Tcl1 enhances Akt kinase activity and mediates its nuclear translocation

TCL1A and ATM are co-expressed in chronic lymphocytic leukemia cells without deletion of 11q

Chronic lymphocytic leukemia is characterized by the accumulation of B cells that are resistant to apoptosis. This resistance is induced by pro-survival stimuli from the microenvironment. TCL1 and ATM are central to the pathogenesis of the disease and associated with more aggressive disease. Their protein products have recently been shown to physically interact in leukemic cells and to impact on NF-κB signaling, which is a key regulator of apoptosis. In the present study we show that TCL1 and ATM are significantly co-expressed and up-regulated in malignant cells compared to non-malignant B cells, and that expression of TCL1 is partially deregulated by aberrant DNA-methylation. In addition, complex external stimuli induce essentially similar TCL1 and ATM time-course kinetics. In line with a coordinative regulation of NF-κB signaling by TCL1, its knockdown induced apoptosis in primary leukemia cells. These findings suggest that both genes functionally cooperate to modulate similar apoptosis-related cellular pathways.

Overexpression of TCL1 activates the endoplasmic reticulum stress response: a novel mechanism of leukemic progression in mice

Chronic lymphocytic leukemia (CLL) represents 30% of adult leukemia. TCL1 is expressed in ~ 90% of human CLL. Transgenic expression of TCL1 in murine B cells (Eμ-TCL1) results in mouse CLL. Here we show for the first time that the previously unexplored endoplasmic reticulum (ER) stress response is aberrantly activated in Eμ-TCL1 mouse and human CLL. This includes activation of the IRE-1/XBP-1 pathway and the transcriptionally up-regulated expression of Derlin-1, Derlin-2, BiP, GRP94, and PDI. TCL1 associates with the XBP-1 transcription factor, and causes the dysregulated expression of the transcription factors, Pax5, IRF4, and Blimp-1, and of the activation-induced cytidine deaminase. In addition, TCL1-overexpressing CLL cells manufacture a distinctly different BCR, as we detected increased expression of membrane-bound IgM and altered N-linked glycosylation of Igα and Igβ, which account for the hyperactive BCR in malignant CLL. To demonstrate that the ER stress-response pathway is a novel molecular target for the treatment of CLL, we blocked the IRE-1/XBP-1 pathway using a novel inhibitor, and observed apoptosis and significantly stalled growth of CLL cells in vitro and in mice. These studies reveal an important role of TCL1 in activating the ER stress response in support for malignant progression of CLL.

Pediatric T-cell prolymphocytic leukemia with an isolated 12(p13) deletion and aberrant CD117 expression

T-cell Prolymphocytic leukemia (T-PLL) is a rare post-thymic T-cell malignancy that follows an aggressive clinical course. The classical presentation includes an elevated white blood cell (WBC) count with anemia and thrombocytopenia, hepatosplenomegaly, and lymphadenopathy. T-PLL is a disease of the elderly and to our knowledge it has never been described in the pediatric age group. We report a case of T-PLL in a 9 year old male who was initially diagnosed with T-cell acute lymphoblastic lymphoma (ALL), the diagnosis was later refined to T-PLL following additional analysis of bone marrow morphology and immunophenotype. Two unusual findings in our patient included CD117 expression and an isolated chromosomal 12(p13) deletion. The patient failed to respond to standard ALL induction chemotherapy, but achieved complete remission following treatment with a fludarabine and alemtuzumab-based regimen.

Aromatase inhibitors, estrogens and musculoskeletal pain: estrogen-dependent T-cell leukemia 1A (TCL1A) gene-mediated regulation of cytokine expression

Introduction

Arthralgias and myalgias are major side effects associated with aromatase inhibitor (AI) therapy of breast cancer. In a recent genome-wide association study, we identified SNPs - including one that created an estrogen response element near the 3' end of the T-cell leukemia 1A (TCL1A) gene - that were associated with musculoskeletal pain in women on adjuvant AI therapy for breast cancer. We also showed estrogen-dependent, SNP-modulated variation in TCL1A expression and, in preliminary experiments, showed that TCL1A could induce IL-17RA expression. In the present study, we set out to determine whether these SNPs might influence cytokine expression and effect more widely, and, if so, to explore the mechanism of TCL1A-related AI-induced side effects.

Methods

The functional genomic experiments performed included determinations of TCL1A, cytokine and cytokine receptor expression in response to estrogen treatment of U2OS cells and lymphoblastoid cell lines that had been stably transfected with estrogen receptor alpha. Changes in mRNA and protein expression after gene knockdown and overexpression were also determined, as was NF-κB transcriptional activity.

Results

Estradiol (E2) increased TCL1A expression and, in a TCL1A SNP-dependent fashion, also altered the expression of IL-17, IL-17RA, IL-12, IL-12RB2 and IL-1R2. TCL1A expression was higher in E2-treated lymphoblastoid cell lines with variant SNP genotypes, and induction of the expression of cytokine and cytokine receptor genes was mediated by TCL1A. Finally, estrogen receptor alpha blockade with ICI-182,780 in the presence of E2 resulted in greatly increased NF-κB transcriptional activity, but only in cells that carried variant SNP genotypes. These results linked variant TCL1A SNP sequences that are associated with AI-dependent musculoskeletal pain with increased E2-dependent TCL1A expression and with downstream alterations in cytokine and cytokine receptor expression as well as NF-κB transcriptional activity.

Conclusions

SNPs near the 3' terminus of TCL1A were associated with AI-dependent musculoskeletal pain. E2 induced SNP-dependent TCL1A expression, which in turn altered IL-17, IL-17RA, IL-12, IL-12RB2, and IL-1R2 expression as well as NF-κB transcriptional activity. These results provide a pharmacogenomic explanation for a clinically important adverse drug reaction as well as insights into a novel estrogen-dependent mechanism for the modulation of cytokine and cytokine receptor expression.

Tcl1 protein functions as an inhibitor of de novo DNA methylation in B-cell chronic lymphocytic leukemia (CLL)

B-cell chronic lymphocytic leukemia (CLL) is the most common human leukemia. Deregulation of the T-cell leukemia/lymphoma 1 oncogene (TCL1) in mouse B cells causes a CD5(+) leukemia similar to aggressive human CLL. To examine the mechanisms by which Tcl1 protein exerts its oncogenic activity in B cells, we performed proteomics experiments to identify its interacting partners. We found that Tcl1 physically interacts with de novo DNA methylthansferases Dnmt3A and Dnmt3B. We further investigated the effects of Tcl1 up-regulation on the enzymatic activity of Dnmt3A and found that Tcl1 overexpression drastically inhibits Dnmt3A function. In addition, B cells from TCL1 transgenic mice showed a significant decrease in DNA methylation compared with WT controls. Similarly, CLL samples with high Tcl1 expression showed a decrease in DNA methylation compared with CLL samples with low Tcl1 expression. Given the previous reports of inactivating mutations of DNMT3A in acute myelogenous leukemia and myelodysplastic syndrome, our results suggest that inhibition of de novo DNA methylation may be a common oncogenic mechanism in leukemogenesis.

The miR-29 family: genomics, cell biology, and relevance to renal and cardiovascular injury

The human miR-29 family of microRNAs has three mature members, miR-29a, miR-29b, and miR-29c. miR-29s are encoded by two gene clusters. Binding sites for several transcriptional factors have been identified in the promoter regions of miR-29 genes. The miR-29 family members share a common seed region sequence and are predicted to target largely overlapping sets of genes. However, the miR-29 family members exhibit differential regulation in several cases and different subcellular distribution, suggesting their functional relevance may not be identical. miR-29s directly target at least 16 extracellular matrix genes, providing a dramatic example of a single microRNA targeting a large group of functionally related genes. Strong antifibrotic effects of miR-29s have been demonstrated in heart, kidney, and other organs. miR-29s have also been shown to be proapoptotic and involved in the regulation of cell differentiation. It remains to be explored how various cellular effects of miR-29s determine functional relevance of miR-29s to specific diseases and how the miR-29 family members may function cooperatively or separately.

