Effect of glucocorticoid on epidermal growth factor receptor in human salivary gland adenocarcinoma cell line HSG

IGF-I and INS receptor expression in the salivary glands of diabetic Nod mice submitted to long-term insulin treatment

This work aimed to characterize the IGF-I and INS receptor expression in the salivary glands of Nod mice, correlating to therapeutic effects of insulin treatment on these receptors. Nod mice were divided into: Groups 1 and 2 (diabetic), Groups 3 and 4 (diabetic with insulin treatment) and Group 5 (non-diabetic). Fragments from the salivary glands were processed for immunohistochemical analysis. The results showed that the prolonged diabetic state led to a steadily increased IGF-I receptor expression. INS receptor expression was gradually decreased. It was concluded that not only was the IGF-I receptor expression affected by the diabetic state but also the INS receptor expression. The period of the diabetic state was directly related to changes in the expression of these receptors. In spite of the insulin treatment having recovered the glycaemic levels, the expression of INS and the IGF-I receptors did not reach the standard level, which certainly hampered glandular function.

Expression of cAMP response element binding protein (CREB)-binding protein (CBP) and the implication in retinoic acid-inducible transcription activation in human salivary gland adenocarcinoma cell line HSG

In the process of retinoic acid (RA) signaling, retinoic acid receptor interacts with a coactivator complex composed of various transcription cofactors such as CREB-binding protein (CBP)/p300 and p160 family member proteins represented by steroid receptor coactivator-1 (SRC-1)/NCoA1 and p300/CBP cointegrator protein (p/CIP)/ACTR. In order to investigate the relationship of CBP to the RA signaling in a human salivary gland (HSG) adenocarcinoma cell line, we examined the expression of CBP in the cells. Immunoprecipitation and immunoblotting of the nuclear extract of HSG cells with anti-human CBP antibody showed a specific 270-kDa band, indicating the expression of CBP in HSG cells. The immunocytochemical analysis confirmed the nuclear localization of CBP. The transfection of HSG cells with a luciferase reporter plasmid harboring an RA-response element at the 5'-upstream region of the reporter gene increased RA-dependent luciferase activity approximately 3-fold. Co-transfection with a CBP-expression plasmid and the luciferase reporter gene enhanced the RA-dependent transcription activation approximately 10-fold. The immunoprecipitates obtained with anti-CBP antibody exhibited a histone acetyl-transferase (HAT) activity 2-fold higher than that obtained with the control antibody, whereas the HAT activity of the immunoprecipitates with anti-SRC-1 and anti-p/CIP, which were used as comparisons, were only a little increased. The RA treatment had no effect on the level of HAT activity except in the case of using the immunoprecipitate obtained with anti-RARalpha, in which case it increased the activity. These findings indicate that CBP expressed in HSG cells mediates the RA-inducible growth and differentiation-regulating transcription activation in concert with the retinoic acid receptors.

Salivary gland P2 nucleotide receptors

The effects of ATP on salivary glands have been recognized since 1982. Functional and pharmacological studies of the P2 nucleotide receptors that mediate the effects of ATP and other extracellular nucleotides have been supported by the cloning of receptor cDNAs, by the expression of the receptor proteins, and by the identification in salivary gland cells of multiple P2 receptor subtypes. Currently, there is evidence obtained from pharmacological and molecular biology approaches for the expression in salivary gland of two P2X ligand-gated ion channels, P2Z/P2X7 and P2X4, and two P2Y G protein-coupled receptors, P2Y1 and P2Y2. Activation of each of these receptor subtypes increases intracellular Ca2+, a second messenger with a key role in the regulation of salivary gland secretion. Through Ca2+ regulation and other mechanisms, P2 receptors appear to regulate salivary cell volume, ion and protein secretion, and increased permeability to small molecules that may be involved in cytotoxicity. Some localization of the various salivary P2 receptor subtypes to specific cells and membrane subdomains has been reported, along with evidence for the co-expression of multiple P2 receptor subtypes within specific salivary acinar or duct cells. However, additional studies in vivo and with intact organ preparations are required to define clearly the roles the various P2 receptor subtypes play in salivary gland physiology and pathology. Opportunities for eventual utilization of these receptors as pharmacotherapeutic targets in diseases involving salivary gland dysfunction appear promising.

