Poly r(C) binding protein (PCBP) 1 expression is regulated by the E3 ligase UBE4A in thyroid carcinoma.

Thyroid cancer patients with high miR-490-3p inhibit translation of PCBP1 mRNA, whereas in patients with low miR-490-3p PCBP1 mRNA expression is high; however, the resultant protein is targeted for degradation through the proteasome. The objective of the present study was to evaluate the molecular mechanism that regulates post-translation degradation of poly r(C) binding protein (PCBP) 1 expression in thyroid cancer cells. Mass spectrometric analysis of PCBP1 immunoprecipitates from MG-132 treated TPC1 cells revealed a list of ubiquitin ligases associated with PCBP1. RNAi-mediated silencing of the candidate ubiquitin ligases revealed that knockdown of the ubiquitin ligase UBE4A stabilized PCBP1 in TPC1 cells. Concurrent overexpression of the candidate ubiquitin ligases in the normal thyroid epithelial cell line Nthy-ori 3-1 confirmed that ubiquitin conjugation factor E4 A (UBE4A) is the ubiquitin ligase that is degrading PCBP1. Coimmunoprecipitation of HA-tagged PCBP1 in TPC1 cells cotransfected with FLAG-UBE4A revealed robust polyubiquitinated smear of PCBP1, thus confirming UBE4A as the ubiquitin ligase of PCBP1. UBE4A expression mimicked PCBP1 mRNA expression in thyroid cancer patients and was inversely correlated to PCBP1 protein expression. Low UBE4A expression level was associated with a better prognosis in thyroid cancer patients. Our data reveal a post-translational regulatory mechanism of regulating PCBP1 expression in thyroid cancer cells.

Poly r(C) binding protein (PCBP) 1 expression is regulated at the post-translation level in thyroid carcinoma.

Poly r(C) binding protein (PCBP) 1 or heterogeneous ribonucleoprotein (hnRNP) E1 is a RNA binding protein that plays a vital role in a wide variety of biological processes. PCBP1 has been shown to function as a tumor suppressor by negatively regulating translation of pro-metastatic proteins in different cancers. Loss of PCBP1 expression or its Akt2-mediated phosphorylation at serine 43 residue has both been indicated to de-repress its regulation of EMT inducer proteins. Our previous work has established that PCBP1 functions as a tumor suppressor in thyroid cancer, where its translation is inhibited by microRNA-490-3p. Here we show that thyroid cancer patients can be divided into 2 cohorts based on miR-490-3p expression and PCBP1 mRNA expression-one cohort with high PCBP1 mRNA expression and basal miR-490-3p expression and a second cohort with low PCBP1 mRNA expression and high miR-490-3p expression. However, PCBP1 protein expression is also downregulated in the cohort with high PCBP1 mRNA expression, with expression levels similar to what is observed in patients with the low PCBP1 mRNA expression. Our analysis shows that PCBP1 mRNA is actively translated in patients with high PCBP1 mRNA expression, but that the protein is post translationally degraded by the proteasome machinery. Our results thus elucidate a novel mechanism responsible for down regulation of PCBP1 expression in thyroid cancer. It will be important in future to identify the mechanism that causes degradation of PCBP1 protein and to identify if similar mechanisms are active in other tumors characterized by low PCBP1 protein expression.

Poly r(C) binding protein (PCBP) 1 is a negative regulator of thyroid carcinoma.

