Annexin A1 and A2: roles in retrograde trafficking of Shiga toxin

Annexins constitute a family of calcium and membrane binding proteins. As annexin A1 and A2 have previously been linked to various membrane trafficking events, we initiated this study to investigate the role of these annexins in the uptake and intracellular transport of the bacterial Shiga toxin (Stx) and the plant toxin ricin. Once endocytosed, both toxins are retrogradely transported from endosomes to the Golgi apparatus and the endoplasmic reticulum before being targeted to the cytosol where they inhibit protein synthesis. This study was performed to obtain new information both about toxin transport and the function of annexin A1 and annexin A2. Our data show that depletion of annexin A1 or A2 alters the retrograde transport of Stx but not ricin, without affecting toxin binding or internalization. Knockdown of annexin A1 increases Golgi transport of Stx, whereas knockdown of annexin A2 slightly decreases the same transport step. Interestingly, annexin A1 was found in proximity to cytoplasmic phospholipase A2 (cPLA(2)), and the basal as well as the increased Golgi transport of Stx upon annexin A1 knockdown is dependent on cPLA(2) activity. In conclusion, annexin A1 and A2 have different roles in Stx transport to the trans-Golgi network. The most prominent role is played by annexin A1 which normally works as a negative regulator of retrograde transport from the endosomes to the Golgi network, most likely by complex formation and inhibition of cPLA(2).     

Effect of the anti-oxidant tempol on fetal growth in a mouse model of fetal growth restriction

Fetal growth restriction (FGR) greatly increases the risk of perinatal morbidity and mortality and is associated with increased uterine artery resistance and levels of oxidative stress. There are currently no available treatments for this condition. The hypothesis that the antioxidant 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (Tempol) would improve uterine artery function and rescue fetal growth was tested in a mouse model of FGR, using the endothelial nitric oxide synthase knockout mouse (Nos3(-/-)). Pregnant Nos3(-/-) and control C57BL/6J mice were treated with the superoxide dismutase-mimetic Tempol (1 mmol/L) or vehicle from Gestational Day 12.5 to 18.5. Tempol treatment significantly increased pup weight (P < 0.05) and crown-rump length (P < 0.01) in C57BL/6J and Nos3(-/-) mice. Uterine artery resistance was increased in Nos3(-/-) mice (P < 0.05); Tempol significantly increased end diastolic velocity in Nos3(-/-) mice (P < 0.05). Superoxide production in uterine arteries did not differ between C57BL/6J and Nos3(-/-) mice but was significantly increased in placentas from Nos3(-/-) mice (P < 0.05). This was not reduced by Tempol treatment. Placental System A activity was reduced in Nos3(-/-) mice (P < 0.01); this was not improved by treatment with Tempol. Treatment of Nos3(-/-) mice with Tempol, however, was associated with reduced vascular density in the placental bed (P < 0.05). This study demonstrated that treatment with the antioxidant Tempol is able to improve fetal growth in a mouse model of FGR. This was associated with an increase in uterine artery blood flow velocity but not an improvement in uterine artery function or placental System A activity.     

A Dynamic C-Terminal Segment in the Mycobacterium tuberculosis Mn/Fe R2lox Protein Can Adopt a Helical Structure with Possible Functional Consequences

Mycobacterium tuberculosis R2-like ligand-binding oxidase (MtR2lox) belongs to a recently discovered group of proteins that are homologous to the ribonucleotide reductase R2 proteins. MtR2lox carries a heterodinuclear Mn/Fe cofactor and, unlike R2 proteins, a large ligand-binding cavity. A unique tyrosine-valine cross link is also found in the vicinity of the active site. To date, all known structures of R2 and R2lox proteins show a disordered C-terminal segment. Here, we present two new crystal forms of MtR2lox, revealing an ordered helical C-terminal. The ability of alternating between an ordered and disordered state agrees well with bioinformatic analysis of the protein sequence. Interestingly, ordering of the C-terminal helix shields a large positively charged patch on the protein surface, potentially used for interaction with other cellular components. We hypothesize that the dynamic C-terminal segment may be involved in control of protein function in vivo.     

In vivo measurements of diffuse reflectance and time‐resolved autofluorescence emission spectra of basal cell carcinomas

We present a clinical investigation of diffuse reflectance and time‐resolved autofluorescence spectra of skin cancer with an emphasis on basal cell carcinoma. A total of 25 patients were measured using a compact steady‐state diffuse reflectance/fluorescence spectrometer and a fibre‐optic‐coupled multispectral time‐resolved spectrofluorometer. Measurements were performed in vivo prior to surgical excision of the investigated region. Singular value decomposition was used to reduce the dimensionality of steady state diffuse reflectance and fluorescence spectra. Linear discriminant analysis was then applied to the measurements of basal cell carcinomas (BCCs) and used to predict the tissue disease state with a leave‐one‐out methodology. This approach was able to correctly diagnose 87% of the BCCs. With 445 nm excitation a decrease in the spectrally averaged fluorescence lifetime was observed between normal tissue and BCC lesions with a mean value of 886 ps. Furthermore, the fluorescence lifetime for BCCs was lower than that of the surrounding healthy tissue in all cases and statistical analysis of the data revealed that this decrease was significant (p = 0.002). (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Persistence of antibiotic resistant bacteria

Bacterial adaptation to antibiotics has been very successful and over the past decade the increase in antibiotic resistance has generated considerable medical problems. Even though many drug resistances confer a fitness cost, suggesting that they might disappear by reducing the volume of antibiotic use, increasing evidence obtained from laboratory and epidemiological studies indicate that several processes will act to cause long-term persistence of resistant bacteria. Compensatory evolution that ameliorates the costs of resistance, the occurrence of cost-free resistances and genetic linkage between non-selected and selected resistances will confer a stabilization of the resistant bacteria. Thus, it is of importance that we forcefully implement strategies to reduce the rate of appearance and spread of resistant bacteria to allow new drug discovery to catch up with bacterial resistance development.