Inhibition of retinoic acid-inducible transcription by COUP-TFI in human salivary gland adenocarcinoma cell line HSG

Human salivary gland adenocarcinoma cells (HSG) express nuclear receptors, all-trans-retinoic acid (at-RA) receptors (RARs), and retinoid X/9-cis-retinoic acid (9-c-RA) receptors (RXRs). In order to investigate whether the endogenous RARs or RXRs of HSG cells can induce transcription activation, the thymidine kinase promoter (TK)-driven luciferase reporter gene containing the retinoic acid response element (RARE), of RARβ, βRARE2-TK-Luc, was transfected into HSG cells and ligand-dependent transcription activation was examined. Luciferase activity of cell lysate increased by the treatment with either at-RA or 9-c-RA. Co-transfection of RARα and (or) RXRα-expression plasmids with the reporter gene enhanced the luciferase activity, suggesting that endogenous RARs and RXRs work as ligand-dependent transfactors in HSG cells. Reverse transcriptase - polymerase chain reaction analysis revealed that HSG cells express chicken ovalbumin upstream promoter - transcription factor I (COUP-TFI). Co-transfection of COUP-TFI-expression plasmid suppressed the at-RA-induced transcription activation of the reporter gene. Similar results were shown using a chromatin-integrated reporter gene system, using a stably transfected β-RARE2-TK-β-galactosidase (β-Gal) reporter gene. The at-RA-dependent increase in the β-Gal expression was completely inhibited by COUP-TFI. The transfection of antisense oligonucleotide of COUP-TFI squelched the RA-dependent growth inhibition induced by RAR-RXR heterodimers. Conclusively, RARs and RXRs of HSG cells are functional and play roles as transactivators in at-RA-sensitive processes such as the proliferation or differentiation of cells. COUP-TFI very likely regulates these processes by repressing the functions of these transactivators.Key words: retinoic acid receptor, retinoid X receptor, COUP-transcription factor (COUP-TF), retinoic acid response element.

Cytokines and growth factors modulate cell growth and insulin-like growth factor binding protein secretion by the human salivary cell line (HSG)

The human salivary cell line (HSG) was investigated for the effect of various growth factors and cytokines on cellular proliferation and on the production of insulin-like growth factor binding proteins (IGFBPs). IGF-I increased cell growth by approximately 25%, and induced the appearances of three distinct protein bands on ligand blot of the cell culture. Two bands with molecular weights of 43 and 45 Kda, respectively, proved to be IGFBP-3 using a specific antibody, and the third was a 24 Kda species (probably, IGFBP-4). Similar IGFBPs were released by the cells following stimulation by EGF and insulin as well as following incubation with the IGF-I receptor antibody alpha IR3. Retinoic acid had an inhibitory effect (50%) on IGF-I-induced cellular proliferation and an attenuative effect on the 24 Kda band when it was combined with IGF-I, and to a lesser effect EGF; however, it enhanced IGFBP-3 production when incubated with IGF-I. The IGF-I receptor antibody had an agonistic effect on IGFBPs production when applied alone or together with IGF-I. TNF-alpha and INF-gamma had minimal effects on cell growth when added alone but when applied in combination, a marked inhibition of cellular proliferation was noted. These cytokines caused increased accumulation of IGFBP-3, -4, and -5. Addition of IGF-I to these cytokines enhanced the expression of these bands. These data demonstrate that growth factors and cytokines which modulate HSG cell growth, induce specific IGFBPs which may play a role in their effects on cell growth.

Co-expression of epidermal growth factor-receptor and c-erb B-2 proto-oncogene product in human salivary-gland adenocarcinoma cell line HSG and the implications for HSG cell autocrine growth

The autonomous proliferation of HSG cells is mediated by an autocrine growth factor, a 46K epidermal growth factor (EGF)-like molecule. The receptor for this molecule was investigated. Immunoprecipitation and immunoblotting revealed the expression of two possible receptor molecules, EGF-R and p185erbB-2, in HSG cells. Northern blotting also revealed the co-expression of 5.6-kb EGF-R mRNA and 4.6-kb c-erb B-2 mRNA. When the purified EGF-like molecule was added to the cultures, EGF-R but not p185erbB-2 was autophosphorylated. These results suggest that, although both EGF-R and p185erbB-2 are co-expressed in HSG cells, the EGF-R is the genuine receptor for the EGF-like molecule. However, there is a possibility that p185erB-2 is involved in the signal transduction system. This possibility was examined by using specific antibodies to human EGF-R (hEGF-R), p185erbB-2, and EGF to inhibit the functions of these molecules. Addition of these three antibodies to the cultures inhibited the growth of HSG cells. The antibodies to EGF-R and p185erbB-2 also caused morphological changes such as disturbances of the plasma membrane, and some cell death. Surprisingly, the effect of the anti-p185erbB-2 antibody on growth inhibition and morphology was stronger than that of the anti-hEGF-R antibody. Thus, p185erB-2 expressed in HSG cells has an important function in the signal transduction of HSG cell growth.

