Ganglioside GM1-mediated Transcytosis of Cholera Toxin Bypasses the Retrograde Pathway and Depends on the Structure of the Ceramide Domain

Cholera toxin causes diarrheal disease by binding ganglioside GM1 on the apical membrane of polarized intestinal epithelial cells and trafficking retrograde through sorting endosomes, the trans-Golgi network (TGN), and into the endoplasmic reticulum. A fraction of toxin also moves from endosomes across the cell to the basolateral plasma membrane by transcytosis, thus breeching the intestinal barrier. Here we find that sorting of cholera toxin into this transcytotic pathway bypasses retrograde transport to the TGN. We also find that GM1 sphingolipids can traffic from apical to basolateral membranes by transcytosis in the absence of toxin binding but only if the GM1 species contain cis-unsaturated or short acyl chains in the ceramide domain. We found previously that the same GM1 species are needed to efficiently traffic retrograde into the TGN and endoplasmic reticulum and into the recycling endosome, implicating a shared mechanism of action for sorting by lipid shape among these pathways.     

Birth Weight,Adult Body Composition,and Subcutaneous Fat Distribution

Objectives: To investigate if birth weight is related to both body mass index (BMI) and distribution of subcutaneous fat at adult age. Research Methods and Procedures: A 9‐year longitudinal study was performed in 229 subjects (192 women) with ages ranging from 27 to 36 years. Birth weight was retrieved by a questionnaire, and adult weight, height, skinfold thicknesses, and waist‐to‐hip ratio (WHR) were repeatedly measured at mean ages 27, 29, 31, and 36 years. BMI, sum of four skinfolds (S4S), the ratio between two truncal skinfolds and S4S (SS/S4S), and the ratio between WHR and the cross‐sectional area of the left thigh were calculated with the available data. Results: The adjusted model showed that in women, birth weight was significantly negatively related to adult S4S [β = ?5.211; (?9.768 to ?0.654)], waist circumference [β = ?1.449; (?2.829 to ?0.069)], and SS/S4S ratio [β = ?3.579; (?5.296 to ?1.862)]. In men, a significant negative association was observed between birth weight and adult WHR [β = ?1.096; (?2.092 to ?0.100)] only. Other relationships showed, although not significantly, the same negative trend, namely that lower birth weight is related to higher adult body fat mass (S4S) and a more truncal subcutaneous fat distribution (SS/S4S). No associations were found between birth weight and either adult BMI or the cross‐sectional area of the thigh. Discussion: Lower birth weight is, in both adult men and women, related to a higher adult subcutaneous fat mass and a more truncal distribution of subcutaneous fat, indicating a higher risk for obesity.     

Functional Characterization of CaVα2δ Mutations Associated with Sudden Cardiac Death

L-type Ca²⁺ channels play a critical role in cardiac rhythmicity. These ion channels are oligomeric complexes formed by the pore-forming Ca_Vα1 with the auxiliary Ca_Vβ and Ca_Vα2δ subunits. Ca_Vα2δ increases the peak current density and improves the voltage-dependent activation gating of Ca_V1.2 channels without increasing the surface expression of the Ca_Vα1 subunit. The functional impact of genetic variants of CACNA2D1 (the gene encoding for Ca_Vα2δ), associated with shorter repolarization QT intervals (the time interval between the Q and the T waves on the cardiac electrocardiogram), was investigated after recombinant expression of the full complement of L-type Ca_V1.2 subunits in human embryonic kidney 293 cells. By performing side-by-side high resolution flow cytometry assays and whole-cell patch clamp recordings, we revealed that the surface density of the Ca_Vα2δ wild-type protein correlates with the peak current density. Furthermore, the cell surface density of Ca_Vα2δ mutants S755T, Q917H, and S956T was not significantly different from the cell surface density of the Ca_Vα2δ wild-type protein expressed under the same conditions. In contrast, the cell surface expression of Ca_Vα2δ D550Y, Ca_Vα2δ S709N, and the double mutant D550Y/Q917H was reduced, respectively, by ≈30–33% for the single mutants and by 60% for the latter. The cell surface density of D550Y/Q917H was more significantly impaired than protein stability, suggesting that surface trafficking of Ca_Vα2δ was disrupted by the double mutation. Co-expression with D550Y/Q917H significantly decreased Ca_V1.2 currents as compared with results obtained with Ca_Vα2δ wild type. It is concluded that D550Y/Q917H reduced inward Ca²⁺ currents through a defect in the cell surface trafficking of Ca_Vα2δ. Altogether, our results provide novel insight in the molecular mechanism underlying the modulation of Ca_V1.2 currents by Ca_Vα2δ.     

