Ubiquitination and degradation of the hominoid-specific oncoprotein TBC1D3 is regulated by protein palmitoylation

Expression of the hominoid-specific oncoprotein TBC1D3 promotes enhanced cell growth and proliferation by increased activation of signal transduction through several growth factors. Recently we documented the role of CUL7 E3 ligase in growth factors-induced ubiquitination and degradation of TBC1D3. Here we expanded our study to discover additional molecular mechanisms that control TBC1D3 protein turnover. We report that TBC1D3 is palmitoylated on two cysteine residues: 318 and 325. The expression of double palmitoylation mutant TBC1D3:C318/325S resulted in protein mislocalization and enhanced growth factors-induced TBC1D3 degradation. Moreover, ubiquitination of TBC1D3 via CUL7 E3 ligase complex was increased by mutating the palmitoylation sites, suggesting that depalmitoylation of TBC1D3 makes the protein more available for ubiquitination and degradation. The results reported here provide novel insights into the molecular mechanisms that govern TBC1D3 protein degradation. Dysregulation of these mechanisms in vivo could potentially result in aberrant TBC1D3 expression and promote oncogenesis.

Ubiquitination and degradation of the hominoid-specific oncoprotein TBC1D3 is mediated by CUL7 E3 ligase

Expression of the hominoid-specific TBC1D3 oncoprotein enhances growth factor receptor signaling and subsequently promotes cellular proliferation and survival. Here we report that TBC1D3 is degraded in response to growth factor signaling, suggesting that TBC1D3 expression is regulated by a growth factor-driven negative feedback loop. To gain a better understanding of how TBC1D3 is regulated, we studied the effects of growth factor receptor signaling on TBC1D3 post-translational processing and turnover. Using a yeast two-hybrid screen, we identified CUL7, the scaffolding subunit of the CUL7 E3 ligase complex, as a TBC1D3-interacting protein. We show that CUL7 E3 ligase ubiquitinates TBC1D3 in response to serum stimulation. Moreover, TBC1D3 recruits F-box 8 (Fbw8), the substrate recognition domain of CUL7 E3 ligase, in pull-down experiments and in an in vitro assay. Importantly, alkaline phosphatase treatment of TBC1D3 suppresses its ability to recruit Fbw8, indicating that TBC1D3 phosphorylation is critical for its ubiquitination and degradation. We conclude that serum- and growth factor-stimulated TBC1D3 ubiquitination and degradation are regulated by its interaction with CUL7-Fbw8.

Cigarette smoking extract causes hypermethylation and inactivation of WWOX gene in T-24 human bladder cancer cells

Genomic, epigenetic and expression alterations of WW domain containing oxidoreductase (WWOX) have been implicated in multiple tumor types. The current study was designed to examine the expression of WWOX in tumor tissues of human bladder transitional cell carcinoma (BTCC) and the influence of cigarette smoke extract (CSE) on WWOX expression and methylation status in T-24 bladder cancer cells. WWOX protein expression was evaluated by immunohistochemistry staining in a series of tumor samples from 78 patients with BTCC and 26 normal bladder tissues. The expression level and methylation status of WWOX in CSE-treated cells were examined by using quantitative Real-Time RT-PCR and methylation specific PCR, respectively. The expression levels of DNA methyltransferases (DNMTs) 1, 3A and 3B were also detected. We found that WWOX expression was absent or reduced in 79.5% (62/78) of BTCC tissues, but only in 19.2% (5/26) of normal bladder tissues. Loss of WWOX expression was correlated with tumor grade (P=0.019) and cigarette smoking (P=0.031), but was not associated with age, gender, tumor size and tumor number. Hypermethylation of WWOX promoter and exon 1 was specifically induced by CSE with a kinetics concurrent to the suppression of WWOX mRNA in T-24 cells. Furthermore, CSE treatment induced a significant time-dependent increase in the level of DNMT1, but has no effects on DNMT3A and DNMT3B. Taken together, these novel findings suggest that hypermethylation of WWOX induced by cigarette smoking may represent one underlying mechanism for the loss expression of WWOX in bladder cancer.

MO-F-213AB-05: Commissioning of Gated RapidArc Radiotherapy for Treatment of Moving Targets

PURPOSE

To commission and evaluate gated RapidArc radiotherapy of a linear accelerator (Varian TrueBeam) for treatment of moving targets using a programmable dynamic phantom.

METHODS

The phantom used had different dosimetry inserts for measurement of dose and dose distribution. It could be programmed to move in the anterior-posterior and superior-inferior axes with different motion patterns, amplitudes and frequencies to simulate lung motions of patients. A set of 4D CT images was acquired with the aid of a Varian RPM system. Images acquired at the 40, 50 and 60% of the motion cycle were selected and transferred to a treatment planning system (Varian Eclipse) for planning. A two-arc RapidArc treatment plan was generated for a C-shaped target volume with a conformity index of 1.49 and transferred to the TrueBeam for treatment delivery. Dose and dose distribution measurements were performed using a 0.057 cc ionization chamber and radiochromic films, respectively and compared with the TPS calculations. Five treatment fractions were given in three days with two different target motion patterns to assess the consistency of the dose delivery.

