH2 and the modified peptide GL13K capture the biological activity of PSP/SPLUNC2 and can serve as lead compounds for the development of novel antimicrobial and anti-inflammatory peptides.

Human parotid secretory protein is a lipopolysaccharide-binding protein: identification of an anti-inflammatory peptide domain

Parotid secretory protein (PSP) (C20orf70) is a salivary protein of unknown function. The protein belongs to the palate, lung, and nasal epithelium clone (PLUNC) family of mucosal secretory proteins that are predicted to be structurally similar to lipid-binding and host-defense proteins including bactericidal/permeability-increasing protein and lipopolysaccharide-binding protein. However, the PLUNC proteins exhibit significant sequence variation and different biological functions have been proposed for different family members. This study tested the functional implications of the proposed similarity of PSP to the acute phase protein lipopolysaccharide-binding protein (LBP). PSP was identified in human saliva and was soluble in 70% ethanol, as shown for other PLUNC proteins. PSP binds lipopolysaccharide and can be eluted by non-ionic detergent, but not by urea or high salt. A synthetic PSP peptide, GL13NH2, which corresponds to a lipopolysaccharide-inhibiting peptide from LBP, inhibited the binding of lipopolysaccharide to both PSP and lipopolysaccharide-binding protein. Peptides from other regions of PSP and the control peptide polymyxin B showed no effect on the binding of PSP to lipopolysaccharide. GL13NH2 also inhibited lipopolysaccharide-stimulated secretion of tumor necrosis factor from macrophages. The other PSP peptides had no effect in this assay. PSP peptides had no or only minor effect on macrophage cell viability. These results indicate that PSP is a lipopolysaccharide-binding protein that is functionally related to LBP, as suggested by their predicted structural similarities.

Regeneration of acinar cells following ligation of rat submandibular gland retraces the embryonic-perinatal pathway of cytodifferentiation

Rat submandibular gland can regenerate following ligation-induced atrophy, eventually recovering its normal morphology and function. Previous studies have suggested that the regeneration process implies both self-proliferation of existing acini and formation of new acinar cells. One hypothesis is that new acinar cells may differentiate from the ductal cells in a similar fashion to the process of cytodifferentiation occurring during submandibular glandular development. In this study atrophy was induced, under recovery anaesthesia, by applying a metal clip on the main duct of the submandibular gland without including the chorda lingual nerve. After 2 weeks the duct was deligated for 3, 5 or 7 days or 8 weeks and the glands collected. Tissue was prepared for immunohistochemistry, biochemical analysis and RNA extraction. The histology of the regenerated glands shows several normal-looking acini, which have regained their glycoprotein content (AB/PAS positive), data also confirmed by biochemical analysis (SDS-PAGE/PAS). Regenerating tissue was characterized by the presence of embryonic-like branched structures ending with AB/PAS positive acinar cells. The proteins SMG-B and PSP are normally expressed in acinar cell precursors during development but only by intercalated ductal cells in the adult stage. In the adult regenerating gland mRNA levels of both SMG-B and PSP were found to be up-regulated compared to ligated glands and SMG-B expression localized to acinar cells whilst the ductal cells were negative. This study of rat submandibular gland regeneration suggests new acinar cells have differentiated from ducts and express markers of acinar cell precursors in a similar manner to the cytodifferentiation process occurring during glandular development.

On approaches to the functional restoration of salivary glands damaged by radiation therapy for head and neck cancer, with a review of related aspects of salivary gland morphology and development

Radiation therapy for cancer of the head and neck can devastate the salivary glands and partially devitalize the mandible and maxilla. As a result, saliva production is drastically reduced and its quality adversely altered. Without diligent home and professional care, the teeth are subject to rapid destruction by caries, necessitating extractions with attendant high risk of necrosis of the supporting bone. Innovative techniques in delivery of radiation therapy and administration of drugs that selectively protect normal tissues can reduce significantly the radiation effects on salivary glands. Nonetheless, many patients still suffer severe oral dryness. I review here the functional morphology and development of salivary glands as these relate to approaches to preventing and restoring radiation-induced loss of salivary function. The acinar cells are responsible for most of the fluid and organic material in saliva, while the larger ducts influence the inorganic content. A central theme of this review is the extent to which the several types of epithelial cells in salivary glands may be pluripotential and the circumstances that may influence their ability to replace cells that have been lost or functionally inactivated due to the effects of radiation. The evidence suggests that the highly differentiated cells of the acini and large ducts of mature glands can replace themselves except when the respective pools of available cells are greatly diminished via apoptosis or necrosis owing to severely stressful events. Under the latter circumstances, relatively undifferentiated cells in the intercalated ducts proliferate and redifferentiate as may be required to replenish the depleted pools. It is likely that some, if not many, acinar cells may de-differentiate into intercalated duct-like cells and thus add to the pool of progenitor cells in such situations. If the stress is heavy doses of radiation, however, the result is not only the death of acinar cells, but also a marked decline in functional differentiation and proliferative capacity of all of the surviving cells, including those with progenitor capability. Restoration of gland function, therefore, seems to require increasing the secretory capacity of the surviving cells, or replacing the acinar cells and their progenitors either in the existing gland remnants or with artificial glands.

Characterisation and expression of SPLUNC2, the human orthologue of rodent parotid secretory protein

We recently described the Palate Lung Nasal Clone (PLUNC) family of proteins as an extended group of proteins expressed in the upper airways, nose and mouth. Little is known about these proteins, but they are secreted into the airway and nasal lining fluids and saliva where, due to their structural similarity with lipopolysaccharide-binding protein and bactericidal/permeability-increasing protein, they may play a role in the innate immune defence. We now describe the generation and characterisation of novel affinity-purified antibodies to SPLUNC2, and use them to determine the expression of this, the major salivary gland PLUNC. Western blotting showed that the antibodies identified a number of distinct protein bands in saliva, whilst immunohistochemical analysis demonstrated protein expression in serous cells of the major salivary glands and in the ductal lumens as well as in cells of minor mucosal glands. Antibodies directed against distinct epitopes of the protein yielded different staining patterns in both minor and major salivary glands. Using RT-PCR of tissues from the oral cavity, coupled with EST analysis, we showed that the gene undergoes alternative splicing using two 5' non-coding exons, suggesting that the gene is regulated by alternative promoters. Comprehensive RACE analysis using salivary gland RNA as template failed to identify any additional exons. Analysis of saliva showed that SPLUNC2 is subject to N-glycosylation. Thus, our study shows that multiple SPLUNC2 isoforms are found in the oral cavity and suggest that these proteins may be differentially regulated in distinct tissues where they may function in the innate immune response.

