Incidence of homogeneously staining regions in non-Hodgkin lymphomas

Association of prolactin receptor (PRLR) variants with prolactinomas

Prolactinomas are the most frequent type of pituitary tumors, which represent 10-20% of all intracranial neoplasms in humans. Prolactinomas develop in mice lacking the prolactin receptor (PRLR), which is a member of the cytokine receptor superfamily that signals via Janus kinase-2-signal transducer and activator of transcription-5 (JAK2-STAT5) or phosphoinositide 3-kinase-Akt (PI3K-Akt) pathways to mediate changes in transcription, differentiation and proliferation. To elucidate the role of the PRLR gene in human prolactinomas, we determined the PRLR sequence in 50 DNA samples (35 leucocytes, 15 tumors) from 46 prolactinoma patients (59% males, 41% females). This identified six germline PRLR variants, which comprised four rare variants (Gly57Ser, Glu376Gln, Arg453Trp and Asn492Ile) and two low-frequency variants (Ile76Val, Ile146Leu), but no somatic variants. The rare variants, Glu376Gln and Asn492Ile, which were in complete linkage disequilibrium, and are located in the PRLR intracellular domain, occurred with significantly higher frequencies (P < 0.0001) in prolactinoma patients than in 60 706 individuals of the Exome Aggregation Consortium cohort and 7045 individuals of the Oxford Biobank. In vitro analysis of the PRLR variants demonstrated that the Asn492Ile variant, but not Glu376Gln, when compared to wild-type (WT) PRLR, increased prolactin-induced pAkt signaling (>1.3-fold, P < 0.02) and proliferation (1.4-fold, P < 0.02), but did not affect pSTAT5 signaling. Treatment of cells with an Akt1/2 inhibitor or everolimus, which acts on the Akt pathway, reduced Asn492Ile signaling and proliferation to WT levels. Thus, our results identify an association between a gain-of-function PRLR variant and prolactinomas and reveal a new etiology and potential therapeutic approach for these neoplasms.

Anti-apoptotic role and clinical relevance of neurotrophins in diffuse large B-cell lymphomas

Background:

Diffuse large B-cell lymphoma (DLBCL) is a fatal malignancy that needs to identify new targets for additional therapeutic options. This study aimed to clarify the clinical and biological significance of endogenous neurotrophin (nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF)) in DLBCL biopsy samples and cell lines.

Methods:

We analysed expression of NGF, BDNF, and their receptors (Trk, p75^NTR) in 51 biopsies and cell lines by immunohistochemistry, immunofluorescence, and western blotting. To investigate the biological role of BDNF/TrkB/p75^NTR axis, effects of neurotrophin signalling inhibition were determined on tumour cell survival and vascular endothelial growth factor (VEGF) secretion. The pharmacological pan-Trk inhibitor K252a was used for in vitro and in vivo studies.

Results:

A BDNF/TrkB axis was expressed in all biopsies, which was independent of the germinal centre B-cell (GCB)/non-GCB profile. p75^NTR, TrkB, and BDNF tumour scores were significantly correlated and high NGF expression was significantly associated with MUM1/IRF4, and the non-GCB subtype. Diffuse large B-cell lymphoma cell lines co-expressed neurotrophins and their receptors. The full-length TrkB receptor was found in all cell lines, which was also phosphorylated at Tyr-817. p75^NTR was associated to Trk and not to its cell death co-receptor sortilin. In vitro, inhibition of neurotrophin signalling induced cell apoptosis. K252a caused cell apoptosis, decreased VEGF secretion, and potentiated rituximab effect, notably in less rituximab-sensitive cells. In vivo, K252a significantly reduced tumour growth and potentiated the effects of rituximab in a GCB-DLBCL xenograft model.

Conclusions:

This work argues for a pro-survival role of endogenous neurotrophins in DLBCLs and inhibition of Trk signalling might be a potential treatment strategy for rituximab resistant subgroups.

Targeting the PI3K pathway for cancer therapy

The PI3K pathway plays an important role in key cellular functions such as cell growth, proliferation and survival. Genetic and epigenetic alterations in different pathway components lead to aberrant pathway activation and have been observed in high frequencies in various tumor types. Consequently, significant effort has been made to develop antineoplastic agents targeting different nodes in this pathway. Additionally, PI3K pathway status may have predictive and prognostic implications, and may contribute to drug resistance in tumor cells. This article provides an overview of our current knowledge of the PI3K pathway with an emphasis on its application in cancer treatment.