RESULTS

Agreement between TPS calculation and measurement were within 1.64% for dose and 3% or 3mm in distance to agreement for dose distribution. Repeatability of dose delivery between treatments was within 0.1% (1SD) in the five treatment fractions delivered in three days. The time required to deliver a dose of 2 Gy to a moving C-shaped target using gated RapidArc technique with two gantry rotations was about 15 minutes.

CONCLUSIONS

The geometric and dosimetric accuracy and consistency of gated RapidArc radiotherapy had been verified. Our study indicated that the accuracy and consistency of the treatment modality were acceptable for clinical implementation.

TBC1D3, a hominoid-specific gene, delays IRS-1 degradation and promotes insulin signaling by modulating p70 S6 kinase activity

Insulin/IGF-1 signaling plays a pivotal role in the regulation of cellular homeostasis through its control of glucose metabolism as well as due to its effects on cell proliferation. Aberrant regulation of insulin signaling has been repeatedly implicated in uncontrolled cell growth and malignant transformations. TBC1D3 is a hominoid specific gene previously identified as an oncogene in breast and prostate cancers. Our efforts to identify the molecular mechanisms of TBC1D3-induced oncogenesis revealed the role of TBC1D3 in insulin/IGF-1 signaling pathway. We document here that TBC1D3 intensifies insulin/IGF-1-induced signal transduction through intricate, yet elegant fine-tuning of signaling mechanisms. We show that TBC1D3 expression substantially delayed ubiquitination and degradation of insulin receptor substrate-1 (IRS-1). This effect is achieved through suppression of serine phosphorylation at S636/639, S307 and S312 of IRS-1, which are key phosphorylation sites required for IRS-1 degradation. Furthermore, we report that the effect of TBC1D3 on IRS-1:S636/639 phosphorylation is mediated through TBC1D3-induced activation of protein phosphatase 2A (PP2A), followed by suppression of T389 phosphorylation on p70 S6 kinase (S6K). TBC1D3 specifically interacts with PP2A regulatory subunit B56γ, indicating that TBC1D3 and PP2A B56γ operate jointly to promote S6K:T389 dephosphorylation. These findings suggest that TBC1D3 plays an unanticipated and potentially unique role in the fine-tuning of insulin/IGF-1 signaling, while providing novel insights into the regulation of tumorigenesis by a hominoid-specific protein.

Supplementation of β-mannanase to starter and grower diets for broilers

Kong, C., Lee, J. H. and Adeola, O. 2011. Supplementation of β-mannanase to starter and grower diets for broilers. Can. J. Anim. Sci. 91: 389–397. Two experiments were conducted to investigate the efficacy of β-mannanase on ileal nutrient digestibility, total tract utilization of dry matter (DM), N, energy, and apparent metabolizable energy (AME, exp. 1), and growth performance (exp. 2) of birds fed practical corn-soybean meal (SBM)-based diets. In each experiment, 192 male broilers were assigned to four diets arranged in a 2×2 factorial of energy level [corn-SBM-based diet that met or exceeded NRC nutrient requirements (AE) or low energy (LE) diet containing 100 kcal of ME kg−1 less than the AE diet] and enzyme supplementation (with or without β-mannanase) for 21 d. Supplementing the diet with β-mannanase increased the birds’ apparent ileal DM digestibility of the experimental diets (P<0.05), whereas there was no effect of energy level. Neither β-mannanase supplementation nor energy level had any effect on apparent ileal digestibility of any of the amino acids. The interaction between enzyme and energy levels was not significant for any criteria measured in the excreta except for DM (P=0.05). Addition of β-mannanase improved (P<0.01) the apparent total tract utilization of DM and energy in the broilers, and there was the same trend (P=0.06) for N utilization. Supplementing the diet with β-mannanase also improved the AME and AMEn of diets by 4.6 and 5.0%, respectively. For all growth performance responses in exp. 2, the interaction between enzyme and energy levels was not significant. During the starter period (day 2 to 22 post-hatch), β-mannanase supplementation significantly (P<0.05) increased the body weight (BW) gain of birds. During the grower period (day 22 to 44 post-hatch) and for the overall period there was no significant difference in BW gain or feed intake of birds regardless of energy level and β-mannanase supplementation. There were no dietary effects on feed efficiency of birds during the starter and the grower periods, whereas the birds fed AE diets had higher feed efficiency (P<0.01) than the birds fed LE diets. The results indicate that supplementing with β-mannanase may improve gain and energy utilization of broilers, whereas it may not affect ileal amino acid digestibility.

