Comprehensive genomic analysis reveals molecular heterogeneity in pediatric ALK-positive anaplastic large cell lymphoma

Anaplastic large cell lymphoma (ALCL) is a mature T-cell lymphoma that accounts for for 10-15% of childhood lymphomas. Despite the observation that more than 90% of pediatric cases harbor the anaplastic lymphoma kinase (ALK) rearrangement resulting in aberrant ALK kinase expression, there is significant clinical, morphologic, and biological heterogeneity. To gain insights into the genomic aberrations and molecular heterogeneity within ALK-positive ALCL(ALK+ ALCL), we analyzed 46 pediatric ALK+ ALCLs by whole-exome sequencing, RNA-sequencing, and DNA methylation profiling. Whole-exome sequencing found on average 25 SNV/Indel events per sample with recurring genetic events in regulators of DNA damage (TP53, MDM4), transcription (JUNB), and epigenetic regulators (TET1, KMT2B, KMT2A, KMT2C, KMT2E). Gene expression and methylation profiling consistently subclassified ALK+ ALCLs into two groups characterized by diferential ALK expression levels. The ALK-low group showed enrichment of pathways associated with immune response, cytokine signaling, and a hypermethylated predominant pattern compared to the ALK- high group, which had more frequent copy number changes, and was enriched with pathways associated with cell growth, proliferation, metabolic pathways, and. Taken together, these findings suggest that there is molecular heterogeneity within pediatric ALK+ALCL, predicting distinct biological mechanisms that may provide novel insights into disease pathogenesis and represent prognostic markers.

Malignant Progression of an Ancestral Bone Marrow Clone Harboring a CIC-NUTM2A Fusion in Isolated Myeloid Sarcoma

Myeloid sarcoma is a rare condition consisting of extramedullary myeloid blasts found in association with acute myeloid leukemia or, in the absence of bone marrow involvement. We identified an infant with isolated myeloid sarcoma whose bone marrow was negative for involvement by flow cytometry. Sequencing revealed the fusion oncogene CIC-NUTM2A and identified the sarcoma to be clonally evolved from the bone marrow, which carried the fusion despite the absence of pathology. Murine modeling confirmed the ability of the fusion to transform hematopoietic cells and identified receptor tyrosine kinase (RTK) signaling activation consistent with disruption of the CIC transcriptional repressor. These findings extend the definition of CIC-rearranged malignancies to include hematologic disease, provide insight into the mechanism of oncogenesis, and demonstrate the importance of molecular analysis and tracking of bone marrow involvement over the course of treatment in myeloid sarcoma, including patients that lack flow cytometric evidence of leukemia at diagnosis.

IMPLICATIONS

This study illustrates molecular involvement of phenotypically normal bone marrow in myeloid sarcoma, which has significant implications in clinical care. Further, it extends the definition of CIC-rearrangements to include hematologic malignancies and shows evidence of RTK activation that may be exploited therapeutically in cancer(s) driven by these fusions.

Case Report: The First Case Report of Visceral Leishmaniasis in Cambodia

Leishmaniasis is considered a neglected tropical disease that is commonly found in Asia, Africa, South America, and Mediterranean countries. Visceral leishmaniasis (VL) is the most severe form of the disease and is almost universally fatal if left untreated. The symptoms of VL overlap with many infectious diseases, malignancies, and other blood disorders. The most common findings include fever, cytopenias, and splenomegaly. Given the nonspecific symptoms, the diagnosis requires detailed laboratory investigations, including bone marrow examination, that can be challenging in low- and middle-income countries. Diagnostic limitations likely lead to the underdiagnosis or delay in diagnosis of VL. We describe, to our knowledge, the first case report of VL in Cambodia in a child presenting with fever, anemia, and thrombocytopenia. The diagnosis required a liver biopsy and multiple bone marrow biopsies to visualize intracellular Leishmania spp. Our case illustrates the diagnostic challenges and the importance of timely diagnosis. This case also highlights the need for heightened awareness of the diagnostic findings of VL and improved reporting of tropical diseases.

ALK+ Anaplastic Large Cell Lymphoma (ALCL)-Derived Exosomes Carry ALK Signaling Proteins and Interact with Tumor Microenvironment

Simple Summary

ALK+ anaplastic large cell lymphoma (ALK+ ALCL) is a distinct type of aggressive non-Hodgkin lymphoma of T-cell origin, which is characterized by overexpression and activation of ALK kinase due to chromosomal translocations of the gene. The most frequent chromosomal aberration is the t(2;5) resulting in the NPM-ALK chimeric protein, which exerts its oncogenic functions through activation of multiple oncogenic pathways. Exosomes, the best characterized type of extracellular vesicles, are secreted from the tumor cells, thus transferring signals to other cells that uptake exosomes. In this study, we demonstrate that ALK+ ALCL cells secrete exosomes that carry critical molecules of ALK signaling, which can be taken up by other cells with significant biologic effects including functional interactions with tumor microenvironment cells, which may contribute to tumor aggressiveness and possibly resistance to treatment.

Abstract

The oncogenic pathways activated by the NPM-ALK chimeric kinase of ALK+ anaplastic large cell lymphoma (ALCL) are well characterized; however, the potential interactions of ALK signaling with the microenvironment are not yet known. Here we report that ALK+ ALCL-derived exosomes contain critical components of ALK signaling as well as CD30, and that exosome uptake by lymphoid cells led to increased proliferation and expression of critical antiapoptotic proteins by the recipient cells. The bone marrow fibroblasts highly uptake ALK+ ALCL-derived exosomes and acquire a cancer-associated fibroblast (CAF) phenotype. Moreover, exosome-mediated activation of stromal cells altered the cytokine profile of the microenvironment. These interactions may contribute to tumor aggressiveness and possibly resistance to treatment.

It Takes a Village

OBJECTIVES

Partnerships between low- to middle-income countries (LMICs) and high-income countries (HICs) is one strategy to mitigate observed health disparities. Cambodia's Angkor Hospital for Children (AHC), an LMIC institution, faces shortages in health care resources, including pathology services. A partnership was created with Children's Wisconsin (CW), an HIC hospital, including provision of pathology services. We describe our established pathology workflow, examine cases seen in AHC patients, and evaluate the impact of CW's interpretations.