Design of bacteria-agglutinating peptides derived from parotid secretory protein, a member of the bactericidal/permeability increasing-like protein family

Parotid secretory protein (PSP) (SPLUNC2), a potential host-defense protein related to bactericidal/permeability-increasing protein (BPI), was used as a template to design antibacterial peptides. Based on the structure of BPI, new PSP peptides were designed and tested for antibacterial activity. The peptides did not exhibit significant bactericidal activity or inhibit growth but the peptide GL-13 induced bacterial matting, suggesting passive agglutination of bacteria. GL-13 was shown to agglutinate the Gram negative bacteria Pseudomonas aeruginosa and Aggregatibacter (Actinobacillus) actinomycetemcomitans, Gram positive Streptococcus gordonii and uncoated sheep erythrocytes. Bacterial agglutination was time and dose-dependent and involved hydrophobic interactions. Variant forms of GL-13 revealed that agglutination also depended on the number of amine groups on the peptide. GL-13 inhibited the adhesion of bacteria to plastic surfaces and the peptide prevented the spread of P. aeruginosa infection in a lettuce leaf model, suggesting that GL-13 is active in vivo. Moreover, GL-13-induced agglutination enhanced the phagocytosis of P. aeruginosa by RAW 264.7 macrophage cells. These results suggest that GL-13 represents a class of antimicrobial peptides, which do not directly kill bacteria but instead reduce bacterial adhesion and promote agglutination, leading to increased clearance by host phagocytic cells. Such peptides may cause less bacterial resistance than traditional antibiotic peptides.

Expression of PLUNC family members in benign and malignant salivary gland tumours

OBJECTIVES

The aim of this study was to determine the expression of PLUNC proteins in benign and malignant salivary gland tumours and thus their potential use as diagnostic and / or prognostic tools.

MATERIALS AND METHODS

A tissue microarray was assembled from 64 salivary gland tumours including adenoid cystic carcinoma, carcinoma ex-pleomorphic adenoma, mucoepidermoid carcinoma, polymorphous low-grade adenocarcinoma, pleomorphic adenoma, acinic cell carcinoma, myoepithelial carcinoma and papillary cystadenocarcinoma. Clinicopathological data were collected retrospectively and immunohistochemical analysis of three PLUNC proteins (SPLUNC1, SPLUNC2 and LPLUNC1) was performed. Immunoreactivity was assessed as positive or negative.

RESULTS

PLUNC expression was only found in mucoepidermoid carcinomas and papillary cystadenocarcinoma; all other tumours studied were negative. Mucin plugs, mucous and intermediate cells of mucoepidermoid carcinomas were positive for LPLUNC1 and SPLUNC2, but areas composed of epidermoid and clear cells were negative for all PLUNCs. Papillary cystadenocarcinoma was positive for all PLUNCs. No correlation was found with tumour grade or outcome.

CONCLUSIONS

Intense expression of two PLUNC proteins in mucous cells and mucin plugs of mucoepidermoid carcinoma and papillary cystadenocarcinoma indicate that they could be used as additional diagnostic tools in some equivocal cases, but further studies are needed to understand the biological processes involved in PLUNC expression.

Identification of a human ortholog of the mouseDcppgene locus, encoding a novel member of the CSP-1/Dcpp salivary protein family

Salivary fluid, the collective product of numerous major and minor salivary glands, contains a range of secretory proteins that play key defensive, digestive, and gustatory roles in the oral cavity. To understand the distinct protein “signature” contributed by individual salivary glands to salivary secretions, we studied a family of proteins shown by in vitro mRNA translation to be abundantly expressed in mouse sublingual glands. Molecular cloning, Southern blotting, and restriction fragment length polymorphism analyses showed these to represent one known and two novel members of the common salivary protein (CSP-1)/Demilune cell and parotid protein (Dcpp) salivary protein family, the genes for which are closely linked in the T-complex region of mouse chromosome 17. Bioinformatic analysis identified a putative human CSP-1/Dcpp ortholog, HRPE773, expressed predominantly in human salivary tissue, that shows 31% amino acid identity and 45% amino acid similarity to the mouse Dcpp query sequence. The corresponding human gene displays a similar structure to the mouse Dcpp genes and is located on human chromosome 16 in a region known to be syntenic with the T-complex region of mouse chromosome 17. The predicted mouse and human proteins both display classical NH2-terminal signal sequences, putative jacalin-related lectin domains, and potential N-linked glycosylation sites, suggesting secretion via sublingual saliva into the oral cavity where they may display antimicrobial activity or provide a defensive coating to enamel. Identification of a human CSP-1/Dcpp ortholog therefore provides a key tool for investigation of salivary protein function in human oral health and disease.

Parotid secretory protein is an HDL-associated protein with anticandidal activity

High-density lipoprotein (HDL) is part of innate immunity, protecting against infection and inflammation. Using a proteomic approach, we identified an amino acid sequence in a hamster HDL protein that showed homology to rat and mouse parotid secretory protein (PSP), a salivary protein secreted from the parotid glands. We cloned the cDNA encoding a putative hamster homolog of rat and mouse PSP. Searches for conserved domains of the protein showed that the COOH terminus of hamster PSP contains a region homologous to the NH2termini of a family of HDL-associated proteins, including LPS-binding protein, cholesteryl ester transfer protein, and phospholipid transfer protein. In mice, PSP was also associated with HDL but was not detected in very-low-density lipoprotein, low-density lipoprotein, or lipoprotein-deficient sera. In addition to salivary glands, we found that PSP mRNA was expressed in lung, testis, and ovary. The level of PSP in HDL was increased after endotoxin injection in hamsters, but not in mice. Recombinant PSP inhibits growth of Candida albicans in culture. In summary, our results showed that PSP is a novel anticandidal protein associated with HDL.

Parotid secretory protein is expressed and inducible in human gingival keratinocytes

BACKGROUND

Parotid secretory protein (PSP) is a major salivary protein that is thought to possess both antibacterial and anti-inflammatory activity. A major question is whether PSP expression can be regulated by humoral factors and bacteria. Periodontitis is an inflammatory lesion initiated by interaction between gingival keratinocytes and periodontopathogenic microorganisms such as the Gram-negative anaerobe Porphyromonas gingivalis. Cytokines and sex hormones have been implicated in the progression of various forms of periodontal diseases.