Apparent ileal digestibility of amino acids in feedstuffs for White Pekin ducks

The apparent ileal amino acid digestibility of 6 feedstuffs, namely corn, wheat, corn distillers dried grains with solubles, canola meal, soybean meal (SBM), and meat and bone meal (MBM) were determined for White Pekin ducks in a 5-d experiment. The feedstuffs served as the sole source of amino acids in semipurified diets composed of dextrose, soy oil, Solka Floc, minerals, and vitamins, with the exception of corn and wheat, in which both lacked dextrose. The ducks received a standard duck starter diet during the first 14 d posthatch. On d 14, ducks were sorted by weight and allocated to 6 dietary treatments in a randomized complete block design. Each assay diet was fed to 8 replicates (6 ducks/replicate) from d 14 to 19 posthatch. Birds were killed on d 19 and digesta from the terminal ileum were collected. Ileal N digestibility was highest (P < 0.01) in SBM (88.3%) and lowest in MBM (72.4%). Ileal digestibility for all of the amino acids was highest in SBM among the feedstuffs. Lysine digestibility was highest (P < 0.01) for SBM followed by canola meal, corn, wheat, MBM, and distillers dried grains with soluble; the values were 90.3, 79.0, 78.0, 76.8, 75.6, and 69.2%, respectively. Methionine digestibility in SBM was highest (P < 0.01), whereas MBM had the lowest digestibility value for methionine (78.4%). For threonine, SBM (84.0%) had the highest digestibility and corn (61.6%) had the lowest digestibility (P < 0.01), but there were no differences among other feedstuffs. Ileal tryptophan digestibility was between 78.9 (MBM) and 93.0% (SBM). In conclusion, the data from the current study show that there are considerable differences among feedstuffs in the digestibility of their amino acids for ducks. Therefore, it is important to take the digestible amino acid content of feedstuffs into account during feed formulation.

Rab5 isoforms differentially regulate the trafficking and degradation of epidermal growth factor receptors

Ligand-mediated endocytosis is an intricate regulatory mechanism for epidermal growth factor receptor (EGFR) signal transduction. Coordinated trafficking of EGFR ensures its temporal and spatial communication with downstream signaling effectors. We focused our work on Rab5, a monomeric GTPase shown to participate in early stages of the endocytic pathway. Rab5 has three isoforms (A, B, and C) sharing more than 90% of sequence identity. We individually ablated endogenous isoforms in HeLa cells with short interfering RNAs and examined the loss-of-function phenotypes. We found that suppression of Rab5A or 5B hampered the degradation of EGFR, whereas Rab5C depletion had very little effect. The differential delay of EGFR degradation also corresponds with retarded progression of EGFR from early to late endosomes. We investigated the activators/effectors of Rab5A that can potentially separate its potency in EGFR degradation from other isoforms and found that Rin1, a Rab5 exchange factor, preferably associated with Rab5A. Moreover, Rab5A activation is sensitive to EGF stimulation, and suppression of Rin1 diminished this sensitivity. Based on our results together with previous work showing that Rin1 interacts with signal transducing adapter molecule to facilitate the degradation of EGFR (Kong, C., Su, X., Chen, P. I., and Stahl, P. D. (2007) J. Biol. Chem. 282, 15294-15301), we hypothesize that the selective association of Rab5A and Rin1 contributes to the dominance of Rab5A in EGFR trafficking, whereas the other isoforms may have major functions unrelated to the EGFR degradation pathway.

Nanoscale analysis of changes in signaling proteins in patients treated with single agent atorvastatin for low-grade or refractory NHL

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Background: In preclinical studies using our transgenic lymphoma model, lymphoma regression upon atorvastatin treatment was associated with increased apoptosis and changes in phosphorylation of key signaling pathways including MAPK and STAT. To determine if statins affect tumor signaling in patients, we designed a single arm phase II study, “Atorvastatin in Patients with Low Grade or Refractory Non-Hodgkin's Lymphoma.” Methods: Patients received 80 mg atorvastatin daily and underwent tumor sampling and PBMC collection by fine needle aspiration (FNA) and blood draw on days 1 and 8. The primary endpoint was to measure a 50% increase in tumor apoptosis on treatment day 8 compared with day 1. To characterize changes in protein profiles, we have developed the use of a novel nano-immunoassay system (NIA) to simultaneously measure both phosphorylated and unphosphorylated protein isoforms. NIA and multi-color flow cytometry were used to evaluate intracellular signaling protein profiles for each patient's tumor cells, monocytes, and T cells. Results: All 14 patients have completed treatment. The primary endpoint was reached in 9 of 14 patients with 50% increase in apoptosis. We distinguished three patterns of signaling changes. First, as expected, pathways that were initially activated in tumor cells decreased upon treatment with atorvastatin, with up to a 70% decrease in phospho-STAT3 and phospho-STAT5. Second, pathways that were initially suppressed in tumor cells (including phospho-PLCγ), normalized upon treatment. Third, expression levels of proteins in apoptotic pathways, including p38, increased upon atorvastatin treatment. Finally, changes in signaling associated with atorvastatin are cell specific: effects on tumor cells were distinct from effects on non-tumor T cells and monocytes. Conclusions: Single agent atorvastatin has a measurable effect on tumor bioactivity in patients with lymphoma. NIA and multi-color phosphoFACS can be used to monitor changes in cell signaling in very small clinical samples during therapeutic interventions. Determining whether specific signaling molecules may be a biomarker for identifying lymphoma patients that respond to atorvastatin is worthy of further investigation.

