[Show abstract][Hide abstract] ABSTRACT: UBIAD1 plays critical roles in physiology including vitamin K and CoQ10 biosynthesis as well as pathophysiology including dyslipimedia-induced SCD (Schnyder's corneal dystrophy), Parkinson's disease, cardiovascular disease and bladder carcinoma. Since the subcellular localization of UBIAD1 varies in different cell types, characterization of the exact subcellular localization of UBIAD1 in specific human disease is vital for understanding its molecular mechanism. As UBIAD1 suppresses bladder carcinoma, we studied its subcellular localization in human bladder carcinoma cell line T24. Since fluorescent images of UBIAD1-EGFP in T24, human prostate cancer cell line PC-3, human embryonic kidney cell line HEK293 and human hepatocyte cell line L02 are similar, these four cell lines were used for present study. Using a combination of fluorescent microscopy and immunohistochemistry, it was found that UBIAD1 localized on the Golgi and endoplasmic reticulum (ER), but not on the plasma membrane, of T24 and HEK293 cells. Using scanning electron microscopy and western blot analysis, we found that UBIAD1 is enriched in the Golgi fraction extracted from the L02 cells, verifying the Golgi localization of UBAID1. Site-directed mutagenesis showed that the RPWS motif, which forms an Arginine finger on the UBIAD1 N terminus, serves as the Golgi retention signal. With both cycloheximide and brefeldin A inhibition assays, it was shown that UBIAD1 may be transported from the endoplasmic reticulum (ER) to the Golgi by a COPII-mediated mechanism. Based upon flow cytometry analysis, it is shown that mutation of the RPWS motif reduced the UBIAD1-induced apoptosis of T24 cells, indicating that the proper Golgi localization of UBIAD1 influences its tumor suppressant activity. This study paves the way for further understanding the molecular mechanism of UBIAD1 in human diseases.
[Show abstract][Hide abstract] ABSTRACT: Conventional macro-scale methods are not appropriate for in vivo neuronal analysis at a single neuron level when experimental subject is small model organism Caenorhabditis elegans. In this paper, we demonstrate a powerful microfluidic device that allowed investigating in vivo chemo-sensing of intact C. elegans by integrating functions of automated manipulation of worms, effective immobilization without damages and well-controllable stimulations. Live C. elegans were effectively immobilized in microfluidic channels by a comb-shaped microvalve without physiological damages. A well-controlled sample introduction system was used to deliver chemicals to the chemosensory cilia at the worm's nose tip. In vivo neuronal responses of the animal to the chemical stimulations were monitored using calcium fluorescence imaging. Dynamic calcium signals related to varying concentrations and durations of stimuli were investigated using this integrated microfluidic device. We anticipate this immobilization approaches can have an impact in a variety of applications, such as neuron responses investigation before and after laser ablation upstream or downstream neurons for studying olfactory or gustatory neural circuits in individual healthy worms, in this high-throughput system.
Full-text · Article · Mar 2013 · Sensors and Actuators B Chemical
[Show abstract][Hide abstract] ABSTRACT: The functional diversity of large conductance Ca(2+)- and voltage-dependent K(+) (BK) channels arises mainly from co-assembly of the pore-forming mSlo alpha subunits with four tissue-enriched auxiliary beta subunits. The structural basis of the interaction between alpha subunits with beta subunits is not well understood. Using computational and experimental methods, we demonstrated that four mSlo turrets decentralized distally from the channel pore to provide a wide open conformation and that the mSlo and hbeta4 subunits together formed a "helmet" containing three basic residues (Lys-120, Arg-121, and Lys-125), which impeded the entry of charybdotoxin (ChTX) by both the electrostatic interaction and limited space. In addition, the tyrosine insert mutant (in100Y) showed 56% inhibition, with a K(d) = 17 nm, suggesting that the hbeta4 lacks an external ChTX-binding site (Tyr-100). We also found that mSlo had an internal binding site (Tyr-294) in the alpha subunits that could "permanently" block 15% of mSlo+hbeta4 currents in the presence of 100 nm ChTX. These findings provide a better understanding of the diverse interactions between alpha and beta subunits and will improve the design of channel inhibitors.
[Show abstract][Hide abstract] ABSTRACT: Large conductance, voltage- and Ca2+-activated K+ (BK) channels encoded by the mslo α and β2 subunits exist abundantly in rat chromaffin cells, pancreatic β cells, and DRG
neurons. The extracellular loop of hβ2 acting as the channel regulator influences the rectification and toxin sensitivity
of BK channels, and the inactivation domain at its N terminus induces rapid inactivation. However, the regulatory mechanism,
especially the trafficking mechanism of hβ2, is still unknown. With the help of immunofluorescence and patch clamp techniques,
we determine that the hβ2 subunit alone resides in the endoplasmic reticulum, suggesting that trafficking mechanism of hβ2
differs from that of hβ1 opposite to what we predicted previously. We further demonstrate that a four-turn α helical segment
at the N terminus of hβ2 prevents the surface expression of hβ2, that is, the helical segment itself is a retention signal.
Using the c-Myc epitope-tagged extracellular loop of hβ2, we reveal that the most accessible site by antibody is located at
the middle of the extracellular loop, which might provide clues to understand how the auxiliary β subunits regulates the toxin
sensitivity and the rectification of BK-type channels.
Full-text · Article · Mar 2008 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: The auxiliary beta subunits of large-conductance Ca(2+)-activated K(+) (BK) channels greatly contribute to the diversity of BK (mSlo1 alpha) channels, which is fundamental to the adequate function in many tissues. Here we describe a functional element of the extracellular segment of hbeta2 auxiliary subunits that acts as the positively charged rings to modify the BK channel conductance. Four consecutive lysines of the hbeta2 extracellular loop, which reside sufficiently close to the extracellular entryway of the pore, constitute three positively charged rings. These rings can decrease the extracellular K(+) concentration and prevent the Charybdotoxin (ChTX) from approaching the extracellular entrance of channels through electrostatic mechanism, leading to the reduction of K(+) inflow or the outward rectification of BK channels. Our results demonstrate that the lysine rings formed by the hbeta2 auxiliary subunits influences the inward current of BK channels, providing a mechanism by which current can be rapidly diminished during cellular repolarization. Furthermore, this study will be helpful to understand the functional diversity of BK channels contributed by different auxiliary beta subunits.