MATERIALS AND METHODS

We investigated the expression of PSP and its regulation in primary cultures of human gingival keratinocytes (HGK). HGK at the third or fourth passage were exposed to heat-killed P. gingivalis, tumor necrosis factor-alpha (TNF-alpha) and 17beta-estradiol. The PSP mRNA levels were examined by real-time polymerase chain reaction (PCR). The protein expression of PSP was confirmed by immunofluorescence.

RESULTS

Heat-killed P. gingivalis, TNF-alpha and 17beta-estradiol all resulted in increased HGK levels of mRNA for PSP as determined by real-time PCR analysis. Immunofluorescence demonstrated increased PSP localized within the cytoplasm of HGK following exposure to killed P. gingivalis.

CONCLUSION

The present study has demonstrated for the first time that PSP is expressed in keratinocytes and that it can be up-regulated by bacteria and humoral factors. Thus PSP may have a role in the innate defense system at the gingival epithelial surface.

Host defense in oral and airway epithelia: chromosome 20 contributes a new protein family

The innate immune response is of pivotal importance in defending the mucosal barriers of the body against pathogenic attack. The list of proteins that contribute to this defense mechanism is constantly being updated. In this review we introduce a novel family of secreted proteins, palate, lung, and nasal epithelium clones (PLUNCs), that are expressed in the mouth, nose and upper airways of humans, mice, rats and cows. In humans, PLUNC genes are located in a compact cluster on chromosome 20, with similar loci being found in synteneic locations in other species. The protein products of this gene cluster are predicted to be structural homologues of the human lipopolysaccharide binding proteins, lipopolysaccharide binding-protein (LBP) and bacterial permeability-increasing protein (BPI), which are known mediators of host defense against Gram-negative bacteria. On the basis of these observations we outline why we believe PLUNC proteins mediate host defense functions in the oral, nasal and respiratory epithelia.

Cloning and expression of a mouse member of the PLUNC protein family exclusively expressed in tongue epithelium

Palate, lung, and nasal epithelium clone (Plunc, now renamed Splunc1) is a small secreted protein expressed in the oropharynx and upper airways of humans, mice, rats, and cows. This protein is structurally homologous to known mediators of host defense against gram-negative bacteria. We have characterized the genomic sequence and expression of a novel but closely related gene from rodents, which we call splunc5. Mouse Splunc5 sequence is 60% identical to mouse Splunc1. The genes also share highly conserved genomic elements including intron-exon structure and intronic sequence. Strikingly, splunc5 is expressed exclusively in the interpapillary epithelium of the tongue's dorsal surface. By comparing the expression profiles of splunc5, splunc1, and a third related sequence, lplunc1, in mice, we show that these genes are expressed in unique domains along a continuous corridor of oral, lingual, pharyngeal, and respiratory epithelia. This expression pattern is consistent with the hypothesis that these proteins protect epithelial surfaces colonized by potentially pathogenic microorganisms.

cDNA cloning, genomic structure, chromosomal mapping, and expression analysis of parotid secretory protein in pig

A novel cDNA has been isolated from pig parotid glands by 3' and 5' rapid amplification of cDNA ends and designated parotid secretory protein (PSP). The open reading frame of this cDNA covers 714 bases, encoding 238 amino acids, which show 56% identity with human PSP at the level of the primary protein structure. The PSP genomic sequence comprises eight exons and seven introns, is approximately 22 kb in size, determined by sequencing, and maps to pig chromosome 17q21-q23. RT-PCR, dot blot, and Northern blot analyses demonstrated that PSP is strongly expressed in parotid glands, but is not present in heart, liver, lung, kidney, muscle, or stomach. A search for functionally significant protein motifs revealed consensus sequences for casein kinase II phosphorylation and N-myristoylation. We observed a unique amino acid sequence pattern consisting of the residues Leu-X(6)-Leu-X(6)-Leu-X(7)-Leu-X(6)-Leu-X(6)-Leu near the amino-terminal portion of the protein, which is similar to the leucine zipper.

Androgen regulation of SMR2 gene expression in rat submandibular gland: evidence for a graded but not a binary response

Expression of SMR2, a member of the gene family encoding salivary glutamine/glutamic acid-rich proteins, is regulated by androgens in rat submandibular gland acinar cells. To further characterize SMR2 regulation, we analyzed SMR2 expression during submandibular gland postnatal development and rat puberty at both a global and a single-cell level. Using in situ detection of mature and primary SMR2 transcripts, we show that SMR2 expression is heterogeneous among acinar cells. However, only one cell population with various amounts of mRNAs can be defined. The number of high-expressing cells increases in males during puberty and in females up to 6 weeks of age, suggesting that some factor in addition to acinar differentiation might be important for SMR2 expression in female rats. Involvement of the beta-adrenergic system in regulating SMR2 expression was tested in rats exposed daily to isoproterenol for 4 days. Under these conditions we found an increase in SMR2 expression in female rats, associated with an increase in SMR2 mRNA levels in most acinar cells. This suggests that a signaling cascade, elicited by beta-adrenergic stimuli, might act in concert with androgens to regulate SMR2 expression.

Identification of tissue-specific genes in nasopharyngeal epithelial tissue and differentially expressed genes in nasopharyngeal carcinoma by suppression subtractive hybridization and cDNA microarray

Suppression subtractive hybridization (SSH) was performed for isolation of tissue-specific genes in nasopharyngeal epithelial tissue, by use of cDNAs from human adult nasopharyngeal epithelial tissue as tester and mixed cDNAs from esophagus, lung, liver, heart, stomach, spleen, skeletal muscle, kidney, and skin as drivers. Fourteen differentially expressed genes in nasopharyngeal epithelial tissue were obtained. Among these genes, LPLUNC1 and SPLUNC1 were confirmed to be specifically expressed in nasopharyngeal epithelial tissue and the trachea. A novel transcript of SPLUNC1, which we designate NASG, was found. We also combined SSH and cDNA microarray hybridization to identify genes whose expressions were altered in nasopharyngeal carcinoma (NPC). We used NPC cell line HNE1 and primary human embryo nasopharyngeal epithelial cells in one SSH experiment, and NPC biopsies and normal adult nasopharyngeal epithelial tissue in another. Some 1,200 SSH inserts from four subtractive cDNA libraries were arrayed onto nylon membranes by use of robotic printing. Differential gene expression was verified by hybridizing of the membranes with radioactively labeled first-strand cDNA from NPC cell line HNE1, primary human embryo nasopharyngeal epithelial cells, NPC biopsies, and normal adult nasopharyngeal epithelial tissue. Seventeen differentially expressed genes in NPC were obtained. Among these genes, we identified SPLUNC1 and LPLUNC1 to be down-expressed in NPC biopsies (34/48, 33/48).

