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

Tlx1 regulates acinar and duct development in mouse salivary glands

Tlx1 encodes a transcription factor expressed in several craniofacial structures of developing mice. The role of Tlx1 in salivary gland development was examined using morphological and immunohistochemical analyses of Tlx1 null mice. Tlx1 is expressed in submandibular and sublingual glands but not parotid glands of neonatal and adult male and female C57Bl/6J (Tlx1+/+ ) mice. TLX1 protein was localized to the nuclei of terminal tubule cells, developing duct cells and mesenchymal cells in neonatal submandibular and sublingual glands, and to nuclei of duct cells and connective tissue cells in adult glands. Occasionally, TLX1 was observed in nuclei of epithelial cells in or adjacent to the acini. Submandibular glands were smaller and sublingual glands were larger in size in mutant mice (Tlx1-/- ) compared to wild-type mice. Differentiation of terminal tubule and proacinar cells of neonatal Tlx1-/- submandibular glands was abnormal; expression of their characteristic products, submandibular gland protein C and parotid secretory protein, respectively, was reduced. At 3 weeks postnatally, terminal tubule cells at the acinar-intercalated duct junction were poorly developed or absent in Tlx1-/- mice. Granular convoluted ducts in adult mutant mice were decreased, and epidermal growth factor and nerve growth factor expression were reduced. Along with normal acinar cell proteins, adult acinar cells of Tlx1-/- mice continued to express neonatal proteins and expressed parotid proteins not normally present in submandibular glands. Sublingual gland mucous acinar and serous demilune cell differentiation were altered. Tlx1 is necessary for proper differentiation of submandibular and sublingual gland acinar cells, and granular convoluted ducts. The mechanism(s) underlying Tlx1 regulation of salivary gland development and differentiation remains unknown.

Opiorphin is a master regulator of the hypoxic response in corporal smooth muscle cells

Men with sickle cell disease (SCD) risk developing priapism. Recognizing that SCD is a disease of hypoxia, we investigated the effect of hypoxia on gene expression in corporal smooth muscle (CSM) cells. Rat CSM cells in vitro were treated with CoCl2 or low oxygen tension to mimic hypoxia. Hypoxic conditions increased expression of genes previously associated with priapism in animal models. Variable coding sequence a1 (Vcsa1; the rat opiorphin homologue, sialorphin), hypoxia-inducible factor 1a (Hif-1a), and A2B adenosine receptor (a2br) were increased by 10-, 4-, and 6-fold, respectively, by treatment with CoCl2, whereas low oxygen tension caused increases in expression of 3-, 4-, and 1.5-fold, respectively. Sialorphin-treated CSM cells increased expression of Hif-1a and a2br by 4-fold, and vcsa1-siRNA treatment reduced expression by ∼50%. Using a Hif-1a inhibitor, we demonstrated up-regulation of a2br by sialorphin is dependent on Hif-1a, and knockdown of vcsa1 expression with vcsa1-siRNA demonstrated that hypoxic-up-regulation of Hif-1a is dependent on vcsa1. In CSM from a SCD mouse, there was 15-fold up-regulation of opiorphin at a life stage prior to priapism. We conclude that in CSM, opiorphins are master regulators of the hypoxic response. Opiorphin up-regulation in response to SCD-associated hypoxia activates CSM "relaxant" pathways; excessive activation of these pathways results in priapism.

Reversal of diabetic vasculopathy in a rat model of type 1 diabetes by opiorphin-related peptides

Diabetes results in a myriad of vascular complications, often referred to as diabetic vasculopathy, which encompasses both microvascular [erectile dysfunction (ED), retinopathy, neuropathy, and nephropathy] and macrovascular complications (hypertension, coronary heart disease, and myocardial infarction). In diabetic animals and patients with ED, there is decreased opiorphin or opiorphin-related gene expression in corporal tissue. Both opiorphin and the rat homologous peptide sialorphin are found circulating in the plasma. In the present study, we investigated if diabetes induced changes in plasma sialorphin levels and if changes in these levels could modulate the biochemistry and physiology of vascular smooth muscle. We show that circulating sialorphin levels are reduced in a rat model of type I diabetes. Intracorporal injection of plasmids expressing sialorphin into diabetic rats restores sialorphin levels to those seen in the blood of nondiabetic animals and results in both improved erectile function and blood pressure. Sialorphin modulated the ability of C-type natriuretic peptide to relax both corporal and aortic smooth muscle strips and of bradykinin to regulate intracellular calcium levels in both corporal and aortic smooth muscle cells. We have previously shown that expression of genes encoding opiorphins is increased when erectile function is improved. Our findings thus suggest that by affecting circulating levels of opiorphin-related peptides, proper erectile function is not only an indicator but also a modulator of overall vascular health of a man.