[Table: see text]

The hominoid-specific oncogene TBC1D3 activates Ras and modulates epidermal growth factor receptor signaling and trafficking

Hominoid- and human-specific genes may have evolved to modulate signaling pathways of a higher order of complexity. TBC1D3 is a hominoid-specific oncogene encoded by a cluster of eight paralogs on chromosome 17. Initial work indicates that TBC1D3 is widely expressed in human tissues ( Hodzic, D., Kong, C., Wainszelbaum, M. J., Charron, A. J., Su, X., and Stahl, P. D. (2006) Genomics 88, 731-736 ). In this study, we show that TBC1D3 expression has a powerful effect on cell proliferation that is further enhanced by epidermal growth factor (EGF) in both human and mouse cell lines. EGF activation of the Erk and protein kinase B/Akt pathways is enhanced, both in amplitude and duration, by TBC1D3 expression, whereas RNA interference silencing of TBC1D3 suppresses the activation. Light microscopy and Western blot experiments demonstrate that increased signaling in response to EGF is coupled with a significant delay in EGF receptor (EGFR) trafficking and degradation, which significantly extends the life span of EGFR. Moreover, TBC1D3 suppresses polyubiquitination of the EGFR and the recruitment of c-Cbl. Using the Ras binding domain of Raf1 to monitor GTP-Ras we show that TBC1D3 expression enhances Ras activation in quiescent cells, which is further increased by EGF treatment. We speculate that TBC1D3 may alter Ras GTP loading. We conclude that the expression of TBC1D3 generates a delay in EGFR degradation, a decrease in ubiquitination, and a failure to recruit adapter proteins that ultimately dysregulate EGFR signal transduction and enhance cell proliferation. Altered growth factor receptor trafficking and GTP-Ras turnover may be sites where recently evolved genes such as TBC1D3 selectively modulate signaling in hominoids and humans.

Target volume definition for head and neck intensity modulated radiotherapy: pre-clinical evaluation of PARSPORT trial guidelines

AIMS

There is considerable controversy surrounding target volume definition for parotid-sparing intensity modulated radiotherapy (IMRT) for head and neck cancer. The aim of this study was to evaluate the dosimetric and radiobiological predictors of outcome anticipated by application of the detailed target volume definition guidelines agreed for the UK multicentre randomised controlled trial of parotid-sparing IMRT (PARSPORT).

MATERIALS AND METHODS

Five patients eligible for the study were delineated using the trial guidelines. Following the protocol, plans were produced to treat these volumes with three-dimensional radiotherapy (control arm) and IMRT aimed to spare dose to the contralateral parotid gland (experimental arm). Dosimetric comparisons were made between plans, and normal tissue complication probability (NTCP) modelling for salivary glands was carried out.

RESULTS

Doses delivered to the planning target volumes (PTV) were similar with each technique, although IMRT produced more homogeneous irradiation of the PTV. Mean doses to the contralateral parotid gland were 22.4+/-1.7 Gy with the IMRT plans vs 60.0+/-7.2 Gy with three-dimensional radiotherapy, P=0.0003. Calculated contralateral parotid gland NTCP values for grade 2 xerostomia were 20-22% for IMRT and 98-100% for three-dimensional radiotherapy (P<0.0001).

CONCLUSION

Pre-clinical evaluation of the PARSPORT trial target volume definition guidelines provides theoretical support for a significant reduction in xerostomia rates. These data await confirmation from the clinical trial results.

GAPex-5 mediates ubiquitination, trafficking, and degradation of epidermal growth factor receptor

Upon ligand stimulation, epidermal growth factor receptor (EGFR) is rapidly ubiquitinated, internalized, and sorted to lysosomes for degradation. Rab5 has been shown to play an important role in the early stages of EGFR trafficking. GAPex-5 is a newly described Rab5 exchange factor. Herein, we investigate the role of GAPex-5 on EGFR trafficking and degradation. Down-regulation of GAPex-5 by RNA interference decreases epidermal growth factor-stimulated EGFR degradation. Moreover, ubiquitination of EGFR is impaired by depletion of GAPex-5. This inhibitory effect is due to a decrease in the interaction between the adapter protein c-Cbl and EGFR, but not the phosphorylation state of EGFR. Consistently, when examined by immunofluorescence microscopy in cells depleted of GAPex-5, ligand-bound EGFR appeared trapped in early endosomes and the trafficking of internalized receptor from early to late endosomes was impaired. In agreement with the depletion studies, EGFR degradation is enhanced by overexpressing GAPex-5 wild type, but not GAPex-5DeltaGAP, a mutant lacking the Ras GTPase-activating protein (GAP) domain. This is consistent with the finding that c-Cbl binds specifically to the Ras GAP domain. Finally, overexpression of dominant negative Rab5a or depletion of all three isoforms of Rab5 does not inhibit ubiquitination of EGFR, which suggests that GAPex-5-mediated EGFR ubiquitination is independent of Rab5 activation. Collectively, the results suggest a novel mechanism by which EGF-stimulated receptor ubiquitination and trafficking are mediated via GAPex-5.

