RESUMEN
Inverted CCAAT box binding protein of 90kDa (ICBP90) is a nuclear protein involved in the topoisomerase IIalpha (TopoIIalpha) gene expression. It belongs to a family of E3 ligases of the RING finger type and its expression is deregulated in cancer cells. Previous studies have shown that high expression of ICBP90 may impair the control of G1/S transition of the cell cycle in various cancer cell lines. Since PKA signaling pathway is involved in G1/S transition of the cell cycle, the aim of the present study was to investigate whether cAMP signaling pathways involve phosphorylation of ICBP90. Here, we show that phosphorylation of ICBP90 through the cAMP signaling pathway accelerates exit of forskolin-treated cells from the G1 phase and increases binding of ICBP90 to the ICB2 element of the TopoIIalpha gene promoter with a subsequent increase of TopoIIalpha expression. We identify S298 of ICBP90 as target for PKA. We propose that cAMP signaling pathway enhances TopoIIalpha expression through ICBP90 phosphorylation, which may be one of the major events involved in the G1/S transition.
Asunto(s)
Proteínas Potenciadoras de Unión a CCAAT/metabolismo , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , ADN-Topoisomerasas de Tipo II/metabolismo , Secuencia de Aminoácidos , Animales , Antígenos de Neoplasias , Sitios de Unión , Proteínas Potenciadoras de Unión a CCAAT/química , Células COS , Colforsina/farmacología , Proteína Quinasa Tipo II Dependiente de AMP Cíclico , ADN-Topoisomerasas de Tipo II/genética , Proteínas de Unión al ADN , Ensayo de Cambio de Movilidad Electroforética , Datos de Secuencia Molecular , Fosforilación , Regiones Promotoras Genéticas , Serina/metabolismo , Ubiquitina-Proteína LigasasRESUMEN
Protein kinase 2 (casein kinase 2 [CK2]) is a protein serine/threonine kinase involved in cell proliferation with an expression that is dysregulated in tumors. ICBP90, a transcription factor exhibiting antiapoptotic properties, has several putative CK2 phosphorylation sites. The aim of the present study was to investigate whether ICBP90 could behave as a CK2 substrate. We observed that ICBP90 was more efficiently phosphorylated by the free CK2a subunit than by the heterotetrameric CK2 (alpha(2), beta(2)). Our results suggest that CK2 is an important regulator of the transcriptional activity of ICBP90 and therefore of the antiapoptotic properties of ICBP90. We propose that the "ICBP90 family" members may be substrates for CK2.
Asunto(s)
Proteínas Potenciadoras de Unión a CCAAT/metabolismo , Quinasa de la Caseína II/metabolismo , Animales , Células COS , Humanos , Mapeo Peptídico , Fosforilación , Especificidad por Sustrato , Ubiquitina-Proteína LigasasRESUMEN
Inhibition of apoptosis, resulting from an increase in anti-apoptotic protein, plays a fundamental role in carcinogenesis. Because ICBP90 gene expression is deregulated in cancer cells, we studied its expression in Jurkat cells under apoptotic conditions to see whether ICBP90 is involved in the regulation of apoptosis. We found that ICBP90 expression and the percentage of living cells were dose-dependently decreased in PHA and ionophore A23187-stimulated Jurkat cells, but not in THP-1 cells. These results suggest that apoptosis is dependent upon ICBP90 expression downregulation and that ICBP90 exhibits anti-apoptotic properties.