METHODS

AHC provides clinical history and impression and ships samples to CW, which processes the samples, and pathologists provide interpretations, sending reports electronically to AHC. For analysis, final diagnoses were considered "concordant," "refined," or "discordant" based on agreement with the clinical impression. Cases were also classified as "did not change management" or "changed management" based on how CW interpretation affected clinical management.

RESULTS

We included 347 specimens (177 malignant, 146 benign, 24 insufficient for diagnosis). Of these cases, 31% were discordant and 44% of cases with clinical follow-up had a change in management with CW interpretation.

CONCLUSIONS

Inclusion of pathology services in LMIC-HIC partnerships is crucial for resolving health disparities between the institutions involved. The described partnership and established pathology workflow can be adapted to the needs and resources of many institutions.

A complex KMT2A::AFF3 fusion resulting from a three-way chromosomal rearrangement in pediatric B lymphoblastic leukemia

The KMT2A::AFF3 fusion, t(2;11)(q11.2;q23.2), is a very rare fusion occurring in pediatric B-cell acute lymphoblastic leukemia (B-ALL). Our patient is a 2-year-old male who presented with three weeks of intermittent fever. Bone marrow biopsy showed 82% blasts and cytogenetic analysis demonstrated a complex 3-way chromosomal rearrangement involving KMT2A and an unknown fusion partner. Molecular testing identified the fusion partner as AFF3, a FLT3-TKD non-D835 mutation, and an NF1 mutation. This case demonstrates a highly complex three-way variant translocation resulting in the rare KMT2A::AFF3 fusion with only a few cases previously described in the literature.

MDMX/MDM4 is highly expressed and contributes to cell growth and survival in anaplastic large cell lymphoma

We hypothesized that murine double minute X (MDMX), a negative p53-regulator, may be involved in dysfunctional p53-signaling in anaplastic large cell lymphoma (ALCL), anaplastic lymphoma kinase (ALK)-positive and ALK-negative, characterized frequently by non-mutated TP53 (wt-p53). By western blot analysis, MDMX was highly expressed in ALK + ALCL and expressed at variable levels in ALK- ALCL cell lines. By immunohistochemistry, high MDMX levels were observed more frequently in ALK + ALCL (36/46; 78%), compared with ALK- ALCL tumors (12/29; 41%) (p < .0018, Mann-Whitney-test). FISH analysis showed MDMX-amplification in 1 of 13 (8%) ALK- ALCL tumors, and low-level MDMX copy gains in 2 of 13 (15%) ALK- ALCL and 3 of 11 (27%) ALK + ALCL tumors. MDMX-pharmacologic inhibition or siRNA-mediated MDMX-silencing were associated with activated p53 signaling, growth inhibition and apoptotic cell death in wt-p53 ALCL cells, providing evidence that targeting MDMX may provide a new therapeutic approach for ALCL patients with wt-p53.

Pathology and genetics of anaplastic large cell lymphoma

Anaplastic large cell lymphomas are a rare subtype of peripheral/mature T-cell lymphomas which are clinically, pathologically and genetically heterogeneous. Both ALK-positive (ALK+) and ALK-negative (ALK-) ALCL are composed of large lymphoid cells with abundant cytoplasm and pleomorphic features with horseshoe-shaped and reniform nuclei. ALK+ ALCL were considered as a definite entity in the 2008 World Health Organization classification of hematopoietic and lymphoid tissues. ALK-ALCL was included as a provisional entity in the WHO 2008 edition and in the most recent 2017 edition, it is now considered a distinct entity that includes cytogenetic subsets that appear to have prognostic implications (e.g. 6p25 rearrangements at IRF4/DUSP22 locus). ALK+ ALCLs are distinct in epidemiology and pathogenetic origin and should be distinguished from ALK-ALCL, cutaneous ALCL and breast implant associated ALCL which have distinct clinical course and pathogenetic features. Breast implant-associated ALCL is now recognized as a new provisional entity distinct from other ALK-ALCL; notably that it is a noninvasive disease associated with excellent outcome. In this article, we will provide an overview of the salient themes relevant to the pathology and genetic mechanisms in ALCL.

Immunophenotypic Analysis of Peripheral T-Cell Lymphomas: A Single-Center Retrospective Review of Flow Cytometric Analysis

Background

Peripheral T-cell lymphomas (PTCLs) are heterogenous, mature T-cell neoplasms that are a diagnostic challenge, requiring a combination of morphologic assessment and ancillary studies. Flow cytometry (FC) is a tool used routinely in lymphoma diagnosis; however, most analyses are limited to B-cell evaluation and pathologists generally lack experience evaluating for PTCL. We aimed to describe the immunophenotypic aberrancies observed by FC in PTCL.

Design

PTCLs with FC were collected, excluding primary leukemic processes. Four- and eight-color FC data were reanalyzed with the following antigens (when available): CD2, CD3, CD4, CD5, CD7, CD8, CD30, CD45, CD45RO, CD56, and CD57. Lymphoma cells were compared to normal T cells and an isotype control. Antigen expression was defined as >20%.

Results

Thirty-eight cases were analyzed (29 males, 9 females, 6-86 years, median 62 years), including 29 PTCLs NOS, 4 angioimmunoblastic T-cell lymphomas (AITLs), 3 anaplastic large cell lymphomas, 1 δγ-TCL, and 1 hepatosplenic TCL from 15 bone marrows, 14 lymph nodes, 6 bloods, 2 fluids, and 1 skin. Twenty cases were CD4+, 4 were CD8+, 3 were dual +, and 10 were dual –. Thirty-seven cases (97%) showed global aberrant antigen patterns, median 4 aberrancies/case (1-8). Lymphoma cells accounted for 0.07% to 68% (median 2.6%) of total events. Aberrant CD7 expression was present in 34 of 38 (89%) and was underexpressed in 22 of 34 (65%). CD3 and CD5 were aberrant in 79% of cases each, with two-thirds showing underexpression. CD2 and CD45RO were aberrant in two-thirds of PTCLs, with overexpression in 61% and 92% of those cases, respectively. One AITL showed no aberrancies.

Conclusions

Nearly all PTCLs show immunophenotypic aberrancy compared to normal T cells. Most commonly, PTCL showed aberrant underexpression of CD7, CD3, and CD5 and overexpression of CD2 and CD45RO. Our data support FC panels with CD2, CD3, CD4, CD5, CD7, CD8, and CD45RO to optimize recovery of aberrant T cells.

