The NPM-ALK oncoprotein abrogates CD30 signaling and constitutive NF-kappaB activation in anaplastic large cell lymphoma

NPM-ALK characterizes anaplastic large cell lymphoma (ALCL), as does the high expression of CD30, a feature shared with H-RS cells of classic Hodgkin's lymphoma. In H-RS cells, ligand-independent signaling by overexpressed CD30 drives constitutive NF-kappaB activation, which is absent in ALCL cells. Here we show that NPM-ALK impedes CD30 signaling and NF-kappaB activation, dependent on both ALK kinase activity and the N-terminal NPM domain. NPM-ALK transduction into H-RS cell lines abrogates recruitment and aggregation of TRAF proteins, inducing an ALCL-like morphology and phenotype. TRAF2 associates with NPM-ALK at a consensus binding motif located in the kinase domain. Thus, NPM-ALK abrogates CD30-driven NF-kappaB activation and can also induce an ALCL phenotype, distinguishing ALCL cells from H-RS cells of T cell origin.     

NPM-ALK signals through glycogen synthase kinase 3β to promote oncogenesis

Anaplastic large cell lymphoma (ALCL) is the most common type of pediatric peripheral T-cell lymphoma. In 70-80% of cases, the chromosomal aberration t(2;5)(p23;q35) results in the juxtaposition of anaplastic lymphoma kinase (ALK) with nucleophosmin (NPM) and the subsequent expression of the NPM-ALK fusion protein. NPM-ALK is a chimeric tyrosine kinase, which induces numerous signaling pathways that drive proliferation and abrogate apoptosis. However, the mechanisms that lead to activation of downstream growth regulatory molecules have not been completely elucidated. Using a mass spectrometry-based phosphoproteomic screen, we identified GSK3β as a signaling mediator of NPM-ALK. Using a selective inhibitor of ALK, we demonstrated that the tyrosine kinase activity of ALK regulates the serine-9 phosphorylation of GSK3β. Expression of NPM-ALK in 293T cells led to an increase of pS(9)-GSK3β (glycogen synthase kinase 3 beta) compared with kinase-defective K210R mutant NPM-ALK, but did not affect total GSK3β levels. Phosphorylation of pS(9)-GSK3β by NPM-ALK was mediated by the PI3K/AKT signaling pathway. ALK inhibition resulted in degradation of GSK3β substrates Mcl-1 and CDC25A, which was recovered upon chemical inhibition of the proteasome (MG132). Furthermore, the degradation of Mcl-1 was recoverable with inhibition of GSK3β. ALK inhibition also resulted in decreased cell viability, which was rescued by GSK3β inhibition. Furthermore, stable knockdown of GSK3β conferred resistance to the growth inhibitory effects of ALK inhibition using viability and colony formation assays. pS(9)-GSK3β and CDC25A were selectively expressed in neoplastic cells of ALK+ALCL tissue biopsies, and showed a significant correlation (P<0.001). Conversely, ALK-ALCL tissue biopsies did not show significant correlation of pS(9)-GSK3β and CDC25A expression (P<0.2). Our results demonstrate that NPM-ALK regulates the phosphorylation of S(9)-GSK3β by PI3K/AKT. The subsequent inhibition of GSK3β activity results in accumulation of CDC25A and Mcl-1, which confers the advantage of growth and protection from apoptosis. These findings provide support for the role of GSK3β as a mediator of NPM-ALK oncogenesis.     

