Pharmacological Modulation of Glycosphingolipid Metabolism.

The experimental approach to deplete cellular glycosphingolipids (GSLs) with the specific inhibitors of glycosphingolipid biosynthesis has the potential to identify functions of endogenous GSLs. Most GSLs are derived from glucosylceramide (GlcCer). D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP) inhibits GIcCer synthase and has been used extensively to study the biological functions of living cells. D-PDMP inhibits mTORC1 activity, which is independent of its inhibitory activity on GlcCer synthase. We also developed an analog of D-PDMP, D-threo-1-phenyl-2-benzyloxycarbonylamino-3-pyrrolidino-1-propanol (D-PBPP) lacking the effect on mTORC1. Here, we summarize the effects of D-PDMP and D-PBPP on the metabolism of GSLs and cell growth.

PDMP, a ceramide analogue, acts as an inhibitor of mTORC1 by inducing its translocation from lysosome to endoplasmic reticulum.

Mammalian or mechanistic target of rapamycin complex 1 (mTORC1) is a master regulator of cell growth, metabolism, and cell differentiation. Recent studies have revealed that the recruitment of mTORC1 to lysosomes is essential for its activation. The ceramide analogue 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), a well known glycosphingolipid synthesis inhibitor, also affects the structures and functions of various organelles, including lysosomes and endoplasmic reticulum (ER). We investigated whether PDMP regulates the mTORC1 activity through its effects on organellar behavior. PDMP induced the translocation of mTORC1 from late endosomes/lysosomes, leading to the dissociation of mTORC1 from its activator Rheb in MC3T3-E1 cells. Surprisingly, we found mTORC1 translocation to the ER upon PDMP treatment. This effect of PDMP was independent of its action as the inhibitor, since two stereoisomers of PDMP, with and without the inhibitor activity, showed essentially the same effect. We confirmed that PDMP inhibits the mTORC1 activity based on the decrease in the phosphorylation of ribosomal S6 kinase, a downstream target of mTORC1, and the increase in LC3 puncta, reflecting autophagosome formation. Furthermore, PDMP inhibited the mTORC1-dependent osteoblastic cell proliferation and differentiation of MC3T3-E1 cells. Accordingly, the present results reveal a novel mechanism of PDMP, which inhibits the mTORC1 activity by inducing the translocation of mTOR from lysosomes to the ER.

OmpA variants affecting the adherence of ulcerative colitis-derived Bacteroides vulgatus.

To investigate the adhesion factor of Bacteroides vulgatus derived from ulcerative colitis (UC), we isolated B. vulgatus strains from the large intestinal mucosa of UC patients and non-UC individuals, and examined their adherence to tissue-cultured cells. The adherence to tissue-cultured cells in UC-derived strains (36.5 +/- 7.9 %) was higher than that in non-UC-derived strains (13.2 +/- 7.7 %). PCR and sequencing analysis of outer membrane proteins revealed that the strains derived from five of seven (71.4 %) UC patients had ompA genes belonging to either ompA variant type A or B. The adherence rates in Escherichia coli DH5 a transformants with ompA type A variants (33.3 +/- 4.6 %) and type B variants (34.6 +/- 7.1 %) were higher than the rate in those with non-UC ompA (16.4 +/- 4.0 %). Our results suggest that B. vulgatus isolates in the mucosal flora of the large intestine of UC patients have a high frequency of ompA variants and that the variation of ompA variants is one of the factor causing an increase in the adherence of the bacterium.

Analysis of plasmid-mediated multidrug resistance in Escherichia coli and Klebsiella oxytoca isolates from clinical specimens in Japan.

This study investigated the relationship of plasmid-mediated quinolone resistance (PMQR) and aminoglycoside resistance among oxyimino-cephalosporin-resistant Escherichia coli (n=46) and Klebsiella oxytoca (n=28) clinical isolates in Japan. Seventy-three isolates appeared to produce an extended-spectrum beta-lactamase (ESBL) and one K. oxytoca isolate produced IMP-1 metallo-beta-lactamase (MBL). Polymerase chain reaction (PCR) and sequencing confirmed that eight CTX-M-9/SHV-12-producing isolates, one IMP-1-producing K. oxytoca isolate, and six ESBL-positive E. coli isolates respectively possessed PMQR genes qnrA1, qnrB6, and aac(6')-Ib-cr. All qnr-positive isolates also carried either aac(6')-Ib or aac(6')-IIc aminoglycoside acetyltransferase genes. Resistance determinants to beta-lactams, quinolones and aminoglycosides were co-transferred with a plasmid of ca. 140 kb. The qnrA1 gene was located downstream of insertion sequence ISCR1 in complex class 1 integrons. A novel qnrA1-carrying class 1 integron with the cassette arrangement aac(6')-IIc-aadA2 as well as a unique class 1 integron with bla(IMP-1)-aac(6')-IIc cassettes on the plasmid carrying qnrB6 were found in K. oxytoca isolates. We describe the identification of qnrB6 and aac(6')-Ib-cr and the close association of qnr with aac(6')-Ib and aac(6')-IIc for the first time in clinical isolates producing ESBL or MBL in Japan.

Molecular characterizations of carbapenem and ciprofloxacin resistance in clinical isolates of Pseudomonas putida.

To analyze the genetic mechanisms of carbapenem and ciprofloxacin resistance in clinical isolates of Pseudomonas putida, 27 clinical isolates (comprising 11 carbapenem- and ciprofloxacin-resistant strains, 13 carbapenem-resistant and ciprofloxacin-susceptible strains, and 3 carbapenem- and ciprofloxacin-susceptible strains) were collected from different patients. Carbapenem resistance was examined by polymerase chain reaction (PCR) and DNA sequencing for metallo-beta-lactamase (MBL) and integrase genes (IntI-1 and IntI-3), and by reverse transcriptase-PCR (RT-PCR) for expression of the porin gene (oprD). Ciprofloxacin resistance was characterized by PCR and DNA sequencing for mutations in the quinoloneresistance determining regions of the gyrA and parC genes. The blaIMP-1 MBL and intI-1 and/or intI-3 genes were detected in all carbapenem-resistant strains, and decreased expression of the oprD gene as compared to carbapenemsusceptible strains was observed in several strains. All the 11 strains with ciprofloxacin minimal inhibitory concentrations (MICs) of > or =64 mg/l had substitution in GyrA (Thr83Ile), and one (ciprofloxacin MIC of 512 mg/l) of these strains also had substitution in ParC (Ser87Leu). Overproduction of the efflux pump was observed in 10 of the 11 ciprofloxacin-resistant strains. We concluded that the production of IMP-1 type MBL was the most critical factor in developing high-level resistance to carbapenems, and mutations in the target proteins and overproduction of the efflux pump synergistically contribute to the acquisition of high-level resistance to ciprofloxacin in clinical isolates of P. putida.