Suzanne D. Turner

Identification of differential and functionally active miRNAs in both anaplastic lymphoma kinase (ALK)+ and ALK− anaplastic large-cell lymphoma

Aberrant anaplastic lymphoma kinase (ALK) expression is a defining feature of many human cancers and was identified first in anaplastic large-cell lymphoma (ALCL), an aggressive non-Hodgkin T-cell lymphoma. Since that time, many studies have set out to identify the mechanisms used by aberrant ALK toward tumorigenesis. We have identified a distinct profile of micro-RNAs (miRNAs) that characterize ALCL; furthermore, this profile distinguishes ALK+ from ALK− subtypes, and thus points toward potential mechanisms of tumorigenesis induced by aberrant ALK. Using a nucleophosmin-ALK transgenic mouse model as well as human primary ALCL tumor tissues and human ALCL-derived cell lines, we reveal a set of overlapping deregulated miRNAs that might be implicated in the development and progression of ALCL. Importantly, ALK+ and ALK− ALCL could be distinguished by a distinct profile of “oncomirs”: Five members of the miR-17–92 cluster were expressed more highly in ALK+ ALCL, whereas miR-155 was expressed more than 10-fold higher in ALK− ALCL. Moreover, miR-101 was down-regulated in all ALCL model systems, but its forced expression attenuated cell proliferation only in ALK+ and not in ALK− cell lines, perhaps suggesting different modes of ALK-dependent regulation of its target proteins. Furthermore, inhibition of mTOR, which is targeted by miR-101, led to reduced tumor growth in engrafted ALCL mouse models. In addition to future therapeutical and diagnostic applications, it will be of interest to study the physiological implications and prognostic value of the identified miRNA profiles.

PDGFR blockade is a rational and effective therapy for NPM-ALK-driven lymphomas

Anaplastic large cell lymphoma (ALCL) is an aggressive non-Hodgkins lymphoma found in children and young adults. ALCLs frequently carry a chromosomal translocation that results in expression of the oncoprotein nucleophosmin–anaplastic lymphoma kinase (NPM-ALK). The key molecular downstream events required for NPM-ALK–triggered lymphoma growth have been only partly unveiled. Here we show that the activator protein 1 family members JUN and JUNB promote lymphoma development and tumor dissemination through transcriptional regulation of platelet-derived growth factor receptor-β (PDGFRB) in a mouse model of NPM-ALK–triggered lymphomagenesis. Therapeutic inhibition of PDGFRB markedly prolonged survival of NPM-ALK transgenic mice and increased the efficacy of an ALK-specific inhibitor in transplanted NPM-ALK tumors. Notably, inhibition of PDGFRA and PDGFRB in a patient with refractory late-stage NPM-ALK+ ALCL resulted in rapid, complete and sustained remission. Together, our data identify PDGFRB as a previously unknown JUN and JUNB target that could be a highly effective therapy for ALCL.

Vav -promoter regulated oncogenic fusion protein NPM-ALK in transgenic mice causes B-cell lymphomas with hyperactive Jun kinase

Anaplastic large-cell lymphoma is associated with a chromosomal translocation generating an oncogenic fusion protein: the nucleophosmin-anaplastic lymphoma kinase (NPM-ALK). We have generated several independent lines of human NPM-ALK transgenic mice using the haematopoietic cell-specific Vav promoter. Lymphomas develop in two transgenic lines in which the Vav promoter regulates NPM-ALK expression. The transgenic line with higher copy number displays an early-onset phenotype in which all mice succumb to aggressive lymph node tumours with intestinal involvement, whereas the second line displays late-onset tumour development in the spleen and/or liver. Lymphomas from both lines are phenotypically distinct and display B-lineage characteristics with aberrant coexpression of myeloid markers. The NPM-ALK kinase is active in primary tumour tissue and forms a multimeric complex with tyrosine-phosphorylated proteins, that is, Shc. Jun and ERK kinase activities in tumours are elevated by up to 30-fold and fivefold, respectively, in comparison with sIgM-stimulated primary B cells. The new transgenic models provide a system for investigating the oncogenic events mediated by NPM-ALK in situ and a physiologically relevant context for developing tyrosine kinase inhibitor therapies of potential use in the clinic.

