The role of lysophosphatidic acid (LPA) in cancer is poorly understood. Here we provide evidence for a role of LPA in the progression of breast cancer bone metastases. LPA receptors LPA1, LPA2, and LPA3 were expressed in human primary breast tumors and a series of human breast cancer cell lines. The inducible overexpression of LPA1 in MDA-BO2 breast cancer cells specifically sensitized these cells to the mitogenic action of LPA in vitro. In vivo, LPA1 overexpression in MDA-BO2 cells enhanced the growth of subcutaneous tumor xenografts and promoted bone metastasis formation in mice by increasing both skeletal tumor growth and bone destruction. This suggested that endogenous LPA was produced in the tumor microenvironment. However, MDA-BO2 cells or transfectants did not produce LPA. Instead, they induced the release of LPA from activated platelets which, in turn, promoted tumor cell proliferation and the LPA1-dependent secretion of IL-6 and IL-8, 2 potent bone resorption stimulators. Moreover, platelet-derived LPA deprivation in mice, achieved by treatment with the platelet antagonist Integrilin, inhibited the progression of bone metastases caused by parental and LPA1-overexpressing MDA-BO2 cells and reduced the progression of osteolytic lesions in mice bearing CHO-β3wt ovarian cancer cells. Overall, our data suggest that, at the bone metastatic site, tumor cells stimulate the production of LPA from activated platelets, which enhances both tumor growth and cytokine-mediated bone destruction.
Ahmed Boucharaba, Claire-Marie Serre, Sandra Grès, Jean Sébastien Saulnier-Blache, Jean-Claude Bordet, Julien Guglielmi, Philippe Clézardin, Olivier Peyruchaud
Prostate cancer is currently the most commonly diagnosed noncutaneous malignancy in American men. When metastatic, usually to the bone, the disease is no longer curable and is usually treated palliatively with androgen ablation. However, after conversion to androgen-independent disease, there is no effective therapy currently available. The “T body” approach, which uses genetically reprogrammed lymphocytes derived from the patient and expressing chimeric receptor genes, combines the effector functions of T lymphocytes and NK cells with the ability of antibodies to recognize predefined surface antigens with high specificity and in a non–MHC-restricted manner. We show here the therapeutic efficacy of human lymphocytes bearing erbB2-specific chimeric receptors on human prostate cancer BM lesions in a SCID mouse model after conditioning of the recipient to allow homing and persistent functioning of the adoptively transferred cells. Induction of stromal cell–derived factor-1 production within the BM using low-dose irradiation or cyclophosphamide combined with IL-2 administration enhanced the homing of systemically delivered T bodies, resulting in decreased tumor growth and prostate-specific antigen secretion, prolongation of survival, and even cure of the treated mice. These preclinical studies strongly support the idea that the T body approach has therapeutic potential in disseminated prostate cancer.
Jehonathan H. Pinthus, Tova Waks, Victoria Malina, Keren Kaufman-Francis, Alon Harmelin, Itzhak Aizenberg, Hannah Kanety, Jacob Ramon, Zelig Eshhar
Aberrant activation of the JAK-STAT pathway has been implicated in tumor formation; for example, constitutive activation of JAK2 kinase or the enforced expression of STAT5 induces leukemia in mice. We show here that the Janus kinase TYK2 serves an opposite function. Mice deficient in TYK2 developed Abelson-induced B lymphoid leukemia/lymphoma as well as TEL-JAK2–induced T lymphoid leukemia with a higher incidence and shortened latency compared with WT controls. The cell-autonomous properties of Abelson murine leukemia virus–transformed (A-MuLV–transformed) TYK2–/– cells were unaltered, but the high susceptibility of TYK2–/– mice resulted from an impaired tumor surveillance, and accordingly, TYK2–/– A-MuLV–induced lymphomas were easily rejected after transplantation into WT hosts. The increased rate of leukemia/lymphoma formation was linked to a decreased in vitro cytotoxic capacity of TYK2–/– NK and NKT cells toward tumor-derived cells. RAG2/TYK2 double-knockout mice succumbed to A-MuLV–induced leukemia/lymphoma faster than RAG2–/–TYK2+/– mice. This defines NK cells as key players in tumor surveillance in Abelson-induced malignancies. Our observations provide compelling evidence that TYK2 is an important regulator of lymphoid tumor surveillance.
