Stepwise Assembly of Fibrinogen Is Assisted by the Endoplasmic Reticulum Lectin-Chaperone System in HepG2 Cells

The endoplasmic reticulum (ER) plays essential roles in protein folding and assembly of secretory proteins. ER-resident molecular chaperones and related enzymes assist in protein maturation by co-operated interactions and modifications. However, the folding/assembly of multimeric proteins is not well understood. Here, we show that the maturation of fibrinogen, a hexameric secretory protein (two trimers from a, b and c subunits), occurs in a stepwise manner. The ac complex, a precursor for the trimer, is retained in the ER by lectin-like chaperones, and the b subunit is incorporated into the ac complex immediately after translation. ERp57, a protein disulfide isomerase homologue, is involved in the hexamer formation from two trimers. Our results indicate that the fibrinogen hexamer is formed sequentially, rather than simultaneously, using kinetic pause by lectin chaperones. This study provides a novel insight into the assembly of most abundant multi-subunit secretory proteins

Usefulness of the Palliative Prognostic Index in patients with lung cancer.

The usefulness of the Palliative Prognostic Index (PPI) has been successfully validated in a variety of clinical settings. However, while lung cancer is the leading cause of death worldwide, patients with lung cancer accounted for only 6.9-25.8 % of the study populations in these previous studies. We conducted a retrospective study to evaluate the usefulness of the PPI for survival prediction in patients with lung cancer. Patients with lung cancer who were admitted to our hospital between 2009 and 2013 to receive palliative care were enrolled. The association between the Palliative Prognostic Index, determined based on the data recorded in the clinical charts at the last admission to our hospital, and survival was evaluated. The patient group with a PPI of >6 showed a significantly shorter survival time than the patient group with a PPI of ≤ 6 (P < 0.0001, log-rank test). The sensitivity and specificity of the PPI determined using the cutoff value of 6 for predicting less than 3 weeks of survival were 61.3 and 86.8 %, respectively. However, the sensitivity decreased to 50.0 % when the assessment was carried out in only patients with small cell lung carcinoma. Our findings suggest the existence of a close association between the PPI and survival in patients with lung cancer receiving palliative care. However, the sensitivity of the index for predicting less than 3 weeks of survival was relatively low in patients with small cell lung carcinoma

Development of Cysteine-Free Fluorescent Proteins for the Oxidative Environment

Molecular imaging employing fluorescent proteins has been widely used to highlight specific reactions or processes in various fields of the life sciences. Despite extensive improvements of the fluorescent tag, this technology is still limited in the study of molecular events in the extracellular milieu. This is partly due to the presence of cysteine in the fluorescent proteins. These proteins almost cotranslationally form disulfide bonded oligomers when expressed in the endoplasmic reticulum (ER). Although single molecule photobleaching analysis showed that these oligomers were not fluorescent, the fluorescent monomer form often showed aberrant behavior in folding and motion, particularly when fused to cysteine-containing cargo. Therefore we investigated whether it was possible to eliminate the cysteine without losing the brightness. By site-saturated mutagenesis, we found that the cysteine residues in fluorescent proteins could be replaced with specific alternatives while still retaining their brightness. cf(cysteine-free)SGFP2 showed significantly reduced restriction of free diffusion in the ER and marked improvement of maturation when fused to the prion protein. We further applied this approach to TagRFP family proteins and found a set of mutations that obtains the same level of brightness as the cysteine-containing proteins. The approach used in this study to generate new cysteine-free fluorescent tags should expand the application of molecular imaging to the extracellular milieu and facilitate its usage in medicine and biotechnology

Phosphorylation of SNAP-23 at Ser95 causes a structural alteration and negatively regulates Fc receptor-mediated phagosome formation and maturation in macrophages

SNAP-23 is a plasma membrane-localized soluble N-ethylmaleimide–sensitive factor attachment protein receptors (SNARE) involved in Fc receptor (FcR)-mediated phagocytosis. However, the regulatory mechanism underlying its function remains elusive. Using phosphorylation-specific antibodies, SNAP-23 was found to be phosphorylated at Ser95 in macrophages. To understand the role of this phosphorylation, we established macrophage lines overexpressing the nonphosphorylatable S95A or the phosphomimicking S95D mutation. The efficiency of phagosome formation and maturation was severely reduced in SNAP-23-S95D–overexpressing cells. To examine whether phosphorylation at Ser95 affected SNAP-23 structure, we constructed intramolecular Förster resonance energy transfer (FRET) probes of SNAP-23 designed to evaluate the approximation of the N termini of the two SNARE motifs. Interestingly, a high FRET efficiency was detected on the membrane when the S95D probe was used, indicating that phosphorylation at Ser95 caused a dynamic structural shift to the closed form. Coexpression of IκB kinase (IKK) 2 enhanced the FRET efficiency of the wild-type probe on the phagosome membrane. Furthermore, the enhanced phagosomal FRET signal in interferon-γ–activated macrophages was largely dependent on IKK2, and this kinase mediated a delay in phagosome-lysosome fusion. These results suggested that SNAP-23 phosphorylation at Ser95 played an important role in the regulation of SNARE-dependent membrane fusion during FcR-mediated phagocytosis

Stepwise Assembly of Fibrinogen Is Assisted by the Endoplasmic Reticulum Lectin-Chaperone System in HepG2 Cells

<div><p>The endoplasmic reticulum (ER) plays essential roles in protein folding and assembly of secretory proteins. ER-resident molecular chaperones and related enzymes assist in protein maturation by co-operated interactions and modifications. However, the folding/assembly of multimeric proteins is not well understood. Here, we show that the maturation of fibrinogen, a hexameric secretory protein (two trimers from α, β and γ subunits), occurs in a stepwise manner. The αγ complex, a precursor for the trimer, is retained in the ER by lectin-like chaperones, and the β subunit is incorporated into the αγ complex immediately after translation. ERp57, a protein disulfide isomerase homologue, is involved in the hexamer formation from two trimers. Our results indicate that the fibrinogen hexamer is formed sequentially, rather than simultaneously, using kinetic pause by lectin chaperones. This study provides a novel insight into the assembly of most abundant multi-subunit secretory proteins.</p></div