c‐Jun blocks cell differentiation but not growth inhibition or apoptosis of chronic myelogenous leukemia cells induced by STI571 and by histone deacetylase inhibitors

Abstract

The constitutively active Bcr-Abl tyrosine kinase plays a crucial role in chronic myelogenous leukemia (CML) pathogenesis. The Bcr-Abl protein induces the upregulation of proto-oncogene c-Jun, which is involved in Bcr-Abl transforming activity in Bcr-Abl positive cells. Recent studies reported that c-Jun inhibited hemoglobin synthesis in human CML cell line K562. However, c-Jun also plays a critical role in cell proliferation and apoptosis. In this study, we investigated the physiological roles of c-Jun in cell proliferation, apoptosis and erythroid differentiation of K562 cells. Firstly, we generated K562 cell lines stably overexpressing c-Jun. These clones have the same proliferation rate as the parental cell line in general culture medium. Endogenous c-Jun expression was analyzed to determine the effective concentration of STI571 for inhibiting Bcr-Abl signaling. Western blots show that STI571 inhibited c-Jun expression in a dose-dependent manner, reaching a maximum inhibition at 1 microM. STI571 could inhibit c-Jun expression in K562 cells, but not in c-Jun-overexpression cells. c-Jun did not alter growth inhibition and apoptotic induction by STI571 treatment, but inhibited STI571-induced erythroid differentiation. Moreover, c-Jun did not alter growth inhibition and apoptotic induction by histone deacetylase (HDAC) inhibitors (apicidin, sodium butyrate, and MS275) treatment, but inhibited HDAC inhibitors-induced erythroid differentiation. These results suggest that c-Jun may modulate anticancer drugs-induced cell differentiation but not growth inhibition and apoptosis in CML cells.

Activin A induction of erythroid differentiation sensitizes K562 chronic myeloid leukemia cells to a subtoxic concentration of imatinib

“…The level of cell apoptosis was measured by annexin V-FITC and propidium iodide (PI) staining, as previously described (26). Results are shown as percentage of early apoptotic (annexin V ϩ PI Ϫ ) and late apoptotic (annexin V ϩ PI ϩ ) cells.…”

“…Erythroid differentiation was determined by hemoglobin synthesis in K562 cells using the benzidine staining assay, as previously described (26).…”

Bean (Phaseolus vulgaris L.) polysaccharides modulate gene expression in human colon cancer cells (HT-29)

“…Butyrate has been extensively studied because of its demonstrated effect on gene expression, cell growth regulation, and differentiation in numerous animal cells (Li & Elsasser, 2005;Milla, 2009;Rouet-Benzineb et al, 2004;Young-Ho, Jong-Wook, Jai-Youl, & Taeg-Kyu, 2004). Butyrate suppresses c-myc mRNA levels, and increases c-jun transcript leading to transcription of specific genes involved in differentiating pathways (Huang & Liu, 2008;Tong et al, 2006). Furthermore, treatment of cultured cells with butyrate produces reversible hyperacetylated histones that are important in modulating chromatin structure and its transcriptional activity (Kiefer, Beyer-Sehlmeyer, & Pool-Zobel, 2006).…”

cJun modulates Gγ-globin gene expression via an upstream cAMP response element

“…Moreover, overlapping tandem AP-1/NF-E2 sites in hypersensitive site 2 of the β-locus control region were previously characterized as enhancers in γ-globin gene expression [13] however a possible negative role has also been implicated when cJun interacts with NF-E2 [14]. Context dependent regulation of γ-globin expression by cJun after drug induction has been investigated by others [15-18]. Increased cJun mRNA levels via post transcriptional stabilization were observed in cells treated with hydroxyurea [15].…”

“…Increased cJun mRNA levels via post transcriptional stabilization were observed in cells treated with hydroxyurea [15]. By contrast, other studies demonstrated that cJun might act as an inhibitor of HDAC inhibitor-induced erythroid differentiation [17,18]. …”