Dagmar Stoiber, Boris Kovacic, Christian Schuster, Carola Schellack, Marina Karaghiosoff, Rita Kreibich, Eva Weisz, Michaela Artwohl, Olaf C. Kleine, Mathias Muller, Sabina Baumgartner-Parzer, Jacques Ghysdael, Michael Freissmuth, Veronika Sexl
Scatter factor (SF), also known as hepatocyte growth factor, is ubiquitously present in the extracellular matrix of tissues in the form of an inactive precursor (pro-SF). In order to acquire biological activity, pro-SF must be cleaved by specific proteases present on the cell surface. The mature form of SF controls invasive cues in both physiological and pathological processes through activation of its receptor, the Met tyrosine kinase. By substituting a single amino acid in the proteolytic site, we engineered an unprocessable form of pro-SF (uncleavable SF). Using lentivirus vector technology, we achieved local or systemic delivery of uncleavable SF in mice. We provide evidence that (a) uncleavable SF inhibits both protease-mediated pro-SF conversion and active SF–induced Met activation; (b) local expression of uncleavable SF in tumors suppresses tumor growth, impairs tumor angiogenesis, and prevents metastatic dissemination; and (c) systemic expression of uncleavable SF dramatically inhibits the growth of transplanted tumors and abolishes the formation of spontaneous metastases without perturbing vital physiological functions. These data show that proteolytic activation of pro-SF is a limiting step in tumor progression, thus suggesting a new strategy for the treatment or prevention of the malignant conversion of neoplastic lesions.
Massimiliano Mazzone, Cristina Basilico, Silvia Cavassa, Selma Pennacchietti, Mauro Risio, Luigi Naldini, Paolo M. Comoglio, Paolo Michieli
Multiple myeloma in humans is frequently associated with mast cell infiltration and neovascularization, which correlate directly with disease severity, but the mechanisms underlying this relationship remain unclear. Here, we report that primary murine mast cells express angiopoietin-1 (Ang-1) and low levels of VEGF-A but not Ang-2 and that 2 established murine plasmacytoma cell lines express high levels of VEGF-A but little or no Ang-1 or Ang-2. An in vivo angiogenesis assay using extracellular matrix components shows that mast cells and plasmacytoma cells, together, promote marked neovascularization composed of dilated vessels, which is prevented by neutralization of VEGF-A and Ang-1 but is only partially reduced by neutralization of either VEGF-A or Ang-1. Mast cells within extracellular matrix components express Ang-1, and recombinant Ang-1 together with plasmacytoma cells promotes extracellular matrix neovascularization similar to that induced by mast cells. A transplantation assay shows that primary mast cells accelerate tumor growth by established plasmacytoma cell lines and that neutralization of Ang-1 alone or with VEGF-A reduces significantly the growth of plasmacytomas containing mast cells. These results demonstrate that mast cell–derived Ang-1 promotes the growth of plasmacytomas by stimulating neovascularization and provide further evidence supporting a causal relationship between inflammation and tumor growth.
Takayuki Nakayama, Lei Yao, Giovanna Tosato
Evasion of apoptosis is a hallmark of cancer, but the molecular circuitries of this process are not understood. Here we show that survivin, a member of the inhibitor of apoptosis gene family that is overexpressed in cancer, exists in a novel mitochondrial pool in tumor cells. In response to cell death stimulation, mitochondrial survivin is rapidly discharged in the cytosol, where it prevents caspase activation and inhibits apoptosis. Selective targeting of survivin to mitochondria enhances colony formation in soft agar, accelerates tumor growth in immunocompromised animals, and abolishes tumor cell apoptosis in vivo. Therefore, mitochondrial survivin orchestrates a novel pathway of apoptosis inhibition, which contributes to tumor progression.