Interplay between HIV-1 infection and host microRNAs

Using microRNA array analyses of in vitro HIV-1-infected CD4⁺ cells, we find that several host microRNAs are significantly up- or downregulated around the time HIV-1 infection peaks in vitro. While microRNA-223 levels were significantly enriched in HIV-1-infected CD4⁺CD8⁻ PBMCs, microRNA-29a/b, microRNA-155 and microRNA-21 levels were significantly reduced. Based on the potential for microRNA binding sites in a conserved sequence of the Nef-3′-LTR, several host microRNAs potentially could affect HIV-1 gene expression. Among those microRNAs, the microRNA-29 family has seed complementarity in the HIV-1 3′-UTR, but the potential suppressive effect of microRNA-29 on HIV-1 is severely blocked by the secondary structure of the target region. Our data support a possible regulatory circuit at the peak of HIV-1 replication which involves downregulation of microRNA-29, expression of Nef, the apoptosis of host CD4 cells and upregulation of microRNA-223.

Tcl1 interacts with Atm and enhances NF-κB activation in hematologic malignancies

The T-cell leukemia/lymphoma 1 (TCL1) oncogene is a target of chromosomal translocations and inversions at 14q31.2, and its rearrangement in T cells causes T-cell prolymphocytic leukemias. TCL1 dysregulation in B cells is responsible for the development of an aggressive form of chronic lymphocytic leukemia (CLL), the most common human leukemia. We have investigated the mechanisms underlying the oncogenic functions of Tcl1 protein using a mass spectrometry approach and have identified Atm (ataxia-telangiectasia mutated) as a candidate Tcl1-interacting protein. The Tcl1-Atm complex formation was validated by coimmunoprecipitation experiments. Importantly, we show that the association of Atm with Tcl1 leads to enhanced IκBα phosphorylation and ubiquitination and subsequent activation of the NF-κB pathway. Our findings reveal functional cross-talk between Atm and Tcl1 and provide evidence for a novel pathway that could be targeted in leukemias and lymphomas.

MicroRNAs in thyroid cancer

CONTEXT

Traditionally, factors predisposing to diseases are either genetic ("nature") or environmental, also known as lifestyle-related ("nurture"). Papillary thyroid cancer is an example of a disease where the respective roles of these factors are surprisingly unclear.

EVIDENCE ACQUISITION

Original articles and reviews summarizing our current understanding of the role of microRNA in thyroid tumorigenesis are reviewed and evaluated.

CONCLUSION

The genetic predisposition to papillary thyroid cancer appears to consist of a variety of gene mutations that are mostly either of low penetrance and common or of high penetrance but rare. Moreover, they likely interact with each other and with environmental factors. The culpable genes may not be of the traditional, protein-coding type. A limited number of noncoding candidate genes have indeed been described, and we propose here that the failure to find mutations in traditional protein-coding genes is not coincidental. Instead, a more likely hypothesis is that changes in the expression of multiple regulatory RNA genes, e.g. microRNAs, may be a major mechanism. Our review of the literature strongly supports this notion in that a polymorphism in one microRNAs (miR-146a) predisposes to thyroid carcinoma, whereas numerous other microRNAs are involved in signaling (mainly PTEN/PI3K/AKT and T3/THRB) that is central to thyroid carcinogenesis.

AP-1 elements and TCL1 protein regulate expression of the gene encoding protein tyrosine phosphatase PTPROt in leukemia

We previously demonstrated that the gene encoding PTPROt, the truncated form of protein tyrosine phosphatase receptor type O expressed predominantly in hematopoietic cells, is a candidate tumor suppressor and is down-regulated in chronic lymphocytic leukemia (CLL). Here, we show that PTPROt expression is significantly reduced in CD19(+) spleen B cells from Eμ-T cell leukemia 1 (TCL1) transgenic mice relative to the wild-type mice. Strikingly, as much as a 60% decrease in PTPROt expression occurs at 7 weeks independently of promoter methylation. To elucidate the potential mechanism for this early suppression of PTPROt in these mice, we explored the role of activating protein-1 (AP-1) in its expression. We first demonstrate that AP-1 activation by 12-O-tetradecanoylphorbol-13-acetate induces PTPROt expression with concurrent recruitment of c-fos and c-jun to its promoter. The PTPROt promoter is also responsive to over- and underexpression of AP-1, confirming the role of AP-1 in PTPROt expression. Next, we demonstrate that TCL1 can repress the PTPROt promoter by altering c-fos expression and c-jun activation state. Finally, using primary CLL cells we have shown an inverse relationship between TCL1 and PTPROt expression. These findings further substantiate the role of TCL1 in PTPROt suppression and its importance in the pathogenesis of CLL.

An Akt-dependent increase in canonical Wnt signaling and a decrease in sclerostin protein levels are involved in strontium ranelate-induced osteogenic effects in human osteoblasts

Sclerostin is an important regulator of bone homeostasis and canonical Wnt signaling is a key regulator of osteogenesis. Strontium ranelate is a treatment for osteoporosis that has been shown to reduce fracture risk, in part, by increasing bone formation. Here we show that exposure of human osteoblasts in primary culture to strontium increased mineralization and decreased the expression of sclerostin, an osteocyte-specific secreted protein that acts as a negative regulator of bone formation by inhibiting canonical Wnt signaling. Strontium also activated, in an apparently separate process, an Akt-dependent signaling cascade via the calcium-sensing receptor that promoted the nuclear translocation of β-catenin. We propose that two discrete pathways linked to canonical Wnt signaling contribute to strontium-induced osteogenic effects in osteoblasts.

Aberrantly activated anti-apoptotic signalling mechanisms in chronic lymphocytic leukaemia cells: clues to the identification of novel therapeutic targets

Chronic lymphocytic leukaemia (CLL) is the commonest haematological malignancy in the western world and is incurable by cytotoxic therapy. Considerable research effort has identified the signal transduction pathways in CLL cells that contribute to anti-apoptotic signalling. Some pathways are constitutively activated in CLL cells but upregulated in normal cells only when protein tyrosine kinases (PTKs) are activated by ligands. This review describes which PTKs are aberrantly activated in CLL cells and are potential targets for inhibition. Additional potential targets within pathways downstream of these PTKs include Mek/Erk, mTorc1, protein kinase C, PI-3 kinase/Akt, nuclear factor-κB and cyclin-dependent protein kinase. Numerous studies have identified chemical agents and antibodies that selectively kill CLL cells, irrespective of their genetic resistance to conventional chemotherapeutic agents, and which can overcome cytoprotective microenvironmental signalling. These studies have resulted in identification of novel therapies, some of which are currently undergoing clinical trials. In vitro and animal model studies and clinical trials could determine which inhibitors of which targets are the likely to be most effective and least toxic either singly or in combination.

Inherited predisposition to chronic lymphocytic leukemia

Inherited susceptibility to chronic lymphocytic leukemia (CLL) has been recognized for decades. Approximately 10% of individuals with CLL report a family history of CLL or a related lymphoproliferative disorder, and genetic predisposition is the best understood risk factor for CLL. Studies of familial CLL have suggested that the disease features are largely similar to sporadic CLL, although recent data suggest that familial CLL may more commonly show somatic hypermutation of the immunoglobulin heavy-chain variable region, suggesting a more indolent disease course. Monoclonal B-cell lymphocytosis (MBL) has been identified recently as a likely precursor to CLL; it is found in the general population with increasing age and enriched in unaffected relatives of individuals with familial CLL. Studies of MBL as well as mouse models of CLL may lead to better understanding of early CLL pathogenesis that is relevant to familial predisposition. To date, the identification of genes that predispose to familial CLL has been slow, primarily due to the relatively few families available for study, the small size of those families and disease causation most likely by multiple genes that each confer smaller risks. In the coming years, the application of systematic genomics approaches to familial CLL should, hopefully, lead to the identification of novel loci involved in the disease.