MicroRNA-17 acts as a tumor chemosensitizer by targeting JAB1/CSN5 in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is the breast cancer subtype with the poorest prognosis. Evidence indicates that aberrant JAB1/CSN5 expression is associated with advanced tumor stage and poor prognosis in breast cancer. In this study, we evaluated expression of JAB1 in TNBC and potential mechanisms regulating this expression. We found that miR-17 expression was lower in TNBC than in normal breast tissue, and miR-17 expression in patients with TNBC was associated with a good prognosis. Furthermore, JAB1 expression was regulated by miR-17 in TNBC cells, and mice with miR-17-overexpressing tumors had less tumor growth and lower tumor JAB1 expression than control mice. We also demonstrated that miR-17 suppressed JAB1's oncogenic function, leading to tumor growth inhibition and sensitizing TNBC cells to chemotherapy treatment. JAB1 knockdown in TNBC cells mimicked the effect of miR-17 overexpression and led to significant decreases in cell proliferation, colony formation, and migration, increased p27 expression, and enhanced cisplatin sensitivity. Our findings suggest that miR-17 acts as a tumor suppressor by directly targeting JAB1 in TNBC; this may lead to novel therapeutic targets and strategies for treating TNBC patients.

Germline deletion of ETV6 in familial acute lymphoblastic leukemia

Recent studies have identified germline mutations in TP53, PAX5, ETV6, and IKZF1 in kindreds with familial acute lymphoblastic leukemia (ALL), but the genetic basis of ALL in many kindreds is unknown despite mutational analysis of the exome. Here, we report a germline deletion of ETV6 identified by linkage and structural variant analysis of whole-genome sequencing data segregating in a kindred with thrombocytopenia, B-progenitor acute lymphoblastic leukemia, and diffuse large B-cell lymphoma. The 75-nt deletion removed the ETV6 exon 7 splice acceptor, resulting in exon skipping and protein truncation. The ETV6 deletion was also identified by optimal structural variant analysis of exome sequencing data. These findings identify a new mechanism of germline predisposition in ALL and implicate ETV6 germline variation in predisposition to lymphoma. Importantly, these data highlight the importance of germline structural variant analysis in the search for germline variants predisposing to familial leukemia.

Two-year-old female with EBV-positive diffuse large B-cell lymphoma and subsequent CNS involvement with neurolymphomatosis

We describe a case of Epstein-Barr virus (EBV) positive, diffuse large B-cell lymphoma in a 2-year-old female who went on to develop relapsed/refractory central nervous system (CNS) disease, manifesting as cranial nerve neurolymphomatosis. Although her atypical presentation was thought to be associated with an immune deficiency, extensive work-up was negative. Despite subsequent treatment with third-party EBV-specific cytotoxic T-lymphocytes, she died of progressive disease. This case report raises questions as to whether tailored treatment approaches should be considered for atypical presentations of pediatric lymphoma (e.g., CNS and virus-associated).

Detection of an Abnormal Myeloid Clone by Flow Cytometry in Familial Platelet Disorder With Propensity to Myeloid Malignancy

OBJECTIVES

To report aberrant myeloblasts detected by flow cytometry immunophenotypic studies in an asymptomatic patient with familial platelet disorder with propensity to myeloid malignancy, a rare autosomal dominant disease caused by germline heterozygous mutations in Runt-related transcription factor 1.

METHODS

Morphologic evaluation, flow cytometry immunophenotypic studies, nanofluidics-based qualitative multiplex reverse transcriptase polymerase chain reaction, Sanger sequencing, and next-generation sequencing-based mutational hotspot analysis of 53 genes were performed on bone marrow biopsy and aspirate samples.

RESULTS

Flow cytometry immunophenotypic analysis showed 0.6% CD34+ blasts with an abnormal immunophenotype: CD13 increased, CD33+, CD38 decreased, CD117 increased, and CD123 increased.

CONCLUSIONS

The acquisition of new phenotypic aberrancies in myeloblasts as detected by flow cytometry immunophenotypic studies might be a harbinger of impending myelodysplastic syndrome or acute myeloid leukemia in a patient with familial platelet disorder with propensity to myeloid malignancy.

Constitutive control of AKT1 gene expression by JUNB/CJUN in ALK+ anaplastic large-cell lymphoma: a novel crosstalk mechanism

Anaplastic lymphoma kinase-positive (ALK+) anaplastic large-cell lymphoma (ALCL) is an aggressive T-cell non-Hodgkin lymphoma characterized by the t(2;5), resulting in the overexpression of nucleophosmin (NPM)-ALK, which is known to activate the phosphatidylinositol-3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway, resulting in cell cycle and apoptosis deregulation. ALK+ ALCL is also characterized by strong activator protein-1 (AP-1) activity and overexpression of two AP-1 transcription factors, CJUN and JUNB. Here, we hypothesized that a biologic link between AP-1 and AKT kinase may exist, thus contributing to ALCL oncogenesis. We show that JUNB and CJUN bind directly to the AKT1 promoter, inducing AKT1 transcription in ALK+ ALCL. Knockdown of JUNB and CJUN in ALK+ ALCL cell lines downregulated AKT1 mRNA and promoter activity and was associated with lower AKT1 protein expression and activation. We provide evidence that this is a transcriptional control mechanism shared by other cell types even though it may operate in a way that is cell context-specific. In addition, STAT3 (signal transducer and activator of transcription 3)-induced control of AKT1 transcription was functional in ALK+ ALCL and blocking of STAT3 and AP-1 signaling synergistically affected cell proliferation and colony formation. Our findings uncover a novel transcriptional crosstalk mechanism that links AP-1 and AKT kinase, which coordinate uncontrolled cell proliferation and survival in ALK+ ALCL.