Takehiko Dohi, Elena Beltrami, Nathan R. Wall, Janet Plescia, Dario C. Altieri
Peptide deformylase activity was thought to be limited to ribosomal protein synthesis in prokaryotes, where new peptides are initiated with an N-formylated methionine. We describe here a new human peptide deformylase (Homo sapiens PDF, or HsPDF) that is localized to the mitochondria. HsPDF is capable of removing formyl groups from N-terminal methionines of newly synthesized mitochondrial proteins, an activity previously not thought to be necessary in mammalian cells. We show that actinonin, a peptidomimetic antibiotic that inhibits HsPDF, also inhibits the proliferation of 16 human cancer cell lines. We designed and synthesized 33 chemical analogs of actinonin; all of the molecules with potent activity against HsPDF also inhibited tumor cell growth, and vice versa, confirming target specificity. Small interfering RNA inhibition of HsPDF protein expression was also antiproliferative. Actinonin treatment of cells led to a tumor-specific mitochondrial membrane depolarization and ATP depletion in a time- and dose-dependent manner; removal of actinonin led to a recovery of the membrane potential consistent with indirect effects on the electron transport chain. In animal models, oral or parenteral actinonin was well tolerated and inhibited human prostate cancer and lung cancer growth. We conclude that HsPDF is a new human mitochondrial enzyme that may provide a novel selective target for anticancer therapy by use of actinonin-based antibiotics.
Mona D. Lee, Yuhong She, Michael J. Soskis, Christopher P. Borella, Jeffrey R. Gardner, Paula A. Hayes, Benzon M. Dy, Mark L. Heaney, Mark R. Philips, William G. Bornmann, Francis M. Sirotnak, David A. Scheinberg
Phosphorylation of the cell adhesion protein CEACAM1 increases insulin sensitivity and decreases insulin-dependent mitogenesis in vivo. Here we show that CEACAM1 is a substrate of the EGFR and that upon being phosphorylated, CEACAM1 reduces EGFR-mediated growth of transfected Cos-7 and MCF-7 cells in response to EGF. Using transgenic mice overexpressing a phosphorylation-defective CEACAM1 mutant in liver (L-SACC1), we show that the effect of CEACAM1 on EGF-dependent cell proliferation is mediated by its ability to bind to and sequester Shc, thus uncoupling EGFR signaling from the ras/MAPK pathway. In L-SACC1 mice, we also show that impaired CEACAM1 phosphorylation leads to ligand-independent increase of EGFR-mediated cell proliferation. This appears to be secondary to visceral obesity and the metabolic syndrome, with increased levels of output of free fatty acids and heparin-binding EGF-like growth factor from the adipose tissue of the mice. Thus, L-SACC1 mice provide a model for the mechanistic link between increased cell proliferation in states of impaired metabolism and visceral obesity.
George A. Abou-Rjaily, Sang Jun Lee, Denisa May, Qusai Y. Al-Share, Anthony M. DeAngelis, Randall J. Ruch, Michael Neumaier, Holger Kalthoff, Sue-Hwa Lin, Sonia M. Najjar
Constitutive activation of signal transducer and activator of transcription 3 (Stat3) has been found in a wide spectrum of human malignancies. Here, we have assessed the effect of Stat3 deficiency on skin tumor development using the 2-stage chemical carcinogenesis model. The epidermis of Stat3-deficient mice showed a significantly reduced proliferative response following treatment with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) because of a defect in G1-to-S-phase cell cycle progression. Treatment with the tumor initiator 7,12-dimethylbenz[a]anthracene (DMBA) resulted in a significant increase in the number of keratinocyte stem cells undergoing apoptosis in the bulge region of hair follicles of Stat3-deficient mice compared with nontransgenic littermates. Notably, Stat3-deficient mice were completely resistant to skin tumor development when DMBA was used as the initiator and TPA as the promoter. Abrogation of Stat3 function using a decoy oligonucleotide inhibited the growth of initiated keratinocytes possessing an activated Ha-ras gene, both in vitro and in vivo. In addition, injection of Stat3 decoy into skin tumors inhibited their growth. To our knowledge, these data provide the first evidence that Stat3 is required for de novo epithelial carcinogenesis, through maintaining the survival of DNA-damaged stem cells and through mediating and maintaining the proliferation necessary for clonal expansion of initiated cells during tumor promotion. Collectively, these data suggest that, in addition to its emerging role as a target for cancer therapy, Stat3 may also be a target for cancer prevention strategies.