Therapeutic Implications of Targeting AKT Signaling in Melanoma

Identification of key enzymes regulating melanoma progression and drug resistance has the potential to lead to the development of novel, more effective targeted agents for inhibiting this deadly form of skin cancer. The Akt3, also known as protein kinase B gamma, pathway enzymes regulate diverse cellular processes including proliferation, survival, and invasion thereby promoting the development of melanoma. Accumulating preclinical evidence demonstrates that therapeutic agents targeting these kinases alone or in combination with other pathway members could be effective for the long-term treatment of advanced-stage disease. However, currently, no selective and effective therapeutic agent targeting these kinases has been identified for clinical use. This paper provides an overview of the key enzymes of the PI3K pathway with emphasis placed on Akt3 and the negative regulator of this kinase called PTEN (phosphatase and tensin homolog deleted on chromosome 10). Mechanisms regulating these enzymes, their substrates and therapeutic implications of targeting these proteins to treat melanoma are also discussed. Finally, key issues that remain to be answered and future directions for interested researchers pertaining to this signaling cascade are highlighted.

Nuclear orphan receptor TLX induces Oct-3/4 for the survival and maintenance of adult hippocampal progenitors upon hypoxia

Hypoxia promotes neural stem cell proliferation, the mechanism of which is poorly understood. Here, we have identified the nuclear orphan receptor TLX as a mediator for proliferation and pluripotency of neural progenitors upon hypoxia. We found an enhanced early protein expression of TLX under hypoxia potentiating sustained proliferation of neural progenitors. Moreover, TLX induction upon hypoxia in differentiating conditions leads to proliferation and a stem cell-like phenotype, along with coexpression of neural stem cell markers. Following hypoxia, TLX is recruited to the Oct-3/4 proximal promoter, augmenting the gene transcription and promoting progenitor proliferation and pluripotency. Knockdown of Oct-3/4 significantly reduced TLX-mediated proliferation, highlighting their interdependence in regulating the progenitor pool. Additionally, TLX synergizes with basic FGF to sustain cell viability upon hypoxia, since the knockdown of TLX along with the withdrawal of growth factor results in cell death. This can be attributed to the activation of Akt signaling pathway by TLX, the depletion of which results in reduced proliferation of progenitor cells. Cumulatively, the data presented here demonstrate a new role for TLX in neural stem cell proliferation and pluripotency upon hypoxia.

Molecular basis of CLL

B-cell chronic lymphocytic leukemia (CLL), the most common leukemia in the Western world, results from an expansion of a rare population of CD5+ mature B-lymphocytes. CLL occurs in two forms, aggressive and indolent. For the most part indolent CLL is characterized by low ZAP-70 expression and mutated IgH V(H); aggressive CLL shows high ZAP-70 expression and unmutated IgH V(H). Although clinical features and genomic abnormalities in CLL have been studied extensively, molecular mechanisms underlying disease development are still emerging. In the last few years, several important insights were reported in this area. MiR-15/16 targeting BCL2 and MCL1 and DLEU7 targeting TNF pathway were proposed as tumor suppressors at 13q14, a commonly deleted region in indolent CLL. Molecular details of how activation of TCL1, a critical oncogene in aggressive CLL, results in the initiation of this malignancy were clarified. Importance of these pathways was supported by investigations of several mouse models of CLL. Here, we present what has been learned from these new pathways, discuss mouse CLL models and how these mouse models recapitulate the molecular mechanisms of this common leukemia.

Akt contributes to activation of the TRIF-dependent signaling pathways of TLRs by interacting with TANK-binding kinase 1

Toll/IL-1R domain-containing adaptor inducing IFN-β (TRIF) is an adaptor molecule that is recruited to TLR3 and -4 upon agonist stimulation and triggers activation of IFN regulatory factor 3 (IRF3) and expression of type 1 IFNs, which are critical for cellular antiviral responses. We show that Akt is a downstream molecule of TRIF/TANK-binding kinase 1 (TBK1) and plays an important role in the activation of IRF3 by TLR3 and -4 agonists. Blockade of Akt by a dominant-negative mutant or by short interfering RNA decreased IRF3 activation and IFN-β expression induced by polyinosinic:polycytidylic acid [poly(I:C)], LPS, TRIF, and TBK1. Association of endogenous TBK1 and Akt was observed in macrophages when stimulated with poly(I:C) and LPS. In vitro kinase assays combined with reversed-phase liquid chromatography mass spectrometry analysis showed that TBK1 enhanced phosphorylation of Akt on Ser(473), whereas knockdown of TBK1 expression by short interfering RNA in macrophages decreased poly(I:C)- and LPS-induced Akt phosphorylation. Embryonic fibroblasts derived from TBK1 knockout mice also showed impaired Akt phosphorylation in response to poly(I:C) and LPS. To our knowledge, our results demonstrate a new regulatory mechanism for Akt activation mediated by TBK1 and a novel role of Akt in TLR-mediated immune responses.

The PI3K-Akt-mTOR pathway in initiation and progression of thyroid tumors

The phosphoinositide-3 (OH) kinase (PI3K) signaling cascade is involved in regulating glucose uptake and metabolism, growth, motility, and other essential functions for cell survival. Unregulated activation of this pathway commonly occurs in cancer through a variety of mechanisms, including genetic mutations of kinases and regulatory proteins, epigenetic alterations that alter gene expression and translation, and posttranslational modifications. In thyroid cancer, constitutive activation of PI3K signaling has been shown to play a role in the genetic predisposition for thyroid neoplasia in Cowden's syndrome, and is recognized to be frequently overactivated in sporadic forms of thyroid cancer including those with aggressive clinical behaviors. In this review, the key signaling molecules in the PI3K signaling cascade, the abnormalities known to occur in thyroid cancer, and the potential for therapeutic targeting of PI3K pathway members will be discussed.

Distinct biological roles for the akt family in mammary tumor progression

The phosphatidylinositol 3' kinase/Akt pathway is frequently dysregulated in cancer, which can have unfavorable consequences in terms of cell proliferation, survival, metabolism, and migration. Increasing evidence suggests that Akt1, Akt2, and Akt3 play unique roles in breast cancer initiation and progression. We have recently shown that in contrast to Akt1, which accelerates mammary tumor induction in transgenic mice, Akt2 promotes metastasis of tumor cells without affecting the latency of tumor development. Despite the distinct phenotypic outputs resulting from Akt1 or Akt2 activation, very little is known about the mode by which such unique functions originate from these highly related kinases. Here we discuss potential mechanisms contributing to the differing functional specificity of Akt1 and Akt2 with respect to migration, invasion, and metastasis.

CD5+CD23+ leukemic cell populations in TCL1 transgenic mice show significantly increased proliferation and Akt phosphorylation

B-cell chronic lymphocytic leukemia (B-CLL) is the most common adult leukemia. Deregulation of the T-cell leukemia/lymphoma 1 (TCL1) oncogene in mouse B cells causes a CD5-positive leukemia similar to aggressive human B-CLLs. We recently reported that levels of TCL1 expression in B-CLL are regulated by miR-29 and miR-181 that target 3' UTR of TCL1. To determine whether treatment with microRNAs targeting TCL1 can inhibit B-CLL in mice, we generated TCL1 transgenic mice using a construct containing the 3' and 5' UTRs of TCL1 under B-cell-specific Emicro promoter (Emicro-TCL1FL). At the age of 16-20 months, these mice showed B-CLL-like disease. Immunophenotyping revealed accumulation of CD5+CD23+B220+ population in spleens and lymph nodes. Our results show that CD5+CD23+ B-cell populations from Emicro-TCL1FL mice actively proliferate and show significantly increased levels of phospho-Akt. Emicro-TCL1FL mice showed immunological abnormalities similar to human B-CLL, including hypoimmunoglobulinemia, abnormal levels of cytokines and impaired immune response. These findings revealed biochemical and immunological similarities between Tcl1-driven B-CLL in mice and human B-CLL.