Functional inhibition of BCL2 is needed to increase the susceptibility to apoptosis to SMO inhibitors in diffuse large B-cell lymphoma of germinal center subtype

Previously, we have demonstrated that inhibition of Hedgehog pathway induces predominantly apoptosis in diffuse large B-cell lymphoma (DLBCL) cell lines of activated B-cell (ABC) type but predominantly cell cycle arrest in those of germinal center (GC). Here, we explored the possibility of overcoming the resistance to apoptosis to SMO inhibitors in five DLBCL cells of GC type using the combination of the SMO inhibitor HhAntag (Genentech Inc) with the BH3 mimetic ABT-737 (Abbott Laboratories). As controls we have used two DLBCL of ABC type (OCI-LY10 and OCI-LY3). Combinatorial treatments were performed with increasing concentrations of the HhAntag with low doses (equal or less than the IC20) of ABT-737. MTS assays were used to detect changes in cell viability and Annexin-V and PARP1 cleavage assays were used to detect apoptosis. Combining low doses of ABT-737 with increasing concentrations of HhAntag in GC DLBCL cell lines resulted in significantly increase of apoptosis in comparison to treatments with the SMO inhibitor alone. We concluded that in GC DLBCL cell lines, in contrast to those of ABC type, functional inhibition of BCL2 family members is usually needed to overcome the resistance to apoptosis to SMO inhibitors. These findings provide a rationale to explore the use of SMO and BCL2 inhibitors as adjuvant therapy for treatment of DLBCL of GC type.

TP53 pathway analysis in paediatric Burkitt lymphoma reveals increased MDM4 expression as the only TP53 pathway abnormality detected in a subset of cases

The TP53 (p53) pathway can be inhibited by TP53 mutation or deletion or by MDM2 overexpression. Both occur in Burkitt lymphoma (BL), but many cases lack either abnormality. Expression patterns of the TP53 inhibitor MDM4 have not been reported in BL, and increased MDM4 could deregulate the TP53 pathway in cases without TP53 or MDM2 abnormalities. We investigated TP53 pathway disruption in paediatric BL patient samples (n = 30) by studying MDM4, MDM2, and CDKN1A (p21) protein and mRNA expression; TP53 mutations; TP53 protein expression; and gene copy number abnormalities. MDM4 protein was expressed in 30/30 tumours, and MDM2 protein was weakly expressed in 7/30 (23%). All cases were negative for CDKN1A protein, and CDKN1A mRNA levels were decreased. TP53 mutations were detected in 5/28 (18%) cases and confirmed by sequencing. TP53 protein was expressed in 15/30 (50%) cases, including 7/8 with TP53 genetic alterations. MDM2 protein and mRNA expression levels did not correlate with lack of TP53 genetic changes or TP53 protein expression; however, there was an inverse relationship between detectable TP53 protein expression and MDM4 copy number gains and mRNA expression. The TP53 pathway is deregulated in paediatric BL cases, and increased MDM4 expression may be the primary mechanism in some cases.

Extracavitary/solid variant of primary effusion lymphoma

Primary effusion lymphoma (PEL) is a distinct clinicopathologic entity associated with human herpesvirus 8 (HHV8) infection that mostly affects patients with immunodeficiency. Primary effusion lymphoma usually presents as a malignant effusion involving the pleural, peritoneal, and/or pericardial cavities without a tumor mass. Rare cases of HHV8-positive lymphoma with features similar to PEL can present as tumor masses in the absence of cavity effusions and are considered to represent an extracavitary or solid variant of PEL. Here, we report 3 cases of extracavitary PEL arising in human immunodeficiency virus-infected men. Two patients had lymphadenopathy and underwent lymph node biopsy. One patient had a mass involving the ileum and ascending colon. In lymph nodes, the tumor was predominantly sinusoidal. The tumor involving the ileum and ascending colon presented as 2 masses, 12.5 × 10.6 × 2.6 cm in the colon and 3.6 × 2.7 × 1.9 cm in the ileum. In each case, the neoplasms were composed of large anaplastic cells, and 2 cases had "hallmark cells." Immunohistochemistry showed that all cases were positive for HHV8 and CD138. One case also expressed CD4 and CD30, and 1 case was positive for Epstein-Barr virus-encoded RNA. Evidence of B-cell differentiation was poorly developed in all tumors. These cases highlight the importance of assessing HHV8 in an anaplastic tumor that arises in a human immunodeficiency virus-positive patient and further contributes to the limited literature currently available for extracavitary PEL.

Expression patterns of endothelin-1 and its receptors in colorectal cancer

BACKGROUND AND OBJECTIVES

Endothelin-1 (ET-1), a potent vasoconstricting peptide, plays an important role in carcinogenesis. Previous in vitro studies have shown that colorectal cancer cells produce ET-1.

METHODS

ET-1 and its receptors ET-A (ET(A) R) and ET-B (ET(B) R) were analyzed in colorectal cancer cell lines and tumors by Western blot and immunohistochemistry. Also, ET-1 levels were measured by ELISA in blood samples collected before and after tumor resection.

RESULTS

ET-1 was immunohistochemically expressed by tumor cells at a variable level in 39 cases tested. The adjacent normal mucosa was negative for ET-1 expression. Strong ET(A) R expression observed in the deeper infiltrating areas at the periphery of neoplastic tissue correlated significantly with tumor stage. ET(B) R levels were very low or undetectable. Western blot analysis in paired (normal, tumor) fresh-frozen samples of colorectal cancers and in four colon carcinoma cell lines confirmed these findings. In addition, lower levels of ET-1 in the peripheral circulation after the tumor resection were found by ELISA as compared to those observed before surgery.

CONCLUSIONS

ET-1 and ET(A) R, but not ET(B) R, are expressed at a higher level in primary and cultured colon carcinoma cells as compared to normal colon mucosa cells. Further functional studies are needed to explore the role of ET-1/ET(A) R axis in colon carcinogenesis.

Yolk sac tumor of the thyroid gland: a case report

Extragonadal yolk sac tumors are uncommon and usually seen in sacrococcygeal, mediastinal, intracranial, and retroperitoneal sites. Yolk sac tumors of the head and neck region are rare, and the few reported cases have arisen in neonates or infants in conjunction with a teratoma or other germ cell tumor subtypes. We report a unique case of a pure yolk sac tumor presenting as a primary lesion in the right thyroid lobe of a 10-year-old girl. The diagnosis was suspected after fine-needle aspiration, and extensive sampling of the thyroidectomy specimen revealed no teratoma or other germ cell tumor. Serum α-fetoprotein levels were markedly elevated 6 days after excision, and imaging disclosed numerous bilateral pulmonary nodules suggestive of metastatic disease but did not reveal a mediastinal mass. The tumor has shown a favorable response to bleomycin, etoposide, and cisplatin chemotherapy. To the best of our knowledge, this is the 1st description of a primary pure yolk sac tumor of the thyroid.

mTOR signaling is activated by FLT3 kinase and promotes survival of FLT3-mutated acute myeloid leukemia cells

