Biomedical subjects

Rebecca S Mason

Publications and source records attributed to Rebecca S Mason.

10 recordsLinked to original sources

PubMed2007

Allosteric activation of the extracellular Ca2+-sensing receptor by L-amino acids enhances ERK1/2 phosphorylation.

The calcium-sensing receptor (CaR) mediates feedback control of Ca2+o (extracellular Ca2+) concentration. Although the mechanisms are not fully understood, the CaR couples to several important intracellular signalling enzymes, including PI-PLC (phosphoinositide-specific phospholipase C), leading to Ca2+i (intracellular Ca2+) mobilization, and ERK1/2 (extracellular-signal-regulated kinase 1/2). In addition to Ca2+o, the CaR is activated allosterically by several subclasses of L-amino acids, including the aromatics L-phenylalanine and L-tryptophan. These amino acids enhance the Ca2+o-sensitivity of Ca2+i mobilization in CaR-expressing HEK-293 (human embryonic kidney) cells and normal human parathyroid cells. Furthermore, on a background of a physiological fasting serum L-amino acid mixture, they induce a small, but physiologically significant, enhancement of Ca2+o-dependent suppression of PTH (parathyroid hormone) secretion. The impact of amino acids on CaR-stimulated ERK1/2, however, has not been determined. In the present study, we examined the effects of L-amino acids on Ca2+o-stimulated ERK1/2 phosphorylation as determined by Western blotting and a newly developed quantitative assay (SureFire). L-Amino acids induced a small, but significant, enhancement of Ca2+o-stimulated ERK1/2. In CaR-expressing HEK-293 cells, 10 mM L-phenylalanine lowered the EC50 for Ca2+o from approx. 2.3 to 2.0 mM in the Western blot assay and from 3.4 to 2.9 mM in the SureFire assay. The effect was stereoselective (L>D), and another aromatic amino acid, L-tryptophan, was also effective. The effects of amino acids were investigated further in HEK-293 cells that expressed the CaR mutant S169T. L-Phenylalanine normalized the EC50 for Ca2+o-stimulated Ca2+i mobilization from approx. 12 mM to 5.0 mM and ERK1/2 phosphorylation from approx. 4.6 mM to 2.6 mM. Taken together, the data indicate that L-phenylalanine and other amino acids enhance the Ca2+o-sensitivity of CaR-stimulated ERK1/2 phosphorylation; however, the effect is comparatively small and operates in the form of a fine-tuning mechanism.

Allosteric Regulation↗

PubMed2006

DLC coatings: effects of physical and chemical properties on biological response.

Recent trials on diamond-like carbon (DLC) coated medical devices have indicated promise for blood interfacing applications. The literature is sparse regarding structural and compositional effects of DLC on cellular response. An important goal in optimizing blood-interfacing implants is minimal macrophage attachment, and maximal albumin:fibrinogen adsorption ratio. DLC coatings deposited by PACVD and FAD, were analysed with respect to sp3 content (EELS), hydrogen content (ERDA), surface composition (XPS), surface roughness (AFM), surface energy, albumin:fibrinogen adsorption ratio, and macrophage viability and attachment. We found that increasing surface roughness and surface energy enhanced the macrophage viability and the albumin:fibrinogen adsorption ratio. We also found that the higher the hydrogen content for a-C:Hs deposited by PACVD, the lower the albumin:fibrinogen adsorption ratio, and macrophage attachment. This suggests that hydrogen content may be an important factor for influencing the biological response of DLC surfaces. Macrophage cells spread well on all DLC surfaces, and the surface results indicated the non-toxic nature of the surfaces on the cells at the time points tested.

Animals↗

PubMed2006

Photoprotection by 1,25 dihydroxyvitamin D3 is associated with an increase in p53 and a decrease in nitric oxide products.