Subcellular localization of activated AKT in estrogen receptor- and progesterone receptor-expressing breast cancers: potential clinical implications

Activated v-AKT murine thymoma viral oncogene homolog 1 (AKT)/protein kinase B (PKB) kinase (pAKT) is localized to the plasma membrane, cytoplasm, and/or nucleus in 50% of cancers. The clinical importance of pAKT localization and the mechanism(s) controlling this compartmentalization are unknown. In this study, we examined nuclear and cytoplasmic phospho-AKT (pAKT) expression by immunohistochemistry in a breast cancer tissue microarray (n = 377) with approximately 15 years follow-up and integrated these data with the expression of estrogen receptor (ER)alpha, progesterone receptor (PR), and FOXA1. Nuclear localization of pAKT (nuclear-pAKT) was associated with long-term survival (P = 0.004). Within the ERalpha+/PR+ subgroup, patients with nuclear-pAKT positivity had better survival than nuclear-pAKT-negative patients (P < or = 0.05). The association of nuclear-pAKT with the ERalpha+/PR+ subgroup was validated in an independent cohort (n = 145). TCL1 family proteins regulate nuclear transport and/or activation of AKT. TCL1B is overexpressed in ERalpha-positive compared with ERalpha-negative breast cancers and in lung metastasis-free breast cancers. Therefore, we examined the possible control of TCL1 family member(s) expression by the estrogen:ERalpha pathway. Estradiol increased TCL1B expression and increased nuclear-pAKT levels in breast cancer cells; short- interfering RNA against TCL1B reduced nuclear-pAKT. Overexpression of nuclear-targeted AKT1 in MCF-7 cells increased cell proliferation without compromising sensitivity to the anti-estrogen, tamoxifen. These results suggest that subcellular localization of activated AKT plays a significant role in determining its function in breast cancer, which in part is dependent on TCL1B expression.

Involvement of RhoH GTPase in the development of B-cell chronic lymphocytic leukemia

RhoH is a hematopoietic-specific, GTPase-deficient member of the Rho GTPase family that functions as a regulator of thymocyte development and T-cell receptor signaling by facilitating localization of zeta-chain-associated protein kinase 70 (ZAP70) to the immunological synapse. Here we investigated the function of RhoH in the B-cell lineage. B-cell receptor (BCR) signaling was intact in Rhoh(-/-) mice. Because RhoH interacts with ZAP70, which is a prognostic factor in B-cell chronic lymphocytic leukemia (CLL), we analyzed the mRNA levels of RhoH in primary human CLL cells and showed a 2.3-fold higher RhoH expression compared with normal B cells. RhoH expression in CLL positively correlated with the protein levels of ZAP70. Deletion of Rhoh in a murine model of CLL (Emu-TCL1(Tg) mice) significantly delayed the accumulation of CD5(+)IgM(+) leukemic cells in peripheral blood and the leukemic burden in the peritoneal cavity, bone marrow and spleen of Rhoh(-/-) mice compared with their Rhoh(+/+) counterparts. Phosphorylation of AKT and ERK in response to BCR stimulation was notably decreased in Emu-TCL1(Tg);Rhoh(-/-) splenocytes. These data suggest that RhoH has a function in the progression of CLL in a murine model and show RhoH expression is altered in human primary CLL samples.

High TCL1 levels are a marker of B-cell receptor pathway responsiveness and adverse outcome in chronic lymphocytic leukemia

Although activation of the B-cell receptor (BCR) signaling pathway is implicated in the pathogenesis of chronic lymphocytic leukemia (CLL), its clinical impact and the molecular correlates of such response are not clearly defined. T-cell leukemia 1 (TCL1), the AKT modulator and proto-oncogene, is differentially expressed in CLL and linked to its pathogenesis based on CD5(+) B-cell expansions arising in TCL1-transgenic mice. We studied here the association of TCL1 levels and its intracellular dynamics with the in vitro responses to BCR stimulation in 70 CLL cases. The growth kinetics after BCR engagement correlated strongly with the degree and timing of induced AKT phospho-activation. This signaling intensity was best predicted by TCL1 levels and the kinetics of TCL1-AKT corecruitment to BCR membrane activation complexes, which further included the kinases LYN, SYK, ZAP70, and PKC. High TCL1 levels were also strongly associated with aggressive disease features, such as advanced clinical stage, higher white blood cell counts, and shorter lymphocyte doubling time. Higher TCL1 levels independently predicted an inferior clinical outcome (ie, shorter progression-free survival, P < .001), regardless of therapy regimen, especially for ZAP70(+) tumors. We propose TCL1 as a marker of the BCR-responsive CLL subset identifying poor prognostic cases where targeting BCR-associated kinases may be therapeutically useful.

PI3-Kinase Regulates Survival of Chronic Lymphocytic Leukemia B-Cells by Preventing Caspase 8 Activation

Studies to investigate signal transduction pathways that support viability and prevent apoptosis of chronic lymphocytic leukemia cells (CLL) were initiated as a result of microarray cDNA analyses which revealed expression of genes whose products regulate cell cycle progression. Immunoblots revealed translation of several genes including caspases, cyclin D1, and the PI3-kinase dependent, survival kinase, Akt. Akt was found to be activated. Inhibition of PI3-kinase with specific inhibitor, LY294002, led to the induction of apoptosis that was caspase 8 dependent, but independent of Akt as LY294002 did not depress a high basal level of Akt activity found in CLL cells. Phosphorylation of Akt was maintained, enzymatic activity undiminished, and phosphorylation of substrates sustained. Caspases, however were activated, PARP cleaved and DNA fragmented. Caspase inhibitors revealed that initiator caspase 8 was required for classic apoptosis when PI3-kinase was inhibited, and specific activity assays demonstrated its early activation. GSK-3beta a kinase regulated via PI3-kinase dependent, down-stream kinases, was responsible for regulating cyclin D1 levels in CLL cells, but neither GSK-3beta nor calpain was responsible for induction of apoptosis, or activation of executioner caspase 3, following LY294002 treatment. PI3-kinase mediated protection against caspase activation in CLL B-cells therefore is not mediated through classic Akt survival pathways. The data further support the hypothesis that signal transducing, membrane associated receptors triggered by extrinsic factors, maintain CLL leukemic B-cell survival in vivo by preventing caspase activation.

The TCL1A oncoprotein interacts directly with the NF-kappaB inhibitor IkappaB

The T cell leukaemia/lymphoma 1A (TCL1A) oncoprotein plays key roles in several B and T cell malignancies. Lacking enzymatic activity, TCL1A's transforming action was linked to its capacity to co-activate the protein kinase AKT via binding to its pleckstrin homology (PH) domain. However, perturbation of AKT signalling alone was recently shown insufficient to explain TCL1A oncogenesis, suggesting that TCL1A has additional cellular partners. Searching for such additional targets, we found that TCL1A binds specifically and directly to the ankyrin domain of IkappaB, the inhibitor of the NF-kappaB transcription factors. Through binding assays and a structural analysis by small angle X-ray scattering, we show that TCL1A and IkappaB interact in yeast-two-hybrid systems, when transiently overexpressed in 293 cells, and as recombinant proteins in vitro. We further establish that the association between TCL1A and IkappaB is compatible with AKT binding to TCL1A, but incompatible with IkappaB binding to NF-kappaB. By interfering with the inhibition of NF-kappaB by IkappaB, TCL1A may increase the concentration of free NF-kappaB molecules sufficiently to trigger expression of anti-apoptotic genes. Thus our data suggest an additional route by which TCL1A might cause cancer.

