Citations

Marine fish drink seawater and eliminate excess salt by active salt transport across gill and gut epithelia. Euryhaline pufferfish ( Takifugu obscurus , mefugu) forms a CaCO3 precipitate on the luminal gut surface after transitioning to seawater. NBCe1 (Slc4a4) at the basolateral membrane of intestinal epithelial cell plays a major role in transepithelial intestinal HCO3− secretion and is critical for mefugu acclimation to seawater. We assayed fugu-NBCe1 (fNBCe1) activity in the Xenopus oocyte expression system. Similar to NBCe1 found in other species, fNBCe1 is an electrogenic Na+/HCO3− cotransporter and sensitive to the stilbene inhibitor DIDS. However, our experiments revealed several unique and distinguishable fNBCe1 transport characteristics not found in mammalian or other teleost NBCe1-orthologs: electrogenic Li+/ nHCO3− cotransport; HCO3− independent, DIDS-insensitive transport; and increased basal intracellular Na+ accumulation. fNBCe1 is a voltage-dependent Na+/ nHCO3− cotransporter that rectifies, independently from the extracellular Na+ or HCO3− concentration, around −60 mV. Na+ removal (0Na+ prepulse) is necessary to produce the true HCO3−-elicited current. HCO3− addition results in huge outward currents with quick current decay. Kinetic analysis of HCO3− currents reveals that fNBCe1 has a much higher transport capacity (higher maximum current) and lower affinity (higher Km) than human kidney NBCe1 (hkNBCe1) does in the physiological range (membrane potential = −80 mV; [HCO3−] = 10 mM). In this state, fNBCe1 is in favor of operating as transepithelial HCO3− secretion, opposite of hkNBCe1, from blood to the luminal side. Thus, fugu-NBCe1 represents the first ortholog-based tool to study amino acid substitutions in NBCe1 and how those change ion and voltage dependence.

Drugs that target novel surfaces on the androgen receptor (AR) and/or novel AR regulatory mechanisms are promising alternatives for the treatment of castrate-resistant prostate cancer. The 52 kDa FK506 binding protein (FKBP52) is an important positive regulator of AR in cellular and whole animal models and represents an attractive target for the treatment of prostate cancer. We used a modified receptor-mediated reporter assay in yeast to screen a diversified natural compound library for inhibitors of FKBP52-enhanced AR function. The lead compound, termed MJC13, inhibits AR function by preventing hormone-dependent dissociation of the Hsp90-FKBP52-AR complex, which results in less hormone-bound receptor in the nucleus. Assays in early and late stage human prostate cancer cells demonstrated that MJC13 inhibits AR-dependent gene expression and androgen-stimulated prostate cancer cell proliferation.

Abstract Purpose: Emerging data from cooperative group trials suggests that not all patients with a positive SLN require completion axillary lymph node dissection (ALND). The controversy regarding who will benefit from additional nodal clearance continues, suggesting a need for improved tools to predict non-SLN involvement. We hypothesized that the size of a SLN metastasis evaluated as a continuous variable would be an important predictor of non-SLN involvement. The goal of this study was to determine clinicopathologic factors including SLN metastasis size that predicted non-SLN involvement and to use these factors to construct an improved predictive nomogram. Methods: Using a prospective database, we identified 509 patients with invasive breast cancer from 1996 - 2007 with a positive SLN who underwent ALND. Patients receiving neoadjuvant therapy were excluded. Clinicopathologic data including age, primary tumor size, presence of multifocal disease, histology (invasive ductal vs. invasive lobular vs. mixed invasive), tumor grade, estrogen receptor, progesterone receptor, and HER2/neu status, presence of lymphovascular invasion (LVI), the number of SLNs identified, number of positive SLNs, the maximum SLN metastasis size and the presence of extranodal extension were recorded. For SLNs described only as containing isolated tumor cells, size was recorded as 0.1 mm. Univariate and multivariate logistic regression analyses were performed to identify factors predictive of positive non-SLNs. Using these variables, a nomogram was constructed and subsequently validated using an external cohort of 464 patients. Results: On univariate analysis, the following factors were predictive of positive non-SLNs: number of SLN identified (p<.001), number of positive SLN (p<.001), maximum SLN metastasis size (p<.001), extranodal extension (p<.001), primary tumor size (p=.001), LVI (p=.019) and histology (p=.034). On multivariate analysis, all factors remained significant at the 5% level except LVI. A nomogram was created using these variables. When applied to an external cohort, the nomogram was accurate and discriminating with an area under the receiver operating characteristic curve of .73 (95% CI: .68 - .77). Conclusions: SLN metastasis size is predictive for identifying additional disease in the axilla. These data have been incorporated into a nomogram that accurately predicts the likelihood of having additional, non-SLN metastasis suggesting that routine reporting of the SLN metastasis size would assist with clinical decision making regarding the need to perform a completion ALND. Figures available in online version. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr PD06-08.