Molecular cloning and characterization of spurt, a human novel gene that is retinoic acid-inducible and encodes a secretory protein specific in upper respiratory tracts

Retinoids, such as all-trans-retinoic acid, play an essential role in the regulation of airway epithelial cell growth, differentiation, and gene expression. Using cDNA microarray, we identified a clone, DD4, that contains the cDNA of a novel gene, spurt (secretory protein in upper respiratory tracts) that was significantly induced by all-trans-retinoic acid in primary cultured human tracheobroncheal epithelia. Two alternatively spliced spurt transcripts of 1090 and 1035 base pairs exist that contain the same open reading frame expressing a 256-amino acid peptide. The full-length spurt cDNA sequence spans a genomic DNA fragment of 7,313 bp, and the gene is located on chromosome 20q11.21. spurt mRNA is notably expressed at high levels in human nasal, tracheal, and lung tissues. In situ hybridization demonstrated that spurt message is often present in secretory cell types. The human spurt gene product is a secretory protein that contains a distinct signal peptide sequence in its first 19 amino acids. Mono-specific antibodies were generated to characterize spurt expression. Our data demonstrate that spurt is secreted onto the apical side of primary human airway epithelial cultures and is present in clinical sputum samples. spurt gene expression is higher in sputum and tissue samples obtained from patients with chronic obstructive lung disease. Our results provide the cloning and characterization of this tissue-specific novel gene and its possible relationship with airway diseases.

The BSP30 salivary proteins from cattle, LUNX/PLUNC and von Ebner's minor salivary gland protein are members of the PSP/LBP superfamily of proteins

Saliva influences rumen function in cattle, yet the biochemical role for most of the bovine salivary proteins (BSPs) has yet to be established. Two cDNAs (BSP30a and BSP30b) from bovine parotid salivary gland were cloned and sequenced, each coding for alternate forms of a prominent protein in bovine saliva. The BSP30 cDNAs share 96% sequence identity with each other at the DNA level and 83% at the amino acid level, and appear to arise from separate genes. The predicted BSP30a and BSP30b proteins share 26-36% amino acid identity with parotid secretory protein (PSP) from mouse, rat and human. BSP30 and PSP are in turn more distantly related to a wider group of proteins that includes lung-specific X protein, also known as palate, lung, and nasal epithelium clone (LUNX/PLUNC), von Ebner's minor salivary gland protein (VEMSGP), bactericidal permeability increasing protein (BPI), lipopolysaccharide binding protein (LBP), cholesteryl ester transfer protein (CETP), and the putative olfactory ligand-binding proteins RYA3 and RY2G5. Bovine cDNAs encoding homologs of LUNX/PLUNC and VEMSGP were isolated and sequenced. Northern blot analysis showed that LUNX/PLUNC, BSP30 and VEMSGP are expressed in bovine salivary tissue and airways, and that they have non-identical patterns of expression in these tissues. The expression of both BSP30a and BSP30b is restricted to salivary tissue, but within this tissue they have distinct patterns of expression. The proximity of the human genes coding for the PSP/LBP superfamily on HSA20q11.2, their similar amino acid sequence, and common exon segmentation strongly suggest that these genes evolved from a common ancestral gene. Furthermore, they imply that the BSP30a and BSP30b proteins may have a function in common with other members of this gene family.

Sorting of an exocrine secretory protein to the regulated secretory pathway in endocrine cells

Regulated secretory proteins are stored in secretory granules. While the sorting and storage process appears similar in endocrine and exocrine cells, the extent of overlap of sorting between endocrine and exocrine cell types is not clear. It is predicted that exocrine regulated secretory proteins that are stored with high efficiency in exocrine granules would also be stored efficiently in endocrine granules. To test this hypothesis, parotid secretory protein (PSP), which is stored efficiently in parotid acinar cells, was expressed in the endocrine cell lines GH4C1 and PC12. PSP undergoes stimulated secretion in both cell types. Secretion is similar to that of the endocrine regulated secretory protein chromogranin A but distinct from secreted alkaline phosphatase, a marker for the constitutive secretory pathway in endocrine cells. Subcellular fractionation of GH4C1 cells revealed that PSP co-fractionates with chromogranin A but not with secreted alkaline phosphatase.

Measuring short-term gamma-irradiation effects on mouse salivary gland function using a new saliva collection device

A restraining device was designed specifically for the collection of whole saliva from mice without using anesthesia. As the procedure does not involve surgical cannulation of the salivary glands, saliva can be collected from the same mouse at different times. The time between the injection of a secretory stimulant (pilocarpine) and the appearance of saliva in the mouth (lag time) was 100.5 +/-8.5 s (mean+/-S.E.M., n=10) for control mice. The volume of saliva collected in the first 5 min was three times greater than that collected between 15 and 20 min. The average flow rate for a collection period of 15 min was 16.7 +/-1.8 microl/min (n=10). The flow rate was decreased 50% (P<0.005) whereas the lag time was increased more than 300% (P<0.05) at 24 h after irradiation. The concentrations of a 23.5-kDa protein and a mucin were decreased after irradiation whereas there was no significant effect on the concentration of amylase or peroxidase.

Biochemical characterization and surfactant properties of horse allergens

A new allergen from horse dander, Equ c 5 has been purified. Its biochemical and biophysical properties have been characterized and compared with those of Equ c 1, Equ c 2 and Equ c 4. Their molecular masses, determined by mass spectrometry, were 22 kDa for Equ c 1, 16 kDa for Equ c 2, 18.7 kDa for Equ c 4 and 16.7 kDa for Equ c 5. Their pI values were between 3.8 and 5.25. Equ c 2 and Equ c 5 are not glycosylated, while Equ c 4 contains a tri-antennary tri-sialylated N-linked glycan. Linkages of terminal N-acetylneuraminic acid to galactose were: alpha-(2-->6) in Equ c 4, and both alpha-(2-->3) and alpha-(2-->6) in Equ c 1. Oligosaccharide portions of Equ c 1 or Equ c 4 were barely involved in IgE-immunoreactivity. Partial N-terminal sequence of Equ c 4 shares a significant sequence homology with the rat submandibular gland protein A. No matching was found for two internal peptides of Equ c 5. Surfactant properties of horse allergens as well as other proteins were investigated. In contrast to Equ c 2 and Equ c 3, solutions of Equ c 1, Equ c 4 and Equ c 5 significantly lowered the surface tension. Relationship between a property such as this, involving oriented hydrophobic patches of a molecule and allergenicity, is addressed.