The tyrosine phosphatase Shp2 interacts with NPM-ALK and regulates anaplastic lymphoma cell growth and migration

Anaplastic large cell lymphomas (ALCL) are mainly characterized by the reciprocal translocation t(2;5)(p23;q35) that involves the anaplastic lymphoma kinase (ALK) gene and generates the fusion protein NPM-ALK with intrinsic tyrosine kinase activity. NPM-ALK triggers several signaling cascades, leading to increased cell growth, resistance to apoptosis, and changes in morphology and migration of transformed cells. To search for new NPM-ALK interacting molecules, we developed a mass spectrometry-based proteomic approach in HEK293 cells expressing an inducible NPM-ALK and identified the tyrosine phosphatase Shp2 as a candidate substrate. We found that NPM-ALK was able to bind Shp2 in coprecipitation experiments and to induce its phosphorylation in the tyrosine residues Y542 and Y580 both in HEK293 cells and ALCL cell lines. In primary lymphomas, antibodies against the phosphorylated tyrosine Y542 of Shp2 mainly stained ALK-positive cells. In ALCL cell lines, Shp2-constitutive phosphorylation was dependent on NPM-ALK, as it significantly decreased after short hairpin RNA (shRNA)-mediated NPM-ALK knock down. In addition, only the constitutively active NPM-ALK, but not the kinase dead NPM-ALK(K210R), formed a complex with Shp2, Gab2, and growth factor receptor binding protein 2 (Grb2), where Grb2 bound to the phosphorylated Shp2 through its SH2 domain. Shp2 knock down by specific shRNA decreased the phosphorylation of extracellular signal-regulated kinase 1/2 and of the tyrosine residue Y416 in the activation loop of Src, resulting in impaired ALCL cell proliferation and growth disadvantage. Finally, migration of ALCL cells was reduced by Shp2 shRNA. These findings show a direct involvement of Shp2 in NPM-ALK lymphomagenesis, highlighting its critical role in lymphoma cell proliferation and migration.     

Downregulation of NPM-ALK by siRNA causes anaplastic large cell lymphoma cell growth inhibition and augments the anti cancer effects of chemotherapy in vitro

The fusion protein, nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), results from the chromosome translocation t(2;5)(p23;q25) and is present in 50-70 percent of anaplastic large-cell lymphomas (ALCLs). NPM-ALK is a constitutively activated kinase that transforms cells through stimulating several mitogenic signaling pathways. To examine if the NPM-ALK is a potential therapeutic target in ALCL, we used siRNA to specifically downregulate the expression of the NPM-ALK in ALCL cell lines. In this report, we demonstrated viability loss in t(2;5)-positive ALCL cell lines, SUDHL-1 and Karpas 299 cells, but not in lymphoma cell lines without the chromosome translocation, Jurkat and Granta 519 cells. Further study demonstrated that the downregulation of NPM-ALK resulted in decreased cell proliferation and increased cell apoptosis. When used in combination with chemotherapeutic agents, such as doxorubicin, the inhibition of the NPM-ALK augments the chemosensitivity of the tumor cells. These results revealed the importance of continuous expression of NPM-ALK in maintaining the growth of ALCL cells. Our data also suggested that the repression of the fusion gene might be a potential novel therapeutic strategy for NPM-ALK positive ALCLs.     

B7-H1 expression is regulated by MEK/ERK signaling pathway in anaplastic large cell lymphoma and Hodgkin lymphoma

B7-H1 is a member of the B7 family that inhibits the function of T-cells through its receptor programmed death-1 (PD-1). We examined B7-H1 expression in anaplastic large cell lymphoma (ALCL) and Hodgkin lymphoma (HL) and found that it was constitutively expressed in both clinical samples and cell lines. In anaplastic lymphoma kinase–positive (ALK⁺) ALCL cells, B7-H1 expression was suppressed by the blocking of extracellular signal-regulated kinase (ERK) signaling and upregulated by the augmentation of ERK activity by phorbol 13-myristate 12-acetate stimulation, suggesting that B7-H1 expression is regulated by ERK signaling pathway in ALCL. ERK is one of the downstream mediators of nucleophosmin (NPM)/ALK signaling in ALK⁺ALCL, and pharmacological inhibition of ALK was shown to dephosphorylate ERK and down-regulate B7-H1. The involvement of NPM/ALK in B7-H1 expression was also demonstrated by introducing the construct into human non-ALCL lymphoid cell lines, which resulted in B7-H1 expression. In the case of HL, B7-H1 expression was shown to be dependent on the ERK and p38 mitogen-activated protein kinase (MAPK) signaling pathways. These results suggest that B7-H1 expression is controlled by common ERK signaling pathways in ALCL and HL cells. Our findings provide a potentially effective immunotherapeutic strategy for these B7-H1-expressing tumors. ( Cancer Sci 2009)     

Model of inhibition of the NPM-ALK kinase activity by herbimycin A.

