Association of CD38 with nonmuscle myosin heavy chain IIA and Lck is essential for the internalization and activation of CD38

Activation of CD38 in lymphokine-activated killer (LAK) cells involves interleukin-8 (IL8)-mediated protein kinase G (PKG) activation and results in an increase in the sustained intracellular Ca(2+) concentration ([Ca(2+)](i)), cADP-ribose, and LAK cell migration. However, direct phosphorylation or activation of CD38 by PKG has not been observed in vitro. In this study, we examined the molecular mechanism of PKG-mediated activation of CD38. Nonmuscle myosin heavy chain IIA (MHCIIA) was identified as a CD38-associated protein upon IL8 stimulation. The IL8-induced association of MHCIIA with CD38 was dependent on PKG-mediated phosphorylation of MHCIIA. Supporting these observations, IL8- or cell-permeable cGMP analog-induced formation of cADP-ribose, increase in [Ca(2+)](i), and migration of LAK cells were inhibited by treatment with the MHCIIA inhibitor blebbistatin. Binding studies using purified proteins revealed that the association of MHCIIA with CD38 occurred through Lck, a tyrosine kinase. Moreover, these three molecules co-immunoprecipitated upon IL8 stimulation of LAK cells. IL8 treatment of LAK cells resulted in internalization of CD38, which co-localized with MHCIIA and Lck, and blebbistatin blocked internalization of CD38. These findings demonstrate that the association of phospho-MHCIIA with Lck and CD38 is a critical step in the internalization and activation of CD38.     

Focal adhesion kinase is negatively regulated by phosphorylation at tyrosine 407

Focal adhesion kinase (FAK) mediates signal transduction in response to multiple extracellular inputs via tyrosine phosphorylation at specific residues. Although several tyrosine phosphorylation events have been linked to FAK activation and downstream signal transduction, the function of FAK phosphorylation at Tyr(407) was previously unknown. Here, we show for the first time that phosphorylation of FAK Tyr(407) increases during serum starvation, contact inhibition, and cell cycle arrest, all conditions under which activating FAK Tyr(397) phosphorylation decreases. Transfection of NIH3T3 cells with a phosphorylation-mimicking FAK 407E mutant decreased autophosphorylation at Tyr(397) and inhibited both FAK kinase activity in vitro and FAK-mediated functions such as cell adhesion, spreading, proliferation, and migration. The opposite effects were observed in cells transfected with nonphosphorylatable mutant FAK 407F. Taken together, these data suggest the novel concept that FAK Tyr(407) phosphorylation negatively regulates the enzymatic and biological activities of FAK.     

Nucleocytoplasmic shuttling of the zinc finger protein EZI Is mediated by importin-7-dependent nuclear import and CRM1-independent export mechanisms

Nucleocytoplasmic translocation constitutes a foundation for nuclear proteins to exert their proper functions and hence for various biological reactions to occur normally in eukaryotic cells. We reported previously that EZI/Zfp467, a 12 zinc finger motif-containing protein, localizes predominantly in the nucleus, yet the underlying mechanism still remains elusive. Here we constructed a series of mutant forms of EZI and examined their subcellular localization. The results delineated a non-canonical nuclear localization signal in the region covering the 9th to the 12th zinc fingers, which was necessary for nuclear accumulation of EZI as well as sufficient to confer nuclear localizing ability to a heterologous protein. We also found that the N-terminal domain of EZI is necessary for its nuclear export, the process of which was not sensitive to the CRM1 inhibitor leptomycin B. An interaction proteomics approach and the following co-immunoprecipitation experiments identified the nuclear import receptor importin-7 as a molecule that associated with EZI and, importantly, short interfering RNA-mediated knockdown of importin-7 expression completely abrogated nuclear accumulation of EZI. Taken together, these results identify EZI as a novel cargo protein for importin-7 and demonstrate a nucleocytoplasmic shuttling mechanism that is mediated by importin-7-dependent nuclear localization and CRM1-independent nuclear export.     

Improved insulin sensitivity and adiponectin level after exercise training in obese Korean youth

Objective: The objective of this study was to investigate the association among adiposity, insulin resistance, and inflammatory markers [high‐sensitivity C‐reactive protein (hs‐CRP), interleukin (IL)‐6, and tumor necrosis factor (TNF)‐α] and adiponectin and to study the effects of exercise training on adiposity, insulin resistance, and inflammatory markers among obese male Korean adolescents. Research Methods and Procedures: Twenty‐six obese and 14 lean age‐matched male adolescents were studied. We divided the obese subjects into two groups: obese exercise group (N = 14) and obese control group (N = 12). The obese exercise group underwent 6 weeks of jump rope exercise training (40 min/d, 5 d/wk). Adiposity, insulin resistance, lipid profile, hs‐CRP, IL‐6, TNF‐α, and adiponectin were measured before and after the completion of exercise training. Results: The current study demonstrated higher insulin resistance, total cholesterol, LDL‐C levels, triglyceride, and inflammatory markers and lower adiponectin and HDL‐C in obese Korean male adolescents. Six weeks of increased physical activity improved body composition, insulin sensitivity, and adiponectin levels in obese Korean male adolescents without changes in TNF‐α, IL‐6, and hs‐CRP. Discussion: Obese Korean male adolescents showed reduced adiponectin levels and increased inflammatory cytokines. Six weeks of jump rope exercise improved triglyceride and insulin sensitivity and increased adiponectin levels.     

Determination of beraprost in human plasma by a high-performance liquid chromatography-tandem mass spectrometry

A simple, rapid, sensitive and specific liquid chromatography-tandem mass spectrometry method was developed and validated for quantification of beraprost, a stable, orally active prostacyclin analogue with vasodilatory, antiplatelet and cytoprotective effects. The analyte and internal standard, indomethacin, were extracted by solid-phase extraction using OASIS HLB cartridge. The chromatographic separation was performed on a C18 column with a mobile of 0.1% formic acid-methanol (30:70, v/v). The highest daughter ion of deprotonated analyte was quantitated in negative ionization by multiple reactions monitoring with a mass spectrometer. The mass transitions m/z 397>269 and m/z 356>312 were used to measure beraprost and internal standard, respectively. The assay exhibited a linear range from 0.02 to 2 ng/mL for beraprost in human plasma. The lower limit of quantitation was 20 pg/mL with a relative standard deviation of less than 20%. The method was validated with respect to linearity, sensitivity, specificity, recovery, accuracy and precision. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic study.