Contributions of intercalated duct cells to the normal parenchyma of submandibular glands of adult rats

The parenchyma of the submandibular gland in the adult male rat is self-renewing, with most newly formed acinar and granular duct cells believed to differentiate from the rapidly proliferating intercalated duct (ID) compartment. Since the ID cells are phenotypically diverse, based on their different expression of perinatal secretory proteins, we systemically injected tritiated thymidine for 24 hours, and followed the pattern of thymidine distribution in cells by autoradiography and immunocytochemistry of defined cellular phenotypes over a 1-month chase period. Proliferating cells were found within all parenchymal cell compartments; they were most numerous in ID, and primarily in those cells lacking immunoreactivity for the perinatal proteins SMG-B1, -C, and -D. The labeling index (LI) of the ID cells reached a peak at 7 days postinjection, and then decreased over the next 3 weeks. Concurrently, the LI increased significantly in those cells at the junctions of ID with both acini and granular ducts, and also within these larger parenchymal elements. We conclude that the ID cells not reactive for perinatal proteins proliferate to expand the ID compartment, and that ID cells at the ends of the ducts differentiate into both acinar and granular duct cells. Our data provide no evidence for the differentiation of ID cells into cells of striated ducts (SD); however, the small number of excretory duct (ED) profiles seen in our preparations showed extremely high LI (>25%), suggesting that more extensive data might reveal a precursor role for the ED in replacement of SD cells. In addition to the stepwise passage of cells from ID to other parenchymal elements at their junctions, the reported occurrence of occasional clusters of B1-positive acini (BAC) among the typical B1-negative acini had suggested an alternate pathway, in which entire segments of newly expanded ID might develop directly into a recapitulated perinatal stage of B1-reactive cell, pursuant to becoming mature acinar cells. Consistent with this suggestion, the BAC had a fourfold greater LI than typical adult acini; moreover, when analyzed by electron microscopic immunocytochemistry, they appeared similar to the novel perinatal Type III cells both ultrastructurally and in their pattern of B1-immunogold labeling. In contrast, the less common acini showing a sublingual gland phenotype had no significant difference in LI from typical acinar cells. Overall, our results emphasize the importance of the nonimmunoreactive ID cells in normal cellular replacement, and the possibility that ID can undergo en bloc differentiation into replacement acini as well as incremental addition of single cells at the boundaries of ID with acini and with granular ducts.

IL-4-dependent effector phase in autoimmune exocrinopathy as defined by the NOD.IL-4-gene knockout mouse model of Sjögren's syndrome

NOD mice manifest many features of autoimmune exocrinopathy (Sjögren's syndrome), a disease generally characterized by a chronic, progressive immunological attack against the exocrine tissues of the salivary and lacrimal glands. Previous studies using the NOD congenic partner strain, NOD.Igmu(null), defined an important role for B lymphocytes in the development of xerostomia, implicating autoantibodies reactive with the acetylcholine muscarinic receptor (M3R) as the possible effector mechanism. In the present study, we have examined the impact of the cytokine, interleukin (IL)-4, on autoimmune exocrinopathy by using the IL-4 gene knockout (KO) NOD mouse strain, NOD.IL-4-/-. Despite manifesting the physiological aberrations and marked leukocytic infiltration of the salivary glands characteristic of autoimmune xerostomia in NOD mice, the NOD.IL-4-/- mice do not develop xerostomia. However, NOD.IL-4-/- mice that received adoptively transferred T lymphocytes derived from NOD.Igmu-/- mice progress to xerostomia, thereby reversing the defect. While progression or lack of progression to xerostomia correlated with the ability of the NOD.IL-4-/- mice to express detectable anti-M3R autoantibodies, the precise mechanism of how IL-4 influences the development of autoimmune xerostomia remains speculative.

Characterisation of the human plunc gene, a gene product with an upper airways and nasopharyngeal restricted expression pattern

Here we report the cloning and characterization of the human homologue of plunc, a murine gene expressed specifically in the upper airways and nasopharyngeal regions. The human plunc cDNA codes for a leucine-rich protein of 256 amino acids which is 72% identical to the murine protein. RNA blot analysis suggests that expression of plunc is restricted to the trachea, upper airway, nasopharyngeal epithelium and salivary gland. The human plunc gene contains nine exons and is localised to chromosome 20q11.2. The unique expression pattern of the human plunc suggest that it may prove a useful model gene with which to study the regulatory mechanisms which direct expression of genes specifically to the upper airways.

Structure and chromosomal localization of the rat salivary Psp and Smgb genes

SMGB and PSP are among the most abundant products of the immature acinar cells in developing rat parotid and submandibular glands and are also products of the sublingual gland serous demilunes. Previous analysis of Smgb and Psp cDNA clones demonstrated a high degree of sequence similarity between the signal peptide-encoding and 3' untranslated regions of these transcripts, although the secreted proteins themselves are more divergent. The current study reports the upstream sequences, genomic organization and localization of the Psp and Smgb genes. Both structural genes contain nine exons and are present at 3q41-3q42, where they are arranged in tandem and separated by 21kb. In addition to the previously observed sequence similarity, Psp and Smgb are highly homologous throughout exon 1 and at 365 of 600bp immediately upstream of the transcription start site. These findings indicate that the Psp and Smgb genes arose by tandem duplication and divergence. The similar neonatal submandibular and parotid gland expression patterns observed for these genes are likely to be due to closely conserved or shared enhancer(s).

Developmental changes of sugar residues and secretory protein in mucous cells of the early postnatal rat parotid gland

Mucous cells have been identified in the terminal portions of the early postnatal parotid gland in human and rat, although mature parotid gland acini are composed of serous cells or seromucous cells. Previously, Ikeda et al. demonstrated that mucous cells are present in the rat parotid gland on days 1 to 8 after birth and that the secretory granules within these mucous cells share some histochemical characteristics with mature serous cells. However, it is still not clear whether the mucous cells change into serous cells as the gland develops. The purpose of this study was to determine whether the mucous cells that appear in the early postnatal rat parotid gland change into serous cells. Parotid glands were obtained from male or female Wistar rats (aged 0-14 days and adults). Fixed tissue sections were reacted with soybean agglutinin (SBA) and wheat germ agglutinin (WGA) to detect glycoconjugates, or were stained using an anti-neonatal submandibular gland protein B1 (SMG-B1) antibody to identify serous acinar cells. The sections were observed by transmission electron microscopy. Electron microscopy revealed that cells with characteristics intermediate between those of mucous and serous cells (transitional cells) appeared around day 8 and that the nuclei of these cells did not show chromatin condensation, a characteristic of apoptotic cells. Lectin histochemistry showed that the mucous cells had the same sugar residues as the serous cells, which appeared after day 10. Immunohistochemistry with an anti-SMG-B1 antibody gave a positive reaction not only in the cells with highly electron-dense granules but also in the electron-dense cores of bipartite or tripartite granules in the transitional cells. Cells with morphological characteristics intermediate between those of mucous and serous cells (transitional cells) appearing in the early postnatal rat parotid gland begin to produce B1-immunoreactive protein common to serous acinar cells during development of the gland.

