High Expression of YB-1 Gene in Erythroid Cells in Patients with Refractory Anemia

YBX1 is required for maintaining myeloid leukemia cell survival by regulating BCL2 stability in an m6A-dependent manner

RNA-binding proteins (RBPs) are critical regulators of transcription and translation that are often dysregulated in cancer. Although RBPs are increasingly recognized as being important for normal hematopoiesis and for hematologic malignancies as oncogenes or tumor suppressors, RBPs that are essential for the maintenance and survival of leukemia remain elusive. Here we show that YBX1 is specifically required for maintaining myeloid leukemia cell survival in an N6-methyladenosine (m6A)-dependent manner. We found that expression of YBX1 is significantly upregulated in myeloid leukemia cells, and deletion of YBX1 dramatically induces apoptosis and promotes differentiation coupled with reduced proliferation and impaired leukemic capacity of primary human and mouse acute myeloid leukemia cells in vitro and in vivo. Loss of YBX1 has no obvious effect on normal hematopoiesis. Mechanistically, YBX1 interacts with insulin-like growth factor 2 messenger RNA (mRNA)-binding proteins (IGF2BPs) and stabilizes m6A-tagged RNA. Moreover, YBX1 deficiency dysregulates the expression of apoptosis-related genes and promotes mRNA decay of MYC and BCL2 in an m6A-dependent manner, which contributes to the defective survival that results from deletion of YBX1. Thus, our findings have uncovered a selective and critical role of YBX1 in maintaining myeloid leukemia survival, which might provide a rationale for the therapeutic targeting of YBX1 in myeloid leukemia.

Expression and network analysis of YBX1 interactors for identification of new drug targets in lung adenocarcinoma

Y-Box Binding protein 1 (YBX-1) is known to be involved in various types of cancers. It's interactors also play major role in various cellular functions. Present work aimed to study the expression profile of the YBX-1 interactors during lung adenocarcinoma (LUAD). The differential expression analysis involved 57 genes from 95 lung adenocarcinoma samples, construction of gene network and topology analysis. A Total of 43 genes were found to be differentially expressed from which 17 genes were found to be down regulated and 26 genes were up-regulated. We observed that Polyadenylate-binding protein 1 (PABPC1), a protein involved in YBX1 translation, is highly correlated with YBX1. The interaction network analysis for a differentially expressed non-coding RNA Growth Arrest Specific 5 (GAS5) suggests that two proteins namely, Growth Arrest Specific 2 (GAS2) and Peripheral myelin protein 22 (PMP22) are potentially involved in LUAD progression. The network analysis and differential expression suggests that Collagen type 1 alpha 2 (COL1A2) can be potential biomarker and target for LUAD.

AUF-1 and YB-1 independently regulate β-globin mRNA in developing erythroid cells through interactions with poly(A)-binding protein

The normal expression of β-globin protein in mature erythrocytes is critically dependent on post-transcriptional events in erythroid progenitors that ensure the high stability of β-globin mRNA. Previous work has revealed that these regulatory processes require AUF-1 and YB-1, two RNA-binding proteins that assemble an mRNP β-complex on the β-globin 3'UTR. Here, we demonstrate that the β-complex organizes during the erythropoietic interval when both β-globin mRNA and protein accumulate rapidly, implicating the importance of this regulatory mRNP to normal erythroid differentiation. Subsequent functional analyses link β-complex assembly to the half-life of β-globin mRNA in vivo, providing a mechanistic basis for this regulatory activity. AUF-1 and YB-1 appear to serve a redundant post-transcriptional function, as both β-complex assembly and β-globin mRNA levels are reduced by coordinate depletion of the two factors, and can be restored by independent rescue with either factor alone. Additional studies demonstrate that the β-complex assembles more efficiently on polyadenylated transcripts, implicating a model in which the β-complex enhances the binding of PABPC1 to the poly(A) tail, inhibiting mRNA deadenylation and consequently effecting the high half-life of β-globin transcripts in erythroid progenitors. These data specify a post-transcriptional mechanism through which AUF1 and YB1 contribute to the normal development of erythropoietic cells, as well as to non-hematopoietic tissues in which AUF1- and YB1-based regulatory mRNPs have been observed to assemble on heterologous mRNAs.

