Heat shock protein 70 interacts with aquaporin-2 and regulates its trafficking

The trafficking of aquaporin-2 (AQP2) involves multiple complex pathways, including regulated, cAMP-, and cGMP-mediated pathways, as well as a constitutive recycling pathway. Although several accessory proteins have been indirectly implicated in AQP2 recycling, the direct protein-protein interactions that regulate this process remain largely unknown. Using yeast two-hybrid screening of a human kidney cDNA library, we have identified the 70-kDa heat shock proteins as AQP2-interacting proteins. Interaction was confirmed by mass spectrometry of proteins pulled down from rat kidney papilla extract using a GST-AQP2 C-terminal fusion protein (GST-A2C) as a bait, by co-immunoprecipitation (IP) assays, and by direct binding assays using purified hsc70 and the GST-A2C. The direct interaction of AQP2 with hsc70 is partially inhibited by ATP, and the Ser-256 residue in the AQP2 C terminus is important for this direct interaction. Vasopressin stimulation in cells enhances the interaction of hsc70 with AQP2 in IP assays, and vasopressin stimulation in vivo induces an increased co-localization of hsc70 and AQP2 on the apical membrane of principal cells in rat kidney collecting ducts. Functional knockdown of hsc70 activity in AQP2 expressing cells results in membrane accumulation of AQP2 and reduced endocytosis of rhodamine-transferrin. Our data also show that AQP2 interacts with hsp70 in multiple in vitro binding assays. Finally, in addition to hsc70 and hsp70, AQP2 interacts with several other key components of the endocytotic machinery in co-IP assays, including clathrin, dynamin, and AP2. To summarize, we have identified the 70-kDa heat shock proteins as a AQP2 interactors and have shown for hsc70 that this interaction is involved in AQP2 trafficking.     

采后光照条件对白凤桃果实品质和挥发性香气物质形成的影响

研究了白凤桃果实贮藏过程中光照条件对果实成熟的影响。在7月12日(未熟期)和7月16日(硬熟期)采收果实,分别贮藏在光条件(白色荧光灯照明,果顶部光强为80μmol m~(-2)s~(-1))和暗条件中,室温均为25℃。硬熟期采收果实贮藏在光条件下,达到完熟期时,乙烯生成量较低。果肉的硬度在各个采收期,各种贮藏条件下均没有差别。光条件贮藏果实中花青苷含量较高。未熟期采收果实贮藏在光条件下时,可溶性固形物含量增加较多。光条件贮藏果实中天冬酰胺的下降比暗贮藏果实中更多。各时期采收的果实中,在光下贮藏时,果肉和果皮γ-癸内酯和γ-十二内酯的含量都明显增加。以上结果表明,白凤桃果实采收后在光下贮藏,可以明显改善果实的品质。     

Cross‐taxon congruence of multiple diversity facets of freshwater assemblages is determined by large‐scale processes across China

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Proline-specific aminopeptidase P prevents replication-associated genome instability

Genotoxic stress during DNA replication constitutes a serious threat to genome integrity and causes human diseases. Defects at different steps of DNA metabolism are known to induce replication stress, but the contribution of other aspects of cellular metabolism is less understood. We show that aminopeptidase P (APP1), a metalloprotease involved in the catabolism of peptides containing proline residues near their N-terminus, prevents replication-associated genome instability. Functional analysis of C. elegans mutants lacking APP-1 demonstrates that germ cells display replication defects including reduced proliferation, cell cycle arrest, and accumulation of mitotic DSBs. Despite these defects, app-1 mutants are competent in repairing DSBs induced by gamma irradiation, as well as SPO-11-dependent DSBs that initiate meiotic recombination. Moreover, in the absence of SPO-11, spontaneous DSBs arising in app-1 mutants are repaired as inter-homologue crossover events during meiosis, confirming that APP-1 is not required for homologous recombination. Thus, APP-1 prevents replication stress without having an apparent role in DSB repair. Depletion of APP1 (XPNPEP1) also causes DSB accumulation in mitotically-proliferating human cells, suggesting that APP1’s role in genome stability is evolutionarily conserved. Our findings uncover an unexpected role for APP1 in genome stability, suggesting functional connections between aminopeptidase-mediated protein catabolism and DNA replication.     