The mechanism of opiorphin-induced experimental priapism in rats involves activation of the polyamine synthetic pathway

Intracorporal injection of plasmids encoding opiorphins into retired breeder rats can result in animals developing a priapic-like condition. Microarray analysis demonstrated that following intracorporal gene transfer of plasmids expressing opiorphins the most significantly upregulated gene in corporal tissue was the ornithine decarboxylase gene (ODC). Quantitative RT-PCR confirmed the upregulation of ODC, as well as other genes involved in polyamine synthesis, such as arginase-I and -II, polyamine oxidase, spermidine synthase, spermidine acetyltransferase (SAT), and S-adenosylmethionine decarboxylase. Western blot analysis demonstrated upregulation of arginase-I and -II, ODC, and SAT at the protein level. Levels of the polyamine putrescine were upregulated in animals treated with opiorphin-expressing plasmids compared with controls. A direct role for the upregulation of polyamine synthesis in the development of the priapic-like condition was supported by the observation that the ODC inhibitor 1,3-diaminopropane, when added to the drinking water of animals treated with plasmids expressing opiorphins, prevented experimental priapism. We also demonstrate that in sickle cell mice, another model of priapism, there is increased expression of the mouse opiorphin homologue in corporal tissue compared with the background strain at a life stage prior to evidence of priapism. At a life stage when there is onset of priapism, there is increased expression of the enzymes involved in polyamine synthesis (ODC and arginase-I and -II). Our results suggest that the upregulation of enzymes involved in the polyamine synthetic pathway may play a role in the development of experimental priapism and represent a target for the prevention of priapism.

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.

Tissue distribution and nucleotide sequence of bovine mRNA for salivary proline-rich protein P-B

The tissue distribution of P-B was investigated to obtain information on the physiological significance of this proline-rich protein. To design primers and probes for a tissue distribution analysis, a polymerase chain reaction (PCR)-based cloning of bovine P-B cDNA was performed using tooth germ and the nucleotide sequence was determined. The cloned bovine P-B cDNA was composed of 356 bp and included the region corresponding to the mature P-B protein and part of the 3' non-coding sequence. This part of the sequence is identical to the corresponding region of human P-B cDNA from the submaxillary gland. DNA corresponding to the P-B mRNA was amplified by PCR using cDNAs from various bovine tissues including tooth germ, submaxillary gland, parotid gland, lachrymal gland, heart, liver, stomach, pancreas, spleen, kidney, adrenal, and ovary. A quantitative analysis indicated the heart, submaxillary gland, tooth germ and kidney to be major sites of P-B expression. The ubiquitous distribution of P-B mRNA among bovine tissues together with findings of the presence of genes hybridizable with a DNA probe for P-B among species such as human, bovine, rat, mouse, and yeast as reported previously suggested a fundamental physiological role for this protein.

Androgen inducibility ofFgf8 in Shionogi carcinoma 115 cells correlates with an adjacent t(5;19) translocation