Rin1 interacts with signal-transducing adaptor molecule (STAM) and mediates epidermal growth factor receptor trafficking and degradation

Rin1, the prototype of a new family of multidomain Rab5 exchange factors, has been shown to play an important role in the endocytosis of the epidermal growth factor receptor (EGFR). Herein, we examined the role of Rin1 in the down-regulation of EGFR following EGF stimulation. We observed that overexpression of Rin1 accelerates EGFR degradation in EGF-stimulated cells. In concordance, depletion of endogenous Rin1 by RNA interference resulted in a substantial reduction of EGFR degradation. We showed that Rin1 interacts with signal-transducing adaptor molecule 2 (STAM2), a protein that associates with hepatocyte growth factor-regulated substrate and plays a key role in the endosomal sorting machinery. Green fluorescent protein (GFP)-Rin1 co-localizes with hemagglutinin (HA)-STAM2 and with endogenous hepatocyte growth factor-regulated substrate. Furthermore, wild type STAM2, but not a deletion mutant lacking the SH3 domain, co-immunoprecipitates with endogenous Rin1. This interaction is dependent on the proline-rich domain (PRD) of Rin1 as Rin1DeltaPRD, a mutant lacking the PRD, does not interact with STAM2. Moreover, EGFR degradation was not accelerated by expression of the Rin1DeltaPRD mutant. Together these results suggest that Rin1 regulates EGFR degradation in cooperation with STAM, defining a novel role for Rin1 in regulating endosomal trafficking.

TBC1D3, a hominoid oncoprotein, is encoded by a cluster of paralogues located on chromosome 17q12

TBC1D3 is a member of the TBC1 domain family of proteins that stimulates the intrinsic GTPase activity of RAB5A, an essential actor in early endosome trafficking. Oncogenic properties of TBC1D3 have been demonstrated previously both in vitro and in mouse models. Although the oncogenic mechanism of TBC1D3 has yet to be elucidated, the TBC1D3 locus (chromosome 17q12) is amplified in 15% of primary prostate tumors. Here, we describe eight highly related TBC1D3 paralogues located within that genomic region, potentially encoding six variant TBC1D3 proteins. We found that human tissues display specific transcription patterns of these paralogues. Furthermore, that pattern was altered in several primary prostate tumors in comparison to healthy prostate tissues. Potential TBC1D3 oncogenic mechanisms are discussed in light of these results.

The SRC homology 2 domain of Rin1 mediates its binding to the epidermal growth factor receptor and regulates receptor endocytosis

Activated epidermal growth factor receptors (EGFRs) recruit intracellular proteins that mediate receptor signaling and endocytic trafficking. Rin1, a multifunctional protein, has been shown to regulate EGFR internalization (1). Here we show that EGF stimulation induces a specific, rapid, and transient membrane recruitment of Rin1 and that recruitment is dependent on the Src homology 2 (SH2) domain of Rin1. Immunoprecipitation of EGFR is accompanied by co-immunoprecipitation of Rin1 in a time- and ligand-dependent manner. Association of Rin1 and specifically the SH2 domain of Rin1 with the EGFR was dependent on tyrosine phosphorylation of the intracellular domain of the EGFR. The recruitment of Rin1, observed by light microscopy, indicated that although initially cytosolic, Rin1 was recruited to both plasma membrane and endosomes following EGF addition. Moreover, the expression of the SH2 domain of Rin1 substantially impaired the internalization of EGF without affecting internalization of transferrin. Finally, we found that Rin1 co-immunoprecipitated with a number of tyrosine kinase receptors but not with cargo endocytic receptors. These results indicate that Rin1 provides a link via its SH2 domain between activated tyrosine kinase receptors and the endocytic pathway through the recruitment and activation of Rab5a.

A novel dimer of a C-type lectin-like heterodimer from the venom of Calloselasma rhodostoma (Malayan pit viper)

We have isolated a potent platelet aggregation inducer from the crude venom of Calloselasma rhodostoma (Malayan pit viper), termed rhodoaggretin, with a novel oligomeric structure consisting of a dimer of C-type lectin-like heterodimers. On the basis of its native molecular mass of 66 kDa, and a M(r) of 30 kDa for its disulfide-linked alphabeta-heterodimer, we propose that rhodoaggretin exists as a (alphabeta)2 complex in the native state. We postulate that the di-dimer is stabilized by non-covalent interactions as well as by an intersubunit disulfide bridge between the two alphabeta-heterodimers. This conclusion is based on the following observations: (a) sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of the non-reduced rhodoaggretin gave a major 28 and a minor 52 kDa band. (b) Prior treatment of rhodoaggretin with a limited amount of 2-mercaptoethanol (2-ME; 0.1%) resulted in the complete abolishment of the 52 kDa band in SDS-PAGE. (c) Two-dimensional SDS-PAGE in the presence of 3% 2-ME showed that both the 28 and 52 kDa bands gave two bands each with M(r)s of 18 (alpha-subunit) and 15 (beta-subunit) kDa. (d) Mass spectrometric analyses showed that purified rhodoaggretin had a M(r) of 30155.39+/-3.25 Da while its s-pyridylethylated alpha- and beta-subunits had M(r)s of 16535.62+/-2.98 and 15209.89+/-1.61 Da respectively. These molecular weight data suggested the presence of 15 cysteinyl residues in rhodoaggretin as compared to the 14 that are reported for the heterodimeric C-type lectin-like proteins. This extra cysteinyl residue is a candidate for the formation of the intersubunit disulfide bond in the (alphabeta)2 complex. (e) Homology structural modeling studies showed that the extra cysteinyl residue can indeed form a disulfide bond that covalently links the two alphabeta-heterodimers as proposed above.