Rationale: Activity of the large conductance Ca 2+ -activated K + (BK) channels is profoundly modulated by its β 1 subunit (BK-β 1 ). However, BK-β 1 expression is downregulated in diabetic vessels. The ubiquitin–proteasome system (UPS) is a major mechanism of intracellular protein degradation. Whether UPS participates in BK-β 1 downregulation in diabetic vessels is unknown. Objective: We hypothesize that UPS facilitates vascular BK-β 1 degradation in diabetes. Methods and Results: Using patch clamp and molecular biological approaches, we found that BK-β 1 –mediated channel activation and BK-β 1 protein expression were reduced in aortas of streptozotocin-induced diabetic rats and in human coronary arterial smooth muscle cells (CASMCs) cultured in high glucose. This was accompanied by upregulation of F-box only protein (FBXO)-9 and FBXO-32 (atrogin-1), the key components of the Skp1-Cullin-F-box (SCF) type ubiquitin ligase complex. BK-β 1 expression was suppressed by the FBXO activator doxorubicin but enhanced by FBXO-9 small interfering RNA or by the proteasome inhibitor MG-132. Cotransfection of atrogin-1 in HEK293 cells significantly reduced Flag-hSlo-β 1 expression by 2.16-fold, compared with expression of Flag-hSlo-β 1 V146A (a mutant without the PDZ-binding motif). After cotransfection with atrogin-1, the ubiquitination of Flag-hSlo-β 1 was increased by 1.91-fold, compared with that of hSlo-β 1 V146A, whereas cotransfection with atrogin-1ΔF (a nonfunctional mutant without the F-box motif) had no effect. Moreover, inhibition of Akt signaling attenuated the phosphorylation of forkhead box O transcription factor (FOXO)-3a and enhanced atrogin-1 expression, which in turn suppressed BK-β 1 protein levels in human CASMCs. Conclusions: Downregulation of vascular BK-β 1 expression in diabetes and in high-glucose culture conditions was associated with FOXO-3a/FBXO-dependent increase in BK-β 1 degradation.

The proton-coupled folate transporter (PCFT-SLC46A1) is required for intestinal folate absorption and is mutated in the autosomal recessive disorder, hereditary folate malabsorption (HFM). This report characterizes properties and requirements of the R376 residue in PCFT function, including a R376Q mutant associated with HFM. Gln, Cys, and Ala substitutions resulted in markedly impaired transport of 5-formyltetrahydrofolate (5-FTHF) and 5-methyltetrahydrofolate (5-MTHF) due to an increase in Km and decrease in Vmax in HeLa R1–11 transfectants lacking endogenous folate transport function. In contrast, although the influx Km for pemetrexed was increased, transport was fully preserved at saturating concentrations and enhanced for the like-charged R376K- and R376H-PCFT. Pemetrexed and 5-FTHF influx mediated by R376Q-PCFT was markedly decreased at pH 5.5 compared with wild-type PCFT. However, while pemetrexed transport was substantially preserved at low pH (4.5–5.0), 5-FTHF transport remained very low. Electrophysiological studies in Xenopus oocytes demonstrated that 1) the R376Q mutant, like wild-type PCFT, transports protons in the absence of folate substrate, and in this respect has channel-like properties; and 2) the influx Km mediated by R376Q-PCFT is increased for 5-MTHF, 5-FTHF, and pemetrexed. The data suggest that mutation of the R376 residue to Gln impairs proton binding which, in turn, modulates the folate-binding pocket and depresses the rate of conformational alteration of the carrier, a change that appears to be, in part, substrate dependent.