Fgf8 (fibroblast growth factor 8) was initially cloned from a mouse mammary tumor cell line derived from the androgen-dependent Shionogi carcinoma 115. The androgen-inducible expression of Fgf8 in this tumor controls its androgen-dependent phenotype, thus stimulating interest in this gene as a possible factor in human prostate cancer and other androgen-sensitive cancers. However, apart from Shionogi carcinoma 115, the androgen inducibility of Fgf8 is controversial. In the present study, having not detected androgen-inducible expression of Fgf8 in other mouse mammary cell lines or mouse prostate, we examined the Shionogi carcinoma 115-derived S115 cell line for mouse mammary tumor virus (MMTV) insertions or other nearby DNA rearrangements that might explain the androgen inducibility of Fgf8 in these cells. Southern blotting did not detect MMTV insertions near Fgf8 but did reveal a specific DNA rearrangement 3.7 kb upstream of Fgf8 in S115 cells and in other cells (SC115) independently derived from Shionogi carcinoma 115. Spectral karyotyping of S115 cells and sequencing of the cloned rearrangement junctions indicate that Fgf8 is involved in a t(5;19) translocation. The chromosome 5 sequence joined to Fgf8 is immediately adjacent to Smr2 (submaxillary gland androgen-regulated protein 2) and includes Muc10 (mucin 10), two genes that we show are testosterone inducible in S115 cells, suggesting that the androgen-dependent expression of Fgf8 in Shionogi carcinoma 115 and derivative cells results from this translocation. Together, these results suggest that androgen inducibility is not an inherent property of the Fgf8 gene, which has implications regarding this gene's proposed role in the etiology of hormone-responsive cancers.

Acinar cells are target cells for androgens in mouse submandibular glands

The variable coding sequence (VCS) multigene family encodes diverse salivary proteins, such as the SMR1 prohormone and the PR-VB1 proline-rich protein in the rat. In situ hybridization was used to study the cell-specific expression of two new mouse VCS genes, Vcs1 and Vcs2. We show that the Vcs1 transcripts, which code for a proline-rich protein, MSG1, are highly abundant in male and female parotid glands, in which they are specifically detected in acinar cells. No expression was seen in the submandibular or sublingual glands. In contrast, Vcs2 transcripts were found only in the acinar cells of the submandibular glands (SMGs) of male mice, in which they are expressed in response to androgens. Expression was found to be heterogeneous within acinar structures. No Vcs2 transcripts were detected in the SMGs of females or castrated males by Northern blot, RNase protection, or in situ hybridization. Androgen administration to females or castrated males induced expression at a level comparable to that of intact males. The Vcs2 gene is the first example of a mouse androgen-regulated gene that is expressed in SMG acinar cells. This result, in addition to our previous observation on SMR1 expression in rats, demonstrates that both acinar cells and granular convoluted tubule (GCT) cells are target cells for androgen action in rodent SMG.

The mouse Vcs2 gene is a composite structure which evolved by gene fusion and encodes five distinct salivary mRNA species

Genes of the VCS (variable coding sequence) family are characterized by an extensive evolutionary divergence in the protein-coding sequence. The VCS family has been characterized by cDNA cloning from submandibular glands in the rat, mouse and humans. At the genomic level, the sequences of two members of this family are known in the rat Rattus norvegicus: the VCSA1 gene, encoding the prohormone-like polypeptide SMR1, and the VCSB1 gene, encoding a salivary Pro-rich polypeptide. No genomic data were available for the VCS genes of other species. To understand the evolution of the VCS gene family better, we have now sequenced 23 kilobases (kb) of the mouse Vcs2 gene. The Vcs2 sequence reveals numerous genomic reorganizations such as an inversion, insertions of short elements and an unusually high number of long interspersed repeated elements (LINEs), which make up 42% of this region. Interestingly, Vcs2 is composed of three different VCS-like regions. The first of these regions contains all the exons necessary to encode the previously described mouse submandibular gland polypeptide MSG2alpha. This region aligns with the entire genomic sequences of rat VCSA1 and VCSB1 genes. The two other regions align with fragments of these rat sequences. The three regions are arrayed in tandem and flanked by LINEs. In particular, the third region also contains exons that were found in mRNA species from the submandibular gland. In total, we have characterized five mRNAs from mouse submandibular glands which have in common their first exon, and are produced by alternative splicing. Vcs2 is thus a single gene that arose by the fusion of three genes (or pseudogenes) of the VCS multigene family.

cDNA cloning of an abundant human lacrimal gland mRNA encoding a novel tear protein

