34 research outputs found
A Second Look or, Not to Mention the Occasional Capsizing of a Windsurfer
Of
all of the epithelial ovarian cancers (EOC), clear cell adenocarcinoma
(CCA) has the worst clinical prognosis. Furthermore, the conventional
EOC biomarker CA125 is more often negative in CCA than in other subtypes
of EOC. This study sought to discover a new diagnostic biomarker that
would allow more reliable detection of CCA. Using mass spectrometry,
we compared proteins in conditioned media from cell lines derived
from CCA and other types of EOC. We identified 30 extracellular or
released proteins specifically present in CCA-derived cell lines.
Bioinformatics analyses identified a serine protease inhibitor, tissue
factor pathway inhibitor 2 (TFPI2), as a potential biomarker for CCA.
Real time RT-PCR and Western blot analyses revealed that TFPI2 was
exclusively expressed in CCA-derived cell lines and tissues. For clinical
validation, we measured levels of TFPI2 and CA125 in a set of sera
from 30 healthy women, 30 patients with endometriosis, and 50 patients
with CCA, using an automated enzyme-linked immunosorbent assay systems.
Serum levels of TFPI2 were significantly elevated in CCA patients,
even those with normal CA125 levels. In terms of area under the receiver
operating characteristic curve (AUC), TFPI2 was superior to CA125
in discriminating CCA patients from healthy women (AUC 0.97 for TFPI2
versus AUC 0.80 for CA125), or from patients with endometriosis (AUC
0.93 for TFPI2 versus 0.80 for CA125). This is the first evidence
for TFPI2 as a serum biomarker of CCA. We propose that this biomarker
may be useful for detection of CCA and for monitoring the transformation
from endometriosis into CCA
Mass Spectrometric Analysis of the Phosphorylation Levels of the SWI/SNF Chromatin Remodeling/Tumor Suppressor Proteins ARID1A and Brg1 in Ovarian Clear Cell Adenocarcinoma Cell Lines
Protein phosphorylation is one of
the major factors involved in
tumor progression and malignancy. We performed exploratory studies
aimed at identifying phosphoproteins characteristic to cell lines
derived from ovarian clear cell adenocarcinoma (CCA), a highly malignant
type of ovarian cancer. Comparative phosphoproteome analysis revealed
that the phosphopeptides of five SWI/SNF chromatin remodeling/tumor
suppressor components, including ARID1A and BRG1, were significantly
down-regulated in CCA cells. We then quantitatively determined the
phosphorylation levels of ARID1A and BRG1 by immunoprecipitation–multiple
reaction monitoring (IP–MRM) that we used for analysis of the
cognate phospho- and nonphosphopeptides of low-abundance proteins.
The phosphorylation level of Brg1 at Ser1452 was down-regulated in
CCA cells, whereas the phosphorylation level of ARID1A at Ser696 did
not significantly differ between CCA and non-CCA cells. These results
were consistent with the results of immunoblotting showing that Brg1
levels were comparable, but ARID1A levels were lower, in CCA cells
relative to non-CCA cells. This is the first report to demonstrate
reduced phosphorylation of Brg1 in CCA-derived cells. Our data also
indicated that the IP–MRM/MS method we used is a powerful tool
for validation of the phosphoproteins detected by shotgun analysis
of phosphopeptides
N‑Myristoylation of the Rpt2 Subunit Regulates Intracellular Localization of the Yeast 26S Proteasome
The 26S proteasome is a large, complex multisubunit protease
involved
in protein quality control and other critical processes in eukaryotes.
More than 110 post-translational modification (PTM) sites have been
identified by a mass spectrometry of the 26S proteasome of <i>Saccharomyces cerevisiae</i> and are predicted to be implicated
in the dynamic regulation of proteasomal functions. Here, we report
that the N-myristoylation of the Rpt2 subunit controls the intracellular
localization of the 26S proteasome. While proteasomes were mainly
localized in the nucleus in normal cells, mutation of the N-myristoylation
site of Rpt2 caused diffusion of the nuclear proteasome into the cytoplasm,
where it formed aggregates. In mutant cells, the level of accumulation
of cytoplasmic proteasomes was significantly increased in the nonproliferating
state. Although the molecular assembly and peptidase activity of the
26S proteasome were totally unchanged in the nonmyristoylated mutants
of Rpt2, an increased level of accumulation of polyubiquitinated proteins
and a severe growth defect were observed in mutant cells induced for
protein misfolding. In addition, polyubiquitinated protein and the
nuclear protein Gcn4 tended not to colocalize with the proteasome
in normal and mutant cells. Our results suggest that N-myristoylation
is involved in regulating the proper intracellular distribution of
proteasome activity by controlling the nuclear localization of the
26S proteasome
N‑Myristoylation of the Rpt2 Subunit Regulates Intracellular Localization of the Yeast 26S Proteasome
The 26S proteasome is a large, complex multisubunit protease
involved
in protein quality control and other critical processes in eukaryotes.
