C/EBP  expression in ALK-positive anaplastic large cell lymphomas is required for cell proliferation and is induced by the STAT3 signaling pathway

Abstract

BackgroundAnaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma is characterized by the t(2;5) chromosomal translocation, resulting in the expression of a fusion protein formed of nucleophosmin (NPM) and ALK. Recently, we reported the abnormal expression of the transcription factor CCAAT/enhancer binding protein-beta (C/EBPβ) in ALK-positive anaplastic large cell lymphomas, and demonstrated its dependence on NPM-ALK activity. Design and MethodsIn this study, the role of C/EBPβ in proliferation and survival of ALK-positive anaplastic large cell lymphomas was investigated, as well as the mechanism of its expression and activity. Highly effective short hairpin RNA sequences and/or pharmacological inhibitors were used to abrogate the expression or activity of C/EBPβ, signal transducer and activator of transcription 3 (STAT3), AKT, extracellular signal-related kinase 1/2 (ERK1/2) and mammalian target of rapamycin (mTOR). ResultsInterference with C/EBPβ expression resulted in a dramatic decrease in cell proliferation in ALK-positive anaplastic large cell lymphomas, with a mild induction of apoptosis after 6 days. Down-regulation of STAT3 resulted in a marked decrease in C/EBPβ mRNA and protein levels with impairment in cell proliferation and viability, underscoring the important role of these two proteins in ALK-mediated oncogenesis. Additionally, we demonstrated that reduction of ERK1/2 activity led to C/EBPβ Thr 235 dephosphorylation and moderate growth retardation. The AKT/mTOR signaling pathway did not have any influence on C/EBPβ expression or C/EBPβ phosphorylation. ConclusionsThese findings reveal the convergence of STAT3 and ERK1/2 signaling pathways activated by NPM-ALK in mediating the regulation of C/EBPβ expression, a transcription factor central to NPM-ALK transformation.Key words: anaplastic large cell lymphoma (ALCL), C/EBPβ, STAT3, RNA interference, cell proliferation. STAT3 signaling pathway. Haematologica 2010;95:760-767. doi:10.3324/haematol.2009 This is an open-access paper. © F e r r a t a S t o r t i F o u n d a t i o n Citation: Anastasov N, Bonzheim I, Rudelius M, Klier M, Dau T, Angermeier D, Duyster J, Pittaluga S, Fend F, Raffeld M, and Quintanilla-Martinez L. C/EBPβ expression in ALK-positive anaplastic large cell lymphomas is required for cell proliferation and is induced by the C/EBPβ expression in ALK-positive anaplastic large cell lymphomas is required for cell proliferation and is induced by the STAT3 signaling pathway

HuR-Mediated Control of C/EBPβ mRNA Stability and Translation in ALK-Positive Anaplastic Large Cell Lymphomas

“…Our results were reinforced by concomitant studies, demonstrating that C/EBPb expression is indeed required to induce ALK þ ALCLs transformation and sustain their growth and survival (5). Like most other members of the C/EBP family, C/EBPb is an intronless gene.…”

“…Its aberrant expression has been implicated in the pathogenesis of several epithelial tumors (7)(8)(9) and more recently, in NPM-ALK lymphoid transformation (5,10,11). In ALK þ ALCLs, C/EBPb expression depends on the tyrosine kinase activity of NPM-ALK and is transcriptionnally induced through the STAT3 signaling pathway, although no STAT3-specific binding sites have been observed in the C/EBP promoter region (5,10,11). On the other hand, C/EBPb, has been intensely studied for its critical role in adipocyte differentiation.…”

“…The dependence of C/EBPb gene transcription on the STAT3 signaling pathway in ALK þ ALCLs has recently been shown in 3 independent studies (5,10,11), consistent with the notion that the C/EBPb promoter is targeted by several transcription factors, including CREB/ATF and Sp1 proteins, C/EBP family members, and STAT3, albeit indirectly, in response to a variety of stimuli (12). However, C/EBPb mRNA also possesses a 3 0 -untranslated region (3 0 -UTR) that contains U-and AU-rich elements (ARE), that has been shown to bind the AU-binding protein (AUBP) HuR in adipocytes (13).…”

Rb1 Haploinsufficiency Promotes Telomere Attrition and Radiation-Induced Genomic Instability

“…Production of lentivirus was done as recently described (21). For all lentiviral transductions, we used a multiplicity of infection of 2 (2 Â 10 5 cells per well and 4 Â 10 5 TU/mL).…”

A novel immunohistochemical classifier to distinguish Hodgkin lymphoma from ALK anaplastic large cell lymphoma

“…37 However, STAT3 is also found to be expressed in ALK þ anaplastic large cell lymphoma. 38 In contrast, pediatric cases of ALK À anaplastic large cell lymphoma were negative for phosphorylated STAT3. 39 Our results fit well with the observations made by Piva et al, 26 when considering the number of ALK À anaplastic large cell lymphoma strongly expressing phosphorylated STAT3 in most if not all neoplastic cells.…”