The role of microRNA-150 as a tumor suppressor in malignant lymphoma

MicroRNA (miRNA; miR) is a class of small regulatory RNA molecules, the aberrant expression of which can lead to the development of cancer. We recently reported that overexpression of miR-21 and/or miR-155 leads to activation of the phosphoinositide 3-kinase (PI3K)-AKT pathway in malignant lymphomas expressing CD3(-)CD56(+) natural killer (NK) cell antigen. Through expression analysis, we show in this study that in both NK/T-cell lymphoma lines and samples of primary lymphoma, levels of miR-150 expression are significantly lower than in normal NK cells. To examine its role in lymphomagenesis, we transduced miR-150 into NK/T-cell lymphoma cells, which increased the incidence of apoptosis and reduced cell proliferation. Moreover, the miR-150 transductants appeared senescent and showed lower telomerase activity, resulting in shortened telomeric DNA. We also found that miR-150 directly downregulated expression of DKC1 and AKT2, reduced levels of phosphorylated AKT(ser473/4) and increased levels of tumor suppressors such as Bim and p53. Collectively, these results suggest that miR-150 functions as a tumor suppressor, and that its aberrant downregulation induces continuous activation of the PI3K-AKT pathway, leading to telomerase activation and immortalization of cancer cells. These findings provide new insight into the pathogenesis of malignant lymphoma.

Rituximab inhibits the constitutively activated PI3K-Akt pathway in B-NHL cell lines: involvement in chemosensitization to drug-induced apoptosis

Rituximab (chimeric anti-CD20 monoclonal antibody) is currently being used, alone or in combination with chemotherapy, in the treatment of B-non-Hodgkin's lymphoma (B-NHL). We have reported that rituximab treatment of B-NHL cell lines sensitizes the drug-resistant tumor cells to apoptosis by various chemotherapeutic drugs and chemosensitization was, in large part, owing to the selective inhibition of the anti-apoptotic Bcl-(XL) gene product. The constitutive activation of the Akt pathway in B-NHL results in overexpression and functional activation of Bcl-(xL). Hence, we hypothesized that rituximab-induced inhibition of Bcl-(xL) expression and chemosensitization may result, in part, from its inhibitory activity of the Akt pathway. This hypothesis was tested using the drug-resistant Ramos and Daudi B-NHL cell lines. Time kinetic analysis revealed that treatment with rituximab inhibited phosphorylation of Akt, but not unphosphorylated Akt, and the inhibition was first detected at 6 h post-rituximab treatment. Similar time kinetics revealed rituximab-induced inhibition of p-PDK1, p-Bad, p-IKKalpha/beta and p-Ikappabetaalpha and no inhibition of unphosphorylated proteins. In addition, rituximab treatment resulted in significant increase of Bcl-(xL)-Bad heterodimeric complexes as compared to untreated cells. The role of the Akt pathway in the regulation of resistance was corroborated by the use of the Akt inhibitor, LY294002, and by transfection with siRNA Akt. Treatment of tumor cells with LY294002 or with Akt siRNA, but not control siRNA, resulted in inhibition of Bcl-(xL) expression and sensitization to drug-induced apoptosis. Although rituximab did not inhibit the Akt pathway nor sensitized the rituximab-resistant Ramos RR1 clone, treatment with LY294002 or Akt siRNA sensitized the clone to drug-induced apoptosis. The present findings demonstrate for the first time that rituximab inhibits the constitutively activated Akt pathway in B-NHL cell lines, and this inhibition contributes to sensitization of drug-resistant cells to apoptosis by chemotherapeutic drugs. The findings also identify the Akt pathway as target for therapeutic intervention in the reversal of rituximab and drug-resistant B-NHL.

Perturbations of the AKT signaling pathway in human cancer

AKT/PKB (protein kinase B) kinases mediate signaling pathways downstream of activated tyrosine kinases and phosphatidylinositol 3-kinase. AKT kinases regulate diverse cellular processes including cell proliferation and survival, cell size and response to nutrient availability, tissue invasion and angiogenesis. Many oncoproteins and tumor suppressors implicated in cell signaling/metabolic regulation converge within the AKT signal transduction pathway in an equilibrium that is altered in many human cancers by activating and inactivating mechanisms, respectively, targeting these inter-related proteins. We review a burgeoning literature implicating aberrant AKT signaling in many sporadic human cancers as well as in several dominantly inherited cancer syndromes known as phakomatoses. The latter include disorders caused by germline mutations of certain tumor suppressor genes, that is, PTEN, TSC2/TSC1, LKB1, NF1, and VHL, encoding proteins that intersect with the AKT pathway. We also review various pathogenic mechanisms contributing to activation of the AKT pathway in human malignancy as well as current pharmacologic strategies to target therapeutically components of this pathway.