Differential display identification of plunc, a novel gene expressed in embryonic palate, nasal epithelium, and adult lung

We have identified a novel gene transcript of approximately 1.1 kilobases in length that is expressed in the presumptive nasal epithelium of the mouse embryo. In situ hybridization analysis shows discrete regions of expression associated with the palate, nasal septum, and nasal conchae. This transcript is also expressed strongly in the trachea and bronchi of the adult lung. Screening of a mouse heart cDNA library yielded several overlapping clones to give a continuous sequence of 1113 bases, containing an open reading frame of 278 codons comprising the complete mRNA. No significant homologies with known genes were observed at the nucleotide level; limited amino acid homology with two salivary gland-specific proteins was noted. A search for functionally significant protein motifs revealed consensus sequences for N-glycosylation, protein kinase C and casein kinase phosphorylation, and a leucine zipper. Additionally, we observed a unique amino acid sequence pattern, consisting of the residues Gly-(Leu/Pro/Gln)-(Pro/Leu)-Leu-Pro-Leu, repeated four times near the amino-terminal portion of the protein with two amino acid residues separating the repeats. Based on these observations, we propose that we have identified a new gene, which we call plunc (for palate, lung, and nasal epithelium clone; GenBankTM accession number U69172).

Expression of gross cystic disease fluid protein-15/Prolactin-inducible protein in rat salivary glands

Gross cystic disease fluid protein-15 (GCDFP-15)/prolactin-inducible protein (PIP) is present at moderate levels in human submandibular and sublingual glands and is barely detectable in human parotid gland. The rodent homologue, PIP, has previously been identified in adult submandibular and lacrimal glands. Here we present the molecular characterization of rat PIP and show that this protein is a product of neonatal and adult rat submandibular, sublingual, and parotid glands. cDNA clones encoding rat PIP were isolated and sequenced. The deduced amino acid sequence of rat PIP shows 56% overall identity and 80% similarity with mouse PIP. By SDS-PAGE, secreted rat PIP has an apparent Mr of 17,000, with a minor proportion present as Mr 20-22,000 N-glycosylated forms. PIP was localized in rat salivary glands by immunogold silver staining. PIP was identified in acinar cells of developing and mature submandibular and parotid glands and at very low levels in sublingual gland serous demilunes. Typically, rat submandibular gland secretory proteins are produced by either acinar cell progenitors (Type III cells) or mature acinar cells. The expression pattern observed for PIP is similar to that previously reported for salivary peroxidase, an important component of nonimmune mucosal defense.

A novel NOD-derived murine model of primary Sjögren's syndrome

OBJECTIVE

The appearance of autoimmune diabetes prior to autoimmune exocrinopathy in the NOD mouse suggests that it is an excellent model of secondary, but not primary, autoimmune sicca complications. Since the unique major histocompatibility complex (MHC) I-A(g7) expression in NOD mice is essential for the development of insulitis and diabetes in these animals, we investigated exocrine gland function in NOD.B10.H2b mice, which have an MHC congenic to NOD, as a potential model for primary Sjögren's syndrome (SS).

METHODS

Histopathologic manifestations of lymphocytic infiltrates into the pancreas and exocrine tissues were examined by light microscopy. Sera were evaluated for the presence of antinuclear antibodies. Saliva, tears, and gland lysates were evaluated for total volume and protein concentration, the aberrant expression and processing of parotid secretory protein, and cysteine protease activity.

RESULTS

NOD.B10.H2b mice exhibited the exocrine gland lymphocytic infiltration typical of the SS-like disease and dysfunction observed in NOD mice, but without the insulitis and diabetes. These mice additionally expressed elevated levels of cysteine protease activity (a measure of apoptotic activity) and abnormal expression and cleavage of parotid secretory protein in the submandibular tissues.

CONCLUSION

The results of this study suggest that the unique NOD MHC I-A(g7) is not essential for exocrine tissue autoimmunity. Furthermore, the findings indicate that sicca syndrome occurs independently of autoimmune diabetes and that the congenic NOD.B10.H2b mouse represents a novel murine model of primary SS.

Elevated levels of cysteine protease activity in saliva and salivary glands of the nonobese diabetic (NOD) mouse model for Sjögren syndrome

Nonobese diabetic (NOD) mice develop an anti-exocrine gland pathology similar to human Sjögren syndrome. Recently, we demonstrated that NOD-scid mice develop severe loss of submandibular acinar cells with concomitant appearance of abnormal isoforms of salivary proteins suggesting de novo enzymatic cleavage. Because these changes may indicate activation of apoptotic proteases, we examined saliva and salivary tissue for cysteine protease activity. Cysteine protease activities were elevated in saliva and gland lysates from 20-week-old NOD and NOD-scid mice as compared with age- and sex-matched BALB/c or 8-week-old NOD mice. This activity appeared in the submandibular glands, but not in the parotid glands. Western blot analyses using antibodies directed against specific apoptotic proteases (interleukin 1beta converting enzyme, Nedd-2, and Apopain/CPP 32) confirmed these findings. Submandibular glands from NOD-scid mice exhibited the greatest increase in proteolytic activity, indicating that infiltrating leukocytes are not responsible for these changes. Western blot analyses also failed to reveal changes in the levels of cystatins (saliva proteins that inhibit protease activity). Thus, increased cysteine protease activity appears to be directly related to submandibular acinar cell loss in NOD-scid mice involving the apoptotic pathway. Additional protease activity in saliva and gland lysates of older NOD and NOD-scid mice, apparently mutually distinct from cysteine proteases, generated an enzymatically cleaved parotid secretory protein. We suggest, therefore, that proteolytic enzyme activity contributes to loss of exocrine gland tolerance by generating abnormally processed protein constituents.

