Impaired degradation followed by enhanced recycling of epidermal growth factor receptor caused by hypo-phosphorylation of tyrosine 1045 in RBE cells

信州大学博士（医学）・学位論文・平成24年6月11日授与（甲第929号）・桂安萍Background: Since cholangiocarcinoma has a poor prognosis, several epidermal growth factor receptor (EGFR)-targeted therapies with antibody or small molecule inhibitor treatment have been proposed. However, their effect remains limited. The present study sought to understand the molecular genetic characteristics of cholangiocarcinoma related to EGFR, with emphasis on its degradation and recycling. Methods: We evaluated EGFR expression and colocalization by immunoblotting and immunofluorescence, cell surface EGFR expression by fluorescence-activated cell sorting (FACS), and EGFR ubiquitination and protein binding by immunoprecipitation in the human cholangiocarcinoma RBE and immortalized cholangiocyte MMNK-1 cell lines. Monensin treatment and Rab11a depletion by siRNA were adopted for inhibition of EGFR recycling. Results: Upon stimulation with EGF, ligand-induced EGFR degradation was impaired and the expression of phospho-tyrosine 1068 and phospho-p44/42 MAPK was sustained in RBE cells as compared with MMNK-1 cells. In RBE cells, the process of EGFR sorting for lysosomal degradation was blocked at the early endosome stage, and non-degradated EGFR was recycled to the cell surface. A disrupted association between EGFR and the E3 ubiquitin ligase c-Cbl, as well as hypo-phosphorylation of EGFR at tyrosine 1045 (Tyr1045), were also observed in RBE cells. Conclusion: In RBE cells, up-regulation of EGFR Tyr1045 phosphorylation is a potentially useful molecular alteration in EGFR-targeted therapy. The combination of molecular-targeted therapy determined by the characteristics of individual EGFR phosphorylation events and EGFR recycling inhibition show promise in future treatments of cholangiocarcinoma.ArticleBMC Cancer. 2012, 12:179journal articl

A Splice Variant of ASC Regulates IL-1β Release and Aggregates Differently from Intact ASC

The apoptosis-associated speck-like protein containing a caspase recruit domain (ASC) is involved in apoptosis and innate immunity and is a major adaptor molecule responsible for procaspase-1 activation. ASC mRNA is encoded by three exons: exons 1 and 3 encode a pyrin domain (PYD) and caspase recruit domain (CARD), respectively, and exon 2 encodes a proline and glycine-rich (PGR) domain. Here, we identified a variant ASC protein (vASC) lacking the PGR domain that was smaller than full length ASC (fASC) derived from fully transcribed mRNA and searched for differences in biochemical and biological nature. Both fASC and vASC were found to activate procaspase-1 to a similar degree, but the efficiency of IL-1β excretion was significantly higher for vASC. There was also a marked structural difference observed in the fibrous aggregates formed by fASC and vASC. These results suggest that although the PGR domain is dispensable for procaspase-1 activation, it plays an important role in the regulation of the molecular structure and activity of ASC

Impaired degradation followed by enhanced recycling of epidermal growth factor receptor caused by hypo-phosphorylation of tyrosine 1045 in RBE cells

Abstract Background Since cholangiocarcinoma has a poor prognosis, several epidermal growth factor receptor (EGFR)-targeted therapies with antibody or small molecule inhibitor treatment have been proposed. However, their effect remains limited. The present study sought to understand the molecular genetic characteristics of cholangiocarcinoma related to EGFR, with emphasis on its degradation and recycling. Methods We evaluated EGFR expression and colocalization by immunoblotting and immunofluorescence, cell surface EGFR expression by fluorescence-activated cell sorting (FACS), and EGFR ubiquitination and protein binding by immunoprecipitation in the human cholangiocarcinoma RBE and immortalized cholangiocyte MMNK-1 cell lines. Monensin treatment and Rab11a depletion by siRNA were adopted for inhibition of EGFR recycling. Results Upon stimulation with EGF, ligand-induced EGFR degradation was impaired and the expression of phospho-tyrosine 1068 and phospho-p44/42 MAPK was sustained in RBE cells as compared with MMNK-1 cells. In RBE cells, the process of EGFR sorting for lysosomal degradation was blocked at the early endosome stage, and non-degradated EGFR was recycled to the cell surface. A disrupted association between EGFR and the E3 ubiquitin ligase c-Cbl, as well as hypo-phosphorylation of EGFR at tyrosine 1045 (Tyr1045), were also observed in RBE cells. Conclusion In RBE cells, up-regulation of EGFR Tyr1045 phosphorylation is a potentially useful molecular alteration in EGFR-targeted therapy. The combination of molecular-targeted therapy determined by the characteristics of individual EGFR phosphorylation events and EGFR recycling inhibition show promise in future treatments of cholangiocarcinoma.</p

Role of ASC in the Mouse Model of Helicobacter pylori Infection

Apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC) is an adaptor molecule activating caspase-1 that stimulates pro-interleukin-1β (pro-IL-1β) and pro-IL-18, two pro-inflammatory cytokines with critical functions in host defense against a variety of pathogens. In this study, we investigated the role of ASC in the host defense against Helicobacter pylori utilizing ASC-deficient mice. Mice were orally inoculated with H. pylori; bacterial load, degree of gastritis, and mucosal levels of inflammatory cytokines were analyzed and compared with those obtained from wild-type mice. We found more prominent H. pylori colonization in ASC-deficient mice, as revealed by colony-forming unit counts. Both groups of mice developed gastritis; however, ASC-deficient mice showed significant attenuation of inflammation despite high H. pylori colonization. ELISA, immunohistochemistry, and quantitative RT-PCR analyses revealed complete suppression of IL-1β and IL-18, and substantial reduction of interferon-γ (IFN-γ) expression, in ASC-deficient mice without apparent upregulation of other cytokines, including IL-10 and tumor necrosis factor-α. These results as a whole indicate that ASC exerts considerable influence on the host defense, acting through IL-1β/IL-18 and subsequent IFN-γ production, which in turn contributes to continuous chronic inflammatory response and consequent reduction of H. pylori colonization. (J Histochem Cytochem 57:327–338, 2009

5'-aza-dC treatment restored ASC expression and overexpression of ASC suppressed cell viability in high cell density cultures.

<p>HT 1080 cells were treated with 8μM 5'-aza-dC, and expression of ASC was detected by (A) quantitative RT-PCR (n = 2) and (B) Western blotting. (C) Expression of ASC inserted into pcDNA3 vectors and stably transfected into cells was confirmed by Western blotting. Viability of ASC-expressing and control cells at (D) a low cell density (n = 8), (E) a high cell density (n = 8), and (F) in colony formation assays (n = 3). *p<0.05.</p

Primer sequences used for quantitative RT-PCR.

<p>Primer sequences used for quantitative RT-PCR.</p