Activation of AKT kinases in cancer: implications for therapeutic targeting

The AKT1, AKT2, and AKT3 kinases have emerged as critical mediators of signal transduction pathways downstream of activated tyrosine kinases and phosphatidylinositol 3-kinase. An ever-increasing list of AKT substrates has precisely defined the multiple functions of this kinase family in normal physiology and disease states. Cellular processes regulated by AKT include cell proliferation and survival, cell size and response to nutrient availability, intermediary metabolism, angiogenesis, and tissue invasion. All these processes represent hallmarks of cancer, and a burgeoning literature has defined the importance of AKT alterations in human cancer and experimental models of tumorigenesis, continuing the legacy represented by the original identification of v-Akt as the transforming oncogene of a murine retrovirus. Many oncoproteins and tumor suppressors intersect in the AKT pathway, finely regulating cellular functions at the interface of signal transduction and classical metabolic regulation. This careful balance is altered in human cancer by a variety of activating and inactivating mechanisms that target both AKT and interrelated proteins. Reprogramming of this altered circuitry by pharmacologic modulation of the AKT pathway represents a powerful strategy for rational cancer therapy. In this review, we summarize a large body of data, from many types of cancer, indicating that AKT activation is one of the most common molecular alterations in human malignancy. We also review mechanisms of activation of AKT kinases, examples of therapeutic modulation of the AKT pathway in animal models, and the current status of efforts to target molecular components of the AKT pathway for cancer therapy and, possibly, cancer prevention.

Molecular cytogenetic characterization of the mantle cell lymphoma cell line GRANTA-519

Combining fluorescence R-banding, fluorescence in situ hybridization and spectral karyotyping allowed us to precisely define chromosomal breakpoints, gains, losses and a newly detected amplification in the human mantle cell lymphoma (MCL) cell line GRANTA-519. GRANTA-519 is characterized by the t(11;14)(q13;q32) resulting in overexpression of cyclin D1, a key player in cell cycle control. Hitherto unresolved complex rearrangements involve 1p, 1q, 3cen, 9p, 11q, 12p, 12q, 16p, 17p, and 18cen. Moreover, a 4- to 6-fold gain of sequences on 18q leads to a low-level amplification of the BCL2 gene and to an overexpression of the BCL2 protein. These results provide the basis for the identification of not only candidate oncogenes responsible for MCL in gained regions, but also for the identification of putative tumor suppressor genes in commonly deleted regions like 1p22, which would eventually enable functional studies of these genes.

Abnormal dicentric chromosome with co-amplification of sequences from chromosomes 11 and 19: a novel rearrangement in a patient with myelodysplastic syndrome transforming to acute myeloid leukemia

A 66-year-old man with a myelodysplastic syndrome transforming to acute myeloid leukemia showed a complex abnormal karyotype on bone marrow aspirate. An unbalanced dicentric translocation with a very long der(11) long arm-dic(11;19)(q25;p13.4)-was present. Fluorescence in situ hybridization studies utilised paints for chromosomes 11 and 19 as well as the locus specific probe MLL, localised to 11q23. The abnormal chromosome 11q contained 6 copies of intact MLL and 6 copies of chromosome 19 (unidentified) sequences. To our knowledge, gene co-amplification of chromosomes 11 and 19 sequences has not been reported before.

An hsr on chromosome 7 was shown to be an insertion of four copies of the 11q23 MLL gene region in an HIV-related lymphoma

A 45-year-old male with AIDS presented with a cecal diffuse large B-cell lymphoma. Cytogenetic and flourescence in situ hybridization (FISH) studies revealed a complex karyotype with multiple aberrations that included a translocation, t(8;14) involving MYC on chromosome 14. This is specific to B-cell lymphomas. There were also frequently observed secondary changes such as chromosome 1 rearrangement leading to trisomy of 1q and loss of tp53 from the deleted chromosome 17. A unique secondary abnormality was an hsr on chromosome 7, which by FISH and SKY investigations was shown to originate from chromosome 11 involving 4 copies of the MLL gene region.