Keith Syson Chan, Shigetoshi Sano, Kaoru Kiguchi, Joanne Anders, Nobuyasu Komazawa, Junji Takeda, John DiGiovanni
A mouse model involving the human papillomavirus type-16 oncogenes develops cervical cancers by lesional stages analogous to those in humans. In this study the angiogenic phenotype was characterized, revealing intense angiogenesis in high-grade cervical intraepithelial neoplasias (CIN-3) and carcinomas. MMP-9, a proangiogenic protease implicated in mobilization of VEGF, appeared in the stroma concomitant with the angiogenic switch, expressed by infiltrating macrophages, similar to what has been observed in humans. Preclinical trials sought to target MMP-9 and angiogenesis with a prototypical MMP inhibitor and with a bisphosphonate, zoledronic acid (ZA), revealing both to be antiangiogenic, producing effects comparable to a Mmp9 gene KO in impairing angiogenic switching, progression of premalignant lesions, and tumor growth. ZA therapy increased neoplastic epithelial and endothelial cell apoptosis without affecting hyperproliferation, indicating that ZA was not antimitotic. The analyses implicated cellular and molecular targets of ZA’s actions: ZA suppressed MMP-9 expression by infiltrating macrophages and inhibited metalloprotease activity, reducing association of VEGF with its receptor on angiogenic endothelial cells. Given its track record in clinical use with limited toxicity, ZA holds promise as an “unconventional” MMP-9 inhibitor for antiangiogenic therapy of cervical cancer and potentially for additional cancers and other diseases where MMP-9 expression by infiltrating macrophages is evident.
Enrico Giraudo, Masahiro Inoue, Douglas Hanahan
The transcription factor NF-κB is activated in a range of human cancers and is thought to promote tumorigenesis, mainly due to its ability to protect transformed cells from apoptosis. To investigate the role of NF-κB in epithelial plasticity and metastasis, we utilized a well-characterized in vitro/in vivo model of mammary carcinogenesis that depends on the collaboration of the Ha-Ras oncoprotein and TGF-β. We show here that the IKK-2/IκBα/NF-κB pathway is required for the induction and maintenance of epithelial-mesenchymal transition (EMT). Inhibition of NF-κB signaling prevented EMT in Ras-transformed epithelial cells, while activation of this pathway promoted the transition to a mesenchymal phenotype even in the absence of TGF-β. Furthermore, inhibition of NF-κB activity in mesenchymal cells caused a reversal of EMT, suggesting that NF-κB is essential for both the induction and maintenance of EMT. In line with the importance of EMT for invasion, blocking of NF-κB activity abrogated the metastatic potential of mammary epithelial cells in a mouse model system. Collectively, these data provide evidence of an essential role for NF-κB during distinct steps of breast cancer progression and suggest that the cooperation of Ras- and TGF-β–dependent signaling pathways in late-stage tumorigenesis depends critically on NF-κB activity.
Margit A. Huber, Ninel Azoitei, Bernd Baumann, Stefan Grünert, Andreas Sommer, Hubert Pehamberger, Norbert Kraut, Hartmut Beug, Thomas Wirth
CD4+ T cells play important roles in orchestrating host immune responses against cancer and infectious diseases. Although EBV-encoded nuclear antigen 1–specific (EBNA1-specific) CD4+ T cells have been implicated in controlling the growth of EBV-associated tumors such as Burkitt lymphoma (BL) in vitro, direct evidence for their in vivo function remains elusive due to the lack of an appropriate experimental BL model. Here, we describe the development of a mouse EBNA1-expressing BL tumor model and the identification of 2 novel MHC H-2I-Ab–restricted T cell epitopes derived from EBNA1. Using our murine BL tumor model and the relevant peptides, we show that vaccination of mice with EBNA1 peptide–loaded DCs can elicit CD4+ T cell responses. These EBNA1-specific CD4+ T cells recognized peptide-pulsed targets as well as EBNA1-expressing tumor cells and were necessary and sufficient for suppressing tumor growth in vivo. By contrast, EBNA1 peptide–reactive CD8+ T cells failed to recognize tumor cells and did not contribute to protective immunity. These studies represent what we believe to be the first demonstration that EBNA1-specific CD4+ T cells can suppress tumor growth in vivo, which suggests that CD4+ T cells play an important role in generating protective immunity against EBV-associated cancer.
