Hydrolysis of sphingosylphosphocholine by neutral sphingomyelinases

Sphingosylphosphocholine (SPC), the N-deacylated form of sphingomyelin (SM), is a naturally occurring lipid mediator. However, little is known about the metabolism of SPC. We here report an in vitro assay system for SPC-phospholipase C (PLC). Using this assay system, we demonstrated that nSMase1 and nSMase2, human neutral sphingomyelinases (SMases), are capable of hydrolyzing SPC efficiently under detergent-free conditions. Bacterial and plasmodial neutral SMases also showed SPC-PLC activity. The substrate specificity of neutral SMases that hydrolyze SM, SPC, and monoradyl glycerophosphocholine, but not diradyl glycerophosphocholine, suggested that a hydrogen-bond donor at the C-2 or sn-2 position in the substrate is required for recognition by the enzymes.     

NMR structure of the N-terminal domain of SUMO ligase PIAS1 and its interaction with tumor suppressor p53 and A/T-rich DNA oligomers

A member of the PIAS (protein inhibitor of activated STAT) family of proteins, PIAS1, have been reported to serve as an E3-type SUMO ligase for tumor suppressor p53 and its own. It also was proposed that the N-terminal domain of PIAS1 interacts with DNA as well as p53. Extensive biochemical studies have been devoted recently to understand sumoylations and its biological implications, whereas the structural aspects of the PIAS family and the mechanism of its interactions with various factors are less well known to date. In this study, the three-dimensional structure of the N-terminal domain (residues 1-65) of SUMO ligase PIAS1 was determined by NMR spectroscopy. The structure revealed a unique four-helix bundle with a topology of an up-down-extended loop-down-up, a part of which the helix-extended loop-helix represented the SAP (SAF-A/B, Acinus, and PIAS) motif. Thus, this N-terminal domain may be referred to as a four-helix SAP domain. The glutathione S-transferase pull-down assay demonstrated that this domain possesses a binding ability to tumor suppressor p53, a target protein for sumoylation by PIAS1, whereas gel mobility assays showed that it has a strong affinity toward A/T-rich DNA. An NMR analysis of the four-helix SAP domain complexed with the 16-bp-long DNA demonstrated that one end of the four-helix bundle is the binding site and may fit into the minor groove of DNA. The three-dimensional structure and its binding duality are discussed in conjunction with the biological functions of PIAS1 as a SUMO ligase.     

NKT cells play a limited role in the neutrophilic inflammatory responses and host defense to pulmonary infection with Pseudomonas aeruginosa

CD1d-restricted NKT cells are reported to play a critical role in the host defense to pulmonary infection with Pseudomonas aeruginosa. However, the contribution of a major subset expressing a Valpha14-Jalpha18 gene segment remains unclear. In the present study, we re-evaluated the role of NKT cells in the neutrophilic inflammatory responses and host defense to this infection using mice genetically lacking Jalpha18 or CD1d (Jalpha18KO or CD1dKO mice). These mice cleared the bacteria in lungs at a comparable level to wild-type (WT) mice. There was no significant difference in the local neutrophilic responses, as shown by neutrophil counts and synthesis of MIP-2 and TNF-alpha, in either KO mice from those in WT mice. Administration of alpha-galactosylceramide, a specific activator of Valpha14+ NKT cells, failed to promote the bacterial clearance and neutrophilic responses, although the same treatment increased the synthesis of IFN-gamma, suggesting the involvement of this cytokine downstream of NKT cells. In agreement against this notion, these responses were not further enhanced by administration of recombinant IFN-gamma in the infected Jalpha18KO mice. Our data indicate that NKT cells play a limited role in the development of neutrophilic inflammatory responses and host defense to pulmonary infection with P. aeruginosa.     

In vitro expression of natriuretic peptides in cardiomyocytes differentiated from monkey embryonic stem cells

Functional characterization of ES cell-derived cardiomyocytes is important for differentiation control and application to the cell therapy. One of the crucial functions of cardiomyocytes is a production of atrial and brain natriuretic peptides (ANP and BNP, respectively), which have important endocrine, autocrine, and paracrine functions. In this study, we focused on the functional aspect of the cardiomyocytes differentiated from monkey ES cells in vitro and investigated the expression of ANP and BNP. Spontaneously contracting cells showed nodal-like action potentials, and expression of ANP and BNP by RT-PCR and immunocytochemistry. Interestingly, ANP and BNP expressions were detected as immunoreactive granules in the perinuclear area and these signals appeared to co-localize with trans-Golgi network. These findings suggest that monkey ES cells were able to differentiate into cardiomyocytes with functional characteristics in vitro and therefore can be used as a useful model to study mechanisms and functions in early cardiogenesis.     

MRGD, a MAS-related G-protein coupled receptor, promotes tumorigenisis and is highly expressed in lung cancer

To elucidate the function of MAS-related GPCR, member D (MRGD) in cancers, we investigated the in vitro and in vivo oncogenic function of MRGD using murine fibroblast cell line NIH3T3 in which MRGD is stably expressed. The expression pattern of MRGD in clinical samples was also analyzed. We found that overexpression of MRGD in NIH3T3 induced focus formation and multi-cellular spheroid formation, and promoted tumors in nude mice. In other words, overexpression of MRGD in NIH3T3 induced the loss of contact inhibition, anchorage-independent growth and in vivo tumorigenesis. Furthermore, it was found that the ligand of MRGD, beta-alanine, enhanced spheroid formation in MRGD-expressing NIH3T3 cells. From investigation of clinical cancer tissues, we found high expression of MRGD in several lung cancers by immunohistochemistry as well as real time PCR. Based on these results, MRGD could be involved in tumorigenesis and could also be a novel anticancer drug target.     

Simultaneous determination of prednisolone, prednisone, cortisol, and cortisone in plasma by GC-MS: estimating unbound prednisolone concentration in patients with nephrotic syndrome during oral prednisolone therapy

Individual variability of the pharmacokinetics of prednisolone based on the unbound concentration in plasma is of significant clinical consideration. The unbound concentrations of prednisolone were measured in 10 patients with nephrotic syndrome, two patients with systemic lupus erythematosus, and one patient with dermatomyositis by examining protein bindings of prednisolone on one or more occasions during prednisolone treatment. In this study, plasma concentrations of prednisolone, prednisone, cortisol, and cortisone were simultaneously analyzed by GC-MS by using stable isotope-labeled internal standards. Equilibrium dialysis was employed to accurately estimate the unbound fractions of prednisolone in plasma. The unbound fraction of prednisolone changed depending on plasma total prednisolone concentration and plasma albumin concentration. The unbound fraction of prednisolone (Y) is calculated: Y=(-0.0101x' + 0.0736) x + 10.23, where x' is the plasma albumin concentration and x is the total prednisolone concentration. The estimated concentrations of unbound prednisolone by using the above equation were in good agreement with the measured concentrations of unbound prednisolone. Since the protein binding of prednisolone did not change in the presence of prednisone (114.0 ng/ml), it appeared that prednisone produced from the therapeutic dose of prednisolone did not affect the unbound fraction of prednisolone.