Analysis of secondary chromosomal alterations in 165 cases of follicular lymphoma with t(14;18)

Follicular lymphoma is characterized by the t(14;18) in up to 85% of cases. Almost all cases display evidence of secondary chromosomal alterations at initial diagnosis. The influence of recurrent secondary changes on disease progression has not been fully determined. The purpose of this study was to define the full spectrum of recurrent karyotypic events present at diagnosis in a large cohort of cases and to evaluate the sequence of cytogenetic evolution in relation to morphologic progression. A total of 165 cases of follicular lymphoma with t(14;18) were ascertained for which complete clinical information, histopathology, immunophenotype, and karyotype were available. One hundred sixty cases showed secondary alterations with an average of 7.9 additional changes per case. Recurrent alterations seen at the 10% or greater level included +X, +1q21-q44, +7, +12q, +18q, del(1)(p36), del(6q), del(10)(q22-q24), the development of polyploidy and sidelines, and the presence of extra marker chromosomes and chromosomal additions. Changes that correlated with morphologic progression included del(1)(p36), del(6q), del(10)(q22-q24), +7, the total number of abnormalities, the number of markers and additions, and the presence of polyploidy. The most frequent second event arising after the t(14;18) was duplication of the der(18)t(14;18). This study demonstrates that the number and type of secondary chromosomal alterations in follicular lymphoma is highly variable between cases, but that a relatively small number of changes are seen repeatedly in different combinations. A consistent pattern of cytogenetic evolution could not be identified. Potentially significant gene duplications or amplifications may be disguised within marker chromosomes and additions. Additional cytogenetic investigation is required to decipher the karyotypic complexity associated with the progression of follicular lymphoma.

Beta-HCG aberrant expression in primary mediastinal large B-cell lymphoma

We report on a primary mediastinal large B-cell lymphoma with aberrant expression of beta-human chorionic gonadotropin (beta-hCG). The patient, a 33-year-old man, had cough, dyspnea, fever, superior vena cava syndrome, and a mediastinal bulky tumor. A biopsy showed that the latter was characterized by large cells, sclerosis, and compartmentalization. The neoplastic elements expressed CD45, CD20, CD79a and, partially, CD30, whereas they were negative for CD3, epithelial membrane antigen and cytokeratins. Surprisingly, they displayed a clear-cut positivity for beta-hCG. The remaining oncofetal markers applied (PLAP and alpha1-fetoprotein) were negative. Electron microscopy demonstrated the presence of numerous nuclear pockets and the lack of intercellular junctions. DNA analysis by polymerase chain reaction showed clonal rearrangement of Ig heavy-chain genes. The patient responded promptly to the administration of MACOP-B. To the best of our knowledge, this is the first example of B-cell lymphoma showing positivity for beta-hCG; a similar aberrant expression was previously observed only in three Japanese patients with human T-cell lymphotropic virus type I+ adult T-cell lymphoma/leukemia. Because primary mediastinal large B-cell lymphoma has in the past been frequently confused with germ cell tumors, pathologists should be aware of possible beta-hCG expression by lymphomatous cells to avoid the risk of misdiagnosis.

Mechanism of protein kinase B activation by insulin/insulin-like growth factor-1 revealed by specific inhibitors of phosphoinositide 3-kinase--significance for diabetes and cancer

Protein kinase B (PKB) is a member of the second messenger subfamily of protein kinases. The three isoforms of PKB identified have an amino-terminal pleckstrin homology domain, a central kinase domain, and a carboxy-terminal regulatory domain. PKB is the major downstream target of receptor tyrosine kinases that signal via the phosphoinositide (PI) 3-kinase. The crucial role of lipid second messengers in PKB activation has been dissected through the use of the PI 3-kinase-specific inhibitors wortmannin and LY294002. Receptor-activated PI 3-kinase synthesises the lipid second messenger PI-3,4,5-trisphosphate, leading to the recruitment of PKB to the membrane. Membrane attachment of PKB is mediated by its pleckstrin homology domain binding to PI-3,4,5-trisphosphate or PI-3,4-bisphosphate with high affinity. Activation of PKB alpha and beta is then achieved at the plasma membrane by phosphorylation of Thr308/309 in the A-loop of the kinase domain and Ser473/474 in the carboxy-terminal regulatory region, respectively. The upstream kinase that phosphorylates PKB on Thr308, termed PI-dependent protein kinase-1, has been identified and extensively characterised. A candidate for the Ser473/474 kinase, termed the integrin-linked kinase, has been identified recently. Activated PKB is implicated in glucose metabolism, transcriptional control, and in the regulation of apoptosis in many different cell types. Stimulation of PKB activity protects cells from apoptosis by phosphorylation and inactivation of the pro-apoptotic protein BAD. These results could explain why PKB is overexpressed in some ovarian, breast, and pancreatic carcinomas.