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Aberrations of the Wnt canonical pathway (WCP) are known to contribute to the pathogenesis of various types of cancer. We hypothesize that these defects may exist in mantle cell lymphoma (MCL). Both the upstream and downstream aspects of WCP were examined in MCL cell lines and tumors. Using WCP-specific oligonucleotide arrays, we found that MCL highly and consistently expressed Wnt3 and Wnt10. ␤-catenin, a transcriptional factor that is a downstream target of WCP, is localized to the nucleus and transcriptionally active in all 3 MCL cell lines examined. By immunohistochemistry, 33 (52%) of 64 MCL tumors showed nuclear localization of ␤-catenin, which significantly correlated with the expression of the phosphorylated/inactive form of GSK3␤ (p-GSK3␤; P ‫؍‬ .011, Fisher). IntroductionMantle cell lymphoma (MCL) is a specific type of non-Hodgkin B-cell lymphoma recognized by the World Health Organization (WHO) Classification Scheme. 1 The genetic hallmark of this disease is the recurrent chromosomal abnormality, the t(11;14)(q13;q32), which brings the cyclin D1 gene under the influence of the enhancer of the immunoglobulin heavy chain (IgH) gene, leading to cyclin D1 overexpression. 2 Although cyclin D1 overexpression is likely to be pathogenetically important in MCL, evidence suggests that additional biochemical defects are necessary for lymphomagenesis. For instance, using Ecyclin D1 transgenic mice, 2 research groups have previously shown that enforced cyclin D1 expression in B cells is not sufficient to induce tumor formation. 3,4 Furthermore, large-scale cDNA microarray studies using frozen MCL tumors have revealed a relatively large number of biochemical abnormalities in MCL, with these defects frequently implicated in the regulation of apoptosis, cell cycle progression, and DNA repair. [5][6][7][8][9][10] Examination of specific cellular signaling pathways also provided additional insights into the biology of these tumors. For instance, a relatively recent study reported constitutive activation of the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway in a subset of MCL tumors, particularly those with a blastoid morphology. 11 The Wnt canonical pathway (WCP) is important for normal cell growth and development. 12,13 Defects of this pathway have been shown to play roles in the pathogenesis of a variety of human cancers, particularly those of epithelial type. 14 Normally, WCP is activated via ligation of the Wnt proteins, which are secreted glycoproteins, to their respective dimeric cell surface receptors composed of the frizzled proteins and the low-density lipoprotein-receptor-related proteins (LRPs). 15 The binding of the Wnt proteins to their receptors is negatively regulated by the Wnt inhibitory factor and the sFRP proteins (sFRP1-5). Upon ligation to their receptors, the disheveled proteins (DvLs), a family of the upstream WCP signaling proteins, are phosphorylated. 16,17 In WCP, Wnt stimulation results in inactivation/phosphorylation of GSK3␤, as well as the dissociation of the "destruction comp...

We sought kinase domain (KD) mutations at the start of treatment with dasatinib in 46 chronic myeloid leukemia (CML) patients resistant to or intolerant of imatinib. We identified BCR-ABL mutant subclones in 12 (26%) cases and used pyrosequencing to estimate subsequent changes in their relative size after starting dasatinib. Four patients lost their mutations, which remained undetectable, 3 patients retained the original mutation or lost it only transiently, 3 lost their original mutations but acquired a new mutation (F317L), and 2 developed another mutation (T315I) in addition to the original mutation within the same subclone. This study shows that expansion of a mutant Ph-positive clone that responds initially to a second generation tyrosine kinase inhibitor may be due either to late acquisition of a second mutation in the originally mutated clone, such as the T315I, or to acquisition of a completely new mutant clone, such as F317L.

One of the characteristic features of anaplastic lymphoma kinase (ALK) þ , anaplastic large cell lymphoma (ALK þ ALCL) is the constitutive activation of signal transducers and activators of transcription-3 (STAT3), a defect believed to be important for the pathogenesis of these tumors. In this report, we describe the existence of an autocrine stimulatory loop involving interleukin-22 (

Sox2 (sex-determining region Y-Box) is one of the master transcriptional factors that are important in maintaining the pluripotency of embryonic stem cells (ESCs). In line with this function, Sox2 expression is largely restricted to ESCs and somatic stem cells. We report that Sox2 is expressed in cell lines and tumor samples derived from ALK-positive anaplastic large cell lymphoma (ALK+ALCL), for which the normal cellular counterpart is believed to be mature T-cells. The expression of Sox2 in ALK+ALCL can be attributed to nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), the oncogenic fusion protein carrying a central pathogenetic role in these tumors. By confocal microscopy, Sox2 protein was detectable in virtually all cells in ALK+ALCL cell lines. However, the transcriptional activity of Sox2, as assessed using a Sox2-responsive reporter construct, was detectable only in a small proportion of cells. Importantly, downregulation of Sox2 using short interfering RNA in isolated Sox2active cells, but not Sox2inactive cells, resulted in a significant decrease in cell growth, invasiveness and tumorigenicity. To conclude, ALK+ALCL represents the first example of a hematologic malignancy that aberrantly expresses Sox2, which represents a novel mechanism by which NPM-ALK mediates tumorigenesis. We also found that the transcriptional activity and oncogenic effects of Sox2 can be heterogeneous in cancer cells.

