The inositol 1,4,5-trisphosphate receptor (InsP3R) is an intracellular Ca2+ channel that plays a role in the regulation of insulin secretion. In rat isolated pancreatic islets the expression of types I, II and III InsP3R mRNA was identified by reverse transcriptase-polymerase chain reaction and confirmed by cDNA cloning and sequencing. The islet ratios of types I, II and III InsP3R mRNA to beta-actin mRNA were 0.08 +/- 0.02, 0.08 +/- 0.03 and 0.25 +/- 0.04 respectively. Types I, II and III InsP3R mRNA were also expressed in rat (RINm5F) and mouse (betaHC9) pancreatic beta-cell lines, and rat cerebellum. Type III InsP3R mRNA was quantitatively the most abundant form in rat islets and RINm5F cells. In betaHC9 cells, types II and III InsP3R mRNA were expressed at similar levels, and in much greater abundance than type I mRNA. Type III was the least abundant InsP3R mRNA in cerebellum. Culture of betaHC9 cells for 5 days at 2.8 and 25 mM glucose, or RINm5F cells for 7 days at 5.5 and 20 mM glucose, resulted in significantly enhanced expression of type III, but not types I and II, InsP3R mRNA in the cells at the higher glucose concentrations. During short-term (0.5-2 h) incubations, betaHC9 cell type III InsP3R mRNA levels increased in response to glucose in a time- and concentration-dependent manner. Actinomycin D inhibited the glucose response. Alpha-ketoisocaproic acid also stimulated betaHC9 cell type III InsP3R mRNA expression in a concentration-dependent manner, whereas 2-deoxyglucose and 3-O-methylglucose were without effect. The different levels of expression of mRNA for three InsP3R isoforms in islets and insulinoma cells, and the influence of glucose and alpha-ketoisocaproic acid on the expression of type III mRNA, suggests that nutrient metabolism plays a role in the regulation of this gene and that the function of InsP3R subtypes may be unique with each playing a distinct role in beta-cell signal transduction and insulin secretion.
Irene I Lee, Nane C Kuznik, Jaice T Rottenberg, Myles Brown, and Andrew C B Cato
Androgens are important determinants of normal and malignant prostate growth. They function by binding to the C-terminal ligand-binding domain (LBD) of the androgen receptor (AR). All clinically approved AR-targeting antiandrogens for prostate cancer therapy function by competing with endogenous androgens. Despite initial robust responses to androgen deprivation therapy, nearly all patients with advanced prostate cancer relapse with lethal castration-resistant prostate cancer (CRPC). Progression to CRPC is associated with ongoing AR signaling, which in part, is due to the expression of constitutively active AR splice variants that contain the N-terminus of the receptor but lack the C-terminus. Currently, there are no approved therapies specifically targeting the AR N-terminus. Current pharmacologic targeting strategies for inhibiting the AR N-terminal region have proven difficult, due to its intrinsically unstructured nature and lack of enzymatic activity. An alternative approach is to target key molecules such as the cochaperone BAG1L that bind to and enhance the activity of the AR AF1. Here, we review recent literature that suggest Bag-1L is a promising target for AR-positive prostate cancer.
Rodolfo Niño Fong, Zahra Fatehi-Hassanabad, Simon C Lee, Hongfang Lu, Michael B Wheeler, and Catherine B Chan
Mutations in the uncoupling protein 2 (Ucp2) gene are linked to type-2 diabetes. Here, a potential mechanism by which lack of UCP2 is cytoprotective in pancreatic β-cells was investigated. Nitric oxide (NO) production was elevated in Ucp2 −/− islets. Proliferation (cyclin D2, Ccnd2) and anti-apoptosis (Tnfaip3) genes had increased expression in Ucp2 −/− islets, whereas the mRNA of pro-apoptosis genes (Jun, Myc) was reduced. TNFAIP3 cellular localization was detected in both α- and β-cells of Ucp2 −/− islets but in neither α- nor β-cells of UCP2+ / + islets, where it was detected in pancreatic polypeptide-expressing cells. TNFAIP3 distribution was not markedly altered 14 days after streptozotocin treatment. Basal apoptosis was attenuated in Ucp2 −/− β-cells, while the nuclear factor κB (NF-κB) pathway was transactivated after islet isolation. Ucp2 +/+ and Ucp2 −/− islets were treated with cytokines for 24 h. Cytokines did not increase NF-κB transactivation or apoptosis in Ucp2 −/− islets and TNFAIP3 was more strongly induced in Ucp2 −/− islets. Inhibition of NO production strongly reduced NF-κB activation and apoptosis. These data show that null expression of Ucp2 induces transactivation of NF-κB in isolated islets, possibly due to NO-dependent up-regulation of inhibitor of κB kinase β activity. NF-κB transactivation appears to result in altered expression of genes that enhance a pro-survival phenotype basally and when β-cells are exposed to cytokines. TNFAIP3 is of particular interest because of its ability to regulate NF-κB signaling pathways.
Katharine B Lee, Vishal Khivansara, Michelle M Santos, Pankaj Lamba, Tony Yuen, Stuart C Sealfon, and Daniel J Bernard
Transforming growth factor β superfamily ligands regulate pituitary FSH production and secretion. The best-described examples are the activins and inhibins, which respectively stimulate and hinder Fshb subunit transcription in gonadotrope cells. More recently, members of the bone morphogenetic protein (BMP) sub-family were shown to regulate FSH production in a manner analogous to the activins. Here, we used the murine gonadotrope cell line, LβT2, to investigate mechanisms through which BMP2 regulates the Fshb gene. Although expressed at low levels in LβT2 cells, Bmp2 mRNA was readily detected in adult murine pituitary gland. Recombinant BMP2 stimulated Fshb promoter-reporter activity, although its effects were weaker than those of equimolar activin A or B. BMP4 stimulated transcription comparably with BMP2, but BMPs 6 and 7 were about tenfold less potent. Remarkably, BMP2 and activin A synergistically upregulated Fshb transcription and endogenous Fshb mRNA levels in LβT2 cells. Although functionally cooperative, the two ligands appeared to use distinct intracellular mechanisms to mediate their responses because neither ligand altered the timing or magnitude of the other’s effects. Receptor overexpression analyses suggested that BMP2 may preferentially signal through complexes of the type II receptor, BMPR2, and the type I receptor, activin receptor like kinase (ALK2; Acvr1), to stimulate Fshb transcription. BMP2 rapidly activated the Smad1/5/8 intracellular signaling cascade and Smad8 overexpression potentiated BMP2’s effects. In summary, BMPs regulate Fshb transcription in LβT2 cells and can amplify the already robust effects of the activins through a distinct signaling mechanism. Because BMP2 is expressed in the adult mouse pituitary, it may act as critical paracrine co-regulator of FSH synthesis by gonadotropes.