The PTEN-AKT3 signaling cascade as a therapeutic target in melanoma

Melanocytes undergo extensive genetic changes during transformation into aggressive melanomas. These changes deregulate genes whose aberrant activity promotes the development of this disease. The phosphoinositide-3-kinase (PI3K) and mitogen-activated protein (MAP) kinase pathways are two key signaling cascades that have been found to play prominent roles in melanoma development. These pathways relay extra-cellular signals via an ordered series of consecutive phosphorylation events from cell surface throughout the cytoplasm and nucleus regulating diverse cellular processes including proliferation, survival, invasion and angiogenesis. It is generally accepted that therapeutic agents would need to target these two pathways to be an effective therapy for the long-term treatment of advanced-stage melanoma patients. This review provides an overview of the PI3 kinase pathway focusing specifically on two members of the pathway, called PTEN and Akt3, which play important roles in melanoma development. Mechanisms leading to deregulation of these two proteins and therapeutic implications of targeting this signaling cascade to treat melanoma are detailed in this review.

Epigenetic changes during disease progression in a murine model of human chronic lymphocytic leukemia

Epigenetic alterations, including gain or loss of DNA methylation, are a hallmark of nearly every malignancy. Changes in DNA methylation can impact expression of cancer-related genes including apoptosis regulators and tumor suppressors. Because such epigenetic changes are reversible, they are being aggressively investigated as potential therapeutic targets. Here we use the Emu-TCL1 transgenic mouse model of chronic lymphocytic leukemia (CLL) to determine the timing and patterns of aberrant DNA methylation, and to investigate the mechanisms that lead to aberrant DNA methylation. We show that CLL cells from Emu-TCL1 mice at various stages recapitulate epigenetic alterations seen in human CLL. Aberrant methylation of promoter sequences is observed as early as 3 months of age in these animals, well before disease onset. Abnormally methylated promoter regions include binding sites for the transcription factor FOXD3. We show that loss of Foxd3 expression due to an NF-kappaB p50/p50:HDAC1 repressor complex occurs in TCL1-positive B cells before methylation. Therefore, specific transcriptional repression is an early event leading to epigenetic silencing of target genes in murine and human CLL. These results provide strong rationale for the development of strategies to target NF-kappaB components in CLL and potentially other B-cell malignancies.

The leukemias of mature lymphocytes

The leukemias of mature B cells and T cells are a limited set of diseases in which blood and bone marrow are the primary sites of involvement. Although they may superficially resemble one another, they have distinct clinical and pathologic features and must be distinguished from one another. In this article, the major clinical, morphologic, phenotypic, and molecular genetic features of the mature B- and T-cell leukemias are reviewed, and differential diagnostic considerations are discussed.

Nuclear and mitochondrial signalling Akts in cardiomyocytes

Biological actions resulting from phosphoinositide synthesis trigger multiple downstream signalling cascades by recruiting proteins with pleckstrin homology domains, including phosphoinositide-dependent kinase-1 and protein kinase B (also known as Akt). Retrospectively, more attention has been focused on the plasma membrane-associated interactions of these molecules and resulting cytoplasmic target activation. The complex biological activities exerted by Akt activation suggest, however, that more subtle and complex subcellular control mechanisms are involved. This review examines the regulation of Akt activity from the perspective of subcellular compartmentalization and focuses specifically upon the actions of Akt activation downstream from phosphoinositide synthesis that influence cell biology by altering nuclear signalling leading to Pim-1 kinase induction as well as hexokinase phosphorylation that, together with Akt, serves to preserve mitochondrial integrity.

Unscheduled Akt-triggered activation of cyclin-dependent kinase 2 as a key effector mechanism of apoptin's anticancer toxicity

Apoptin, a protein from the chicken anemia virus, has attracted attention because it specifically kills tumor cells while leaving normal cells unharmed. The reason for this tumor selectivity is unclear and depends on subcellular localization, as apoptin resides in the cytoplasm of normal cells but in the nuclei of transformed cells. It was shown that nuclear localization and tumor-specific killing crucially require apoptin's phosphorylation by an as yet unknown kinase. Here we elucidate the pathway of apoptin-induced apoptosis and show that it essentially depends on abnormal phosphatidylinositol 3-kinase (PI3-kinase)/Akt activation, resulting in the activation of the cyclin-dependent kinase CDK2. Inhibitors as well as dominant-negative mutants of PI3-kinase and Akt not only inhibited CDK2 activation but also protected cells from apoptin-induced cell death. Akt activated CDK2 by direct phosphorylation as well as by the phosphorylation-induced degradation of the inhibitor p27(Kip1). Importantly, we also identified CDK2 as the principal kinase that phosphorylates apoptin and is crucially required for apoptin-induced cell death. Immortalized CDK2-deficient fibroblasts and CDK2 knockdown cells were markedly protected against apoptin. Thus, our results not only decipher the pathway of apoptin-induced cell death but also provide mechanistic insights for the selective killing of tumor cells.

The expression of protein kinase B in gastric cancer cell apoptosis induced by 12-O-tetradecanoylphorbol-1, 3-acetate

Protein kinase B (PKB/Akt) is a serine-threonine kinase functioning downstream of phosphatidylinositol 3-kinase (PI-3 kinase) in response to mitogen or growth factor stimulation. In several cell types, it plays an important anti-apoptotic role. TPA is a potent regulator of the growth of many different cell types. Here, we detected that TPA could induce cell apoptosis in the gastric cancer cell line, BGC-823. We also found that TPA inhibited the expression of PKB/Akt in a TPA concentration- and time-dependent manner. Furthermore, TPA inhibited the phosphorylation of PKB at Ser473, but did not affect the phosphorylation of Thr308. It only attenuated the expression of PKB/Akt and the phosphorylation of Ser473 in the cell nucleus, whereas it did not change the PKB/Akt distribution in BGC-823 cells. These results suggest that PKB/Akt inhibition by TPA may be the important factor in the mechanism of effect of TPA on gastric cell lines.

Dysregulation of Frizzled 6 is a critical component of B-cell leukemogenesis in a mouse model of chronic lymphocytic leukemia

Wnt/Fzd signaling is known to play a key role in development, tissue-specific stem-cell maintenance, and tumorigenesis, particularly through the canonical pathway involving stabilization of beta-catenin. We have previously shown that Fzd9(-/-) mice have a deficiency in pre-B cells at a stage when self-renewing division is occurring in preference to further differentiation, before light chain immunoglobulin recombination. To determine whether pathologic usurpation of this pathway plays a role in B-cell leukemogenesis, we examined the expression of Wnt/Fzd pathway genes in the Emu-TCL1 mouse model of chronic lymphocytic leukemia. We find that, in the course of leukemogenesis, the expression of Wnt16, Wnt10alpha, Fzd1, and most dramatically, Fzd6, is progressively up-regulated in the transformed CD5(+) B cells of these mice, as are beta-catenin protein levels. Elimination of Fzd6 expression by crossing into Fzd6(-/-) mice significantly delays development of chronic lymphocytic leukemia in this model. Our findings suggest that the self-renewal signals mediated by Wnt/Fzd that are enlisted during B-cell development may be pathologically reactivated in the neoplastic transformation of mature B cells.

TLR9-activating DNA up-regulates ZAP70 via sustained PKB induction in IgM+ B cells

In the past, ZAP70 was considered a T cell-specific kinase, and its aberrant expression in B-CLL cells was interpreted as a sign of malignant transformation and dedifferentiation. It was only recently that ZAP70 was detected in normal human B cells. In this study, we show that TLR9-activated B cells resemble B-cell chronic lymphocytic leukemia cells with regard to CD5, CD23, CD25, and heat shock protein 90 expression. Furthermore, stimulatory CpG and GpC DNA oligonucleotides target CD27(+)IgM(+) and CD27(-)IgM(+) B cells (but not IgM(-) B cells) and enhance ZAP70 expression predominantly in the IgM(+)CD27(+) B cell subset. ZAP70 is induced via activation of TLR-7 or -9 in a MyD88-dependent manner, depends on protein kinase B (PKB)/mammalian target of rapamycin signaling and is rapamycin sensitive. Furthermore, ZAP70 expression levels correlate with induction of cyclin A2, prolonged B cell proliferation, and sustained induction of PKB. These events are not observed upon CD40 ligation. However, this deficit can be overcome by the expression of constitutively active PKB, given that CD40 ligation of PKB-transgenic B cells induces B cell proliferation and ZAP70 expression. These results highlight a major difference between CD40- and TLR-7/9-mediated B cell activation and suggest that ZAP70 expression levels in B cells give an estimate of the proliferative potential and the associated PKB availability.