STAT3 regulated ARF expression suppresses prostate cancer metastasis.

Prostate cancer (PCa) is the most prevalent cancer in men. Hyperactive STAT3 is thought to be oncogenic in PCa. However, targeting of the IL-6/STAT3 axis in PCa patients has failed to provide therapeutic benefit. Here we show that genetic inactivation of Stat3 or IL-6 signalling in a Pten-deficient PCa mouse model accelerates cancer progression leading to metastasis. Mechanistically, we identify p19ARF as a direct Stat3 target. Loss of Stat3 signalling disrupts the ARF–Mdm2–p53 tumour suppressor axis bypassing senescence. Strikingly, we also identify STAT3 and CDKN2A mutations in primary human PCa. STAT3 and CDKN2A deletions co-occurred with high frequency in PCa metastases. In accordance, loss of STAT3 and p14ARF expression in patient tumours correlates with increased risk of disease recurrence and metastatic PCa. Thus, STAT3 and ARF may be prognostic markers to stratify high from low risk PCa patients. Our findings challenge the current discussion on therapeutic benefit or risk of IL-6/STAT3 inhibition.

Genotoxicity studies on the azo dye Direct Red 2 using the in vivo mouse bone marrow micronucleus test

The clastogenicity of the azo dye Direct Red 2 (DR2) has been investigated using the murine bone marrow micronucleus assay. A potent dose-dependent response was observed following oral gavage of DR2 up to 4 mg/kg, after which significant toxicity to the erythroid compartment was observed. The route of administration had a significant effect on the frequency of micronucleus formation: intraperitoneal injection was approximately two-fold less clastogenic than the equivalent dose delivered orally (p<0.05). The requirement for activation of DR2 by intestinal microflora was indicated by the fact that mice given acid-treated water prior to administration of DR2 showed a significant reduction (40%; p<0.001) in micronucleated polychromatic erythrocyte formation. The implications of these findings for the health and safety of occupationally exposed workers are discussed.

NPM-ALK inhibits the p53 tumor suppressor pathway in an MDM2 and JNK-dependent manner

Anaplastic large cell lymphoma (ALCL) is characterized by the presence of the t(2;5)(p23;q35) generating the nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) fusion protein, a hyperactive kinase with transforming properties. Among these properties is the ability to regulate activity of the p53 tumor suppressor protein. In many human cancers, p53 is inactivated by mutation or other means, in some cases as a result of up-regulation of the negative regulator MDM2. However, the majority of ALK-expressing ALCL carry wild-type p53 and do not over express MDM2. We demonstrate a novel p53-dependent pathogenetic mechanism in ALK-expressing lymphoma. We confirm previously published reports of NPM-ALK-induced activation of the phosphoinositide (PI) 3-kinase and Jun N-terminal kinase (JNK) stress-activated protein (SAP) kinase proteins, but in this study demonstrate a role for these in the regulation of p53 activity in an intricate signaling system. Specifically, constitutive ALK signaling leads to the functional inactivation and/or degradation of p53 in JNK and MDM2 dependent manners. We also show nuclear exclusion of p53 in a PI 3-kinase-dependent manner. Furthermore, we demonstrate that reactivation of p53 in ALK-expressing cells as a result of pharmacologic inhibition of JNK, PI 3-kinase, and/or MDM2 activities results in the induction of apoptosis suggesting a novel therapeutic modality.

Jailbreak: oncogene-induced senescence and its evasion.

