RESUMEN
Transcription initiation factor 90 (TIF-90), an alternatively spliced variant of TIF-IA, differs by a 90 base pair deletion of exon 6. TIF-90 has been shown to regulate ribosomal RNA (rRNA) synthesis by interacting with polymerase I (Pol I) during the initiation of ribosomal DNA (rDNA) transcription in the nucleolus. Recently, we showed that TIF-90-mediated rRNA synthesis can play an important role in driving tumorigenesis in human colon cancer cells. Here we show that TIF-90 binds GTP at threonine 310, and that GTP binding is required for TIF-90-enhanced rRNA synthesis. Overexpression of activated AKT induces TIF-90 T310, but not a GTP-binding site (TIF-90 T310N) mutant, to translocate into the nucleolus and increase rRNA synthesis. Complementing this result, treatment with mycophenolic acid (MPA), an inhibitor of GTP production, dissociates TIF-90 from Pol I and hence abolishes AKT-increased rRNA synthesis by way of TIF-90 activation. Thus, TIF-90 requires bound GTP to fulfill its function as an enhancer of rRNA synthesis. Both TIF variants are highly expressed in colon cancer cells, and depletion of TIF-IA expression in these cells results in significant sensitivity to MPA-inhibited rRNA synthesis and reduced cell proliferation. Finally, a combination of MPA and AZD8055 (an inhibitor of both AKT and mTOR) synergistically inhibits rRNA synthesis, in vivo tumor growth, and other oncogenic activities of primary human colon cancer cells, suggesting a potential avenue for the development of therapeutic treatments by targeting the regulation of rRNA synthesis by TIF proteins.
Asunto(s)
Carcinogénesis/genética , Neoplasias del Colon/genética , Guanosina Trifosfato/genética , ARN Ribosómico/genética , Ribosomas/genética , Factores de Transcripción/genética , Transcripción Genética/genética , Línea Celular Tumoral , Proliferación Celular/genética , ADN Ribosómico/genética , Células HCT116 , Humanos , ARN Polimerasa I/genética , Transducción de Señal/genéticaRESUMEN
The ErbB3-binding protein 1 (Ebp1) has been reported as either an oncogenic regulator or a tumor suppressor in a variety of cancers. Here, we show that Ebp1 p48, a predominant expression isoform, is highly expressed in the majority of human colon tumor cells compared with normal adjacent tissues and its expression is required for the oncogenic activities of these cells. Depletion of Ebp1 expression in primary colon cancer cells inhibits cell proliferation, colony forming, and invasion in vitro as well as tumor formation in vivo and enhances cell sensitivity to irradiation. We further demonstrated that Ebp1 interacts with TIF-90, a splice variant of transcription initiation factor IA (TIF-IA) of the RNA polymerase I complex, allowing for regulation of ribosomal RNA (rRNA) synthesis and oncogenesis in human colon cancer cells. Moreover, Ebp1 expression is essential for Akt protected TIF-90 stability by preventing TIF-90's ubiquitination by Mdm2 and hence, its proteasomal degradation. The results of the present study support a mechanism of underlying oncogenic activities by means of Ebp1 through regulation of TIF-90-mediated rRNA synthesis and suggest the potential therapeutic treatment of colon cancer by targeting Ebp1 and its signaling.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales/metabolismo , Neoplasias del Colon/metabolismo , Proteínas del Complejo de Iniciación de Transcripción Pol1/metabolismo , ARN Ribosómico/biosíntesis , Proteínas de Unión al ARN/metabolismo , Proteínas Adaptadoras Transductoras de Señales/genética , Carcinogénesis/genética , Carcinogénesis/metabolismo , Neoplasias del Colon/genética , Neoplasias del Colon/patología , Regulación Neoplásica de la Expresión Génica , Humanos , Modelos Biológicos , Isoformas de Proteínas/genética , Isoformas de Proteínas/metabolismo , Estabilidad Proteica , Proteínas Proto-Oncogénicas c-mdm2/metabolismo , ARN Ribosómico/genética , Proteínas de Unión al ARN/genética , Transducción de Señal , Células Tumorales Cultivadas , UbiquitinaciónRESUMEN
Scabies is a neglected tropical disease and represents a considerable global burden. Although consensus diagnostic criteria for scabies have been recently published, diagnosing scabies infestation remains challenging in clinical practice. We investigated the diagnostic utility of complete blood cell count (CBC) and CBC-derived ratios obtained at diagnosis in a set of 167 patients who are Vietnamese with confirmed scabies. These parameters were compared with those of patients with dermatophytosis (N = 800) and urticaria (N = 2023), two diseases frequent in Vietnam, which can present with similar skin manifestations to scabies and tend to pose a diagnostic challenge in vulnerable populations. Our analysis revealed that white blood cell, monocyte, and eosinophil counts were significantly higher among patients with scabies than the other two diseases. Similarly, the monocyte-to-lymphocyte ratio (MLR) and eosinophil-to-lymphocyte ratio (ELR) were significantly higher among patients with scabies. The optimal cut-off values to distinguish scabies from dermatophytosis and urticaria were 0.094 for ELR (sensitivity: 74.85%, specificity: 70.7%) and 0.295 for MLR (sensitivity: 52.69%, specificity: 73.54%). CBC, ELR, and MLR are low-cost and easily calculated parameters that may be helpful for the diagnosis of scabies.