Activating mutations of the FLT3 gene mediate leukemogenesis, at least in part, through activation of PI3K/AKT. The mammalian target of rapamycin (mTOR)-Raptor signaling pathway is known to act downstream of AKT. Here we show that the mTOR effectors, 4EBP1, p70S6K and rpS6, are highly activated in cultured and primary FLT3-mutated acute myeloid leukemia (AML) cells. Introduction of FLT3-ITD expressing constitutively activated FLT3 kinase further activates mTOR and its downstream effectors in BaF3 cells. We also found that mTOR signaling contributes to tumor cell survival, as demonstrated by pharmacologic inhibition of PI3K/AKT/mTOR, or total silencing of the mTOR gene. Furthermore, inhibition of FLT3 kinase results in downregulation of mTOR signaling associated with decreased survival of FLT3-mutated AML cells. These findings suggest that mTOR signaling operates downstream of activated FLT3 kinase thus contributing to tumor cell survival, and may represent a promising therapeutic target for AML patients with mutated-FLT3.

Essential roles of Jab1 in cell survival, spontaneous DNA damage and DNA repair

Jun activation domain-binding protein 1 (JAB1) is a multifunctional protein that participates in the control of cell proliferation and the stability of multiple proteins. JAB1 overexpression has been implicated in the pathogenesis of human cancer. JAB1 regulates several key proteins and thereby produces varied effects on cell cycle progression, genome stability and cell survival. However, the biological significance of JAB1 activity in these cellular signaling pathways is unclear. Therefore, we developed mice that were deficient in Jab1 and analyzed the null embryos and heterozygous cells. This disruption of Jab1 in mice resulted in early embryonic lethality due to accelerated apoptosis. Loss of Jab1 expression sensitized both mouse primary embryonic fibroblasts and osteosarcoma cells to γ-radiation-induced apoptosis, with an increase in spontaneous DNA damage and homologous recombination (HR) defects, both of which correlated with reduced levels of the DNA repair protein Rad51 and elevated levels of p53. Furthermore, the accumulated p53 directly binds to Rad51 promoter, inhibits its activity and represents a major mechanism underlying the HR repair defect in Jab1-deficient cells. These results indicate that Jab1 is essential for efficient DNA repair and mechanistically link Jab1 to the maintenance of genome integrity and to cell survival.

Cuplike nuclei (prominent nuclear invaginations) in acute myeloid leukemia are highly associated with FLT3 internal tandem duplication and NPM1 mutation

BACKGROUND

A small subset of patients with acute myeloid leukemia (AML) have cuplike nuclei. Other investigators have demonstrated that these neoplasms have distinctive clinicopathologic and molecular features.

METHODS

The authors searched for patients who had AML with cuplike nuclei at their institution over a 10-year interval. A strict definition for cuplike nuclei was used: >or=10% blasts with nuclear invaginations in >or=25% of the nuclear area. The relevant data were reviewed, and the results were compared with a control group of patients who had AML without cuplike nuclei.

RESULTS

In total, 22 patients who had AML with cuplike nuclei were identified and were classified as AML without maturation (French-American-British classification M1) (AML M1). Compared with the control group (AML M1), patients who had AML with cuplike nuclei were associated significantly with fms-like tyrosine kinase 3 (FLT3)-internal tandem duplication (ITD) (86% vs 38%, respectively; P = .002); nucleophosmin 1 (NPM1) mutations (86% vs 19%; P < .0001); both mutations (77% vs 14%; P < .0001); normal karyotype (86% vs 40%; P = .003); bone marrow blast count (90% vs 84%; P = .016); myeloperoxidase positivity (95% vs 30% blasts; P = .001); higher D-dimer levels (>5000 ng/mL vs 569 ng/mL; P = .001); and the absence of CD7 (91% vs 52%; P = .007), CD34 (82% vs 5%; P < .0001), and human leukocyte antigen, D-related (59% vs 10%; P = .001). There were no differences in age, sex, or peripheral blood counts. The positive predictive value of recognizing AML with cuplike nuclei for FLT3-ITD, NPM1, and both mutations was 81%, 86%, and 77%, respectively.

CONCLUSIONS

Cuplike nuclei in AML were highly associated with the presence of NPM1 and FLT3-ITD mutations and with several clinicopathologic and immunophenotypic features. Recognition of the distinctive morphologic features of AML with cuplike nuclei may be helpful in streamlining the workup of these neoplasms.

Expression of eukaryotic initiation factor 4E predicts clinical outcome in patients with mantle cell lymphoma treated with hyper-CVAD and rituximab, alternating with rituximab, high-dose methotrexate, and cytarabine

BACKGROUND

Oncogenic AKT/mammalian target of rapamycin (mTOR) signaling has recently been shown to contribute to tumor survival and proliferation in mantle cell lymphoma (MCL) through its downstream effector eukaryotic initiation factor 4E (eIF4E), which may control cyclin D1 protein levels. However, the clinical significance of eIF4E expression in MCL is unknown.

METHODS

The authors investigated the prognostic significance of eIF4E expression in 70 MCL patients uniformly treated with hyper-CVAD and rituximab, alternating with the rituximab, high-dose methotrexate, and cytarabine regimen (R-hyper-CVAD). eIF4E expression was assessed using tissue biopsy specimens obtained before treatment, immunohistochemical methods, and a highly specific monoclonal antibody. Failure-free (FFS) and overall (OS) survival were used as endpoints in univariate and multivariate survival analysis.

RESULTS

High eIF4E expression was found in 28 (40%) MCL tumors. After a median follow-up of 51 months for survivors, the 5-year FFS was 20.6% for patients with high eIF4E expression, compared with 63.5% for patients with low or no eIF4E expression (P=.01, log-rank). Similarly, the 5-year OS was 40.1% for patients with high eIF4E expression, compared with 73.8% for patients with low or no eIF4E expression (P=.018, log-rank). In multivariate analysis, eIF4E expression was associated with poorer FFS and OS, along with age>60 years and high beta2-microglobulin in the final prognostic model.

CONCLUSIONS

In summary, eIF4E, which seems to recapitulate most of the biologic effects of mTOR signaling in MCL, is an independent predictor of clinical outcome in MCL patients uniformly treated with the R-hyper-CVAD regimen.

