Regulation of proto-oncogenes in rat parotid acinar cells in vitro after stimulation of beta-adrenergic receptors

Neurobiology of cancer: Definition, historical overview, and clinical implications

Studies published in the last two decades have clearly demonstrated that the nervous system plays a significant role in carcinogenesis, the progression of cancer, and the development of metastases. These studies, combining oncological and neuroscientific approaches, created the basis for the emergence of a new field in oncology research, the so‐called “neurobiology of cancer.” The concept of the neurobiology of cancer is based on several facts: (a) psychosocial factors influence the incidence and progression of cancer diseases; (b) the nervous system affects DNA mutations and oncogene‐related signaling; (c) the nervous system modulates tumor‐related immune responses; (d) tumor tissues are innervated; (e) neurotransmitters released from nerves innervating tumor tissues affect tumor growth and metastasis; (f) alterations or modulation of nervous system activity affects the incidence and progression of cancers; (g) tumor tissue affects the nervous system. The aim of this review is to characterize the pillars that create the basis of cancer neurobiology, to describe recent research advances of the nervous system's role in cancer diseases, and to depict potential clinical implications for oncology.

Expressions of CCAAT-enhancer-binding proteins and c-Myc in the parotid gland of the rat: in vivo effects of isoprenaline, bethanechol, vasoactive intestinal peptide and food intake

Parotid glands of adult female rats were exposed to agonists mimicking sympathetic (isoprenaline, 1mg/kg, I.P.) or parasympathetic activity (bethanechol, 10 microg/kg/min i.v. for 30 min, and vasoactive intestinal peptide, VIP, 0.2 microg/kg/min, i.v. for 30 min) or they were reflexly activated by a meal demanding chewing. The stimulated glands were removed at varying times (15(30)-360 min) following the onset of the agonist administration or 75-300 min after the start of a 1h long feeding period, and a number of transcription factors was studied using Western blot. The protein bands were semi-quantitatively measured by densitometry. In response to isoprenaline, C/EBPalpha of 42, 38 and 30 kDa increased by 45-50% above control value, C/EBPbeta LAP (38/35 kDa) by 80% and C/EBPdelta (35 kDa) by 230%, while C/EBPbeta LIP (20 kDa) decreased by 45%. In response to VIP, C/EBPalpha of 42 kDa increased by 75% and C/EBPalpha of 30 kDa by 10%, C/EBPbeta LAP by 65% and C/EBPdelta by 410%, while C/EBPalpha of 38 kDa as well as C/EBPbeta LIP were not changed. In response to bethanechol, C/EBPalpha of 42 kDa increased by 105%, C/EBPbeta LAP by 40% and C/EBPdelta by 170%, while C/EBPalpha of 30 kDa decreased by 30% and C/EBPalpha of 38 kDa and C/EBPbeta LIP remained unchanged. c-Myc increased in response to isoprenaline and VIP by 40-55%, but not to bethanechol. In rats offered a pelleted diet, the parotid glands displayed increases in C/EBPalpha of 42 kDa by 105%, of 30 kDa by 40% and of 38 kDa, by 10%, in C/EBPbeta LAP by 65% and in C/EBPdelta by 215%, whereas C/EBPbeta LIP decreased by 25%. Thus, in parotid glands transcription factors of importance for growth and metabolism were shown to be influenced by autonomimetics as well as by nervous activity.

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.

Inhibition of rat parotid gland growth response induced by chronic isoproterenol following treatment with quinolone antibiotics

While antibiotics are broadly used in dental and medical therapy, little attention has been directed towards the potential toxic side effects of antibiotics on tissue regeneration. Here we examined the effect of a quinolone antibiotic, pefloxacin (Rhone Poulenc) on rat parotid gland responses to chronic isoproterenol treatment. Groups of rats received injections of isoproterenol to induce glandular growth, saline (controls), pefloxacin, or isoproterenol and pefloxacin in combination. Parotid gland weight decreased significantly after pefloxacin treatment for 7 days as well as inhibiting glandular enlargement provoked by isoproterenol. The same trend was observed for the rates of DNA synthesis, with the incorporation of [3H]-thymidine in isoproterenol/pefloxacin-treated rats reduced to 49% of isoproterenol treatment alone levels. Saline-treated animals were 42% of the rate of [3H]-thymidine incorporation into DNA observed in isoproterenol treated rats. While isoproterenol treatment increased steady-state mRNA levels for fos, jun, myc, src, c-erbB-2, ras and topo II, inclusion of pefloxacin with the isoproterenol regimen blocked these increases. Pefloxacin treatment by itself did not alter proto-oncogene mRNA levels in the parotid gland. Glandular amylase activity was decreased in the pefloxacin treated group, while the combination of isoproterenol with pefloxacin did not decrease glandular amylase levels to the extent of that observed with beta-agonist treatment alone. In acute experiments, pefloxacin significantly decreased the volume of saliva secreted by the parotid gland. These results suggest that quinolone-based antibiotics disturb the secretory function of the parotid gland and can inhibit cell proliferation and regeneration.