An abundant 1.05 kb human lacrimal gland mRNA has been characterized by cDNA cloning. It encodes a predicted 180 residue, 20546 Da secreted protein, with a charge of +11 at ph 7 and 24.5% proline, designated as Basic Proline-rich Lacrimal Protein (BPLP), Southern blot analysis is consistent with a single BPLP gene. BPLP lacks any distinct repetitive structure, and is unrelated to the salivary proline-rich protein super-family. The pre-proprotein shows modest overall similarity to a superfamily comprising human PRPb, the mouse MSG proteins, and rat VCS-alpha 1, VCS-beta 1 and submandibular apomucin. BPLP also contains a domain with similarity to the Zp2 protein domain found in several otherwise unrelated proteins. Northern blot analysis indicated that the BPLP gene is also expressed at modest levels in the human submandibular gland, and in situ hybridization demonstrated expression of BPLP in the secretory endpieces of the human lacrimal gland. The BPLP cDNA clone defines a new human tear protein, and should provide a useful phenotypic marker of differentiation in in vitro studies of lacrimal gland function.

Various transcripts are generated from the VCSA1 gene by alternative splicing and poly(A) processing in the rat submandibular gland

The members of the VCS (variable coding sequence) multigene family display extensive evolutionary divergence in the protein-coding region. The first described gene (VCSA1) was found to encode a major 0.7-kb mRNA (VCSA1*1T1) coding for a prohormone-like preproprotein, SMR1-VA1, in the submandibular gland (SMG) of Rattus norvegicus. We report here the cloning of four other VCSA1 cDNAs corresponding to mRNAs (VCSA1*1T2 to *1T5) expressed in the SMG. VCSA1*1T1 to *1T4 mRNAs share the three exons previously described and differ in their 3' untranslated regions (UTR). Their differences originate from the alternative utilization of four polyadenylation sites. Comparison of the tissue levels of VCSA1*1T1 and VCSA1*1T4 during post-natal development of the male rat SMG suggests that the poly(A) addition sites are both used at each stage. The fifth RNA transcript (VCSA1*1T5) contains only the first two exons. The nucleotide sequence of the cDNA reveals that VCSA1 has an additional exon (exon 4) which is spliced to exon 2 in VCSA1*1T5. In addition to VCSA1*1T1, at least VCSA1*1T4 and VCSA1*1T5 are actively translated in vivo, as revealed by their association to the polysomal fractions. The protein, P2-VA1, coded by VCSA1*1T5 is 68 amino acids in length and it is likely to be a glycosylated secretory protein. The putative mature P2-VA1 protein completely differs from the SMR1-VA1 pro-protein and very likely has a different function. VCSA1*1T1 is accumulated in the male rat SMG 200-1000-fold more than the other transcripts. Run-on experiments reveal that almost all transcription proceeds several hundred bp downstream from the poly(A) site corresponding to VCSA1*1T1.(ABSTRACT TRUNCATED AT 250 WORDS)

Recent evolution of genes encoding the prohormone-like protein SMR1 in the rat submandibular gland

The Variable Coding Sequence (VCS) multigene family of Rattus norvegicus, is composed of at least 10 members, and shows extensive evolutionary divergence in the protein-coding region. Three members of the VCSA subclass, have been characterized: one of them, the VCSA1 gene mainly expressed in the submandibular gland (SMG) encodes the prohormone-like protein, SMR1-VA1. As VCSA-related genes have not been detected in Mus musculus, the VCSA genes subclass is presumed to have recently emerged. To study the evolution of this subclass, we have looked for VCSA genes in a closely related species, Rattus rattus. By Northern analysis, we demonstrate that VCS-related mRNAs are present in the SMG, and that the level of VCSA mRNA accumulation is approximately equal in both sexes. By contrast, in R. norvegicus, males accumulate about 3,000 times more VCSA1 mRNA than females. Using total SMG mRNA, an almost full-length cDNA, homologous to the cDNA of the R. norvegicus VCSA1 gene, was cloned by reverse transcriptase polymerase chain reaction (RT-PCR). The putative corresponding SMR1-VA1 protein is 146 amino acids long and presents the features characteristic of a secreted protein, with a potential signal peptide of 22 amino acids in the amino-terminal portion. The presence of potential processing multibasic sites suggests that small peptides could be generated (particularly a hexapeptide: Arg-Gln-His-Asn-Leu-Arg), as in the case of the SMR1-VA1 protein of R. norvegicus. From Southern blot analysis there appears that species-species modifications of VCSA gene copy number have occurred; R. rattus contains a greater VCSA1 copy number than R. norvegicus (two or three and one, respectively).