Inhibition of p53-murine double minute 2 interaction by nutlin-3A stabilizes p53 and induces cell cycle arrest and apoptosis in Hodgkin lymphoma

PURPOSE

p53 is frequently expressed but rarely mutated in Hodgkin and Reed-Sternberg (HRS) cells of Hodgkin's lymphoma (HL). p53 protein levels are regulated by murine double minute 2 (MDM2) through a well-established autoregulatory feedback loop. In this study, we investigated the effects of nutlin-3A, a recently developed small molecule that antagonizes MDM2 and disrupts the p53-MDM2 interaction, on p53-dependent cell cycle arrest and apoptosis in cultured HRS cells.

EXPERIMENTAL DESIGN

HL cell lines carrying wild-type (wt) or mutated p53 gene were treated with the potent MDM2 inhibitor nutlin-3A or a 150-fold less active enantiomer, nutlin-3B.

RESULTS

We show that nutlin-3A, but not nutlin-3B, stabilizes p53 in cultured HRS cells carrying wt p53 gene resulting in p53-dependent cell cycle arrest and apoptosis. Cell cycle arrest was associated with up-regulation of the cyclin-dependent kinase inhibitor p21. Nutlin-3A-induced apoptotic cell death was accompanied by Bax and Puma up-regulation and caspase-3 cleavage and was abrogated, in part, by inhibition of caspase-9 and caspase-3 activity. By contrast, no effects on cell cycle or apoptosis were found in HL cell lines harboring mutated p53 gene. Furthermore, combined treatment with nutlin-3A and doxorubicin revealed enhanced cytotoxicity in HRS cells with wt p53 gene. Blocking of nuclear export by leptomycin B, or inhibition of proteasome by MG132, stabilized p53 at a level comparable with that of nutlin-3A treatment in HRS cells with wt p53.

CONCLUSIONS

These data suggest that nutlin-3A stabilized p53 by preventing MDM2-mediated p53 degradation in HRS cells. wt p53 stabilization and activation by nutlin-3A may be a novel therapeutic approach for patients with HL.

NPM-ALK oncogenic kinase promotes cell-cycle progression through activation of JNK/cJun signaling in anaplastic large-cell lymphoma

Anaplastic large-cell lymphoma (ALCL) frequently carries the t(2;5)(p23;q35), resulting in aberrant expression of nucleophosmin-anaplastic lymphoma kinase (NPM-ALK). We show that in 293T and Jurkat cells, forced expression of active NPM-ALK, but not kinase-dead mutant NPM-ALK (210K>R), induced JNK and cJun phosphorylation, and this was linked to a dramatic increase in AP-1 transcriptional activity. Conversely, inhibition of ALK activity in NPM-ALK(+) ALCL cells resulted in a concentration-dependent dephosphorylation of JNK and cJun and decreased AP-1 DNA-binding. In addition, JNK physically binds NPM-ALK and is highly activated in cultured and primary NPM-ALK(+) ALCL cells. cJun phosphorylation in NPM-ALK(+) ALCL cells is mediated by JNKs, as shown by selective knocking down of JNK1 and JNK2 genes using siRNA. Inhibition of JNK activity using SP600125 decreased cJun phosphorylation and AP-1 transcriptional activity and this was associated with decreased cell proliferation and G2/M cell-cycle arrest in a dose-dependent manner. Silencing of the cJun gene by siRNA led to a decreased S-phase cell-cycle fraction associated with upregulation of p21 and downregulation of cyclin D3 and cyclin A. Taken together, these findings reveal a novel function of NPM-ALK, phosphorylation and activation of JNK and cJun, which may contribute to uncontrolled cell-cycle progression and oncogenesis.

Differential expression of the human MIXL1 gene product in non-Hodgkin and Hodgkin lymphomas

The Mix1 homeobox-like (MIXL1) gene encodes a paired class homeobox transcription factor that is involved in embryogenesis. Previous studies have shown that the MIXL1 gene product is expressed in B- and T-cell progenitors of normal bone marrow and, in some cell lines derived from hematopoietic neoplasms. The status of MIXL1 expression and subcellular localization in human lymphomas is unknown. Using a highly specific antibody, we assessed for MIXL1 expression in lymphoma cell lines of B- and T-cell lineage by reverse transcriptase-polymerase chain reaction, Western blot analysis, and immunohistochemistry. We also assessed for MIXL1 expression using immunohistochemical methods in 193 lymphoid tumors, including 140 B-cell non-Hodgkin lymphomas (NHL), 36 T-cell NHL, and 17 Hodgkin lymphomas (HL). MIXL1 was detected predominantly in the nuclear fraction of all cell lines tested and was predominantly nuclear in primary tumor specimens. Based on the distribution of the staining results (histogram), a 50% cutoff was selected for high versus low MIXL1 expression. High MIXL1 expression was detected more frequently in Burkitt lymphoma and diffuse large B-cell lymphoma compared with other types of B-cell NHL (P < .0001, chi(2) test). Most cases of T-cell NHL and all cases of HL also highly expressed MIXL1. Most plasma cell myelomas were negative for MIXL1, but rare cases had low MIXL1 expression. MIXL1 expression significantly correlated with proliferation index (Ki-67) in B-cell NHL (P < .0001). The frequent and high expression of MIXL1 in aggressive B-cell NHL, T-cell NHL, and HL suggests that MIXL1 may be involved in lymphomagenesis.

c-Jun Expression and Activation are Restricted to CD30+ Lymphoproliferative Disorders

Cellular Jun (c-Jun), a member of the JUN family, is an activator protein-1 transcription factor involved in cell differentiation, proliferation, and apoptosis that can be activated by phosphorylation at serine-73 and -63 residues. Using tissue microarrays and immunohistochemistry, we investigated c-Jun expression and serine-73 phosphorylation in 112 CD30 lymphomas and 232 CD30 lymphomas of B- or T-cell lineage, and 24 cases of lymphomatoid papulosis. c-Jun was expressed exclusively by CD30 lymphoproliferative disorders including 41/41 (100%) classical Hodgkin lymphoma (cHL), 20/23 (87%) anaplastic lymphoma kinase (ALK)+ anaplastic large cell lymphoma (ALCL), 18/26 (69%) ALK- ALCL, 5/9 (56%) primary cutaneous ALCL, 4/11 (36%) CD30 diffuse large B-cell lymphoma (DLBCL), and 11/24 (46%) cases of lymphomatoid papulosis. The percentage of c-Jun-positive tumor cells was highest in cHL and ALCL (P=0.002). In contrast, all CD30 lymphomas, including nodular lymphocyte predominant HL and CD30 non-Hodgkin lymphomas of B- or T-cell lineage were negative for c-Jun. Serine-73 phosphorylated c-Jun (p-c-Jun), the activated form of c-Jun, was expressed more frequently and at a higher level in cHL and ALK+ ALCL than other CD30 tumors. The percentage of p-c-Jun-positive tumor cells correlated significantly with the percentage of total c-Jun-positive cells (P<0.0001), suggesting that activated c-Jun positively regulates total c-Jun levels in CD30 lymphomas through a well-established positive feedback loop. We conclude that CD30 lymphomas are characterized by common patterns of c-Jun expression and activation suggesting a potential role of c-Jun in the pathogenesis of these tumors.