Vitamin D is produced in skin by UVB radiation (290-320 nm) acting on 7-dehydrocholesterol. The hypotheses that the active vitamin D hormone, 1,25 dihydroxyvitamin D3 (1,25(OH)2D3), would increase the survival of skin cells after UV irradiation and that surviving cells after 1,25(OH)2D3 treatment would have no increase in DNA damage were tested. The survival of keratinocytes post-UVR was significantly greater after treatment with 1,25(OH)2D3 compared to vehicle (P<0.01). Significant reductions in thymine dimers (TDs) in surviving keratinocytes after UVR were noted in the presence of 1,25(OH)2D3 (P<0.001). Nuclear p53 protein expression increased after UVR and was significantly higher in keratinocytes treated with 1,25(OH)2D3 (P<0.01), whereas NO products were significantly reduced (P<0.05). Both the increase in nuclear accumulation of p53 protein and reduced formation of nitric oxide products may contribute to the reduction in TDs seen with 1,25(OH)2D3 after UVR. Reductions in numbers of sunburn cells (P<0.01) and in TDs (P<0.05) were observed 24 hours after UVR in skin sections from Skh:hr1 mice treated with 1,25(OH)2D3. These results are consistent with the proposal that the vitamin D system in skin may be part of an intrinsic protective mechanism against UV damage.

Animals↗

PubMed2006

Elevated serum FGF23 concentrations in plasma cell dyscrasias.

Fibroblast growth factor 23 (FGF23) is now recognized as a key regulator of phosphate metabolism. Numerous reports have found elevated serum FGF23 concentrations in oncogenic osteomalacia associated with mesenchymal tumors. Hypophosphatemic osteomalacia more rarely occurs in non-mesenchymal tumors. We identified elevated serum FGF23 levels in one patient with chronic lymphatic leukemia (CLL) and hypophosphatemia, prompting us to examine FGF23 concentrations in other patients with B-cell neoplasms. FGF23 levels were elevated in several patients with myeloma and monoclonal gammopathy of undetermined significance (MGUS), and were significantly associated with serum paraprotein and beta-2 microglobulin concentrations in these patients. Hypophosphatemia was not observed even in those patients with elevated FGF23, and a weak positive correlation was noted between serum FGF23 and phosphate concentrations. Malignant plasma cells in bone marrow trephines from patients with myeloma showed cytoplasmic expression of FGF23, similar to the cytoplasmic localization of FGF23 already described in mesenchymal tumors associated with oncogenic osteomalacia. Our findings contribute to an expanding literature regarding abnormal FGF/FGF receptor-signaling in myeloma. The absence of hypophosphatemia in these cases suggests either that FGF23 produced by clonal B-cells lacks systemic bioactivity or that other factors contribute to maintain serum phosphate. We suggest that the relationship between FGF23 and skeletal disease associated with plasma cell dyscrasias deserves further study.

Aged↗

PubMed2005

ErbB receptors mediate both migratory and proliferative activities in human melanocytes and melanoma cells.

Epidermal growth factor receptor (EGFR) activation by transforming growth factor alpha (TGFalpha) has been implicated in autocrine growth in melanoma, but does not alter melanocyte proliferation. This raises the possibility that different signalling pathways are activated via EGFR or ErbB receptors. Here, we demonstrate that ErbB2, ErbB3 and ErbB4 are expressed in cultured human melanocytes. Western analyses with receptor-specific antisera revealed protein bands with Mr values of 185 and 160 kDa, corresponding to ErbB2 and ErbB3, respectively. Blots probed with ErbB4 antibodies showed bands with Mr values of 180, 120 and 80 kDa, corresponding to the receptor and its reported variants. Two malignant melanoma cell lines expressed ErbB2 and ErbB3, but not the full-length ErbB4 receptor. As TGFalpha binds to EGFR and the heregulins (HRG) bind to ErbB3 and ErbB4, these growth factors were examined for effects on receptor activation and on cell growth and motility in a scratch wound closure assay. In normal melanocytes, HRGbeta1 activated the phosphorylation of tyrosine residues of proteins that immunoprecipitated with EGFR and ErbB4 antisera, and significantly enhanced cell migration but not proliferation. Neither TGFalpha nor HRGalpha1 promoted migration or growth in normal melanocytes. By contrast, TGFalpha stimulated migratory activity in the MM96L cell line, but not in the MELJG line, whereas HRGbeta1 significantly enhanced cell growth, but not migration, in both malignant cell lines. The apparent transition of HRGbeta1 from a migratory to a proliferative function after malignant transformation, and the change in TGFalpha from a non-migratory to a migratory activity in one melanoma line, suggests multiple switches in ErbB signalling pathways via EGFR/ErbB heterodimer formation.