The role of phosphotyrosine signaling pathway in a parotid gland proliferation and function

Tyrosine phosphorylation and the intracellular signaling processes associated with it have been the focus of intense study due to its importance in the regulation of biological processes as diverse as cell proliferation and cell differentiation. While much of what we now understand has been derived from the study of cell lines and tumor cells, the salivary glands provide a model to examine the effects of tyrosine kinases and tyrosine phosphatases in a normal differentiated tissue. This review will focus, therefore, on the role tyrosine kinases and phosphatases play in inducing the transition from stasis to active proliferation and their potential role in mediating secretory function of the salivary glands.

Transection of corticostriatal afferents reduces amphetamine- and apomorphine-induced striatal Fos expression and turning behaviour in unilaterally 6-hydroxydopamine-lesioned rats

Corticofugal fibres from the prefrontal, prelimbic and anterior sensorimotor cortices were transected by a wide coronal knife-cut through the forceps minor. The cut was performed on the dopamine-depleted side of unilaterally 6-hydroxydopamine-lesioned rats, or on either the right or the left side of intact rats. Sham-lesioned controls received a superficial cortical cut at the same level. Seven days after surgery, apomorphine (0.25 mg/kg s.c.) was administered to 6-hydroxydopamine-lesioned animals and D-amphetamine (5 mg/kg i.p.) was administered to the non-dopamine-denervated ones. Two hours later, the animals were perfusion-fixed for the immunohistochemical detection of the nuclear protein Fos. A computerized image analysis technique was used to quantify, bilaterally, striatal Fos expression in 11 areas of the striatum. The frontocortical transection reduced both apomorphine- and amphetamine-induced Fos expression by 33-66% within the ipsilateral caudate-putamen. The effect was observed throughout the rostral portion of the striatal complex, where the lesioned cortical fibres terminate most densely. A separate batch of unilaterally 6-hydroxydopamine-lesioned rats were used to test the effect of frontocortical transection on amphetamine- and apomorphine-induced turning behaviour. Two groups of rats, showing similar rates of contralateral turning (7-8 turns/min) in response to apomorphine (0.25 mg/kg s.c.), were subjected to either a complete frontocortical transection or a sham lesion on the dopamine-denervated side. An additional two groups, showing comparable rates of ipsilateral turning (15 turns/min) in response to amphetamine (5 mg/kg i.p.), received similar lesions, but now on the side ipsilateral to the intact dopaminergic innervation.(ABSTRACT TRUNCATED AT 250 WORDS)

The c-fos cAMP-response element: regulation of gene expression by a beta 2-adrenergic agonist, serum and DNA methylation

The transcription control region of the proto-oncogene c-fos contains multiple cis-acting elements to which specific trans-acting factors bind. One such well-studied binding motif in the c-fos promoter is the major cyclic AMP response element (CRE) TGACGT located at -62/-57. In this study we investigated the role of this element in gene regulation by beta 2-adrenergic/adenylate cyclase signalling and DNA methylation. By transient gene expression assays we were able to show that the c-fos regulatory sequences spanning nucleotides -361 to +13 could mediate gene expression by the beta 2-adrenergic agonist isoproterenol and the phosphodiesterase inhibitor theophylline. For isoproterenol however, a stimulating effect was observed in serum-starved cells, while an inhibitory effect was measured in cells supplemented with serum. The gene regulation by the cAMP elevating agents could be due, at least partially, to the major CRE since this isolated motif mediated gene expression by these drugs. Distinct protein-DNA complexes were obtained with nuclear extracts prepared from cells exposed to isoproterenol or/and theophylline under different serum conditions. We further show that DNA methylation of this CRE may also be involved in gene regulation as methylation of the CRE motif strongly reduced the binding of nuclear proteins.