Y-box-binding protein 1 (YB-1) and its functions

This review describes the structure and functions of Y-box binding protein 1 (YB-1) and its homologs. Interactions of YB-1 with DNA, mRNAs, and proteins are considered. Data on the participation of YB-1 in DNA reparation and transcription, mRNA splicing and translation are systematized. Results on interactions of YB-1 with cytoskeleton components and its possible role in mRNA localization are discussed. Data on intracellular distribution of YB-1, its redistribution between the nucleus and the cytoplasm, and its secretion and extracellular functions are summarized. The effect of YB-1 on cell differentiation, its involvement in extra- and intracellular signaling pathways, and its role in early embryogenesis are described. The mechanisms of regulation of YB-1 expression in the cell are presented. Special attention is paid to the involvement of YB-1 in oncogenic cell transformation, multiple drug resistance, and dissemination of tumors. Both the oncogenic and antioncogenic activities of YB-1 are reviewed. The potential use of YB-1 in diagnostics and therapy as an early cancer marker and a molecular target is discussed.

AUF-1 and YB-1 are critical determinants of β-globin mRNA expression in erythroid cells

The normal accumulation of β-globin protein in terminally differentiating erythroid cells is critically dependent on the high stability of its encoding mRNA. The molecular basis for this property, though, is incompletely understood. Factors that regulate β-globin mRNA within the nucleus of early erythroid progenitors are unlikely to account for the constitutively high half-life of β-globin mRNA in the cytoplasm of their anucleate erythroid progeny. We conducted in vitro protein-RNA binding analyses that identified a cytoplasm-restricted β-globin messenger ribonucleoprotein (mRNP) complex in both cultured K562 cells and erythroid-differentiated human CD34(+) cells. This novel mRNP targets a specific guanine-rich pentanucleotide in a region of the β-globin 3'untranslated region that has recently been implicated as a determinant of β-globin mRNA stability. Subsequent affinity-enrichment analyses identified AUF-1 and YB-1, 2 cytoplasmic proteins with well-established roles in RNA biology, as trans-acting components of the mRNP. Factor-depletion studies conducted in vivo demonstrated the importance of the mRNP to normal steady-state levels of β-globin mRNA in erythroid precursors. These data define a previously unrecognized mechanism for the posttranscriptional regulation of β-globin mRNA during normal erythropoiesis, providing new therapeutic targets for disorders of β-globin gene expression.

PTP1B and TC-PTP: novel roles in immune-cell signaling

It has recently been demonstrated that the protein tyrosine phosphatase (PTP) PTP1B and the T-cell PTP (TC-PTP) target several substrates involved in immune cell signaling. Recent data have furthered the view of these 2 PTP members as key regulators of the immune response. This review will focus on the substrate specificities of PTP1B and TC-PTP and their roles in immune cell signaling, and will discuss some new data implicating PTP1B and TC-PTP in myeloid development.

Induction of erythroid-specific genes by overexpression of GATA-2 in K562 cells

GATA transcription factors have been shown to play important roles in hematopoiesis. GATA-2 is expressed in stem and progenitor cells, and has been speculated to control the proliferation and maintain the immaturity of these cells. To examine whether the function of GATA-2 is changeable according to the differentiation stage, we established GATA-2 overexpressing subclones of K562, which is a leukemic cell line committed to the erythroid lineage. Via an increase in the GATA-2 expression level, the expression levels of erythroid-specific genes including alpha-, beta-, and gamma-globin were increased compared to control cells, while the expression level of GATA-1 was unchanged. Expression of the transferrin receptor was also increased in GATA-2 overexpressing K562 cells when examined by flow cytometry. In addition, the heme content of GATA-2 overexpressing K562 cells was more than 2 times higher than control cells. Chromatin immunoprecipitation analysis showed that GATA-2 protein binding to the GATA element in alpha-globin LCR was increased in GATA-2 overexpressing K562 cells. These findings suggest that GATA-2 could induce erythroid-specific genes without competition with GATA-1 when expressed in erythroid-committed cells, and thus further suggest that temporal and spatial regulation may be important for displaying specific functions of GATA-2.

