Faculty Bibliography

FRET is widely used for the study of protein-protein interactions in biological samples. However, it is difficult to quantify both the FRET efficiency (E) and the affinity (Kd) of the molecular interaction from intermolecular FRET signals in samples of unknown stoichiometry. Here, we present a method for the simultaneous quantification of the complete set of interaction parameters, including fractions of bound donors and acceptors, local protein concentrations, and dissociation constants, in each image pixel. The method makes use of fluorescence lifetime information from both donor and acceptor molecules and takes advantage of the linear properties of the phasor plot approach. We demonstrate the capability of our method in vitro in a microfluidic device and also in cells, via the determination of the binding affinity between tagged versions of glutathione and glutathione S-transferase, and via the determination of competitor concentration. The potential of the method is explored with simulations.

The interplay between host genetics, tumor microenvironment and environmental exposure in cancer susceptibility remains poorly understood. Here we assessed the genetic control of stromal mediation of mammary tumor susceptibility to low dose ionizing radiation (LDIR) using backcrossed F1 into BALB/c (F1Bx) between cancer susceptible (BALB/c) and resistant (SPRET/EiJ) mouse strains. Tumor formation was evaluated after transplantation of non-irradiated Trp53-/- BALB/c mammary gland fragments into cleared fat pads of F1Bx hosts. Genome-wide linkage analysis revealed 2 genetic loci that constitute the baseline susceptibility via host microenvironment. However, once challenged with LDIR, we discovered 13 additional loci that were enriched for genes involved in cytokines, including TGFbeta1 signaling. Surprisingly, LDIR-treated F1Bx cohort significantly reduced incidence of mammary tumors from Trp53-/- fragments as well as prolonged tumor latency, compared to sham-treated controls. We demonstrated further that plasma levels of specific cytokines were significantly correlated with tumor latency. Using an ex vivo 3-D assay, we confirmed TGFbeta1 as a strong candidate for reduced mammary invasion in SPRET/EiJ, which could explain resistance of this strain to mammary cancer risk following LDIR. Our results open possible new avenues to understand mechanisms of genes operating via the stroma that affect cancer risk from external environmental exposures.

The generation of long-lived plasma cells and memory B cells producing high-affinity antibodies depends on the maturation of B cell responses in germinal centers. These processes are essential for long-lasting antibody-mediated protection against infections. IgE antibodiesIgE antibodies are important for defense against parasites and toxins and can also mediate anti-tumor immunity. However, high-affinity IgE is also the main culprit responsible for the manifestations of allergic disease, including life-threatening anaphylaxisAnaphylaxis . Thus, generation of high-affinity IgE must be tightly regulated. Recent studies of IgE B cell biology have unveiled two mechanisms that limit high-affinity IgE memory responses: First, B cells that have recently switched to IgE production are programmed to rapidly differentiate into plasma cells,Plasma cells and second, IgE germinal centerGerminal center cells are transient and highly apoptotic. Opposing these processes, we now know that germinal center-derived IgG B cells can switch to IgE production, effectively becoming IgE-producing plasma cells. In this chapter, we will discuss the unique molecular and cellular pathways involved in the generation of IgE antibodies.

BACKGROUND: Diabetes mellitus (DM) and metabolic syndrome are important targets for secondary prevention in cardiovascular disease. However, the prevalence in patients undergoing elective percutaneous coronary intervention (PCI) is not well defined. We aimed to analyze the prevalence and characteristics of patients undergoing PCI with previously unrecognized prediabetes, diabetes and metabolic syndrome. METHODS: Data were collected from 740 patients undergoing elective PCI between November 2010 and March 2013 at a tertiary referral center. Prevalence of DM and prediabetes was evaluated using Hemoglobin A1c (A1c >/= 6.5% for DM, A1c 5.7-6.4% for prediabetes). A modified definition was used for metabolic syndrome [3 or more of the following criteria: body mass index (BMI) >/=30 kg/m2; triglycerides >/= 150 mg/dL; high density lipoprotein <40 mg/dL in men and <50 mg/dL in women; systolic blood pressure >/= 130 mmHg and/or diastolic >/= 85 mmHg; A1c >/= 5.7% or on therapy]. RESULTS: Mean age was 67 years, median BMI was 28.2 kg/m2 , and 39% had known DM. Of those without known DM, 8.3% and 58.5% met A1c criteria for DM and for prediabetes at time of PCI. Overall, 54.9% met criteria for metabolic syndrome (69.2% of patients with DM and 45.8% of patients without DM). CONCLUSION: Among patients undergoing elective PCI, a substantial number were identified with new DM, prediabetes, and/or metabolic syndrome. Routine screening for an abnormal glucometabolic state at the time of revascularization may be useful for identifying patients who may benefit from additional targeting of modifiable risk factors

Here we describe a preparative differential centrifugation protocol for the isolation of ribosomes from a crude cell homogenate. The subcellular fraction obtained is enriched in ribosome monomers and polysomes. The protocol has been optimized for the homogenization and collection of the ribosomal fraction from prokaryotic cells, mammalian and plant tissues, reticulocytes, and chloroplasts. The quality of the ribosomal preparation is enhanced by the removal of the remaining cellular components and adsorbed proteins by pelleting through a sucrose cushion with a high concentration of monovalent salts, NH4Cl or KCl. The different components of the ribosomal fraction isolated using this protocol can be further purified by sucrose gradient centrifugation.