Aberrant oncogenic signals are typically counteracted by anti-proliferative mechanisms governed principally by the p53 and Rb tumour-suppressor proteins. Apoptosis is firmly established as a potent anti-proliferative mechanism to prevent tumour growth but it is only in recent years that oncogene-induced senescence has achieved similar recognition. Senescence is defined as an irreversible cell-cycle arrest suggesting that entry of oncogene-expressing cells into this static yet viable state is permanent. However, tumours do develop and express the very same oncogenes that landed them in jail. We ask whether this is because rogue incipient cancer cells find ways to escape this imposed imprisonment or otherwise entirely avoid capture by senescence gate-keepers.

What have we learnt from mouse models of NPM-ALK-induced lymphomagenesis?

The nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) is generated as a t(2;5) chromosomal breakpoint product, typically in CD30+ anaplastic large cell lymphomas. Activation of the NPM-ALK tyrosine kinase by NPM dimerisation causes autophosphorylation at multiple tyrosine residues and the consequent recruitment of a ‘signalosome’ that couples the fusion protein to pathways regulating mitogenesis and apoptosis. This review focuses on recent advances in our understanding of the transforming signals induced by this fusion protein in mouse models.

Anaplastic large cell lymphoma (ALCL) and breast implants: breaking down the evidence.

Systemic anaplastic large cell lymphoma (ALCL) is a distinct disease classification provisionally sub-divided into ALCL, Anaplastic Lymphoma Kinase (ALK)(+) and ALCL, ALK(-) entities. More recently, another category of ALCL has been increasingly reported in the literature and is associated with the presence of breast implants. A comprehensive review of the 71 reported cases of breast implant associated ALCL (iALCL) is presented indicating the apparent risk factors and main characteristics of this rare cancer. The average patient is 50 years of age and most cases present in the capsule surrounding the implant as part of the periprosthetic fluid or the capsule itself on average at 10 years post-surgery suggesting that iALCL is a late complication. The absolute risk is low ranging from 1:500,000 to 1:3,000,000 patients with breast implants per year. The majority of cases are ALK-negative, yet are associated with silicone-coated implants suggestive of the mechanism of tumorigenesis which is discussed in relation to chronic inflammation, immunogenicity of the implants and sub-clinical infection. In particular, capsulotomy alone seems to be sufficient for the treatment of many cases suggesting the implants provide the biological stimulus whereas others require further treatment including chemo- and radiotherapy although reported cases remain too low to recommend a therapeutic approach. However, CD30-based therapeutics might be a future option.

Fusion tyrosine kinase mediated signalling pathways in the transformation of haematopoietic cells.

The fusion tyrosine kinases (FTKs) are generated by chromosomal translocations creating bipartite proteins in which the kinase is hyperactivated by an adjoining oligomerization domain. Autophosphorylation of the FTK generates a ‘signalosome’, an ensemble of signalling proteins that transduce signals to downstream pathways. At the earliest stages of oncogenesis, FTKs can mimic mitogenic cytokine signalling pathways involving the GAB-2 adaptor protein and signal transducers and activators of transcription (STAT) factors, generating replicative stress and thereby promoting a mutator phenotype. In parallel, FTKs couple to survival pathways that upregulate prosurvival proteins such as Bcl-xL, so preventing DNA-damage-induced apoptosis. Following transformation, FTKs induce resistance to genotoxic attack by upregulating DNA repair mechanisms such as STAT5-dependent RAD51 transcription. The phenomenon of ‘oncogene addiction’ reflects the continued requirement of an active FTK ‘signalosome’ to mediate survival and mitogenic signals involving the PI 3-kinase and mitogen-activated protein stress-activated protein kinase pathways, and the nuclear factor-kappa B, activator protein 1 and STAT transcription factors. The available data so far suggest that FTKs, with some possible exceptions, induce and maintain the transformed state using similar panoplies of signals, a finding with important therapeutic implications. The FTK signalling field has matured to an exciting phase in which rapid advances are facilitating rational drug design.