What Happened before Losses of Photosynthesis in Cryptophyte Algae?

In many lineages of algae and land plants, photosynthesis was lost multiple times independently. Comparative analyses of photosynthetic and secondary nonphotosynthetic relatives have revealed the essential functions of plastids, beyond photosynthesis. However, evolutionary triggers and processes that drive the loss of photosynthesis remain unknown. Cryptophytes are microalgae with complex plastids derived from a red alga. They include several secondary nonphotosynthetic species with closely related photosynthetic taxa. In this study, we found that a cryptophyte, Cryptomonas borealis, is in a stage just prior to the loss of photosynthesis. Cryptomonas borealis was mixotrophic, possessed photosynthetic activity, and grew independent of light. The plastid genome of C. borealis had distinct features, including increases of group II introns with mobility, frequent genome rearrangements, incomplete loss of inverted repeats, and abundant small/medium/large-sized structural variants. These features provide insight into the evolutionary process leading to the loss of photosynthesis.     

Effect of bile acids on the uptake of irinotecan and its active metabolite, SN-38, by intestinal cells

The intestinal transport of irinotecan (CPT-11) and its active metabolite, SN-38, has been previously reported (K. Kobayashi et al., Int. J. Cancer, 83 (1999) 491-496). In the present study, the effect of the two major primary bile acids, cholic acid (CA) and taurocholic acid (TCA), on the uptake of CPT-11 and SN-38 by hamster intestinal epithelial cells was investigated. These two bile acids at concentrations up to 200 microM did not directly alter the cellular uptake of CPT-11 and SN-38. However, under physiologically acidic intestinal pH conditions, micelle formation induced by 20 mM TCA significantly reduced the cellular uptake of CPT-11 and SN-38 by 60% and 80%, respectively.     

Phosphorylation of proteins and apoptosis induced by c-Jun N-terminal kinase1 activation in rat cardiomyocytes by H(2)O(2) stimulation

Cytokines and various cellular stresses are known to activate c-Jun N-terminal kinase-1 (JNK1), which is involved in physiological function. Here, we investigate the activation of JNK1 by oxidative stress in H9c2 cells derived from rat cardiomyocytes. H(2)O(2) (100 microM) significantly induces the tyrosine phosphorylation of JNK1 with a peak 25 min after the stimulation. The amount of JNK1 protein remains almost constant during stimulation. Immunocytochemical observation shows that JNK1 staining in the nucleus is enhanced after H(2)O(2) stimulation. To clarify the physiological role of JNK1 activation under these conditions, we transfected antisense JNK1 DNA into H9c2 cells. The antisense DNA (2 microM) inhibits JNK1 expression by 80% as compared with expression in the presence of the sense DNA, and significantly blocks H(2)O(2)-induced cell death. Consistent with the decrease in cell number, we detected condensation of the nuclei, a hallmark of apoptosis, 3 h after H(2)O(2) stimulation in the presence of the sense DNA for JNK1. The antisense DNA of JNK1 inhibits the condensation of nuclei by H(2)O(2). Under these conditions, the H(2)O(2)-induced phosphorylation of proteins with molecular masses of 55, 72, and 78 kDa is blocked by treatment with the antisense DNA for JNK1 as compared with the sense DNA for JNK1. These findings suggest that JNK1 induces apoptotic cell death in response to H(2)O(2), and that the cell death may be involved in the phosphorylations of 55, 72, and 78 kDa proteins induced by JNK1 activation.     

Why and how are peptide-lipid interactions utilized for self-defense? Magainins and tachyplesins as archetypes

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