Activation of mammalian target of rapamycin signaling promotes cell cycle progression and protects cells from apoptosis in mantle cell lymphoma

Mantle cell lymphoma (MCL) is characterized by the t(11;14) and cyclin D1 overexpression. However, additional molecular events are most likely required for oncogenesis, possibly through cell cycle and apoptosis deregulation. We hypothesized that mammalian target of rapamycin (mTOR) is activated in MCL and contributes to tumor proliferation and survival. In MCL cell lines, pharmacological inhibition of the phosphoinositide 3-kinase/AKT pathway was associated with decreased phosphorylation (activation) of mTOR and its downstream targets phosphorylated (p)-4E-BP1, p-p70S6 kinase, and p-ribosomal protein S6, resulting in apoptosis and cell cycle arrest. These changes were associated with down-regulation of cyclin D1 and the anti-apoptotic proteins cFLIP, BCL-XL, and MCL-1. Furthermore, silencing of mTOR expression using mTOR-specific short interfering RNA decreased phosphorylation of mTOR signaling proteins and induced cell cycle arrest and apoptosis. Silencing of eukaryotic initiation factor (eIF4E), a downstream effector of mTOR, recapitulated these results. We also assessed mTOR signaling in MCL tumors using immunohistochemical methods and a tissue microarray: 10 of 30 (33%) expressed Ser473p-AKT, 13 of 21 (62%) Ser2448p-mTOR, 22 of 22 (100%) p-p70S6K, and 5 of 20 (25%) p-ribosomal protein S6. Total eIF4E binding protein 1 and eukaryotic initiation factor 4E were expressed in 13 of 14 (93%) and 16 of 29 (55%) MCL tumors, respectively. These findings suggest that the mTOR signaling pathway is activated and may contribute to cell cycle progression and tumor cell survival in MCL.

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.

c-FLIP confers resistance to FAS-mediated apoptosis in anaplastic large-cell lymphoma

We hypothesized that inhibition of the FAS-mediated apoptosis pathway by FLICE-like inhibitory protein (c-FLIP) may contribute to oncogenesis in ALK+ anaplastic large-cell lymphoma (ALCL). Treatment with increasing concentrations of CH-11 (CD95/FAS agonistic antibody) had no effect on cell viability of 2 ALK+ ALCL cell lines, Karpas 299 and SU-DHL1, each expressing high levels of c-FLIP. However, inhibition of endogenous c-FLIP expression by specific c-FLIP siRNA in Karpas 299 and SU-DHL1 cells treated with CH-11 resulted in FAS-mediated cell death associated with increased annexin V binding, apoptotic morphology, and cleavage of caspase-8. In 26 ALK+ ALCL tumors, assessed for expression of DISC-associated proteins, CD95/FAS and c-FLIP were commonly expressed, in 23 (92%) of 25 and 21 (91%) of 23 tumors, respectively. By contrast, CD95L/FASL was expressed in only 3 (12%) of 26 ALCL tumors, although it was strongly expressed by surrounding small reactive lymphocytes. Our findings suggest that overexpression of c-FLIP protects ALK+ ALCL cells from death-receptor-induced apoptosis and may contribute to ALCL pathogenesis.

Selective inhibition of STAT3 induces apoptosis and G(1) cell cycle arrest in ALK-positive anaplastic large cell lymphoma

Nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) is an aberrant fusion gene product expressed in a subset of cases of anaplastic large cell lymphoma (ALCL). It has been shown that NPM-ALK binds to and activates signal transducer and activator of transcription 3 (STAT3) in vitro, and that STAT3 is constitutively active in ALK(+) ALCL cell lines and tumors. In view of the oncogenic potential of STAT3, we further examined its biological significance in ALCL using two ALK(+) ALCL cell lines (Karpas 299 and SU-DHL-1) and an adenoviral vector that carries dominant-negative STAT3 (AdSTAT3DN). Infection by AdSTAT3DN led to the expression of STAT3DN in both ALK(+) ALCL cell lines at a similar efficiency. Subcellular fractionation studies showed that a significant proportion of the expressed STAT3DN protein translocated to the nucleus, despite the fact that STAT3DN has a mutation at residue 705(tyrosine --> phenylalanine), a site that is believed to be crucial for STAT3 activation and nuclear translocation. Introduction of STAT3DN induced apoptosis and G(1) cell cycle arrest. Western blot studies showed that expression of STAT3DN resulted in caspase-3 cleavage, downregulation of Bcl-2, Bcl-xL, cyclin D3, survivin, Mcl-1, c-Myc and suppressor of cytokine signaling 3. These results support the concept that STAT3 activation is pathogenetically important in ALCL cells by deregulating the expression of multiple target proteins that are involved in the control of apoptosis and cell cycle progression.

Differential expression and clinical significance of tyrosine-phosphorylated STAT3 in ALK+ and ALK- anaplastic large cell lymphoma

PURPOSE

Recent data suggest that nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) activates signal transducers and activators of transcription 3 (STAT3) directly, and ALK expression correlates with STAT3 activation in non-Hodgkin's lymphomas. In this study, we evaluated comprehensively STAT3 activation status in anaplastic large cell lymphoma (ALCL) cell lines and pretreatment ALCL tumors.

EXPERIMENTAL DESIGN

The study included five ALK(+)ALCL cell lines and 80 systemic ALCL tumors (31 ALK(+), 49 ALK(-)) that were formalin fixed and paraffin embedded. All 80 patients with systemic ALCL were treated with doxorubicin-based chemotherapy. The STAT3 activation status in cell lines was determined using Western blots and an antibody that reacts specifically with the phosphorylated tyrosine 705 of STAT3, pSTAT3(tyr705). In ALCL tumors, STAT3 was considered active when > or =20% of neoplastic cells show unequivocal nuclear immunostaining for pSTAT3(tyr705).

