Identification and characterization of the beta-adrenergic receptor on neuroblastoma x glioma hybrid NG108-15 cells

β adrenergic receptor modulated signaling in glioma models: promoting β adrenergic receptor-β arrestin scaffold-mediated activation of extracellular-regulated kinase 1/2 may prove to be a panacea in the treatment of intracranial and spinal malignancy and extra-neuraxial carcinoma

Neoplastically transformed astrocytes express functionally active cell surface β adrenergic receptors (βARs). Treatment of glioma models in vitro and in vivo with β adrenergic agonists variably amplifies or attenuates cellular proliferation. In the majority of in vivo models, β adrenergic agonists generally reduce cellular proliferation. However, treatment with β adrenergic agonists consistently reduces tumor cell invasive potential, angiogenesis, and metastasis. β adrenergic agonists induced decreases of invasive potential are chiefly mediated through reductions in the expression of matrix metalloproteinases types 2 and 9. Treatment with β adrenergic agonists also clearly reduce tumoral neoangiogenesis, which may represent a putatively useful mechanism to adjuvantly amplify the effects of bevacizumab. Bevacizumab is a monoclonal antibody targeting the vascular endothelial growth factor receptor. We may accordingly designate βagonists to represent an enhancer of bevacizumab. The antiangiogenic effects of β adrenergic agonists may thus effectively render an otherwise borderline effective therapy to generate significant enhancement in clinical outcomes. β adrenergic agonists upregulate expression of the major histocompatibility class II DR alpha gene, effectively potentiating the immunogenicity of tumor cells to tumor surveillance mechanisms. Authors have also demonstrated crossmodal modulation of signaling events downstream from the β adrenergic cell surface receptor and microtubular polymerization and depolymerization. Complex effects and desensitization mechanisms of the β adrenergic signaling may putatively represent promising therapeutic targets. Constant stimulation of the β adrenergic receptor induces its phosphorylation by β adrenergic receptor kinase (βARK), rendering it a suitable substrate for alternate binding by β arrestins 1 or 2. The binding of a β arrestin to βARK phosphorylated βAR promotes receptor mediated internalization and downregulation of cell surface receptor and contemporaneously generates a cell surface scaffold at the βAR. The scaffold mediated activation of extracellular regulated kinase 1/2, compared with protein kinase A mediated activation, preferentially favors cytosolic retention of ERK1/2 and blunting of nuclear translocation and ensuant pro-transcriptional activity. Thus, βAR desensitization and consequent scaffold assembly effectively retains the cytosolic homeostatic functions of ERK1/2 while inhibiting its pro-proliferative effects. We suggest these mechanisms specifically will prove quite promising in developing primary and adjuvant therapies mitigating glioma growth, angiogenesis, invasive potential, and angiogenesis. We suggest generating compounds and targeted mutations of the β adrenergic receptor favoring β arrestin binding and scaffold facilitated activation of ERK1/2 may hold potential promise and therapeutic benefit in adjuvantly treating most or all cancers. We hope our discussion will generate fruitful research endeavors seeking to exploit these mechanisms.

A functional assay for G-protein-coupled receptors using stably transformed insect tissue culture cell lines

Insect cells are an underexplored resource for functional G-protein-coupled receptor (GPCR) assays, despite a strong record in biochemical (binding) assays. Here we describe the use of vectors capable of creating stably transformed insect cell lines to generate a cell-based functional GPCR assay. This assay employs the luminescent photoprotein aequorin and the promiscuous G-protein subunit Galpha16 and is broadly applicable to human GPCRs. We demonstrate that the assay can quantitate ligand concentration-activity relationships for seven different human GPCRs, can differentiate between partial and full agonists, and can determine rank order potencies for both agonists and antagonists that match those seen with other assay systems. Human Galpha16 improves signal strength but is not required for activity with some receptors. The coexpression of human and bovine betagamma subunits and/or phospholipase Cbeta makes no difference to agonist efficacy or potency. Two different receptors expressed in the same cell line respond to their specific agonists, and two different cell lines (Sf9 and High 5) are able to functionally detect the same expressed GPCR. Sf9 cells have the capability to produce fully functional human receptors, allied to a low background of endogenous receptors, and so are a valuable system for investigating orphan GPCRs and receptor dimerization.

Cellular response to latent TGF-beta1 is facilitated by insulin-like growth factor-II/mannose-6-phosphate receptors on MS-9 cells

This study was conducted to explore the mechanism of activation of TGF-beta1 which is critical to its role in many physiological and pathological conditions. We have previously demonstrated that latent TGF-beta1 modulates ECM through interaction with IGF-II/M6P receptors on dermal fibroblasts. In this report, we provide evidence that large (270 kDa) but not small (46 kDa) M6P receptors facilitate the cellular response to LTGF-beta1 released from genetically modified cells. As a source of LTGF-beta1, PA317 cells were transfected with either pLin-TGF-beta1 vector or pLin vector with no TGF-beta1 insert using calcium phosphate precipitation. Conditioned medium from transfected cells was removed after 3 days and used to evaluate the latency and bioactivity of TGF-beta1 using ELISA and mink lung epithelial cell growth inhibition assay, respectively. The level of TGF-beta1 was 20-fold greater (2142 +/- 369 vs 102 +/- 23 pg/ml) in conditioned medium derived from pLin-TGF-beta1-transfected cells than in that of controls. Various volumes of this conditioned medium were then used to treat MS-9, SR-2, and MS cells bearing the large, small, and no IGF-II/M6P receptors, respectively, for 24 h. [(3)H]Thymidine incorporation, used as an index for cell proliferation, showed a markedly lower level of proliferation in MS-9 cells in response to a given concentration of LTGF-beta1 than was seen in SR-2 and MS cells. Interestingly, under similar experimental conditions, either addition of M6P at 1 mM concentration or anti-TGF-beta1 antibody abrogated the MS-9 cell proliferative response to LTGF-beta1. In contrast, the inhibitory response of these three cell strains to heat-activated conditioned medium was the same. As another measure of LTGF-beta1-induced cellular response, the expression of mRNA for pro alpha1(I) of type I collagen was also evaluated. A marked increase in expression of this transcript in MS-9 cells in response to LTGF-beta1 was observed. To further examine the possible correlation between the large IGF-II/M6P receptors and cellular responses to LTGF-beta1, expression of IGF-II/M6P receptors at the protein and mRNA levels were evaluated by ligand binding and RT-PCR, respectively. Using (125)I-IGF-II as a ligand, the number of specific IGF-II/M6P receptors was found to be threefold greater on MS-9 than on SR-2 and MS cells. This finding was consistent with the level of IGF-II/M6P receptor mRNA detected by RT-PCR in MS-9 cells. In conclusion, the result of this study shows a direct link between large but not small IGF-II/M6P receptors on MS-9 cells and their response to LTGF-beta1.