Cell Movement↗

PubMed2004

Influence of glucocorticoids on human osteoclast generation and activity.

UNLABELLED: Using human peripheral blood mononuclear cells as osteoclast precursors, we showed that dexamethasone stimulated osteoclast generation at a pharmacological concentration but did not affect the life span of human osteoclasts. Dexamethasone also dose-dependently increased signals for osteoclastogenesis. INTRODUCTION: Glucocorticoid-induced osteoporosis is a common and serious disease. Glucocorticoids predominantly affect osteoblast proliferation and life span. Much of the bone loss is caused by reduced bone formation, but there is also an element of increased bone resorption. MATERIALS AND METHODS: Human peripheral blood mononuclear cells were cultured on whale dentine and induced to differentiate to osteoclasts by RANKL and human macrophage-colony stimulating factor (M-CSF). Osteoclast activity was quantified by pit area. RANKL and osteoprotegerin (OPG) expression in osteoblasts were measured by real-time RT-PCR. RESULTS: In the early phase of osteoclast generation (0-16 days), cultures from two different donors showed that dexamethasone at 10(-8) M increased pit area by 2.5-fold, whereas lower concentrations had no effect. At the highest dexamethasone concentration (10(-7) M), pit area was reduced. In 21-day cultures from three other donors, a similar increase was seen with dexamethasone at 10(-8) M. There was, however, no evidence of increased life span of osteoclasts with dexamethasone. In human primary osteoblasts, dexamethasone dose-dependently reduced OPG and increased RANKL expression as measured by quantitative real time RT-PCR. CONCLUSION: These data provide some explanation at a cellular and molecular level for the observed increase in bone resorption seen in patients treated with glucocorticoids and indicate that there are clear direct effects of glucocorticoids on bone resorption in human cell systems that may differ from other species.

Carrier Proteins↗

PubMed2004

Bone as a source of FGF23: regulation by phosphate?

The identification of FGF23 as a factor involved in several disorders of phosphate regulation and of PHEX as the gene mutated in X-linked Hypophosphatemic Rickets indicates that both these genes may be involved in phosphate homeostasis, although their physiological roles are unclear. In this study, FGF23 mRNA expression was analyzed by real-time RT-PCR and found to be higher in normal human bone than in kidney, liver, thyroid, or parathyroid tissue, while expression in oncogenic osteomalacia tumor tissue was several hundred-fold higher than in bone. Expression of FGF23 mRNA in human osteoblast-like bone cells, quantitated by real-time RT-PCR, increased with increasing extracellular phosphate and was 2-fold higher in cells treated with 2 mM extracellular phosphate compared to 0 mM phosphate treatment. PHEX mRNA expression increased 1.3-fold after treatment with 2 mM phosphate. FGF23 expression in the bone cells increased with increased mineralization over a 20-day treatment period under mineralizing conditions with beta-glycerophosphate, while PHEX expression decreased. The results indicate that FGF23 mRNA expression in bone cells is regulated by extracellular phosphate and by mineralization. These results support proposals that bone may be a source of circulating FGF23 and suggest that FGF23 expression by bone is regulated.