Tihui Fu, Kui Shin Voo, Rong-Fu Wang
The MHC class I chain–related molecules (MICs) have previously been shown to be induced on most epithelial tumor cells. Engagement of MIC by the activating immune receptor NKG2D triggers NK cells and augments antigen-specific CTL anti-tumor immunity. The MIC-NKG2D system was proposed to participate in epithelial tumor immune surveillance. Paradoxically, studies suggest that tumors may evade MIC-NKG2D–mediated immunity by MIC shedding–induced impairment of effector cell function. Here we demonstrate the first evidence to our knowledge of a significant correlation of MIC shedding and deficiency in NK cell function with the grade of disease in prostate cancer. MIC is widely expressed in prostate carcinoma. The presence of surface target MIC, however, is counteracted by shedding. A significant increase in serum levels of soluble MIC (sMIC) and deficiency in NK cell function was shown in patients with advanced cancer. Finally, the deficiency in NK cell function can be overcome by treatment with IL-2 or IL-15 in vitro. Our results suggest that (a) deficiency in MIC-NKG2D immune surveillance may contribute to prostate cancer progression, (b) sMIC may be a novel biomarker for prostate cancer, and (c) using cytokines to restore MIC-NKG2D–mediated immunity may have clinical significance for prostate cancer in cell-based adaptive immunotherapy.
Jennifer D. Wu, Lily M. Higgins, Alexander Steinle, David Cosman, Kathy Haugk, Stephen R. Plymate
Cachexia is a syndrome characterized by wasting of skeletal muscle and contributes to nearly one-third of all cancer deaths. Cytokines and tumor factors mediate wasting by suppressing muscle gene products, but exactly which products are targeted by these cachectic factors is not well understood. Because of their functional relevance to muscle architecture, such targets are presumed to represent myofibrillar proteins, but whether these proteins are regulated in a general or a selective manner is also unclear. Here we demonstrate, using in vitro and in vivo models of muscle wasting, that cachectic factors are remarkably selective in targeting myosin heavy chain. In myotubes and mouse muscles, TNF-α plus IFN-γ strongly reduced myosin expression through an RNA-dependent mechanism. Likewise, colon-26 tumors in mice caused the selective reduction of this myofibrillar protein, and this reduction correlated with wasting. Under these conditions, however, loss of myosin was associated with the ubiquitin-dependent proteasome pathway, which suggests that mechanisms used to regulate the expression of muscle proteins may be cachectic factor specific. These results shed new light on cancer cachexia by revealing that wasting does not result from a general downregulation of muscle proteins but rather is highly selective as to which proteins are targeted during the wasting state.
Swarnali Acharyya, Katherine J. Ladner, Lori L. Nelsen, Jeffrey Damrauer, Peter J. Reiser, Steven Swoap, Denis C. Guttridge
Mutant isoforms of the KIT or PDGF receptors expressed by gastrointestinal stromal tumors (GISTs) are considered the therapeutic targets for STI571 (imatinib mesylate; Gleevec), a specific inhibitor of these tyrosine kinase receptors. Case reports of clinical efficacy of Gleevec in GISTs lacking the typical receptor mutations prompted a search for an alternate mode of action. Here we show that Gleevec can act on host DCs to promote NK cell activation. DC-mediated NK cell activation was triggered in vitro and in vivo by treatment of DCs with Gleevec as well as by a loss-of-function mutation of KIT. Therefore, tumors that are refractory to the antiproliferative effects of Gleevec in vitro responded to Gleevec in vivo in an NK cell–dependent manner. Longitudinal studies of Gleevec-treated GIST patients revealed a therapy-induced increase in IFN-γ production by NK cells, correlating with an enhanced antitumor response. These data point to a novel mode of antitumor action for Gleevec.