Effects of sialagogues on ornithine decarboxylase induction and proto-oncogene expression in murine parotid gland

The mechanism of a sialagogue-induced increase in ornithine decarboxylase (ODC) activity and the expressions of proto-oncogenes in murine parotid gland were investigated by use of isoproterenol (IPR), carbachol (CC), and methoxamine (MTX). The results were as follows: (1) The three sialagogues had similar effects on the parotid in vivo (mouse parotid after a single injection of IPR) and/or in vitro (rat parotid explants cultured on siliconized lens paper floating on 199 medium containing IPR, CC, or MTX), the order of their effectiveness being IPR > CC > MTX. (2) Northern/dot and Western blot analyses revealed that the sialagogues elevated the steady-state levels of ODC mRNA and ODC protein to maxima at two h and six h, respectively, after stimulation. The increases were roughly proportional to those in ODC activity, suggesting that sialagogue-dependent enzyme induction is regulated at the transcriptional level. (3) The mRNAs of four of nine proto-oncogenes examined showed sialagogue-dependent increases to maxima at 30 min (c-fos) or 60 min (c-jun, c-myc, and c-src) after the beginning of stimulation. These increases were all transient, with the levels returning to the control values (without sialagogue) within 60 min. (4) The IPR-dependent elevations of ODC activity and the mRNAs of ODC, c-fos, and c-jun were inhibited by monensin, but not by polymyxin B. On the other hand, the CC-dependent increases in these parameters were inhibited by polymyxin B but not by monensin.(ABSTRACT TRUNCATED AT 250 WORDS)

Pleiotropic effects of a null mutation in the c-fos proto-oncogene

The c-fos proto-oncogene has been implicated as a central regulatory component of the nuclear response to mitogens and other extracellular stimuli. Embryonic stem cells targeted at the c-fos locus have been used to generate chimeric mice that have transmitted the mutated allele through the germline. Homozygous mutants show reduced placental and fetal weights and significant loss of viability at birth. Approximately 40% of the homozygous mutants survive and grow at normal rates until severe osteopetrosis, characterized by foreshortening of the long bones, ossification of the marrow space, and absence of tooth eruption, begins to develop at approximately 11 days. Among other abnormalities, these mice show delayed or absent gametogenesis, lymphopenia, and altered behavior. Despite these defects, many live as long as their wild-type or heterozygous littermates (currently 7 months). These data indicate that c-fos is not required for the growth of most cell types but is involved in the development and function of several distinct tissues.

Reciprocal expression of c-jun, proline-rich protein and amylase genes during rat parotid salivary gland development

We have investigated the temporal expression and cellular localization of the c-jun proto-oncogene and two major rat parotid gland secretory protein genes, PRP (proline-rich protein) and amylase, during postnatal development. c-jun mRNA steady-state levels increased at days 1, 7 and 14 after birth and decreased to basal levels at 21 days and older. PRP mRNA was first detected at 14 days and abruptly increased to adult levels at day 21. Amylase transcripts were first seen at day 7 and progressively increased to adult levels by 28 days. In situ hybridization demonstrated c-jun mRNA accumulation in the differentiating acinar cells and the ducts. The c-jun mRNA accumulation with time corresponds with the proliferative activity reported to occur in these two cellular populations. PRP transcripts were present exclusively in the well differentiated acinar cells while the accumulation of amylase mRNA corresponded to the progressive commitment of parotid cells to acinar differentiation. Our data suggest that during the postnatal development of the rat parotid gland: (a) c-jun expression associates with parotid gland proliferation and precedes the expression of PRP and amylase genes, and (b) activation of PRP and amylase genes is not concomitant and apparently occurs only in differentiating acinar cells.

Down-regulation of cellular proto-oncogenes during inhibition of rat parotid acinar cell proliferation

The role of cell surface galactosyltransferase in mediating isoproterenol-induced parotid gland hypertrophy and hyperplasia was examined in rat parotid gland acinar cells. Introduction of the transferase modifier, alpha-lactalbumin, or galactosyltransferase-associated kinase inhibitor trifluoperazine, into beta-agonist-treated rats prevented acinar cell proliferation as determined by [3H]thymidine incorporation after 96 h of treatment. However, [3H]thymidine incorporation into DNA after 24 h of treatment, with injection of a combination of isoproterenol/alpha-lactalbumin or isoproterenol/trifluoperazine, was similar to injections of isoproterenol alone; suggesting that acinar cells could be stimulated to undergo a single round of DNA synthesis. Northern blot analysis of myc and fos expression followed a similar pattern of down-regulation to control levels after 96 h but not after 24 h. Hybridization with erb B showed little change with proliferation, confirming previous observations on protein levels of the EGF-receptor in acinar cells. Western blot analysis of nuclear protein expression of myc revealed that isoproterenol caused an increase in a 62-kDa protein which was again down-regulated with inhibition of cell proliferation. Analysis of protein levels of Rb110 protein showed no change in protein level in the nucleus with cell proliferation, but did show an associated increase in protein phosphorylation in response to growth stimulation.

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.

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.