RESULTS

All five ALK(+)ALCL cell lines showed strong pSTAT3(tyr705) expression on Western blots. In systemic ALCL, STAT3 activation was detected in 49 of 80 (61%) ALCL tumors: 26 of 31 (84%) ALK(+) tumors and 23 of 49 (47%) ALK(-) tumors. ALK expression correlated significantly with STAT3 activation (P < 0.0001). Clinical follow-up data were available for 72 patients. In the ALK(-) group, the lack of STAT3 activation correlated with a favorable 5-year overall survival (P = 0.0076) but not failure-free survival. In the ALK(+) group, patients with inactive STAT3 showed a trend toward longer overall survival (P = 0.09) and failure-free survival (P = 0.19). Importantly, all five ALK(+) ALCL patients with inactive STAT3 survived without treatment failure after a median follow-up of 83 months.

CONCLUSIONS

STAT3 activation correlates with but is not strictly dependent on ALK expression in ALCL. Lack of STAT3 activation appears to correlate with a favorable clinical outcome in ALCL.

Inhibition of JAK3 induces apoptosis and decreases anaplastic lymphoma kinase activity in anaplastic large cell lymphoma

Signal transducer and activator of transcription 3 (STAT3), normally activated by Janus kinase (JAK) in response to cytokine stimulation, has been shown to have oncogenic potential. In addition to JAK, recent data suggest that STAT3 can also be activated by other proteins such as the aberrant fusion protein, NPM-ALK, which is expressed in a subset of systemic anaplastic large cell lymphoma (ALCL). In this study, we investigated the possible role of JAK in activating STAT3 in ALCL using two ALK-positive ALCL cell lines, Karpas 299 and SU-DHL-1. At the steady state, JAK3 showed detectable tyrosine phosphorylation by immunoprecipitation. Treatment with AG490, a JAK inhibitor, decreased but did not completely abrogate tyrosine phosphorylation of JAK3 and STAT3 in a concentration-dependent manner. Similar results were obtained using two other inhibitors of JAK3, WHI-P131 and WHI-P154. These biochemical changes were associated with apoptosis in both cell lines that was coupled with activation of caspase 3 and decreased bcl-xL and bcl-2. Cell cycle analysis revealed a decrease in the S phase, which may be attributed to cyclin D3 downregulation and p21(waf1) upregulation. Importantly, the tyrosine kinase activity of NPM-ALK, as assessed by an in vitro assay, decreased with increasing concentrations of AG490. Our findings highlight the importance of JAK3 in activating STAT3 in ALCL, and that NPM-ALK-mediated activation of STAT3 is influenced by the functional status of JAK3.

Characterization of 4 mantle cell lymphoma cell lines

CONTEXT

Mantle cell lymphoma (MCL) is a distinct type of B-cell non-Hodgkin lymphoma characterized by t(11;14)(q13;q32) and cyclin D1 overexpression. The pathogenesis of MCL has not been comprehensively studied, which can be attributed in part to the paucity of well-characterized MCL cell lines.

OBJECTIVES

We collected 4 previously developed MCL cell lines and performed extensive characterization, including the susceptibly of these cell lines to transduction by adenovirus vectors. Our aim was to facilitate the establishment of an in vitro model that can be reliably used to study the pathogenesis of MCL.

METHODS

Standard techniques were used to compare the morphologic, immunophenotypic, and cytogenetic features of the 4 cell lines. In addition, Western blotting was used to investigate the presence of several cell cycle- and apoptosis-related proteins. TP53 DNA sequencing was also performed on the cell lines. The adenoviral transduction efficiency was assessed using an adenoviral vector carrying the gene encoding for the green fluorescence protein (Ad-GFP).

RESULTS

All cell lines demonstrated evidence of t(11;14)(q13;q32) and overexpression of cyclin D1. Cyclin D2 was not detectable in all cell lines, whereas cyclin D3 was weakly expressed in JeKo-1 and SP-53. Other abnormalities of the cell cycle G1 phase regulatory pathway were detected, including loss of expression of p53 (JeKo-1) and p16(INK4a) (SP-53 and Granta 519), as well as TP53 mutation (Mino). All cell lines express high levels of cyclin E, c-Myc, Bcl-2, Bax, Bcl-x(L), and Mcl-1. Retinoblastoma protein is hyperphosphorylated in all cell lines. With the exception of Mino, MCL cell lines are highly transducible with adenoviral vectors.

CONCLUSION

These cell lines are representative of MCL and can be used as an in vitro model to further explore the pathogenesis of this disease. The susceptibility of these cell lines to gene transfer provides opportunities to evaluate the importance of various oncogenes and tumor suppressor genes that may have an impact on developing effective therapeutic regimens for MCL.

Expression of STAT3 and its phosphorylated forms in mantle cell lymphoma cell lines and tumours

The pathogenesis of mantle cell lymphoma (MCL) is incompletely understood, although cyclin D1 overexpression leading to deregulated cell proliferation is probably important. Recent data suggest that interleukin (IL)-10 can increase the proliferative activity of MCL cells. STAT3 (signal transducer and activator of transcription 3) is the signal transducer of IL-10, and STAT3 is activated by phosphorylation. The hypothesis of this study is that STAT3 is activated in MCL. The expression of the two phosphorylated (i.e. active) forms of STAT3, pSTAT3-tyr (phosphorylated at the tyrosine(705) residue) and pSTAT3-ser (phosphorylated at the serine(727) residue), was assessed in four MCL cell lines and 12 MCL tumours using western blots and/or immunofluorescence staining techniques. All MCL cell lines expressed STAT3, but only one had detectable pSTAT3-tyr and none had pSTAT3-ser. Addition of IL-10 rapidly resulted in expression of pSTAT3-tyr but not pSTAT3-ser. All eight cases of frozen MCL tumours examined had detectable pSTAT3-tyr and pSTAT3-ser. Immunofluorescence studies using four formalin-fixed, paraffin wax-embedded MCL tumours demonstrated cytoplasmic localization of STAT3, as opposed to the nuclear localization of the pSTAT3 species. In conclusion, these findings provide evidence that STAT3 is constitutively activated in MCL, supporting the concept that STAT3 signalling may be important in the pathogenesis of these tumours.