Tcl1 functions as a transcriptional regulator and is directly involved in the pathogenesis of CLL

B cell chronic lymphocytic leukemia (B-CLL) is the most common human leukemia. Deregulation of the T cell leukemia/lymphoma 1 (TCL1) oncogene in mouse B cells causes a CD5-positive leukemia similar to aggressive human B-CLLs. To examine the mechanisms by which Tcl1 protein exerts oncogenic activity in B cells, we investigated the effect of Tcl1 expression on NF-kappaB and activator protein 1 (AP-1) activity. We found that Tcl1 physically interacts with c-Jun, JunB, and c-Fos and inhibits AP-1 transcriptional activity. Additionally, Tcl1 activates NF-kappaB by physically interacting with p300/CREB binding protein. We then sequenced the TCL1 gene in 600 B-CLL samples and found 2 heterozygous mutations: T38I and R52H. Importantly, both mutants showed gain of function as AP-1 inhibitors. The results indicate that Tcl1 overexpression causes B-CLL by directly enhancing NF-kappaB activity and inhibiting AP-1.

A subcortical maternal complex essential for preimplantation mouse embryogenesis

We have identified a subcortical maternal complex (SCMC) that assembles during oocyte growth and is essential for zygotes to progress beyond the first embryonic cell divisions. At least four maternally encoded proteins contribute to this MDa complex: FLOPED, MATER, and TLE6 interact with each other while Filia binds independently to MATER. Although the transcripts encoding these proteins are degraded during meiotic maturation and ovulation, the SCMC proteins persist in the early embryo. The SCMC, located in the subcortex of eggs, is excluded from regions of cell-cell contact in the cleavage-stage embryo and segregates to the outer cells of the morulae and blastocyst. Floped(tm/tm) and/or Mater(tm/tm) eggs lack the SCMC but can be fertilized. However, these embryos do not progress beyond cleavage stage development and female mice are sterile. The proteins are conserved in humans, and similar maternal effect mutations may result in recurrent embryonic loss.

Heterogeneous nuclear ribonucleoprotein A1 regulates cyclin D1 and c-myc internal ribosome entry site function through Akt signaling

The translation of the cyclin D1 and c-myc mRNAs occurs via internal ribosome entry site (IRES)-mediated initiation under conditions of reduced eIF-4F complex formation and Akt activity. Here we identify hnRNP A1 as an IRES trans-acting factor that regulates cyclin D1 and c-myc IRES activity, depending on the Akt status of the cell. hnRNP A1 binds both IRESs in vitro and in intact cells and enhances in vitro IRES-dependent reporter expression. Akt regulates this IRES activity by inducing phosphorylation of hnRNP A1 on serine 199. Serine 199-phosphorylated hnRNP A1 binds to the IRESs normally but is unable to support IRES activity in vitro. Reducing expression levels of hnRNP A1 or overexpressing a dominant negative version of the protein markedly inhibits rapamycin-stimulated IRES activity in cells and correlated with redistribution of cyclin D1 and c-myc transcripts from heavy polysomes to monosomes. Importantly, knockdown of hnRNP A1 also renders quiescent Akt-containing cells sensitive to rapamycin-induced G(1) arrest. These results support a role for hnRNP A1 in mediating rapamycin-induced alterations of cyclin D1 and c-myc IRES activity in an Akt-dependent manner and provide the first direct link between Akt and the regulation of IRES activity.

A novel Epac-Rap-PP2A signaling module controls cAMP-dependent Akt regulation

Rap1b has been implicated in the transduction of the cAMP mitogenic signal. It is phosphorylated and activated by cAMP, and its expression in models where cAMP is mitogenic leads to proliferation and tumorigenesis. Akt is a likely downstream effector of cAMP-Rap1 action. cAMP elevation induced a rapid and transient Akt inhibition that required activated and phosphorylated Rap1b. However, the mechanism(s) by which cAMP-Rap regulates Akt remains unclear. Here we show that (i) upstream regulators, PIK and PDK1, are not the target(s) of the cAMP inhibitory action; (ii) constitutively active Akt and calyculin A-stimulated Akt are resistant to cAMP inhibition, suggesting the action of a phosphatase; (iii) cAMP increases the rate of Akt dephosphorylation, directly implicating an Akt-phosphatase; (iv) Epac- and protein kinase A (PKA)-specific analogs synergistically inhibit Akt, indicating the involvement of both cAMP-dependent effector pathways; (v) H89 and dominant negative Epac 279E block cAMP-inhibitory action; (vi) Epac associates in a complex with Akt and PP2A, and the associated-phosphatase activity is positively modulated by cAMP in a PKA- and Rap1-dependent manner; (vii) like its action on Akt inhibition, PKA- and Epac-specific analogs synergistically activate Epac-associated PP2A; and (viii) dominant negative PP2A blocks cAMP-inhibitory action. Thus, we uncovered a novel cAMP-Epac/PKA-Rap1b-PP2A signaling module involved in Akt regulation that may represent a physiological event in the process of cAMP stimulation of thyroid mitogenesis.

Interaction between TCL1 and Epac1 in the activation of Akt kinases in plasma membranes and nuclei of 8-CPT-2-O-Me-cAMP-stimulated macrophages

Epac1 is a cAMP-stimulated guanine exchange factor that activates Rap1. The protein product of the T cell leukemia 1 (TCL1) proto-oncogene binds to Akt enhancing its kinase activity. TCL1 and Epac promote cellular proliferation because of their activating effects on Akt. Employing macrophages, we have studied the mechanisms whereby these proteins function in the regulation of Akt kinase activity. Cells were treated with 8-CPT-2-O-Me-cAMP, a cAMP analog which acts selectively and specifically via Epac1. Epac1 co-immunoprecipitated with TCL1 in plasma membrane and nuclear fractions of 8-CPT-2-O-Me-cAMP-stimulated macrophages. Interaction of TCL1 and Epac1 was also observed in a [125I]GST-Epac1 pulldown assay. A two-threefold increase in Akt Thr-308 and Akt Ser-473 protein kinase activities and their phosphoprotein levels was observed in TCL1 immunoprecipitates of plasma membranes and nuclei of the treated cells. Elevated Akt Thr-308 protein kinase activity and its phosphoprotein levels were significantly reduced in TCL1 immunoprecipitates of plasma membranes of 8-CPT-2-O-Me-cAMP-treated cells where Epac1 gene expression was silenced. In contrast, Akt Ser-473 protein kinase activity and its phosphoprotein levels were reduced only in plasma membranes. Our studies suggest that a ternary complex of TCL1, Epac1, and Akt forms in activated macrophages both promoting Akt activation and regulating intracellular distribution of Akt.

The role of microRNA and other non-coding RNA in the pathogenesis of chronic lymphocytic leukemia

New findings support the view that chronic lymphocytic leukemia (CLL) is a genetic disease in which the main alterations occur in a new class of genes named microRNAs (miRNAs). Cases with good prognostic features typically are characterized by miRNA down-regulation of genes miR-15a and miR-16-1, located at 13q14.3. Both microRNAs negatively regulate BCL2 at a post-transcriptional level. On the other hand, in CLL cases that use unmutated immunoglobulin heavy-chain variable-region genes (IgV(H)) or have high-level expression of the 70-kD zeta-associated protein (ZAP-70) have high levels of TCL1 due to low-level expression of miR-29 and miR-181, which directly target this oncogene. Conceivably, these miRNAs might be used to target BCL2 or TCL1 for therapy of this disease.