Cocaine induces striatal c-fos-immunoreactive proteins via dopaminergic D1 receptors

The protooncogene c-fos produces a phosphoprotein, Fos, which regulates gene transcription processes. In neuronal systems, Fos has been proposed to couple synaptic transmission to changes in gene expression by acting in the cell nucleus in concert with other proteins to form complexes in the promoter regions of target genes. We report here that the acute administration of a single dose of the indirect-acting dopaminergic agonist cocaine increases multiple Fos proteins in rat caudate nucleus. The increase is dose-dependent and is apparent immunocytochemically at 1 hr, maximal at 2 hr, and absent 48 hr after treatment. The increase seen immunocytochemically is composed of several molecular weight species as assessed by Western blotting of proteins from isolated striatal cell nuclei. Administration of the specific dopaminergic receptor antagonists sulpiride and SCH-23390 prior to cocaine support a significant role for D1 but not for D2 receptors in mediating this effect. These data indicate that D1 dopamine receptors are linked to a cellular immediate-early gene system(s) and suggest an action of cocaine at one or more levels of gene expression via modulation of transcriptional processes in activated cells.

Regulation of cell-surface galactosyltransferase in isoproterenol-treated mouse parotid glands

Chronic injection of isoproterenol into mice resulted in hypertrophy and hyperplasia of the parotid gland. As previously described for the rat, cell proliferation was accompanied by an increase in total membrane-associated galactosyltransferase. A plasma membrane localization was determined by fluorescence-activated sorting of intact cells. Co-administration of the galactosyltransferase modifier protein, alpha-lactalbumin, or the calmodulin inhibitor, trifluoperazine, blocked acinar cell proliferation by 96 h post-treatment but not at 24 h. While alpha-lactalbumin appeared to interfere with galactosyltransferase-substrate interactions, trifluoperazine prevented the appearance of cell-surface enzyme in isoproterenol-treated animals.

Two novel c-abl mRNAs are expressed in rat parotid salivary glands during in vivo beta-adrenergic receptor stimulation

The c-abl proto-oncogene is transcribed in most cell lines and tissues into two mRNAs of 6.5 and 5.3 kb, which have different 5' ends and encode two 150 kDa proteins that are largely colinear, but have different N-termini. We show here that two unusually short and abundant c-abl-related mRNAs of 1.5 and 1.3 kb appear in rat parotid salivary glands, within 1 day of in vivo administration of the beta-adrenergic receptor agonist isoproterenol. These transcripts are not found in the submandibular salivary gland or in the heart and they are too short to encode the known c-abl proteins. RNA blot, S1 nuclease protection and primer extension analysis suggest that the isoproterenol inducible parotid gland mRNAs do not contain the kinase domain, but represent part of the C-terminal segment of the abl reading frame.

Regulation of proto-oncogenes and salivary gland cell proliferation

The proto-oncogenes c-fos and c-jun express proteins targeted into the nucleus. The fos and jun proteins form a heterodimeric complex that binds to regulatory elements in the promoter region of specific genes to influence their transcription. Through such a mechanism, the fos and jun proteins have been suggested to link extracellular stimuli to short- and long-term functional changes in cells. Recently we have shown that beta-adrenergic receptor stimulation of rat parotid acinar cells in vitro or addition of 8-BrcAMP in a rat submandibular cell line (RSMT-A5) increases the expression of the c-fos gene in a time-dependent manner. Maximal responses were found at 60 min. The expression of the c-fos gene did not correlate with DNA synthesis in either cell type, and c-fos transcripts were undetectable in the glands of animals treated for eight days with isoproterenol. The new data presented here extended our observations to c-jun gene expression in both salivary cell types where a similar pattern of expression for this proto-oncogene was seen. Conversely, treatment of rats with isoproterenol for nine days resulted in the appearance of two c-abl mRNAs of unique size, in addition to the known 5.3-kb c-abl transcripts. The data suggest that beta-adrenergic receptor stimulation or exposure to 8-BrcAMP induces the early expression of the "nuclear proto-oncogenes" c-fos and c-jun before changes are noted in salivary epithelial cell proliferation. Differences in c-abl mRNA size, occurring later, may be associated with the morphological and biochemical changes known to occur in rat parotid glands after chronic beta-adrenoreceptor stimulation.

Dissociation between c-fos gene expression and DNA synthesis in rat parotid glands

Two experimental approaches were used to examine the relationship between c-fos gene expression and tissue proliferative responses. Beta-Adrenergic and muscarinic receptor stimulation yielded equivalent levels of c-fos expression, although only beta-adrenergic receptor agonists are reported as capable of eliciting DNA synthesis in parotid cells. Similarly, beta-adrenergic stimuli evoked comparable levels of c-fos expression in parotid cells from 2- and 12-month-old rats, whereas DNA synthesis has been shown to be much greater in younger animals. The results indicate that enhanced c-fos expression by itself is incapable of eliciting proliferative responses in rat parotid glands.