Glucocorticoids enhance the potency of Schwann cell mitogens

Previous studies have documented that cultured Schwann cells require serum-containing medium to respond maximally to mitogens. We now report that Schwann cells are able to proliferate to a mitogenic response in a serum-free defined medium termed oligodendrocyte defined media (ODM). Glucocorticoids are the essential component of ODM which allow Schwann cell proliferation in the serum-free medium. Charcoal treatment of the fetal calf serum decreases the mitogenic potency of the axolemma-enriched fraction (AEF) by 50%. The addition of 2 microM hydrocortisone to charcoal-treated fetal calf serum restores 75% of the lost mitogenicity. These observations are consistent with the view that glucocorticoids present in fetal calf serum are potent co-mitogens essential for AEF-induced Schwann cell proliferation. The synthetic glucocorticoid, dexamethasone, is a more potent co-mitogen than hydrocortisone, with a maximal effect at concentrations less than 10 nM. In contrast, other steroids including aldosterone, progesterone, testosterone, and 17 beta-estradiol have no effect on enhancing the mitogenic response of Schwann cells to the AEF. The glucocorticoid antagonists RU 486 and dehydroepiandrosterone (DHEA), but not the antiestrogenic compound tamoxifen, block AEF-induced Schwann cell proliferation. These results suggest that glucocorticoid-induced Schwann cell proliferation is mediated through a glucocorticoid receptor (GR) mechanism. We detected immunoreactivity to the GR in the cytoplasm, but not in the nuclei of Schwann cells grown in ODM lacking dexamethasone. The addition of 100 nM dexamethasone to these cultures resulted in immunoreactivity in the nucleus. This data suggests that glucocorticoids working through the GR are potent co-mitogens for Schwann cell proliferation.

Retinoic acid receptor in subclone of human salivary gland adenocarcinoma cell line HSG and effect of retinoic acid on cellular growth

Retinoic acid (RA) binding has been detected in the nuclei of a subclone (CL-1) of human submandibular adenocarcinoma cell line HSG conditioned to grow in a serum-free defined medium. Competition assay confirmed the specificity of the RA binding. Scatchard analysis showed the binding molecule to have a high affinity and low capacity. From the analyses by gel-filtration and glycerol density gradient centrifugation, the nuclear binding molecule appears to be distinct from cellular RA binding protein (CRABP) in terms of molecular weight. Furthermore, immunoblotting analysis revealed a band (Mr 47,000) reactive with specific antibody to RA receptor (RAR) alpha in the gel containing the nuclear fraction of CL-1 cells. Northern blotting analysis with specific cDNA probes revealed the expression of RAR alpha and RAR gamma in CL-1 cells. These results indicate that CL-1 cells express two types of RAR subtype, suggesting that these receptor molecules may mediate biological effects of RA. Treatment of CL-1 cells with RA resulted in an increase in the incorporation of [3H]thymidine into TCA-insoluble materials. The maximal increase was observed at 10(-6) M around 48 h. Previously, we demonstrated the autocrine growth of HSG cells mediated by epidermal growth factor (EGF) receptors and EGF-like molecules (Kurokawa et al. (1989) Cancer Res. 49, 5136-5142) and showed that RA had no significant effect on the secretion of the EGF-like molecule. RA induced an increase in [125I]EGF binding to CL-1 cells. The increase in the EGF binding was maximal at 24 h at 10(-6) M RA. RA also increased the amount of [3H]leucine-labeled EGF receptor dose-dependently. No significant change was observed in total protein synthesis of CL-1 cells by treatment with RA. These results suggest that RA stimulates the growth of CL-1 cells by increasing EGF receptor levels.

Ontogeny of dexamethasone binding and sodium potassium ATPase activity in experimental murine polycystic kidney disease

The induction of polycystic kidney disease (PKD) by glucocorticoids in newborn mice behaves as a "threshold" trait, with prevalence of PKD varying in different inbred strains after exposure to an inducing steroid. C3H mice (low threshold for PKD) demonstrated greater specific dexamethasone binding than DBA mice (high threshold) on the second day of life. Treatment with methylprednisolone acetate (MPA), a cyst-inducing steroid, down regulated dexamethasone binding earlier than in DBA mice. C3H mice demonstrated greater whole kidney homogenate Na-K ATPase activity than DBA mice within 24h of MPA injection. Specific renal glucocorticoid binding may be a regulator of threshold for murine glucocorticoid induced PKD. Our findings support in vitro evidence that glucocorticoid induced Na-K ATPase activity during critical periods of nephron development is an important regulatory point of this model.