Fatty acid synthase (FASN), a key player in the de novo synthetic pathway of long-chain fatty acids, has been shown to contribute to the tumorigenesis in various types of solid tumors. We here report that FASN is highly and consistently expressed in mantle cell lymphoma (MCL), an aggressive form of B-cell lymphoid malignancy. Specifically, the expression of FASN was detectable in all four MCL cell lines and 15 tumors examined. In contrast, benign lymphoid tissues and peripheral blood mononuclear cells from normal donors were negative. Treatment of MCL cell lines with orlistat, a FASN inhibitor, resulted in significant apoptosis. Knockdown of FASN expression using siRNA, which also significantly decreased the growth of MCL cells, led to a dramatic decrease in the cyclin D1 level. β-catenin, which has been previously reported to be upregulated in a subset of MCL tumors, contributed to the high level of FASN in MCL cells, Interesting, siRNA knock-down of FASN in turn down-regulated β-catenin. In conclusion, our data supports the concept that FASN contributes to the pathogenesis of MCL, by collaborating with β-catenin. In view of its high and consistent expression in MCL, FASN inhibitors may hold promises for treating MCL.

The online version of this article has a Supplementary Appendix. BackgroundThe role of b-catenin in cancer has been most studied in tumors of epithelial cell origin. The functional status and biological significance of this protein in anaplastic lymphoma kinase (ALK)-positive anaplastic large cell lymphoma is unknown. Design and MethodsALK-positive anaplastic large cell lymphoma cell lines and patients' tumor samples were examined for status of b-catenin expression and signaling. The subcellular localization of b-catenin was assessed using immunohistochemistry, sub-cellular fractionation and confocal microscopy, while its transcriptional activity was studied using the TOPFlash/FOPFlash luciferase reporter assay. To examine the biological significance of b-catenin, short interfering RNA was used to knock-down its expression; the resulting biological effects were studied using trypan-blue exclusion and MTS assay, and the impact on its various downstream targets was assessed using quantitative real-time polymerase chain reaction and western blots. Resultsb-catenin was transcriptionally active in three of three ALK-positive anaplastic large cell lymphoma cell lines, and this finding correlates with the nuclear localization of b-catenin in these cells and the neoplastic cells identified in most of the patients' tumor samples. b-catenin is biologically significant in ALK-positive anaplastic large cell lymphoma, since down-regulation of b-catenin resulted in a significant reduction in their cell growth. Down-regulation of b-catenin led to a marked reduction in both the total protein level and the activated/phosphorylated form of STAT3, another signaling protein previously shown to be important in the pathogenesis of ALK-positive anaplastic large cell lymphoma. In contrast to some of the oncogenic tyrosine kinases, modulation of nucleophosmin-anaplastic lymphoma kinase expression did not result in any detectable change in the protein level, nuclear localization or tyrosine phosphorylation of b-catenin; however, inhibition of nucleophosmin-anaplastic lymphoma kinase expression significantly down-regulated the transcriptional activity of b-catenin. Conclusionsb-catenin signaling is constitutively active in ALK-positive anaplastic large cell lymphoma and represents a previously unknown mechanism by which the high levels of STAT3 expression and activation in these tumors are sustained. Our results suggest that the interaction between oncogenic tyrosine kinases and various cell signaling proteins may be more complex than previously believed.

Mantle cell lymphoma (MCL) is a specific type of aggressive B-cell non-Hodgkin lymphoma. We recently found that IL-22RA1, one of the two subunits of the interleukin 22 (IL-22) receptor, is expressed in MCL cell lines but not benign lymphocytes. In view of normal functions of IL-22 signaling, we hypothesized that the aberrant expression of IL-22RA1 may contribute to the deregulation of various cell signaling pathways, thereby promoting cell growth in MCL. In this study, we first demonstrated the expression of IL-22RA1 in all three MCL cell lines and eight frozen tumors examined using reverse transcription-polymerase chain reaction and Western blot analysis. In support of the concept that IL-22 signaling is biologically important in MCL, we found that MCL cells treated with recombinant IL-22 had a significant increase in cell growth that was associated with STAT3 activation. To investigate the mechanism underlying the aberrant expression of IL-22RA1, we analyzed the gene promoter of IL-22RA1, and we found multiple binding sites for NF-κB, a transcriptional factor strongly implicated in the pathogenesis of MCL. Pharmacologic inhibition of NF-κB resulted in a substantial reduction in the level of IL-22RA1 protein expression in MCL cells. To conclude, IL-22RA is aberrantly expressed in MCL, and we have provided evidence that IL-22 signaling contributes to the pathogenesis of MCL.