Christophe Borg, Magali Terme, Julien Taïeb, Cédric Ménard, Caroline Flament, Caroline Robert, Koji Maruyama, Hiro Wakasugi, Eric Angevin, Kris Thielemans, Axel Le Cesne, Véronique Chung-Scott, Vladimir Lazar, Isabelle Tchou, Florent Crépineau, François Lemoine, Jacky Bernard, Jonhantan A. Fletcher, Ali Turhan, Jean-Yves Blay, Alain Spatz, Jean-François Emile, Michael C. Heinrich, Salah Mécheri, Thomas Tursz, Laurence Zitvogel
One mechanism contributing to immunologic unresponsiveness toward tumors may be presentation of tumor antigens by tolerogenic host APCs. We show that mouse tumor-draining LNs (TDLNs) contained a subset of plasmacytoid DCs (pDCs) that constitutively expressed immunosuppressive levels of the enzyme indoleamine 2,3-dioxygenase (IDO). Despite comprising only 0.5% of LN cells, these pDCs in vitro potently suppressed T cell responses to antigens presented by the pDCs themselves and also, in a dominant fashion, suppressed T cell responses to third-party antigens presented by nonsuppressive APCs. Adoptive transfer of DCs from TDLNs into naive hosts created profound local T cell anergy, specifically toward antigens expressed by the transferred DCs. Anergy was prevented by targeted disruption of the IDO gene in the DCs or by administration of the IDO inhibitor drug 1-methyl-D-tryptophan to recipient mice. Within the population of pDCs, the majority of the functional IDO-mediated suppressor activity segregated with a novel subset of pDCs coexpressing the B-lineage marker CD19. We hypothesize that IDO-mediated suppression by pDCs in TDLNs creates a local microenvironment that is potently suppressive of host antitumor T cell responses.
David H. Munn, Madhav D. Sharma, Deyan Hou, Babak Baban, Jeffrey R. Lee, Scott J. Antonia, Jane L. Messina, Phillip Chandler, Pandelakis A. Koni, Andrew L. Mellor
Bone marrow of breast cancer patients was found to contain CD8+ T cells specific for peptides derived from breast cancer–associated proteins MUC1 and Her-2/neu. Most of these cells had a central or effector memory phenotype (CD45RA–CD62L+ or CD45RA–CD62L–, respectively). To test their in vivo function, we separated bone marrow–derived CD45RA+ naive or CD45RA–CD45RO+ memory T cells, stimulated them with autologous dendritic cells pulsed with tumor lysate, and transferred them into NOD/SCID mice bearing autologous breast tumors and normal skin transplants. CD45RA– memory but not CD45RA+ naive T cells infiltrated autologous tumor but not skin tissues after the transfer. These tumor-infiltrating cells had a central or effector memory phenotype and produced perforin. Many of them expressed the P-selectin glycoprotein ligand 1 and were found around P-selectin+ tumor endothelium. Tumor infiltration included cluster formation in tumor tissue by memory T cells with cotransferred dendritic cells. It was associated with the induction of tumor cell apoptosis and significant tumor reduction. We thus demonstrate selective homing of memory T cells to human tumors and suggest that tumor rejection is based on the recognition of tumor-associated antigens on tumor cells and dendritic cells by autologous specifically activated central and effector memory T cells.
Philipp Beckhove, Markus Feuerer, Mathias Dolenc, Florian Schuetz, Carmen Choi, Nora Sommerfeldt, Jochen Schwendemann, Katrin Ehlert, Peter Altevogt, Gunther Bastert, Volker Schirrmacher, Viktor Umansky
Deregulated expression of both Myc and Bcl-XL are consistent features of human plasma cell neoplasms (PCNs). To investigate whether targeted expression of Myc and Bcl-XL in mouse plasma cells might lead to an improved model of human PCN, we generated Myc transgenics by inserting a single-copy histidine-tagged mouse Myc gene, MycHis, into the mouse Ig heavy-chain Cα locus. We also generated Bcl-XL transgenic mice that contain a multicopy Flag-tagged mouse Bcl-xFlag transgene driven by the mouse Ig κ light-chain 3′ enhancer. Single-transgenic Bcl-XL mice remained tumor free by 380 days of age, whereas single-transgenic Myc mice developed B cell tumors infrequently (4 of 43, 9.3%). In contrast, double-transgenic Myc/Bcl-XL mice developed plasma cell tumors with short onset (135 days on average) and full penetrance (100% tumor incidence). These tumors produced monoclonal Ig, infiltrated the bone marrow, and contained elevated amounts of MycHis and Bcl-XLFlag proteins compared with the plasma cells that accumulated in large numbers in young tumor-free Myc/Bcl-XL mice. Our findings demonstrate that the enforced expression of Myc and Bcl-XL by Ig enhancers with peak activity in plasma cells generates a mouse model of human PCN that recapitulates some features of human multiple myeloma.
