Structure, organization, and regulation of a hamster proline-rich protein gene. A multigene family

Salivary Proteins as a Defense Against Dietary Tannins

Tannins, a diverse group of water-soluble phenolics with high affinity to proteins, are widely distributed in various parts of plants, and have negative effects in herbivores after ingestion. Some mammalian species are thought to counteract tannins by secreting tannin-binding salivary proteins (TBSPs). Several types of TBSPs are found in the saliva of laboratory animals, livestock, and wildlife. Among them, proline-rich proteins (PRPs) and histatins are effective precipitators of tannins. It is widely accepted that, at the least, PRPs act as a first line of defense against tannins. Many observations support this idea: in vitro affinity of PRPs to tannins is far higher than that of other proteins such as bovine serum albumin; complexes formed between PRPs and tannins are stable even under the conditions in the stomach and intestine; and PRP production is induced by ingesting tannins. It is believed that species that usually ingest tannins as part of their natural diets produce high levels of PRPs, whereas species not exposed to tannins produce little or no PRPs. This hypothesis is generally supported, although studies on TBSPs in wildlife are limited. This work stresses the importance of gathering basic information on such items as the characteristics of unidentified TBSPs, and seasonal and geographical variations in PRP production.

Novel cDNA clones obtained by antibody screening of a mouse cerebellar cDNA expression library

In order to obtain cDNAs of genes that are expressed in cerebellar granule cells (GC), an antiserum was raised against GC isolated from mouse cerebella. Western blot analysis demonstrated that antibodies against multiple proteins were present and immunohistochemical analysis showed that at least some of these proteins were localized to cerebellar GC. The antiserum was used to screen an expression library derived from mouse cerebellar cDNA. Twenty-two granule cell antibody-positive (GCAP) clones were obtained. Of these, eight represented genes previously described and 14 were novel clones (not found in the GenBank database). In situ hybridization histochemistry showed that eight of the novel clones had moderate to strong expression in cerebellar GC and some of these clones were expressed also in the hippocampal formation. One such clone, GCAP-7, appears to represent a single-copy gene and the entire cDNA insert (2,688 bp) has been sequenced. The clone appears to consist primarily of the 3' untranslated portion, including a poly(A) tail and polyadenylation signals, of a 5 kb transcript. The GCAP clones should be useful for future studies of molecular biology of GC in normal individuals and in inherited neurologic disease with GC degeneration.

Structure, organization and regulation of a rat cysteine proteinase inhibitor-encoding gene

During postnatal development, submandibular glands of rats produce the secretory protein, cystatin S (CysS), which belongs to family 2 of the mammalian cysteine proteinase inhibitor superfamily. While the rat CysS gene is not expressed in the salivary glands of adult rats, it can be induced by isoproterenol (IPR), which acts via beta-adrenergic receptor/adenylate cyclase/cyclic AMP (cAMP) mechanisms. In addition, IPR-induction of CysS mRNA in submandibular glands is more pronounced in females than in males, at both prepuberal and mature ages. These results suggest that sex hormones may participate in the regulation of the rat CysS gene via estrogen-responsive elements (ERE), and IPR induction of this gene supports the hypothesis that cAMP-responsive elements (CRE) may also play a role in regulating CysS gene expression. We have isolated, sequenced and characterized the complete gene. The CysS gene contains three exons interrupted by two intervening sequences, with consensus splice junctions. The transcription start point is 73 nucleotides upstream from the start codon which is surrounded by a typical Kozak sequence. CCAAT and TATA boxes are present in the 5'-flanking region of the CysS gene. This region also contains several possible regulatory elements that resemble those of other eukaryotic genes, i.e., ERE, CRE, and glucocorticoid-responsive elements. The first intron sequence contains other potential CRE highly homologous to those found in the IPR-inducible mouse and hamster proline-rich-protein-encoding genes.

Gene sequence of mouse B-type proline-rich protein MP4. Transcriptional start point and an upstream phylogenetic footprint with ets-like and rel/NFkB-like elements

A mouse genomic B-type proline-rich protein (PRP) cosmid clone was isolated by cDNA hybridisation and mapped, the gene region was subcloned and 3770 bp were sequenced. This gene (MP4) contained three introns and encoded a 1020-nt (nt, nucleotide) mRNA for a PRP precursor 300 amino acids long arranged with 11 imperfect 18-residue proline-rich repeats. The transcriptional start point was determined by S1 nuclease mapping and primer extension to be 26 bp downstream of a TATAA sequence. Sequence comparisons revealed that only two regions from positions -650 bp - -30 bp were highly conserved in all other PRP genes, PRP boxes 1 and 2. Box 1 at positions -112 to -135 contained ets-like and rel/NFkB-like elements and was 74% conserved over 23 bp. Box 2 at positions -33 - -51 was 53% conserved over 19 bp. A search of the EMBL and GenBank sequence libraries indicated that PRP box 1 was only present upstream of the known mammalian PRP gene sequences and was absent from other genes. These conserved sequences may thus be relevant to the tissue-specific and beta-adrenergic regulation of PRP gene transcription.