Bone and Bones↗

PubMed2004

Vitamin D in Australia. Issues and recommendations.

BACKGROUND: A significant number of Australians and people from specific groups within the community are suffering from vitamin D deficiency. It is no longer acceptable to assume that all people in Australia receive adequate vitamin D from casual exposure to sunlight. OBJECTIVE: This article provides information on causes, consequences, treatment and prevention of vitamin D deficiency in Australia. DISCUSSION: People at high risk of vitamin D deficiency include the elderly, those with skin conditions where avoidance of sunlight is required, dark skinned people (particularly women during pregnancy or if veiled) and patients with malabsorption, e.g. coeliac disease. For most people, deficiency can be prevented by 5-15 minutes exposure of face and upper limbs to sunlight 4-6 times per week. If this is not possible then a vitamin D supplement of at least 400 IU per day is recommended. In cases of established vitamin D deficiency, supplementation with 3000-5000 IU per day for at least 1 month is required to replete body stores. Increased availability of larger dose preparations of cholecalciferol would be a useful therapy in the case of severe deficiencies.

Accidental Falls↗

PubMed2003

Clinical case seminar: Fibroblast growth factor 23: a new clinical marker for oncogenic osteomalacia.

The phosphate-wasting condition, oncogenic osteomalacia, is problematic to diagnose and manage clinically due to difficulty in locating the causative tumor. Fibroblast growth factor 23 (FGF23) has recently been implicated in the pathogenesis of oncogenic osteomalacia. In this case the patient presented with clinical features typical of oncogenic osteomalacia. Removal of an angiolipoma from the thigh did not correct the clinical or biochemical abnormalities. Subsequent identification and removal of a benign giant cell tumor in the pubic ramus, however, did result in normalization of his symptoms and signs. Positive staining for FGF23 protein by immunohistochemistry was demonstrated in the giant cell tumor, but not in the angiolipoma. The serum concentration of FGF23 was elevated in preoperative serum, then normalized after removal of the giant cell tumor. Expression of both FGF23 mRNA and protein was demonstrated in the giant cell tumor tissue, and FGF23 mRNA expression and renal phosphate uptake inhibitory activity were also detected in cultured giant cell tumor cells. This case provides further evidence for the involvement of FGF23 in the pathogenesis of oncogenic osteomalacia and for the utility of serum FGF23 measurement and immunohistochemical detection of FGF23 in the diagnosis and clinical management of this condition.

Biomarkers↗

PubMed2002

Bioactivity of PTH/PTHrP analogs lacking the 1-14 N-terminal domain.

The N-terminal regions of 1-34 parathyroid hormone (PTH) and 1-34 parathyroid hormone related protein (PTHrP) are thought to be required for full agonist activity of these molecules and for signal transduction by cyclic AMP (cAMP). The C-terminal regions are thought to be involved in receptor binding and protein kinase C activation. In this study, two analogs of PTH/PTHrP lacking the segment 1-14 exhibited agonist activity in opossum kidney (OK) 3B2 cells. Analogs cPTHrP(15-34) and ANA NPY(13-36), an analog of neuropeptide Y, which both have amphipathic alpha helices, inhibited phosphate uptake and stimulated cAMP production in a dose-dependent manner, with half maximal activity in the microM range, compared to the nM range for hPTHrP(1-34) and hPTH(1-34). They also exhibited proportionately lower receptor binding affinities. cAMP production by these analogs was suppressed by the antagonist hPTHrP(7-34). Inhibition of phosphate uptake in response to the analogs was partially suppressed by H-89, but not by bisindolylmaleimide. The analogs also inhibited phosphate uptake and stimulated cAMP in parent OK cells and stimulated cAMP production in UMR-106 cells. These studies present the novel finding that in these cell types, a C-terminal region encompassing PTH/PTHrP(24-31), with the alpha-helical structure maintained, is sufficient for full activity at reduced potency.

Amino Acid Sequence↗