GATA Transcription Factors and Hematological Diseases

The development of mature blood cells from hematopoietic stem cells is regulated by transcription factors that control and coordinate the expression of lineage-specific genes. The GATA family consists of six transcription factors that function in hematopoietic and endodermal development. Among them, GATA-1 is expressed in erythroid, megakaryocytic, eosinophil and mast cell lineages, and GATA-2 is expressed in stem and progenitor cells, at more immature stage compared with GATA-1. Based on the characteristic phenotypes of GATA-1 and GATA-2 mutant mice, it has been suggested that mutations of these GATA genes in humans may result in the onset of certain clinical diseases. To date, mutations of GATA-1 gene have been found in inherited anemia and thrombocytopenia, and Down syndrome-related acute leukemia, which exhibits megakaryocytic phenotypes and frequently occurs in patients with Down syndrome. In contrast, no mutation of GATA-2 gene has been identified in hematological diseases; however, we found the expression level of GATA-2 is significantly decreased in CD34 positive cells in patients with aplastic anemia. Since GATA-2 functions in the proliferation of hematopoietic stem cells, the reduction of GATA-2 expression in CD34 positive cells may result in the decreased number of hematopoietic stem cells, which is the characteristic feature of aplastic anemia. Based on these lines of evidence, some types of hematological diseases may be defined as transcription factor diseases.

Accelerated lymphangiogenesis in malignant lymphoma: possible role of VEGF-A and VEGF-C

There is little information regarding the lymphangiogenesis of malignant lymphoma. In this study, we evaluated the lymphangiogenesis and angiogenesis in 44 lymph nodes of 39 malignant lymphomas and five non-reactive normal lymph nodes, based on the lymphatic vessel density (LVD) and microvessel density (MVD) calculated by the computer-assisted assessment of vessel density. The LVD of malignant lymphomas was significantly higher than that of non-reactive normal lymph nodes, irrespective of subtypes (P = 0.00077). On the contrary, there was no difference in MVD between malignant lymphomas and non-reactive normal lymph nodes, except for diffuse large B cell lymphomas, which had a significantly low value of MVD, in comparison with non-reactive normal lymph nodes (P = 0.009). We further examined the expression of vascular endothelial growth factor (VEGF)-C and VEGF-A, which function on lymphangiogenesis in lymph node samples. VEGF-C was expressed in 36 of 39 malignant lymphomas. All 39 of the malignant lymphoma samples expressed VEGF-A. Furthermore, the level of LVD and VEGF-A or VEGF-C was positively correlated. These findings suggest that lymphangiogenesis is actively developed in lymph nodes of malignant lymphomas and it may be induced by both VEGF-A and VEGF-C secreted from lymphoma cells.

Characterization of the organic cation transporter SLC22A16: A doxorubicin importer

Specific efflux transporters, such as P-glycoprotein, have been shown to confer drug resistance by decreasing the intracellular accumulation of anticancer drugs. Understanding influx transporters, as well as efflux transporters, is essential to overcome this resistance. We report the expression profile and pharmacological characterization of an organic cation transporter, SLC22A16. The results of our experiments indicate that SLC22A16 is a mediator of doxorubicin uptake in cancer cells. Quantitative real-time RT-PCR analyses show that SLC22A16 is expressed in primary samples taken from patients with acute leukemia. Xenopus oocytes injected with SLC22A16 cRNA import doxorubicin, a widely used anticancer drug for hematological malignancies, in a saturable and dose-dependent manner. The apparent Km value for doxorubicin import was 5.2+/-0.4 microM. In cytotoxic assays, stable transfectants of leukemic Jurkat cells overexpressing SLC22A16 cells became significantly more sensitive to doxorubicin (2 microM) treatment. Characterization of SLC22A16 will help in designing novel therapies targeting hematological malignancies.