Characterization of the gene encoding the salivary Gln/Glu-rich C-terminal variant A protein

The rat submandibular gland-specific GRP-Ca gene (encoding C-terminal variant A of the glutamine/glutamic acid-rich protein) has been cloned from a male Wistar/Furth genomic library. The complete sequence, including 2.0 kb of 5' flanking and 0.5 kb of 3' flanking DNA has been determined. Electron microscopic heteroduplex analysis and sequence analysis established that transcripts coding for GRP-Ca and GRP-Cb are encoded by separate genes. The GRP-Ca gene is approx. 4.5 kb in size and is comprised of four exons and three introns. Comparison of this gene with several rodent and human salivary proline-rich protein-encoding genes (PRP) indicates that GRP-Ca shares this exon-intron structure with the rat SMR-2 gene, the hamster H29 gene, and the human PRP genes. In addition, a 28-bp element found in the proximal promoter region of GRP-Ca was found to be highly conserved among the superfamily of PRP genes.

Sequence and expression of the MnP4 gene encoding basic proline-rich protein in macaque salivary glands

We report here the macaque MnP4 cDNA and genomic sequences which encode a basic proline-rich protein (PRP), which is synthesized in macaque parotid gland and submandibular gland. The locations of intron positions and the prototype of the tandem 20-amino-acid repeat motif with the sequence, PPPPGKPQGPPQQGGNKPQG, in MnP4, were compared to those in related genes encoding PRP and glutamic/glutamine-rich proteins (GRP) in humans and rodents. Exceedingly high homology of the first exon and 40-bp region immediately upstream of exon I is observed with other PRP genes of all species studied. In order to identify the regulatory elements involved in control of MnP4 gene expression, a rat submandibular gland-derived cell line (RSMT-A5) was transfected with MnP4-cat constructs that contained the promoter and 5'-flanking regions of the macaque MnP4 gene fused to the bacterial cat gene. Deletion analysis revealed that putative positive and negative regulatory elements reside between nucleotides (nt) -107 and +5, and nt -586 and -108, respectively. As part of this study, the promoter of the macaque MnP4 gene appears to be salivary gland specific. This salivary gland-specific gene expression attests to the complexity of transcriptional regulation in eukaryotes.

Molecular characterization of rat multigene family encoding proline-rich proteins

Three members of the rat proline-rich protein multigene family have been characterized. Each of these genes, RP4, RP13, and RP15, contains three exons and they are approximately 4.8, 5.7, and 5.4 kb, respectively. The DAN sequences of RP4 and RP13 are greater than 93% homologous in the 3.1-kb segment extending from the 5'-upstream region (approximately nucleotide -930) to 238 nucleotides after the second exon/intron junction; however, regions further downstream, intron II and exon III, share less than 43% identity. In contrast, exon III from RP15, RP13, and the previously sequenced mouse PRP gene MP2 are more than 73% conserved. These analyses suggest that the duplication of the ancestral genes to RP13 and RP4 occurred prior to the divergence of the rat PRP genes. The results also indicate that in the past 21.5 million years, multiple recombination events have resulted in a very high degree of divergence among intron II and exon III of RP4 and RP13. This divergence is due in part to the insertion of members of the rat long interspersed repeat DNA family at -930 bp upstream from the transcription initiation site and within intron II of RP13. Comparisons of the nucleotide sequences and organization of exon I with the genomic organization of PRP and glutamic acid/glutamine-rich protein genes in this and previous studies reveal striking resemblance among these genes. These observations are consistent with the notion that this super multigene family arose from duplication of progenitor genes via unequal crossing over events. In addition, the results suggest that concerted evolution has occurred within the tandemly repeated motif of exon II.

Genetic regulation of salivary proteins in rodents

The presence of a protein in the cell is the result of a complex pathway that is known by the term gene expression. In this article we review the existing literature on the structure and expression of representative salivary gland genes and their regulated expression during development and upon extracellular stimulation. The expression of one of the "nuclear" protooncogenes, c-fos, in rat parotid glands is also discussed. Finally, we present some suggestions for future studies that will help to understand the mechanisms leading to gene regulation in rat salivary glands.

Proline-rich proteins and glycoproteins: expression of salivary gland multigene families

Our recent research interests have focused on a group of unusual proteins and glycoproteins high in proline content, or the so-called proline-rich proteins (PRPs). The PRPs are tissue-specific expressions of salivary gland multigene families. Normally PRPs are not detected or are present in very low amounts in rat, mouse and hamster salivary glands, but these unusual proteins are dramatically induced by treatment with the catecholamine isoproterenol. The structures and organizations of several PRP mRNAs and PRP genes have been determined. The amino acid sequences of all PRPs show 4 distinct regions, namely, a signal peptide, a transition region, a repeat region and a carboxyl-terminal region. Glycoproteins induced by isoproterenol treatment may be N-glycosylated or O-glycosylated. The N-glycosylated glycoprotein GP-158 from rat submandibular glands has a 12 amino acid glycopeptide which repeats possibly 49 times. Proline-rich proteins of the parotid glands of rats and mice are also greatly induced by dietary tannins. The apparent unique occurrence of PRPs in saliva suggests that one biological role is to neutralize the detrimental effects of dietary tannins and other polyphenols. The upstream regions of the mouse and hamster PRP genes contain cyclic AMP-regulated sequences as demonstrated by deletions and transient transfections. The PRP multigene family members of mouse are all located on chromosome 8.