More than 110 post-translational modification (PTM) sites have been
identified by a mass spectrometry of the 26S proteasome of <i>Saccharomyces cerevisiae</i> and are predicted to be implicated
in the dynamic regulation of proteasomal functions. Here, we report
that the N-myristoylation of the Rpt2 subunit controls the intracellular
localization of the 26S proteasome. While proteasomes were mainly
localized in the nucleus in normal cells, mutation of the N-myristoylation
site of Rpt2 caused diffusion of the nuclear proteasome into the cytoplasm,
where it formed aggregates. In mutant cells, the level of accumulation
of cytoplasmic proteasomes was significantly increased in the nonproliferating
state. Although the molecular assembly and peptidase activity of the
26S proteasome were totally unchanged in the nonmyristoylated mutants
of Rpt2, an increased level of accumulation of polyubiquitinated proteins
and a severe growth defect were observed in mutant cells induced for
protein misfolding. In addition, polyubiquitinated protein and the
nuclear protein Gcn4 tended not to colocalize with the proteasome
in normal and mutant cells. Our results suggest that N-myristoylation
is involved in regulating the proper intracellular distribution of
proteasome activity by controlling the nuclear localization of the
26S proteasome
N‑Myristoylation of the Rpt2 Subunit Regulates Intracellular Localization of the Yeast 26S Proteasome
The 26S proteasome is a large, complex multisubunit protease
involved
in protein quality control and other critical processes in eukaryotes.
More than 110 post-translational modification (PTM) sites have been
identified by a mass spectrometry of the 26S proteasome of <i>Saccharomyces cerevisiae</i> and are predicted to be implicated
in the dynamic regulation of proteasomal functions. Here, we report
that the N-myristoylation of the Rpt2 subunit controls the intracellular
localization of the 26S proteasome. While proteasomes were mainly
localized in the nucleus in normal cells, mutation of the N-myristoylation
site of Rpt2 caused diffusion of the nuclear proteasome into the cytoplasm,
where it formed aggregates. In mutant cells, the level of accumulation
of cytoplasmic proteasomes was significantly increased in the nonproliferating
state. Although the molecular assembly and peptidase activity of the
26S proteasome were totally unchanged in the nonmyristoylated mutants
of Rpt2, an increased level of accumulation of polyubiquitinated proteins
and a severe growth defect were observed in mutant cells induced for
protein misfolding. In addition, polyubiquitinated protein and the
nuclear protein Gcn4 tended not to colocalize with the proteasome
in normal and mutant cells. Our results suggest that N-myristoylation
is involved in regulating the proper intracellular distribution of
proteasome activity by controlling the nuclear localization of the
26S proteasome
Mass Spectrometric Identification of Glycosylphosphatidylinositol-Anchored Peptides
Glycosylphosphatidylinositol
(GPI) anchoring is a post-translational
modification widely observed among eukaryotic membrane proteins. GPI
anchors are attached to proteins via the carboxy-terminus in the outer
leaflet of the cell membrane, where GPI-anchored proteins (GPI-APs)
perform important functions as coreceptors and enzymes. Precursors
of GPI-APs (Pre-GPI-APs) contain a C-terminal hydrophobic sequence
that is involved in cleavage of the signal sequence from the protein
and addition of the GPI anchor by the transamidase complex. In order
to confirm that a given protein contains a GPI anchor, it is essential
to identify the C-terminal peptide containing the GPI-anchor modification
site (ω-site). Previously, efficient identification of GPI-anchored
C-terminal peptides by mass spectrometry has been difficult, in part
because of complex structure of the GPI-anchor moiety. We developed
a method to experimentally identify GPI-APs and their ω-sites.
In this method, a part of GPI-anchor moieties are removed from GPI-anchored
peptides using phosphatidylinositol-specific phospholipase C (PI-PLC)
and aqueous hydrogen fluoride (HF), and peptide sequence is then determined
by mass spectrometry. Using this method, we successfully identified
10 GPI-APs and 12 ω-sites in the cultured ovarian adenocarcinoma
cells, demonstrating that this method is useful for identifying efficiently
GPI-APs
Mass Spectrometric Identification of Glycosylphosphatidylinositol-Anchored Peptides
Glycosylphosphatidylinositol
(GPI) anchoring is a post-translational
modification widely observed among eukaryotic membrane proteins. GPI
anchors are attached to proteins via the carboxy-terminus in the outer
leaflet of the cell membrane, where GPI-anchored proteins (GPI-APs)
perform important functions as coreceptors and enzymes. Precursors
of GPI-APs (Pre-GPI-APs) contain a C-terminal hydrophobic sequence
that is involved in cleavage of the signal sequence from the protein
and addition of the GPI anchor by the transamidase complex. In order
to confirm that a given protein contains a GPI anchor, it is essential
to identify the C-terminal peptide containing the GPI-anchor modification
site (ω-site). Previously, efficient identification of GPI-anchored
C-terminal peptides by mass spectrometry has been difficult, in part
because of complex structure of the GPI-anchor moiety. We developed
a method to experimentally identify GPI-APs and their ω-sites.