Identification of zinc proteins in rat parotid saliva

The presence of unique zinc-binding proteins in human saliva is well documented. These observations have not, however, been extended to other species. The rat has been used extensively to study the salivary gland and its secretion, and it is therefore important to determine if the spectrum of zinc-binding proteins in this experimental model resembles that found in humans. To begin the analysis of zinc-binding proteins in stimulated rat parotid saliva, the saliva was fractionated by DEAE Sephadex and Sepharose 6B chaelate chromatography and the protein patterns analysed by electrophoresis. Zinc-binding proteins from the parotid saliva were identified by incubating Western blots with 65Zn and identifying any bound zinc by autoradiography. Comparison of the autoradiograms with the Coomassie blue-stained filter revealed several proteins with zinc-binding capacity. Isolation of the major zinc-binding proteins revealed an amino acid composition of proline 28%, glutamine 19% and glycine 15%, which is consistent with the amino acid composition of rat salivary acidic proline-rich protein. In addition to the proline-rich proteins, one other zinc-binding protein was analysed. The N-terminal sequence of this protein was found to bear a striking similarity (16 out of 20 amino acids) to secreted carbonic anhydrase VI of the mouse, a known zinc-binding protein. These data demonstrate that rat acidic proline-rich proteins, having an amino acid composition similar to that in humans, have zinc-binding potential. The data also confirm previous reports suggesting secreted carbonic anhydrase in rat parotid saliva.

Salivary glands: a paradigm for diversity of gland development

The major salivary glands of mammals are represented by three pairs of organs that cooperate functionally to produce saliva for the oral cavity. While each type of gland produces a signature secretion that complements the secretions from the other glands, there is also redundancy as evidenced by secretion of functionally similar and, in some cases, identical products in the three glands. This, along with their common late initiation of development, in fetal terms, their similarities in developmental pattern, and their proximate sites of origin, suggests that a common regulatory cascade may have been shared until shortly before the onset of overt gland development. Furthermore, occasional ectopic differentiation of individual mature secretory cells in the "wrong" gland suggests that control mechanisms responsible for the distinctive cellular composition of each gland also share many common steps, with only minor differences providing the impetus for diversification. To begin to address this area, we examine here the origins of the salivary glands by reviewing the expression patterns of several genes with known morphogenetic potential that may be involved based on developmental timing and location. The possibility that factors leading to determination of the sites of mammalian salivary gland development might be homologous to the regulatory cascade leading to salivary gland formation in Drosophila is also evaluated. In a subsequent section, cellular phenotypes of neonatal and adult glands are compared and evaluated for insights into the mechanisms and lineages leading to cellular diversification. Finally, the phenomena of proliferation, repair, and regeneration in adult salivary glands are reviewed, with emphasis on the extent to which the cellular diversity is reversible and which cell type other than stem cells has the ability to redifferentiate into other cell types.

Regulation of salivary-gland-specific gene expression

The results from in vivo transgenic and in vitro transfection studies designed to identify cis-element(s) and transfactor(s) governing the salivary proline-rich proteins (PRPs), amylase, and parotid secretory protein (PSP) gene expression are utilized as a paradigm to discuss the regulation of salivary-specific gene expression. Particular attention is given to the molecular mechanism(s) underlying the salivary PRP R15 gene regulation. In rodents, the PRPs are selectively expressed in the acinar cells of salivary glands, and are inducible by the beta-agonist isoproterenol and by dietary tannins. The results from a series of experiments using chimeric reporter constructs containing different lengths of the R15 distal enhancer region, their mutations, and various expressing constructs are analyzed and discussed. These data suggest that the inducible nuclear orphan receptor NGFI-B may participate in the regulation of salivary acinar-cell-specific and inducible expression of the rat R15 gene via three distinct distal NGFI-B sites. Taken together, a model for the induction of R15 gene expression by Ipr is proposed. However, the exact molecular basis of this NGFI-B-mediated transactivation of cAMP-regulated R15 expression remains to be established.

Two regulated secretory pathways for newly synthesized parotid salivary proteins are distinguished by doses of secretagogues

Low doses of the muscarinic agonist pilocarpine (0.1-1 microM) and the beta-adrenergic agonist isoproterenol (0.5-4 nM) stimulate a minor regulated secretory pathway for salivary proteins in rat parotid lobules. Newly synthesized proteins (labeled biosynthetically) are selectively discharged, and they are secreted in the same relative proportions as observed in constitutive-like unstimulated secretion but different from the proportions of older proteins that are discharged by granule exocytosis in response to higher doses of secretagogue. The response to low doses of agonists is transient and involves output of no more than 1–2% of tissue-associated amylase. The same increase in output of pulse-labeled proteins is observed when agonist is added at various chase times (1.5-6 hours), implying that release occurs from a post-Golgi storage pool. Stimulation for 40 minutes significantly depletes the storage pool as a second stimulation elicits smaller output. Stimulation also partially depletes labeled proteins from subsequent constitutive-like secretion after the agonist is removed implying that the constitutive-like and low dose agonist mediated pathways draw on the same pool of secretory proteins. While these results indicate that acinar cells have a second regulated secretory pathway, this new pathway is unlikely to contribute uniquely to the protein composition of parotid secretion. Rather it may serve a different role in secretion at the apical cell surface.

Effects of protein deficiency and diet consistency on the parotid gland and parotid saliva of rats

Protein deficiency results in an increased susceptibility to dental caries, suggesting that oral host-defense properties are compromised. An important component of oral host defense is salivary gland function, which is affected by both protein deficiency and diet consistency. This study describes the effects on rat parotid gland growth and secretory function induced by feeding rats diets of normal (20%) or moderately low (7%) protein content, provided in either a powdered or solid form. In addition, since protein deficiency may result in a secondary zinc deficiency which, in turn, may affect salivary gland function, the effects of these diets on liver zinc concentration were also measured. From 22 to 47 days of age, rats (18/group) were fed the following diets: normal protein, powdered; normal protein, solid; low protein, powdered; and low protein, solid. With each diet consistency, liver zinc was higher for the normal protein group. Within each protein level, liver zinc was higher for the solid diet. This latter observation suggests that food mastication and the resultant stimulation of salivary gland function may also play a role in zinc metabolism. With the normal-protein diet, parotid gland weight was higher for the solid diet; with the low-protein diet, parotid gland weight was similar for both consistencies and did not differ from that of the group fed the "normal protein, powdered" diet. For both consistencies, parotid saliva protein concentration was greater for malnourished rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative immunocytochemical study of secretory protein expression in parotid glands of rats chronically treated with isoproterenol