Anaplastic large cell lymphoma (ALCL) exhibiting the t(2;5) translocation is characterized by the resulting expression of the oncogenic fusion protein nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) gene product. The ALK domain of NPM-ALK contains kinase activity, which is responsible for the autophosphorylation of tyrosine residues of the oncogenic protein and phosphorylation of SH2-protein substrates. Herbimycin A is a general protein tyrosine kinase inhibitor active as an antiproliferative compound against different types of mammalian cells. Herbimycin A inhibited the NPM-ALK-associated autophosphorylating activity in an in vitro cell-free kinase assay. The inhibition was specific when tested against other kinase inhibitors and extended to other cell lines derived from t(2;5)-ALCL. SUDHL-1 cells showed increasing percentage of cells in G(1) after 18 h of incubation with a dose of herbimycin A. NPM-ALK, Akt, and pAkt were down-regulated after 24 h of incubation with herbimycin A. Apoptosis was observed only if the dose of inhibitor was given every 12 h for prolonged time. Our results show that herbimycin A interferes with NPM-ALK and Akt pathways in SUDHL-1 cells. It seems that prolonged inhibition of these biochemical pathways may lead to cell cycle arrest and apoptosis. This study supports the idea of investigating protein kinase inhibitors as therapeutic compounds for t(2;5)-ALCL.     

The anaplastic lymphoma kinase controls cell shape and growth of anaplastic large cell lymphoma through Cdc42 activation

Anaplastic large cell lymphoma (ALCL) is a non-Hodgkin's lymphoma that originates from T cells and frequently expresses oncogenic fusion proteins derived from chromosomal translocations or inversions of the anaplastic lymphoma kinase (ALK) gene. The proliferation and survival of ALCL cells are determined by the ALK activity. Here we show that the kinase activity of the nucleophosmin (NPM)-ALK fusion regulated the shape of ALCL cells and F-actin filament assembly in a pattern similar to T-cell receptor-stimulated cells. NPM-ALK formed a complex with the guanine exchange factor VAV1, enhancing its activation through phosphorylation. VAV1 increased Cdc42 activity, and in turn, Cdc42 regulated the shape and migration of ALCL cells. In vitro knockdown of VAV1 or Cdc42 by short hairpin RNA, as well as pharmacologic inhibition of Cdc42 activity by secramine, resulted in a cell cycle arrest and apoptosis of ALCL cells. Importantly, the concomitant inhibition of Cdc42 and NPM-ALK kinase acted synergistically to induce apoptosis of ALCL cells. Finally, Cdc42 was necessary for the growth as well as for the maintenance of already established lymphomas in vivo. Thus, our data open perspectives for new therapeutic strategies by revealing a mechanism of regulation of ALCL cell growth through Cdc42.     

Nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), a novel Hsp90-client tyrosine kinase: down-regulation of NPM-ALK expression and tyrosine phosphorylation in ALK(+) CD30(+) lymphoma cells by the Hsp90 antagonist 17-allylamino,17-demethoxygeldanamycin