High TCL1 expression and intact T-cell receptor signaling define a hyperproliferative subset of T-cell prolymphocytic leukemia

The T-cell leukemia 1 (TCL1) oncoprotein is overexpressed by chromosomal rearrangement in the majority of cases of T-cell prolymphocytic leukemia (T-PLL). In vitro, TCL1 can modulate the activity of the serine-threonine kinase AKT, a downstream effector of T-cell receptor (TCR) signaling. In a series of 86 T-PLL tumors, we show that expression of TCR, and levels of TCL1 and activated AKT are adverse prognostic markers. High-level TCL1 in TCR-expressing T-PLL is associated with higher presenting white blood cell counts, faster tumor cell doubling, and enhanced in vitro growth response to TCR engagement. In primary tumors and TCL1-transfected T-cell lines, TCR engagement leads to rapid recruitment of TCL1 and AKT to transient membrane activation complexes that include TCR-associated tyrosine kinases, including LCK. Pharmacologic inhibition of AKT activation alters the localization, stability, and levels of these transient TCL1-AKT complexes and reduces tumor cell growth. Experimental introduction and knockdown of TCL1 influence the kinetics and strength of TCR-mediated AKT activation. We propose that in T-PLL, TCL1 represents a highly regulated, targetable modulator of TCR-mediated AKT growth signaling.

TORC2 regulates germinal center repression of the TCL1 oncoprotein to promote B cell development and inhibit transformation

Aberrant expression of the TCL1 oncoprotein promotes malignant transformation of germinal center (GC) B cells. Repression of TCL1 in GC B cells facilitates FAS-mediated apoptosis and prevents lymphoma formation. However, the mechanism for this repression is unknown. Here we show that the CREB coactivator TORC2 directly regulates TCL1 expression independent of CREB Ser-133 phosphorylation and CBP/p300 recruitment. GC signaling through CD40 or the BCR, which activates pCREB-dependent genes, caused TORC2 phosphorylation, cytosolic emigration, and TCL1 repression. Signaling via cAMP-inducible pathways inhibited TCL1 repression and reduced apoptosis, consistent with a prosurvival role for TCL1 before GC selection and supporting an initiating role for aberrant TCL1 expression during GC lymphomagenesis. Our data indicate that a novel CREB/TORC2 regulatory mode controls the normal program of GC gene activation and repression that promotes B cell development and circumvents oncogenic progression. Our results also reconcile a paradox in which signals that activate pCREB/CBP/p300 genes concurrently repress TCL1 to initiate its silencing.

Dissecting Oct3/4-regulated gene networks in embryonic stem cells by expression profiling

POU transcription factor Pou5f1 (Oct3/4) is required to maintain ES cells in an undifferentiated state. Here we show that global expression profiling of Oct3/4-manipulated ES cells delineates the downstream target genes of Oct3/4. Combined with data from genome-wide chromatin-immunoprecipitation (ChIP) assays, this analysis identifies not only primary downstream targets of Oct3/4, but also secondary or tertiary targets. Furthermore, the analysis also reveals that downstream target genes are regulated either positively or negatively by Oct3/4. Identification of a group of genes that show both activation and repression depending on Oct3/4 expression levels provides a possible mechanism for the requirement of appropriate Oct3/4 expression to maintain undifferentiated ES cells. As a proof-of-principle study, one of the downstream genes, Tcl1, has been analyzed in detail. We show that Oct3/4 binds to the promoter region of Tcl1 and activates its transcription. We also show that Tcl1 is involved in the regulation of proliferation, but not differentiation, in ES cells. These findings suggest that the global expression profiling of gene-manipulated ES cells can help to delineate the structure and dynamics of gene regulatory networks.

Expression of Tcl-1 as a Potential Prognostic Factor for Treatment Outcome in B-Cell Chronic Lymphocytic Leukemia

Chronic Lymphocytic Leukemia (CLL) is primarily characterized by the presence of leukemic B lymphocytes resistant to the process of apoptosis. Causes for this resistance include aberrant expression of multiple anti-apoptotic proteins, perhaps including Tcl-1 (1). Tcl-1 is expressed during normal development of both B and T cells and activates Akt to provide a survival signal through phosphorylation and inactivation of apoptotic pathway components. Overexpression of Tcl-1 in the B cells of transgenic mice results in a B-cell leukemia phenotype typical of human CLL, suggesting a primary role for Tcl-1 in CLL tumorigenesis. A recent report showed that Tcl-1 protein expression in CLL cells correlated with other biological parameters, but no data were available as to its clinical relevance (2). We therefore examined Tcl-1 expression in relation to clinical outcome using 51 peripheral blood mononuclear cell samples from a Phase II clinical trial testing the combination of pentostatin, cyclophosphamide, and rituximab in previously untreated CLL patients (Kay et al., ASH 2006). Tcl-1 protein expression was measured by immunoblot using GAPDH as a normalization control across lanes and lysate from a single Tcl-1 transgenic mouse spleen as a normalization control across immunoblots. All samples were run at least in duplicate and digital quantitation was performed using a ChemiDoc instrument (BioRad). Tcl-1 expression in patient cells was calculated in comparison to Tcl-1 expression in the mouse lysate, arbitrarily set to 1.0. Data were analyzed as a continuous measure as well as by specific cutoffs. Higher Tcl-1 expression was associated with failure to achieve a minimal residual disease-negative state after treatment. Specifically, Tcl-1 expression (measured as a continuous variable) was associated with residual disease measured by post-treatment CD5+/CD19+ cell percentages (continuous variable as well as dichotomized by cutpoint of 1.0% for CD5+/CD19+; p=0.03 for both comparisons). For the dichotomized Tcl-1 expression with the cutpoint of 0.275 (second tertile), this variable was marginally significantly associated with whether or not post-treatment CD5+/CD19+ was less than 1.0%. Using this same cutoff, there was also a suggestion that patients with reduced Tcl-1 were more likely to achieve a complete response. Finally, progression-free survival was shorter in patients with increased Tcl-1 expression, although these data did not reach statistical significance in this sample set.

Tcl-1 < 0.275 Tcl-1≥ 0.275 p value CD5/CD19≥ 1% 15 10 0.046 CD5/CD19 < 1% 16 2 CR 17 3 0.064 No CR 18 13 Median PFS (mos.) 36.5 17.1 0.137

Statistically significant associations with other parameters including Rai stage, IgVH mutation status, ZAP-70 expression, CD38 expression, and interphase cytogenetics categories were not detected in this sample set. These data further support the clinical relevance of the Tcl-1 mouse model to human CLL, and provide preliminary evidence that Tcl-1 protein expression correlates with clinical outcome of CLL patients treated with chemoimmunotherapy. If validated in larger studies, Tcl-1 expression may serve as a novel prognostic factor.

Expression of TCL1 and CD27 in primary cutaneous B-cell lymphomas

AIMS

To investigate by immunohistochemical analysis the expression of the TCL1 oncogene product and of CD27 in 25 cases of primary cutaneous B-cell lymphomas (PCBCL) classified according to the World Health Organization-European Organization for Research and Treatment of Cancer classification of cutaneous lymphomas. In B-cell ontogenesis TCL1 is mainly expressed by 'naive' B lymphocytes and by a subset of germinal centre B cells, whereas CD27 is expressed by a subset of germinal centre B cells, 'memory' B lymphocytes and plasma cells, suggesting that their expression in physiological conditions is mutually exclusive.

METHODS AND RESULTS

Overall, TCL1 was expressed in 5/25 cases (20%) and CD27 in 15/25 cases (60%). Furthermore, 7/25 cases (28%) were TCL1- and CD27- and 2/25 cases (8%) were TCL1+ and CD27+. In particular, primary cutaneous follicle-centre lymphomas (10 cases) showed a variable expression of both TCL1 and CD27, whereas primary cutaneous marginal-zone B-cell lymphomas (eight cases) showed, with the exception of a single case, a definite CD27+/TCL1- profile.