Multiple endocrine neoplasia type 1Burin from Mauritius: a novel MEN1 mutation

We describe a kindred from Mauritius with an incomplete variant of multiple endocrine neoplasia type 1 (MEN 1Burin). In this family the syndrome is related to a novel MEN 1 gene mutation (deletion of A) at nucleotide 1021 of codon 304 resulting in frame shift and downstream protein truncation at codon 320. Compared to mainstream MEN 1, MEN 1Burin is characterized by a high prevalence of prolactin-secreting pituitary adenomas, late-onset of hyperparathyroidism and rare pancreatic involvement. The family described represents the fifth in the literature with the MEN 1 Burin phenotype; 2 out of the other 4 were related to R460X, Y312X respectively and no mutation within the coding sequence of MEN 1 was found in the other 2. Thus, similar to the classic syndrome, MEN 1Burin phenotype shows poor correlation to MEN 1 genotype.

Apoptotic cell death and Smad4 expression in transitional cell carcinoma of the renal pelvis and ureter

PURPOSE

To investigate the frequency of apoptosis and the expression of Smad4 protein as well as their roles in transitional cell carcinoma (TCC) of the renal pelvis and ureter.

METHODS

Apoptosis was detected by using terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) technique in 34 formalin-fixed and paraffin-embedded specimens of renal pelvic and ureteral TCC. The expression of Smad4 was immunohistochemically studied.

RESULTS

The incidence of apoptosis ranged from 1.10 to 3.75% with a median of 2.50% in TCC of the renal pelvis and ureter. The incidence of apoptosis was noted to be closely related to histologic grade but not to pathologic stage of the cancer. The expression of Smad4 was detected in six of 34 cases (17.6%). Regarding subcellular distribution, Smad4 protein was localized both in cytoplasm and nucleus of the cancer cells. In comparing the incidence of apoptosis with the expression of Smad4, no significant associations were seen between them. The expression of Smad4 was not related to the tumor grade nor stage of the cancer.

CONCLUSIONS

The present study demonstrated close association of the incidence of apoptosis with the tumor grade of TCC of the renal pelvis and ureter. Significance of Smad4 expression was not noted in the study. It suggests that apoptotic cell death may play an important role in the tumor progression of renal pelvic and ureteral TCC.

Purification and characterization of a variant of rhodocetin from Calloselasma rhodostoma (Malayan pit viper) venom

Rhodocetin is a novel C-type lectin-related protein (CLP) purified from the venom of Calloselasma rhodostoma. Thus far, it is the only reported CLP whose alpha and beta subunits are not linked by an interdisulfide bond. We report here the isolation of a variant of rhodocetin from a different source of venom. This variant of rhodocetin exhibited a different elution profile in reverse-phase HPLC as compared to the rhodocetin reported in our original publication [Wang et al., (1999), Biochemistry 38, 7584-7593]. Specifically, the alpha subunit of the variant was eluted at a considerably lower percentage of acetonitrile, which suggested a less hydrophobic polypeptide chain as compared to the original rhodocetin. Using a combination of microcharacterization techniques such as peptide mapping, mass spectrometry, and amino acid sequencing, we identified an amino acid substitution, 163K, in the polypeptide chain that could account for the difference in elution behavior of the alpha subunit. In addition, we also found a conserved E88D substitution in the beta chain which was not apparent during reverse-phase HPLC. However, neither of these substitutions resulted in the alteration of the functional properties of the rhodocetin variant.

Smoking is associated with increased hepatic lipase activity, insulin resistance, dyslipidaemia and early atherosclerosis in Type 2 diabetes

We have studied the relationships between hepatic lipase activity, smoking, dyslipidaemia insulin resistance, and early atherosclerosis in 67 Type 2 diabetic subjects, 47 non-smokers and 20 smokers. Insulin resistance was measured using an insulin modified frequently sampled intravenous glucose tolerance test. Early atherosclerosis was assessed using high-resolution ultrasound to measure carotid intima media thickness (IMT) and an arterial ultrasonic score (AUS). Smokers had higher serum cholesterol and triglyceride, lower HDL and HDL2 cholesterol as well as increased hepatic lipase activity. They were also more insulin resistant than non-smokers. Smokers also had higher patient AUS scores. On multiple regression analysis, hepatic lipase activity emerged as the most significant variable affecting patient AUS. We suggest that smoking accentuates the dyslipidaemia of Type 2 diabetic subjects and this is associated with increased hepatic lipase activity. This may be one mechanism whereby smoking further increases the risk of cardiovascular disease in Type 2 diabetes.