Poly r(C) binding protein (PCBP) 1 or heterogeneous ribonucleoprotein (hnRNP) E1 is a RNA binding protein functional in multiple biological processes. PCBP1 has been shown to function as a tumor suppressor by negatively regulating translation of EMT inducer proteins in different cancers. Loss of PCBP1 expression or its Akt2-mediated phosphorylation at serine residue 43 has both been indicated to de-repress its regulation of EMT inducer proteins. However, its role in thyroid carcinoma has not been elucidated. Here we report that PCBP1 expression is significantly downregulated in thyroid carcinoma patients. In vitro kinase assay revealed that immunoprecipitated PCBP1 from transient or stably transfected thyroid carcinoma cells can be phosphorylated by recombinant Akt2 kinase. In situ analysis revealed that PCBP1 is a putative target of miR-490-3p, which was further confirmed by PCBP1 3'UTR-based reporter assays using the wild-type or a miR-490 seed mutant 3'UTR. The endogenous regulation of the PCBP1 3'UTR reporter by miR-490-3p could be rescued by transfection of miR-490 antagomir in WRO and BCPAP cells. Stably overexpressing PCBP1 BCPAP cells attenuated tumor formation completely as compared to empty vector overexpressing cells in xenograft assay. Cumulatively, our results indicate that PCBP1 functions as a tumor suppressor in thyroid carcinoma and that its expression is down regulated by high expression of the miR-490-3p observed in thyroid carcinoma patients.

IgG4-related retroperitoneal fibrosis: a newly characterized disease.

Retroperitoneal fibrosis (RPF) is a rare disease characterized by chronic, nonspecific inflammatory and sclerotic or fibrotic tissue in the periaortic or periiliac retroperitoneum that encases adjacent structures. There will be a series of clinical manifestations once the proliferated fibrous tissues encase the abdominal aorta, iliac arteries and urinary duct. RPF is generally divided into two types: idiopathic retroperitoneal fibrosis (IRPF) without identified pathogenesis, making up about two-thirds of cases, and secondary retroperitoneal fibrosis. Recent studies on Immunoglobulin G4-related disease (IgG4-RD) reveal that abundant infiltration of IgG4 positive plasma cells is found in biopsies on the mass of RPF of some IRPF patients, which is identified as one spectrum of IgG4-RD and is named IgG4-related RPF. IgG4-related RPF is often misdiagnosed as retroperitoneal visceral malignancy and is treated with surgery. In addition, because of its good response to glucocorticoid, early detection and treatment is important. We review the definition, epidemiology, clinical features, diagnostic criteria, treatment and prognosis of IgG4-related RPF in this article to raise awareness of this newly characterized disease.

Giant solitary fibrous tumor of the lung: A case report.

A solitary fibrous tumor arising from the lung parenchyma is rarely described. Here, we present the clinical, imaging, and histological features of a case of a 54-year-old woman with an incidental lung mass of the right lower lobe on a chest radiograph.

Negative regulation of mTOR activity by LKB1-AMPK signaling in non-small cell lung cancer cells.

AIM: To investigate the role of LKB1 in regulation of mTOR signaling in non-small cell lung cancer (NSCLC) cells. METHODS: LKB1 protein expression and phosphorylation of AMPK, 4E-BP1 and S6K in the cells were assessed using Western blotting in various NSCLC cell lines (A549, H460, H1792, Calu-1 and H1299). Energy stress was mimicked by treating the cells with 2-deoxyglucose (2-DG). Compound C was used to inhibit AMPK activity. Cell growth was measured using the MTS assay. RESULTS: LKB1 protein was expressed in LKB1 wild-type Calu-1, H1299 and H1792 cells, but it was undetected in LKB1 mutant A549 and H460 cells. Treatment of the LKB1 wild-type cells with 2-DG (5, 10 and 25 mmol/L) augmented the phosphorylation of AMPK in dose- and time-dependent manners. In the LKB1 wild-type cells, 2-DG dramatically suppressed the phosphorylation of two mTOR targets, 4E-BP1 and S6K, whereas the LKB1 mutant A549 and H460 cells were highly resistant to 2-DG-induced inhibition on mTOR activity. In addition, stable knockdown of LKB1 in H1299 cells impaired 2-DG-induced inhibition on mTOR activity. Pretreatment of H1299 and H1792 cells with the AMPK inhibitor compound C (10 µmol/L) blocked 2-DG-induced inhibition on mTOR activity. 2-DG inhibited the growth of H1299 cells more effectively than that of H460 cells; stable knockdown of LKB1 in H1299 cells attenuated the growth inhibition caused by 2-DG. CONCLUSION: In non-small cell lung cancer cells, LKB1/AMPK signaling negatively regulates mTOR activity and contributes to cell growth inhibition in response to energy stress.