CONCLUSIONS

These findings indicate: (i) the TCL1 oncogene product is uncommonly expressed in PCBCL (20% of cases, mainly of the follicle-centre subtype); (ii) in contrast, CD27 is often expressed in PCBCL (60% of cases), mainly of the marginal-zone subtype; (iii) the coexpression of TCL1 and CD27 may be seldom observed in PCBCL (8% of cases); (iv) PCBCL does not seem to show, in terms of either TCL1 or CD27 expression, significant differences compared with its systemic counterparts.

Nuclear targeting of Akt antagonizes aspects of cardiomyocyte hypertrophy

The serine/threonine kinase Akt regulates cellular survival, proliferation, gene transcription, protein translation, metabolism, and differentiation. Although Akt substrates are found throughout the cell, activated Akt normally accumulates in the nucleus, suggesting that biologically relevant targets are located there. Consequences of nuclear Akt signaling in cardiomyocytes were explored by using nuclear-targeted Akt (Akt-nuc). Accumulation of Akt-nuc did not provoke hypertrophy, unlike constitutively activated Akt. Instead, Akt-nuc inhibited hypertrophy concurrent with increased atrial natriuretic peptide (ANP) expression that depended upon phosphatidylinositol-3 kinase activity. Akt-nuc antihypertrophic effects were blocked by inhibition of either guanylyl cyclase A receptor or cyclic guanosine monophosphate-dependent protein kinase in cultured cardiomyocytes. Corroborating evidence showed blunted acute hypertrophic remodeling in Akt-nuc transgenic mice after transverse aortic constriction coincident with higher ANP expression and smaller myocyte volume. In addition, Akt-nuc expression improved systolic function and survival in the chronic phase of transverse aortic constriction-induced hypertrophy. Thus, Akt-nuc antagonizes certain aspects of hypertrophy through autocrine/paracrine stimulation of a phosphatidylinositol-3 kinase-dependent signaling cascade that promotes ANP expression, resulting in a unique combination of prosurvival coupled with antihypertrophic signaling.

B cell receptors in TCL1 transgenic mice resemble those of aggressive, treatment-resistant human chronic lymphocytic leukemia

B cell chronic lymphocytic leukemia (B-CLL) is a clonal overgrowth of CD5(+) B lymphocytes. In this disease, the B cell antigen receptor (BCR) is intimately linked to disease severity, because patients with BCRs, comprised of unmutated V(H) genes, follow a much more aggressive course. This and related observations suggest that B-CLL derives from a B cell subset comprised of restricted BCR structural diversity and that antigen-selection and drive are major factors promoting the disease. Nevertheless, the initiating event(s) that lead to the development of B-CLL are still unclear, in part because of the lack of an animal model that spontaneously evolves the molecular abnormalities that occur in the human disease. Because overexpression of the TCL1 gene in murine B cells leads to a CD5(+) B cell lymphoproliferative disorder with many of the features of human B-CLL, we studied leukemias emerging in these mice to examine the extent to which their BCRs resemble those in B-CLL. Our data indicate that the immunoglobulin heavy and light chain rearrangements in TCL1 mice display minimal levels of somatic mutations and exhibit several molecular features found in the human disease. Like human B-CLL, TCL1 leukemic rearrangements from different mice can be very similar structurally and closely resemble autoantibodies and antibodies reactive with microbial antigens. Antigen-binding analyses confirm that selected TCL1 clones react with glycerophospholipid, lipoprotein, and polysaccharides that can be autoantigens and be expressed by microbes. This (auto)antigen-driven mouse model reliably captures the BCR characteristics of aggressive, treatment-resistant human B-CLL.

Fhit modulation of the Akt-survivin pathway in lung cancer cells: Fhit-tyrosine 114 (Y114) is essential

The Fhit tumor suppressor binds and hydrolyses diadenosine polyphosphates and the Fhit-substrate complex has been proposed as a proapoptotic effector, as determined by infection of susceptible cancer cells with adenoviruses carrying wild-type fragile histidine triad (FHIT) or catalytic site mutants. The highly conserved Fhit tyrosine 114 (Y114), within the unstructured loop C-terminal of the catalytic site, can be phosphorylated by Src family tyrosine kinases, although endogenous phospho-Fhit is rarely detected. To explore the importance of Y114 and identify Fhit-mediated signaling events, wild-type and Y114 mutant FHIT-expressing adenoviruses were introduced into two human lung cancer cell lines. Caspase-dependent apoptosis was effectively induced only by wild-type but not Y114 mutant Fhit proteins. By expression profiling of FHIT versus mutant FHIT-infected cells, we found that survivin, an Inhibitor of Apoptosis Protein (IAP) family member, was significantly decreased by wild-type Fhit. In addition, Fhit inhibited activity of Akt, a key effector in the phosphatidylinositol 3-OH kinase (PI3K) pathway; loss of endogenous Fhit expression caused increased Akt activity in vitro and in vivo, and overexpression of constitutively active Akt inhibited Fhit-induced apoptosis. The results indicate that the Fhit Y114 residue plays a critical role in Fhit-induced apoptosis, occurring through inactivation of the PI3K-Akt-survivin signal pathway.

Dysregulated TCL1 requires the germinal center and genome instability for mature B-cell transformation

Most lymphomas arise by transformation of germinal center (GC) B cells. TCL1, a proto-oncogene first recognized for its role in T-cell transformation, also induces GC B-cell malignancies when dysregulated in pEmu-B29-TCL1 transgenic (TCL1-tg) mice. Clonal B-cell lymphomas develop from polyclonal populations with latencies of 4 months or more, suggesting that secondary genetic events are required for full transformation. The goals of this study were to determine the GC-related effects of TCL1 dysregulation that contribute to tumor initiation and to identify companion genetic alterations in tumors that function in disease progression. We report that compared with wild-type (WT) cells, B cells from TCL1-tg mice activated in a manner resembling a T-dependent GC reaction show enhanced resistance to FAS-mediated apoptosis with CD40 stimulation, independent of a B-cell antigen receptor (BCR) rescue signal. Mitogenic stimulation of TCL1-tg B cells also resulted in increased expression of Aicda. These GC-related enhancements in survival and Aicda expression could underlie B-cell transformation. Supporting this notion, no B-cell lymphomas developed for 20 months when TCL1-tg mice were crossed onto an Oct coactivator from B cell (OCA-B)-deficient background to yield mice incapable of forming GCs. Spectral karyotype analyses showed that GC lymphomas from TCL1-tg mice exhibit recurrent chromosome translocations and trisomy 15, with corresponding MYC overexpression. We conclude that pEmu-B29-TCL1 transgenic B cells primed for transformation must experience the GC environment and, for at least some, develop genome instability to become fully malignant.

Characterization of the TCL-1 transgenic mouse as a preclinical drug development tool for human chronic lymphocytic leukemia

Drug development in human chronic lymphocytic leukemia (CLL) has been limited by lack of a suitable animal model to adequately assess pharmacologic properties relevant to clinical application. A recently described TCL-1 transgenic mouse develops a chronic B-cell CD5(+) leukemia that might be useful for such studies. Following confirmation of the natural history of this leukemia in the transgenic mice, we demonstrated that the transformed murine lymphocytes express relevant therapeutic targets (Bcl-2, Mcl-1, AKT, PDK1, and DNMT1), wild-type p53 status, and in vitro sensitivity to therapeutic agents relevant to the treatment of human CLL. We then demonstrated the in vivo clinical activity of low-dose fludarabine in transgenic TCL-1 mice with active leukemia. These studies demonstrated both early reduction in blood-lymphocyte count and spleen size and prolongation of survival (P = .046) compared with control mice. Similar to human CLL, an emergence of resistance was noted with fludarabine treatment in vivo. Overall, these studies suggest that the TCL-1 transgenic leukemia mouse model has similar clinical and therapeutic response properties to human CLL and may therefore serve as a useful in vivo tool to screen new drugs for subsequent development in CLL.