In this method, a part of GPI-anchor moieties are removed from GPI-anchored
peptides using phosphatidylinositol-specific phospholipase C (PI-PLC)
and aqueous hydrogen fluoride (HF), and peptide sequence is then determined
by mass spectrometry. Using this method, we successfully identified
10 GPI-APs and 12 ω-sites in the cultured ovarian adenocarcinoma
cells, demonstrating that this method is useful for identifying efficiently
GPI-APs
Role of LRP1 and ERK and cAMP Signaling Pathways in Lactoferrin-Induced Lipolysis in Mature Rat Adipocytes
<div><p>Lactoferrin (LF) is a multifunctional glycoprotein present in milk. A clinical study showed that enteric-coated bovine LF tablets decrease visceral fat accumulation. Furthermore, animal studies revealed that ingested LF is partially delivered to mesenteric fat, and <i>in vitro</i> studies showed that LF promotes lipolysis in mature adipocytes. The aim of the present study was to determine the mechanism underlying the induction of lipolysis in mature adipocytes that is induced by LF. To address this question, we used proteomics techniques to analyze protein expression profiles. Mature adipocytes from primary cultures of rat mesenteric fat were collected at various times after exposure to LF. Proteomic analysis revealed that the expression levels of hormone-sensitive lipase (HSL), which catalyzes the rate-limiting step of lipolysis, were upregulated and that HSL was activated by protein kinase A within 15 min after the cells were treated with LF. We previously reported that LF increases the intracellular concentration of cyclic adenosine monophosphate (cAMP), suggesting that LF activates the cAMP signaling pathway. In this study, we show that the expression level and the activity of the components of the extracellular signal-regulated kinase (ERK) signaling pathway were upregulated. Moreover, LF increased the activity of the transcription factor cAMP response element binding protein (CREB), which acts downstream in the cAMP and ERK signaling pathways and regulates the expression levels of adenylyl cyclase and HSL. Moreover, silencing of the putative LF receptor low-density lipoprotein receptor-related protein 1 (LRP1) attenuated lipolysis in LF-treated adipocytes. These results suggest that LF promoted lipolysis in mature adipocytes by regulating the expression levels of proteins involved in lipolysis through controlling the activity of cAMP/ERK signaling pathways via LRP1.</p></div
Analysis of the effects of LF on the phosphorylation of HSL and PLIN by PKA and determination of PKA activity.
<p>Phosphorylation of HSL and PLIN by PKA was detected in the presence or absence (0 min) of 1 mg/ml of LF. Phosphorylation levels normalized to protein expression levels of HSL and PLIN are shown. <b>(A)</b> Phosphorylation of HSL Ser660 and <b>(B)</b> PLIN Ser497 by PKA. <b>(C)</b> Analysis of PKA activity in adipocytes treated with LF. PKA activity in adipocytes was detected using an ELISA before (0 min) and after treatment with LF. Kinase activity normalized to the total protein determined by BCA is shown. The statistical significance of the data at each sampling time compared with the 0-min sample was evaluated using Dunnett’s multiple comparison test, and the data represent the mean ± SD values of triplicate determinations of one of three identical experiments. *<i>p</i> < 0.05, ***<i>p</i> < 0.001 HSL, hormone-sensitive lipase; LF, lactoferrin; PLIN, perilipin; PKA, protein kinase A; SD, standard deviation.</p
LF-induced lipolysis in LRP1-silenced adipocytes.
<p><b>(A)</b> Activation of lipolysis by LF. To quantitate lipolysis, the amount of glycerol in the medium was analyzed 24 h after adding 1 mg/ml of LF. The statistical significance of the differences between LF treated and untreated cells was evaluated using the Student <i>t</i> test. **<i>p</i> < 0.01. The data represent the mean ± SD values of triplicate determinations of one of three identical experiments. <b>(B)</b> Activation of HSL by LF treatment. Phosphorylation of HSL was detected in the presence or absence of 1 mg/ml LF 15 min after the addition of LF. Phosphorylation levels normalized to protein expression levels are shown. The statistical significance was evaluated using the Student <i>t</i> test vs LF untreated control. **<i>p</i> < 0.01; n.s., no significant difference. The data represent the mean ± SD values of triplicate determinations of one of three identical experiments. <b>(C)</b> LRP1 silencing by siRNA. Adipocytes were transiently transfected with negative control siRNA (siNC) or LRP1 siRNA (siLRP1) (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141378#sec002" target="_blank">Materials and methods</a>). LRP1 protein expression was monitored by immunoblotting during each assay. Distinctive data is shown. β-actin was used as a loading control. HSL, hormone-sensitive lipase; LF, lactoferrin; LRP1, lipoprotein receptor-related protein 1; SD, standard deviation.</p