Anaplastic large cell lymphomas (ALCL) are characterized by the expression of a chimeric protein, NPM-ALK, which originates from fusion of the nucleophosmin (NPM) and the membrane receptor anaplastic lymphoma kinase (ALK) genes. The NPM-ALK kinase, on dimerization, shows phosphotransferase activity and, through its interaction with various ALK-adapter proteins, induces cell transformation and increases cell proliferation in vitro. The chaperones heat shock proteins 90 (Hsp90) and 70 (Hsp70) play a critical role in the folding and maturation of several oncogenic protein kinases, and perturbation of Hsp90 structure affects the stability and degradation of Hsp90- and Hsp70-bound substrates. This process is triggered by benzoquinone ansamycin antibiotics, Hsp90-binding small molecules. We have studied the effect of 17-allylamino,17-demethoxygeldanamycin (17-AAG), a benzoquinone ansamycin, on NPM-ALK steady-state level in ALCL cells. Treatment with 17-AAG decreased NPM-ALK expression and phosphorylation, thus impairing its association with phospholipase C-gamma, Src homology 2 domain-containing protein (Shc), growth factor receptor-bound protein 2 (Grb2), and insulin receptor substrate-1 (IRS-1). We also observed that NPM-ALK associates with Hsp90, and incubation with 17-AAG disrupts this complex without affecting Hsp90 expression. As shown previously for other Hsp90 client proteins, destabilization of the Hsp90/NPM-ALK complex induced by 17-AAG resulted in increased binding of the chimeric protein to Hsp70, which is known to affect protein degradation. Hsp/NPM-ALK complex formation appears to be independent of NPM sequences, because we were unable to coimmunoprecipitate NPM with either Hsp90 or Hsp70. Similar to NPM-ALK, the exogenously expressed variant fusion protein TPR-ALK showed decreased expression and phosphorylation after 17-AAG treatment, suggesting that the effect of 17-AAG on ALK chimeric proteins depends on the ALK portion and not on the partner protein moiety. Our data demonstrate that NPM-ALK cell content is determined by its interaction with Hsp90 and Hsp70, and suggest that the alteration of such associations can interfere with NPM-ALK function in ALCL cells.     

Activation of mammalian target of rapamycin signaling pathway contributes to tumor cell survival in anaplastic lymphoma kinase-positive anaplastic large cell lymphoma

Anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma (ALCL) frequently carries the t(2;5)(p23;q35) resulting in aberrant expression of chimeric nucleophosmin-ALK. Previously, nucleophosmin-ALK has been shown to activate phosphatidylinositol 3-kinase (PI3K) and its downstream effector, the serine/threonine kinase AKT. In this study, we hypothesized that the mammalian target of rapamycin (mTOR) pathway, which functions downstream of AKT, mediates the oncogenic effects of activated PI3K/AKT in ALK+ ALCL. Here, we provide evidence that mTOR signaling phosphoproteins, including mTOR, eukaryotic initiation factor 4E-binding protein-1, p70S6K, and ribosomal protein S6, are highly phosphorylated in ALK+ ALCL cell lines and tumors. We also show that AKT activation contributes to mTOR phosphorylation, at least in part, as forced expression of constitutively active AKT by myristoylated AKT adenovirus results in increased phosphorylation of mTOR and its downstream effectors. Conversely, inhibition of AKT expression or activity results in decreased mTOR phosphorylation. In addition, pharmacologic inhibition of PI3K/AKT down-regulates the activation of the mTOR signaling pathway. We also show that inhibition of mTOR with rapamycin, as well as silencing mTOR gene product expression using mTOR-specific small interfering RNA, decreased phosphorylation of mTOR signaling proteins and induced cell cycle arrest and apoptosis in ALK+ ALCL cells. Cell cycle arrest was associated with modulation of G(1)-S-phase regulators, including the cyclin-dependent kinase inhibitors p21(waf1) and p27(kip1). Apoptosis following inhibition of mTOR expression or function was associated with down-regulation of antiapoptotic proteins, including c-FLIP, MCL-1, and BCL-2. These findings suggest that the mTOR pathway contributes to nucleophosmin-ALK/PI3K/AKT-mediated tumorigenesis and that inhibition of mTOR represents a potential therapeutic strategy in ALK+ ALCL.