The Rab8 GTPase regulates apical protein localization in intestinal cells

A number of proteins are known to be involved in apical/basolateral transport of proteins in polarized epithelial cells. The small GTP-binding protein Rab8 was thought to regulate basolateral transport in polarized kidney epithelial cells through the AP1B-complex-mediated pathway. However, the role of Rab8 (Rab8A) in cell polarity in vivo remains unknown. Here we show that Rab8 is responsible for the localization of apical proteins in intestinal epithelial cells. We found that apical peptidases and transporters localized to lysosomes in the small intestine of Rab8-deficient mice. Their mislocalization and degradation in lysosomes led to a marked reduction in the absorption rate of nutrients in the small intestine, and ultimately to death. Ultrastructurally, a shortening of apical microvilli, an increased number of enlarged lysosomes, and microvillus inclusions in the enterocytes were also observed. One microvillus inclusion disease patient who shows an identical phenotype to Rab8-deficient mice expresses a reduced amount of RAB8 (RAB8A; NM_005370). Our results demonstrate that Rab8 is necessary for the proper localization of apical proteins and the absorption and digestion of various nutrients in the small intestine.     

Variation in the DEPDC5 locus is associated with progression to hepatocellular carcinoma in chronic hepatitis C virus carriers

Chronic viral hepatitis is the most important risk factor for progression to hepatocellular carcinoma (HCC). To identify genetic risk factors for progression to HCC in individuals with chronic hepatitis C virus (HCV), we analyzed 467,538 SNPs in 212 Japanese individuals with chronic HCV with HCC and 765 individuals with chronic HCV without HCC. We identified one intronic SNP in the DEPDC5 locus on chromosome 22 associated with HCC risk and confirmed the association using an independent case-control population (710 cases and 1,625 controls). The association was highly significant when we analyzed the stages separately as well as together (rs1012068, P(combined) = 1.27 × 10(-13), odds ratio = 1.75). The significance level of the association further increased after adjustment for gender, age and platelet count (P = 1.35 × 10(-14), odds ratio = 1.96). Our findings suggest that common variants within the DEPDC5 locus affect susceptibility to HCC in Japanese individuals with chronic HCV infection.     

Crossover assurance and crossover interference are distinctly regulated by the ZMM proteins during yeast meiosis

Meiotic crossing-over is highly regulated such that each homolog pair typically receives at least one crossover (assurance) and adjacent crossovers are widely spaced (interference). Here we provide evidence that interference and assurance are mechanistically distinct processes that are separated by mutations in a new ZMM (Zip, Msh, Mer) protein from Saccharomyces cerevisiae, Spo16. Like other zmm mutants, spo16 cells have defects in both crossing-over and synaptonemal complex formation. Unlike in previously characterized zmm mutants, the residual crossovers in spo16 cells show interference comparable to that in the wild type. Spo16 interacts with a second ZMM protein, Spo22 (also known as Zip4), and spo22 mutants also show normal interference. Notably, assembly of the MutS homologs Msh4 and Msh5 on chromosomes occurs in both spo16 and spo22, but not in other zmm mutants. We suggest that crossover interference requires the normal assembly of recombination complexes containing Msh4 and Msh5 but does not require Spo16- and Spo22-dependent extension of synaptonemal complexes. In contrast, crossover assurance requires all ZMM proteins and full-length synaptonemal complexes.     