Targeting head and neck tumoral stem cells: From biological aspects to therapeutic perspectives

Head and neck squamous cell cancer(HNSCC) is the sixth most common cancer in the world. Effective therapeutic modalities such as surgery, radiation, chemotherapy and combinations of each are used in the management of the disease. In most cases, treatment fails to obtain total cancer cure. In recent years, it appears that one of the key determinants of treatment failure may be the presence of cancer stem cells(CSCs) that escape currently available therapies. CSCs form a small portion of the total tumor burden but may play a disproportionately important role in determining outcomes. CSCs have stem features such as self-renewal, high migration capacity, drug resistance, high proliferation abilities. A large body of evidence points to the fact that CSCs are particularly resistant to radiotherapy and chemotherapy. In HNSCC, CSCs have been increasingly shown to have an integral role in tumor initiation, disease progression, metastasis and treatment resistance. In the light of such observations, the present review summarizes biological characteristics of CSCs in HNSCC, outlines targeted strategies for the successful eradication of CSCs in HNSCC including targeting the self-renewal controlling pathways, blocking epithelial mesenchymal transition, niche targeting, immunotherapy approaches and highlights the need to better understand CSCs biology for new treatments modalities.     

Balanced hereditary polymorphism and the mortality from cardiovascular diseases in the populations of 17 countries of Europe. I. A correlation analysis

The correlation analysis of ratios between six polymorphic genetic systems (ABO, MNSs, Rh, Hp, Gm, HLA) and mortality from ishemic heart disease, brain vascular lesions, and hypertensive disease in 17 European populations has been made. A statistically significant correlation has been established between the populational frequency of most of the 50 phenotypes and genes under study, and mortality. The qualitative structure of correlations and their quantitative expression depend on the cause of death, age and sex. The possible mechanisms of relationship between the genetic populational differences and mortality from cardiovascular diseases are discussed.     

Sex Ratios in a Socially Parasitic Bee and Implications for Host-Parasite Interactions

Obligate social parasites of Hymenoptera, known as inquilines, have received enormous attention due to the elaborate adaptations they exhibit for exploiting their hosts, and because they have frequently been used to infer sympatric speciation. Their population biology can be difficult to infer as they are both rare and difficult to extract from host nests. Sex allocation has been studied for very few inquilines of social Hymenoptera. Here we report sex ratio patterns in the allodapine bee Inquilina schwarzi, which is an obligate social parasite of another allodapine, Exoneura robusta. We show that the sex ratio of this inquiline varies with its brood number, it is female-biased in the smallest broods, but becomes more even in larger broods, where the population-wide sex ratio is close to parity. We argue that this pattern of bias is consistent with local resource competition, where inquiline females compete to inherit their natal colony. We also argue that extremely female-biased sex ratios of the host species, combined with overall sex ratio parity in the parasite, may help ameliorate disparity in effective population sizes between these two species which are locked in an evolutionary arms race.     

Crystal Structure and Pathophysiological Role of the Pneumococcal Nucleoside-binding Protein PnrA

Nucleotides are important for RNA and DNA synthesis and, despite a de novo synthesis by bacteria, uptake systems are crucial. Streptococcus pneumoniae, a facultative human pathogen, produces a surface-exposed nucleoside-binding protein, PnrA, as part of an ABC transporter system. Here we demonstrate the binding affinity of PnrA to nucleosides adenosine, guanosine, cytidine, thymidine and uridine by microscale thermophoresis and indicate the consumption of adenosine and guanosine by ¹H NMR spectroscopy. In a series of five crystal structures we revealed the PnrA structure and provide insights into how PnrA can bind purine and pyrimidine ribonucleosides but with preference for purine ribonucleosides. Crystal structures of PnrA:nucleoside complexes unveil a clear pattern of interactions in which both the N- and C- domains of PnrA contribute. The ribose moiety is strongly recognized through a conserved network of H-bond interactions, while plasticity in loop 27–36 is essential to bind purine- or pyrimidine-based nucleosides.Further, we deciphered the role of PnrA in pneumococcal fitness in infection experiments. Phagocytosis experiments did not show a clear difference in phagocytosis between PnrA-deficient and wild-type pneumococci. In the acute pneumonia infection model the deficiency of PnrA attenuated moderately virulence of the mutant, which is indicated by a delay in the development of severe lung infections. Importantly, we confirmed the loss of fitness in co-infections, where the wild-type out-competed the pnrA-mutant. In conclusion, we present the PnrA structure in complex with individual nucleosides and show that the consumption of adenosine and guanosine under infection conditions is required for virulence.