Wan Cheung Cheung, Joong Su Kim, Michael Linden, Liangping Peng, Brian Van Ness, Roberto D. Polakiewicz, Siegfried Janz
PTEN is a tumor suppressor gene mutated in many human cancers, and its expression is reduced or absent in almost half of hepatoma patients. We used the Cre-loxP system to generate a hepatocyte-specific null mutation of Pten in mice (AlbCrePtenflox/flox mice). AlbCrePtenflox/flox mice showed massive hepatomegaly and steatohepatitis with triglyceride accumulation, a phenotype similar to human nonalcoholic steatohepatitis. Adipocyte-specific genes were induced in mutant hepatocytes, implying adipogenic-like transformation of these cells. Genes involved in lipogenesis and β-oxidation were also induced, possibly as a result of elevated levels of the transactivating factors PPARγ and SREBP1c. Importantly, the loss of Pten function in the liver led to tumorigenesis, with 47% of AlbCrePtenflox/flox livers developing liver cell adenomas by 44 weeks of age. By 74–78 weeks of age, 100% of AlbCrePtenflox/flox livers showed adenomas and 66% had hepatocellular carcinomas. AlbCrePtenflox/flox mice also showed insulin hypersensitivity. In vitro, AlbCrePtenflox/flox hepatocytes were hyperproliferative and showed increased hyperoxidation with abnormal activation of protein kinase B and MAPK. Pten is thus an important regulator of lipogenesis, glucose metabolism, hepatocyte homeostasis, and tumorigenesis in the liver.
Yasuo Horie, Akira Suzuki, Ei Kataoka, Takehiko Sasaki, Koichi Hamada, Junko Sasaki, Katsunori Mizuno, Go Hasegawa, Hiroyuki Kishimoto, Masahiro Iizuka, Makoto Naito, Katsuhiko Enomoto, Sumio Watanabe, Tak Wah Mak, Toru Nakano
The IL-12Rβ2 gene is expressed in human mature B cell subsets but not in transformed B cell lines. Silencing of this gene may be advantageous to neoplastic B cells. Our objective was to investigate the mechanism(s) and the functional consequence(s) of IL-12Rβ2 gene silencing in primary B cell tumors and transformed B cell lines. Purified tumor cells from 41 patients with different chronic B cell lymphoproliferative disorders, representing the counterparts of the major mature human B cell subsets, tested negative for IL-12Rβ2 gene expression. Hypermethylation of a CpG island in the noncoding exon 1 was associated with silencing of this gene in malignant B cells. Treatment with the DNA methyltransferase inhibitor 5-Aza-2′-deoxycytidine restored IL-12Rβ2 mRNA expression in primary neoplastic B cells that underwent apoptosis following exposure to human recombinant IL-12 (hrIL-12). hrIL-12 inhibited proliferation and increased the apoptotic rate of IL-12Rβ2–transfected B cell lines in vitro. Finally, hrIL-12 strongly reduced the tumorigenicity of IL-12Rβ2–transfected Burkitt lymphoma RAJI cells in SCID-NOD mice through antiproliferative and proapoptotic effects, coupled with neoangiogenesis inhibition related to human IFN-γ–independent induction of hMig/CXCL9. The IL-12Rβ2 gene acts as tumor suppressor in chronic B cell malignancies, and IL-12 exerts direct antitumor effects on IL-12Rβ2–expressing neoplastic B cells.
Irma Airoldi, Emma Di Carlo, Barbara Banelli, Lidia Moserle, Claudia Cocco, Annalisa Pezzolo, Carlo Sorrentino, Edoardo Rossi, Massimo Romani, Alberto Amadori, Vito Pistoia