In spite of the many key cellular functions of chloride channels, the mechanisms that mediate their subcellular localization are largely unknown. ClC-2 is a ubiquitous chloride channel usually localized to the basolateral domain of epithelia that regulates cell volume, ion transport and acid-base balance; mice knocked-out for ClC-2 are blind and sterile. Previous work has suggested that CLC-2 is sorted basolaterally by TIFS812LL, a dileucine motif in CLC-2's C-terminal domain. However, our in silico modelling of ClC-2 suggested that this motif was buried within the channel's dimerization interface and identified two cytoplasmically exposed dileucine motifs, ESMI623LL and QVVA635LL, as candidate sorting signals. Alanine mutagenesis and trafficking assays support a scenario in which ESMI623LL acts as the authentic basolateral signal of ClC-2. Silencing experiments and yeast three hybrid assays demonstrated that both ubiquitous (AP-1A) and epithelial-specific (AP-1B) forms of the tetrameric clathrin adaptor AP-1 are capable of carrying out basolateral sorting ClC-2 through interactions of ESMI623LL with a highly conserved pocket in their gamma1-sigma1A hemicomplex.

Isolated polysomes (also known as translating ribosomes or polyribosomes) are mRNA-ribosome complexes that are frequently used for the in vitro study of the regulation of protein synthesis. Here we describe a protocol for the isolation of prokaryotic and plant polysomes by sucrose gradient sedimentation. The protocol allows for the separation of multiple ribosomes attached to mRNA from run-off ribosome monomers. In addition to collecting the polysome pellet, if the sucrose gradients used in this protocol are fractionated, it is possible to isolate and quantify the polysomes, the ribosome monomers, and the ribosomal subunits.

Purpose: Calcium regulates many functions of retinal pigment epithelium (RPE). Its concentration in the subretinal space and RPE cytoplasm is closely regulated. Transient receptor potential (TRP) channels are a superfamily of ion channels that are moderately calcium-selective. This study investigates the subcellular localization and potential functions of TRP channels in a first-passage culture model of human fetal RPE (hfRPE). Methods: RPE isolated from 15-16 week-gestation fetuses were maintained in serum-free media. Cultures were treated with BaCl2 in the absence and presence of TRP channel inhibitors and monitored by the transepithelial electrical resistance (TER). The expression of TRP channels was determined using quantitative RT-PCR, immunoblotting, and immunofluorescence confocal microscopy. Results: BaCl2 substantially decreased TER and disrupted cell-cell contacts when added to the apical surface of RPE, but not when added to the basolateral surface. The effect could be partially blocked by the general TRP inhibitor, LaCl3, (~75%) or an inhibitor of calpain (~25%). Family member-specific inhibitors, ML204 (TRPC4) and HC-067047 (TRPV4), had no effect on basal channel activity. Expression of TRPC4, TRPM1, TRPM3, TRPM7, and TRPV4 were detected by RT-PCR and immunoblotting. TRPM3 localized to the base of the primary cilium, and TRPC4 and TRPM3 localized to apical tight junctions. TRPV4 localized to apical microvilli in a small subset of cells. Conclusions: TRP channels localized to subdomains apical membrane, and BaCl2 was only able to dissociate tight junctions when presented to the apical membrane. The data suggest a potential role for TRP channels as sensors of [Ca2+] in the subretinal space.

Here we describe the further purification of prokaryotic ribosomal particles obtained after the centrifugation of a crude cell lysate through a sucrose cushion. In this final purification step, a fraction containing ribosomes, ribosomal subunits, and polysomes is centrifuged through a 7%-30% (w/w) linear sucrose gradient to isolate tight couple 70S ribosomes, as well as dissociated 30S and 50S subunits. The tight couples fraction, or translationally active ribosome fraction, is composed of intact vacant ribosomes that can be used in cell-free translation systems.

The aim of the present study is to determine whether ADAMTS-7 contributes to the onset and severity of joint inflammation in the pathogenesis of inflammatory arthritis. ADAMTS-7 was found to be elevated in the course of collagen-induced arthritis (CIA). ADAMTS-7 transgenic (TG) mice were more susceptible to the induction of CIA. The onset of CIA was accelerated and the arthritic severity was increased in TG mice compared to wild-type mice. The overall incidence was also significantly higher in TG mice. In addition, arthritic TG mice displayed significantly higher clinical and histological arthritis scores. The COMP degradative fragments were significantly elevated in articular cartilage and sera in CIA models of TG mice. Furthermore, the production of tumor necrosis factor-alpha and interleukin-17 was also increased in serum and draining lymph nodes of arthritic TG mice. Therefore, these data provided the in vivo evidence, suggesting that ADAMTS-7 may play an important role in the pathogenesis of inflammatory arthritis, and that inhibition of ADAMTS-7 may be a potential target to ameliorate the severity of inflammatory arthritis.