Oncogenic mutations of ALK kinase in neuroblastoma

Neuroblastoma in advanced stages is one of the most intractable paediatric cancers, even with recent therapeutic advances. Neuroblastoma harbours a variety of genetic changes, including a high frequency of MYCN amplification, loss of heterozygosity at 1p36 and 11q, and gain of genetic material from 17q, all of which have been implicated in the pathogenesis of neuroblastoma. However, the scarcity of reliable molecular targets has hampered the development of effective therapeutic agents targeting neuroblastoma. Here we show that the anaplastic lymphoma kinase (ALK), originally identified as a fusion kinase in a subtype of non-Hodgkin's lymphoma (NPM-ALK) and more recently in adenocarcinoma of lung (EML4-ALK), is also a frequent target of genetic alteration in advanced neuroblastoma. According to our genome-wide scans of genetic lesions in 215 primary neuroblastoma samples using high-density single-nucleotide polymorphism genotyping microarrays, the ALK locus, centromeric to the MYCN locus, was identified as a recurrent target of copy number gain and gene amplification. Furthermore, DNA sequencing of ALK revealed eight novel missense mutations in 13 out of 215 (6.1%) fresh tumours and 8 out of 24 (33%) neuroblastoma-derived cell lines. All but one mutation in the primary samples (12 out of 13) were found in stages 3-4 of the disease and were harboured in the kinase domain. The mutated kinases were autophosphorylated and displayed increased kinase activity compared with the wild-type kinase. They were able to transform NIH3T3 fibroblasts as shown by their colony formation ability in soft agar and their capacity to form tumours in nude mice. Furthermore, we demonstrate that downregulation of ALK through RNA interference suppresses proliferation of neuroblastoma cells harbouring mutated ALK. We anticipate that our findings will provide new insights into the pathogenesis of advanced neuroblastoma and that ALK-specific kinase inhibitors might improve its clinical outcome.     

Mantle superplasticity and its self-made demise

The unusual capability of solid crystalline materials to deform plastically, known as superplasticity, has been found in metals and even in ceramics. Such superplastic behaviour has been speculated for decades to take place in geological materials, ranging from surface ice sheets to the Earth's lower mantle. In materials science, superplasticity is confirmed when the material deforms with large tensile strain without failure; however, no experimental studies have yet shown this characteristic in geomaterials. Here we show that polycrystalline forsterite + periclase (9:1) and forsterite + enstatite + diopside (7:2.5:0.5), which are good analogues for Earth's mantle, undergo homogeneous elongation of up to 500 per cent under subsolidus conditions. Such superplastic deformation is accompanied by strain hardening, which is well explained by the grain size sensitivity of superplasticity and grain growth under grain switching conditions (that is, grain boundary sliding); grain boundary sliding is the main deformation mechanism for superplasticity. We apply the observed strain-grain size-viscosity relationship to portions of the mantle where superplasticity has been presumed to take place, such as localized shear zones in the upper mantle and within subducting slabs penetrating into the transition zone and lower mantle after a phase transformation. Calculations show that superplastic flow in the mantle is inevitably accompanied by significant grain growth that can bring fine grained (≤1?μm) rocks to coarse-grained (1-10?mm) aggregates, resulting in increasing mantle viscosity and finally termination of superplastic flow.     

Endogenous inhibitor of ecdysone synthesis in crabs

Summary Attempts to isolate the molt-inhibiting hormone (MIH) of crustaceans from crab eyestalks (ES) resulted in the characterization of xanthurenic acid as an inhibitor of ecdysone biosynthesis in the cultured Y-organ-complex (YOC) homogenate. It was also found that 3-hydroxyl-l-kynurenine present in the ES is transformed into xanthurenic acid in the YOC and body fluid. Its mode of inhibitory action in ecdysone biosynthesis is probably inactivation of cytochrome P-450.Acknowledgments. We thank Prof. M. Oka (Nagasaki University) and Dr J. Cappuzo (Oceanographic Inst.) for information on Y-organ and molting stages, Dr J. Termini and Mr J. Cesarelli (Columbia University) for organ excision of blue crabs and experiments in the early stage of this study, the Japan Sea Farming Association for aqua culture of crabs, Prof. Y. Umebachi (Kanazawa University) for a gift of 3-OH-l-Kyn, and Mr J. Rudloe (Gulf Specimen Co.) for collection and shipping of some selected crabs. This study was partially supported by NIH grant AI 10 187 (to K. N., at Columbia University).