Evaluation of cell proliferation, apoptosis, and angiogenesis in transitional cell carcinoma of the renal pelvis and ureter

OBJECTIVES

To investigate cell proliferation, apoptosis, and angiogenesis and their roles in transitional cell carcinoma (TCC) of the renal pelvis and ureter.

METHODS

Formalin-fixed and paraffin-embedded tissue blocks from 42 patients with TCC of the renal pelvis and ureter were studied. Cell proliferation was assessed by Ki-67 immunostaining, and the proliferation index (PI) was expressed as a percentage of Ki-67-positive cells. Apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL), and the apoptotic index (AI) was expressed as a percentage of TUNEL positive cells. Angiogenesis was evaluated by CD31 immunostaining, and microvessel density (MVD) was expressed as the average of the microvessel count.

RESULTS

The PI ranged from 5.9% to 48.0% (median 20.03%), AI from 1.0% to 4.2% (median 2.26%), and MVD from 16.0 to 146.0 (median 56.88) in TCC of the renal pelvis and ureter. Statistical analysis revealed close associations of both PI and MVD with tumor stage and of AI with tumor grade. Our study demonstrated a strong relationship between PI and MVD, but did not show associations of AI with PI or MVD in TCC of the renal pelvis and ureter.

CONCLUSIONS

It is suggested that the high activity of tumor cell proliferation with rich neovascularization may be related to the high malignant potential of the cancer, and evaluation of cell proliferation combined with angiogenesis may be useful in predicting the progression of the renal pelvic and ureteral TCC.

Requirement for N-ethylmaleimide-sensitive factor activity at different stages of bacterial invasion and phagocytosis

Bacterial invasion, like the process of phagocytosis, involves extensive and localized protrusion of the host cell plasma membrane. To examine the molecular mechanisms of the membrane remodeling that accompanies bacterial invasion, soluble NSF attachment protein receptor (SNARE)-mediated membrane traffic was studied in cultured cells during infection by Salmonella typhimurium. A green fluorescent protein-tagged chimera of VAMP3, a SNARE characteristic of recycling endosomes, was found to accumulate at sites of Salmonella invasion. To analyze the possible role of SNARE-mediated membrane traffic in bacterial infection, invasion was measured in cells expressing a dominant-negative form of N-ethylmaleimide-sensitive factor (NSF), an essential regulator of membrane fusion. Inhibition of NSF activity did not affect cellular invasion by S. typhimurium nor the associated membrane remodeling. By contrast, Fcgamma receptor-mediated phagocytosis was greatly reduced in the presence of the mutant NSF. Most important, dominant-negative NSF significantly impaired the fusion of Salmonella-containing vacuoles with endomembranes. These observations indicate that the membrane protrusions elicited by Salmonella invasion, unlike those involved in phagocytosis, occur via an NSF-independent mechanism, whereas maturation of Salmonella-containing vacuoles is NSF-dependent.

Insulin resistance, cardiovascular risk factors and ultrasonically measured early arterial disease in normotensive Type 2 diabetic subjects

BACKGROUND

The objective of the study was to examine the relationship between serum fasting insulin, insulin sensitivity S(i), cardiovascular risk factors, and asymptomatic early atherosclerosis in normotensive Type 2 diabetic subjects.

METHODS

Specific insulin was measured using an enzyme-linked immunosorbent assay (ELISA) and insulin sensitivity was assessed with an insulin-modified frequently sampled intravenous glucose tolerance test (FSIVGTT). Early atherosclerotic change was assessed using carotid intima media thickness (IMT) and an arterial ultrasound score (AUS) measured by high-resolution B-mode ultrasound.

RESULTS

On bivariate analysis, there was a positive correlation between S(i) and high density lipoprotein (HDL) cholesterol (r(s)=0.27, p<0.05), and a negative correlation between S(i) and body mass index (BMI) (r(s)=-0.42, p<0.001), HbA(1c) (r(s)=-0.29, p<0.05) and serum triglyceride (r(s)=-0.30, p<0.05). There was a positive correlation between carotid IMT and age (r(s)=0.41, p<0.0005), and a positive association with male sex (p<0.0001) as well as with smoking (p<0.0001). However, we found no correlation between carotid IMT and fasting specific insulin (r(s)=-0.04) or S(i) (r(s)=-0.08). On multiple regression analyses, only age and serum triglycerides appeared to be significant independent variables with respect to carotid IMT whereas age, male sex and smoking emerged jointly significant with respect to AUS. There were no independent associations between carotid IMT or AUS with other variables including using either fasting specific insulin or S(i) as markers on insulin resistance separately.

CONCLUSION

Carotid IMT and AUS in Type 2 diabetes are closely associated with age, male sex and smoking. The relationships between serum insulin and insulin resistance with ultrasonically measured early arterial disease in Type 2 diabetes remain unclear.