Chronic treatment of mice and rats with isoproterenol (IPR) causes marked hypertrophy and hyperplasia of the salivary glands, and alters the expression of several secretory proteins. We used quantitative postembedding immunogold labeling to study the cellular responses in the rat parotid gland during daily (up to 10 days) injections of IPR and during recovery (up to 14 days) after cessation of IPR treatment. Labeling densities of acinar cell secretory granules with antibodies to amylase and protein SMG-B1 (cross-reactive with the rat homologue of Parotid Secretory Protein, PSP) fell to 10% of control levels after 8-10 IPR injections, then increased during recovery, paralleling previous biochemical determinations of changes in protein and mRNA levels. With antibodies to proline-rich proteins (PRP), labeling densities initially fell, then subsequently showed considerable variability, but never exceeded control levels. These results contrast with biochemical determinations showing a marked induction of PRP synthesis, and may have both immunological and structural explanations. Occasional intercalated duct cells located close to the acini underwent differentiation toward an acinar-like phenotype as a result of IPR treatment. After 1-2 IPR injections, the secretory granules of these cells labeled with antibodies to amylase and PRP. Subsequently, the granules appeared electron-lucent and were increased in size and number. These observations support earlier work, suggesting that intercalated duct cells may differentiate into other gland cell types.

cDNA cloning, sequencing and in situ localization of a transcript specific to both sublingual demilune cells and parotid intercalated duct cells in mouse salivary glands

A cDNA clone derived from mouse sublingual gland was isolated from lambda-phage cDNA library. Northern blot hybridization indicated that the transcript from which it was derived was approx. 700 nucleotides in length. This mRNA encoded a protein of about 20 kDa, as determined by hybrid selection and cell-free translation. Conceptual translation of the cDNA clones showed that p20 is 170 amino acids in length. The putative protein is hydrophobic in nature, is neither a mucin-like protein nor does its amino acid sequence or composition resemble the other known mouse proteins. However, the amino acid sequence of p20 suggests that it may be from a gene or gene family homologous to rat common salivary protein 1. The p20 mRNA also appears to share a non-random degree of sequence homology with the cysteine-rich domains of bovine and porcine submandibular mucins. The p20 mRNA is abundant in the mouse sublingual gland, and its expression is approx. nine times greater than in the parotid gland. In situ hybridizations localized the p20 mRNA exclusively in the demilune cells of the sublingual gland and in the intercalated duct cells of the parotid gland. It is detectable in the neonatal and adult submandibular gland at very low levels, but is absent from liver, heart, brain, thymus, spleen, lens and lacrimal glands.

Three novel SMR1-related cDNAs characterized in the submaxillary gland of mice show extensive evolutionary divergence in the protein coding region

We have previously characterized an abundant male-specific mRNA from the submaxillary gland (SMG) of rats, encoding the SMR1 (androgen-regulated) protein, which has the structure of a prohormone and is processed by maturation enzymes to release a small peptide in the blood and saliva. We have now characterized three SMR1-related cDNAs in the SMG of Balb/c mice. These cDNAs encode three novel proteins, designated MSG1, MSG2 and MSG3. They are 639, 662 and 471 nucleotides (nt) long, respectively, and the corresponding mRNAs appear to be expressed only in the SMG. The putative polypeptides they encode carry an N-terminal secretory peptide sequence and are, therefore, presumably secreted into saliva. Although closely related, the three mRNAs show striking differences: a particularly different expression pattern and an extremely high degree of variability observed in the central part of the molecules. The MSG1 and MSG3 cDNAs are identical, except for a 173-bp insert found only in MSG1. This insert contains three Pro-rich repeats (GPGIGRPPPPPP), reminiscent of the most abundant multigenic family of the SMG, the Pro-rich proteins (PRP). Although MSG1 shares several common features with PRP, it is structurally related to SMR1. The unusually high ratio of replacement/silent nt changes provides a basis to address complex aspects concerning the molecular events leading to the emergence of new proteins in the SMG.

The B1-immunoreactive proteins of the perinatal submandibular gland: similarity to the major parotid gland protein, RPSP

The B1-immunoreactive proteins of type III cells of the perinatal rat submandibular gland are immunologically cross-reactive with proteins of both the sublingual and parotid glands; in particular, protein SMG-A appears similar to a major parotid protein. We isolated SMG-A and the parotid protein (known as M1 or leucine-rich protein), prepared polyclonal antibodies to them, and compared their biochemical properties and immunological reactivities. They were identical in their molecular weight on SDS-PAGE (23.5 kDa), tenacious binding to Affi-gel Blue, isoelectric point (pH 4.53), and proteolysis to a 14 kDa peptide: Antibodies to SMG-A showed reactivity with protein SMG-C, a product of the neonatal type I cells, as well as with proteins SMG-B1 and SMG-B2, contrasted with the absence of reactivity of anti-M1 IgG with these proteins. Anti-M1 reacted with the "parotid secretory protein" (PSP) of the mouse, and M1 appears to be the homologue, in the rat, of mouse PSP.

Molecular cloning of developmentally regulated neonatal rat submandibular gland proteins

At birth, the rat submandibular gland (SMG) contains two transient secretory cell types that produce several characteristic salivary proteins. Proteins SMG-A, B1, and B2 (23.5, 26 and 27.5 kDa) are products of the neonatal type III cells, but not the adult acinar cells. Protein C (89 kDa), a major product of the neonatal type I cells, is either absent or present at greatly diminished levels in the secretory cells of the adult gland. The decrease in biosynthesis of these neonatal salivary proteins occurs concomitantly with the increase in levels of characteristic adult SMG products. In order to understand these developmentally regulated changes in SMG salivary protein gene expression, we have initiated the molecular cloning and characterization of neonatal submandibular gland proteins from a 5-d-old rat submandibular gland cDNA library. Clones encoding SMG-A were isolated by homology to the mouse parotid secretory protein (PSP). SMG-A was shown to be derived from a salivary protein multigene family that also includes PSP. Cloning and characterization of additional neonatal rat submandibular gland proteins was initiated by screening the 5-d-old rat submandibular gland cDNA library with first strand cDNA prepared from 1-d-old rat submandibular glands. Clones corresponding to a highly abundant 3 kb transcript present in the neonatal rat SMG, but not in adult submandibular, sublingual, or parotid gland have been identified. The size, abundance, and organ specificity of this transcript suggest that it may encode protein C.(ABSTRACT TRUNCATED AT 250 WORDS)