Prevalence of renal artery stenosis in subjects with type 2 diabetes and coexistent hypertension

OBJECTIVE

To assess the prevalence of renal artery stenosis (RAS) in subjects with type 2 diabetes and coexistent hypertension by using magnetic resonance angiography (MRA) of the renal arteries, to assess clinical and biochemical predictors of RAS, and to assess the hemodynamic significance of RAS, by using the captopril test (a measure of the response of plasma renin activity to a single oral dose of captopril).

RESEARCH DESIGN AND METHODS

A total of 117 subjects with type 2 diabetes and coexistent hypertension between 40 and 70 years of age and with creatinine concentrations < 150 micromol/l were recruited from two inner-city general diabetes clinics. All subjects underwent MRA of the renal arteries. In a subgroup of 85 subjects, data concerning possible clinical and biochemical predictors of RAS were collected, and the captopril test was performed. For comparison of a continuous variable between subjects with a positive MRA and those with a negative MRA, the Mann-Whitney test was used. For comparison of a discrete variable between subjects with a positive MRA and those with a negative MRA, Fisher's exact test was used.

RESULTS

The prevalence of RAS detected by using MRA in 117 hypertensive type 2 diabetic subjects was 17%; 19 subjects had unilateral RAS, and only 1 subject had bilateral RAS. A femoral bruit was significantly more common in subjects with a positive MRA versus subjects with a negative MRA (21 vs. 0%; Fisher's exact test P < 0.005); however, other clinical features of atherosclerotic disease were not statistically associated. Greater duration of hypertension and treatment with statins were features of subjects with RAS (P < 0.05). The captopril test was negative in all subjects, although the antihypertensive response to oral captopril was significantly greater in subjects with RAS detected by MRA.

CONCLUSIONS

RAS is common in hypertensive type 2 diabetic subjects. The presence of a femoral bruit is a useful predictive clinical marker. The captopril test is not useful in predicting the hemodynamic significance of RAS in this patient group.

Is the endogenous peroxyl-radical scavenging capacity of plasma protective in systemic inflammatory disorders in humans?

Systemic inflammatory response syndrome (SIRS) in humans is associated with heightened intravascular oxidative stress. The clinical significance of plasma endogenous antioxidative capability in SIRS remains undetermined. Time-sequence changes of plasma total radical-trapping antioxidant parameter (TRAP) and its components were measured in 135 patients with various clinical conditions leading to SIRS. The results were correlated with clinical parameters. Plasma TRAP significantly depressed upon diagnosis of SIRS (SIRS vs. healthy subjects (n = 50), 605.7 +/- 20.4 vs. 803.4 +/- 30.8 microM Trolox equivalent, p <.001). In survivors (n = 86), TRAP declined further during the course of SIRS, followed by a mild recovery at the end of follow-up. General linear mixed model analysis revealed that uric acid, vitamin C, vitamin E and unidentified antioxidants contributed to most of the changes in TRAP (each factor p <.001). In nonsurvivors (n = 49), TRAP increased steadily until death, and the increase was predominantly the result of the increased contribution of bilirubin (p <.01). Higher TRAP levels were not correlated with diminished blood oxidants formation (r = -0.13, p.05), lower intensity of lipid peroxidation (r = 0.261, p <.05) or lesser disease severity of SIRS. The results do not support the hypothesis that the endogenous peroxyl radical scavenging ability of plasma plays a protective role in the course of SIRS.

Phosphatidylinositol polyphosphate binding to the mammalian septin H5 is modulated by GTP

BACKGROUND

Septins are members of a conserved family of GTPases found in organisms as diverse as budding yeast and mammals. In budding yeast, septins form hetero-oligomeric filaments that lie adjacent to the membrane at the mother-bud neck, whereas in mammals, they concentrate at the cleavage furrow of mitotic cells; in both cases, septins provide a required function for cytokinesis. What directs the location and determines the stability of septin filaments, however, remains unknown.

RESULTS

Here we show that the mammalian septin H5 is associated with the plasma membrane and specifically binds the phospholipids phosphatidylinositol 4, 5-bisphosphate (PtdIns(4,5)P(2)) and phosphatidylinositol 3,4, 5-trisphosphate (PtdIns(3,4,5)P(3)). Deletion analysis revealed that this binding occurs at a site rich in basic residues that is conserved in most septins and is located adjacent to the GTP-binding motif. Phosphoinositide binding was inhibited by mutations within this motif and was also blocked by agents known to associate with PtdInsP(2) or by a peptide corresponding to the predicted PtdInsP(2)-binding sequence of H5. GTP binding and hydrolysis by H5 significantly reduced its PtdInsP(2)-binding capability. Treatment of cells with agents that occluded, dephosphorylated or degraded PtdInsP(2) altered the appearance and localization of H5.

CONCLUSIONS

These results indicate that the interaction of septins with PtdInsP(2) might be an important cellular mechanism for the spatial and temporal control of septin accumulation.