Inhibition of STAT3 signaling leads to apoptosis of leukemic large granular lymphocytes and decreased Mcl-1 expression

Activation of Stat3 by receptor tyrosine kinases and cytokines regulates survival in human non-small cell carcinoma cells

Overexpression of receptor tyrosine kinases including the epidermal growth factor receptor (EGF-R) as well as nonreceptor tyrosine kinases, such as Src, have been implicated in the formation of human lung cancers. In addition, cytokines like interleukin-6 (IL-6) have been demonstrated to modulate lung cancer cell growth and elevated levels of IL-6 have been shown to be an adverse prognostic factor for patients with lung cancer. Despite a large body of evidence pointing to their potential importance, few direct studies into the role of signal transducers and activators of transcription (STAT) pathways in human lung cancer have been undertaken. Here we demonstrate that multiple nonsmall cell lung cancer cell lines demonstrate constitutive Stat3 DNA-binding activity. Stat3 DNA-binding activity is specifically upregulated by the addition of epidermal growth factor (EGF), IL-6, and hepatocyte-derived growth factor (HGF). Furthermore, the stimulation of Stat3 DNA-binding activity by EGF requires the activity of EGF-R tyrosine kinase as well as Src-kinase, while the upregulation of Stat3 activity by IL-6 or HGF requires only Src-kinase activity. Treatment of A549 lung cancer cells with PD180970 or SU6656, both pharmacological inhibitors of Src-kinase, resulted in reduced Src and Stat3 activity, cell cycle arrest in G2, and reduced viability of cells accompanied by induction of apoptosis. Treatment of Stat3-positive A549 and H358 cells with antisense Stat3 oligonucleotides results in complete loss of Stat3 DNA-binding activity and apoptosis, while Stat3-positive H1299 cells remained healthy. Finally, an adenoviral vector expressing a dominant-negative Stat3 isoform results in loss of Stat3 DNA-binding activity, apoptosis, and reduced cellular viability. These results demonstrate a role of Stat3 in transducing survival signals downstream of tyrosine kinases such as Src, EGF-R, and c-Met, as well as cytokines such as IL-6, in human nonsmall cell lung cancers.

Serine phosphorylation of STAT3 is essential for Mcl-1 expression and macrophage survival

The Bcl-2 family member Mcl-1 is essential for macrophage survival. However, the mechanisms that contribute to the expression of Mcl-1 in these cells have not been fully characterized. The present study focused on the role of signal transducer and activator of transcription 3 (STAT3) in regulation of Mcl-1 in macrophages. Sodium salicylate (NaSal) treatment induced apoptotic cell death in primary human macrophages in a dose- and time-dependent fashion. Incubation with NaSal resulted in the loss of mitochondrial transmembrane potential, the release of cytochrome c and second mitochondria-derived activator of caspase/direct IAP binding protein with low pH of isoelectric point (pI) from the mitochondria, and the activation of caspases 9 and 3. Western blot analysis and reverse transcription-polymerase chain reaction demonstrated that NaSal down-regulated the expression of Mcl-1. Electrophoretic mobility shift assay and Western blot analysis for phosphorylated STAT3 demonstrated that STAT3 was constitutively activated in macrophages and that this STAT3 activation was suppressed by NaSal. The activation of STAT3 in macrophages was dependent on Ser727 phosphorylation, in the absence of detectable Tyr705 phosphorylation. Ectopic expression of STAT3 in murine RAW264.7 macrophages rescued the inhibition of Mcl-1 promoter-reporter gene activation and the cell death induced by NaSal treatment, while a dominant-negative STAT3 resulted in cell death. To confirm its role in primary macrophages, STAT3 antisense (AS) oligodeoxynucleotides (ODNs) were employed. STAT3 AS, but not control, ODNs decreased STAT3 and Mcl-1 expression and resulted in macrophage apoptosis. These observations demonstrate that the STAT3-mediated expression of Mcl-1 is essential for the survival of primary human in vitro differentiated macrophages.

Survival signals in leukemic large granular lymphocytes

The central hypothesis of our laboratory research program in large granular lymphocyte (LGL) leukemia is that leukemic LGL represent antigen-driven cytotoxic T lymphocytes (CTL) with characteristics of dysregulated apoptosis. The clinical features of LGL leukemia highlight the association of autoimmune diseases such as rheumatoid arthritis with the T-cell form of LGL leukemia. We therefore used LGL leukemia as a model disease of dysregulated apoptosis leading to both malignant and autoimmune diseases. Here, we review our understanding of survival signals activated in leukemic LGL in the context of knowledge concerning apoptotic pathways in activated normal lymphocytes.

A major role for Mcl-1 antiapoptotic protein in the IL-6-induced survival of human myeloma cells

Interleukin-6 (IL-6) is a major survival factor for malignant plasma cells involved in multiple myeloma. Using an RNase protection assay, we looked for gene expression of 10 anti- and proapoptotic Bcl-2-family proteins in 12 IL-6-dependent human myeloma cell lines (HMCL). A high Mcl-1 gene expression was found in all HMCLs and the other genes were variably expressed. Out of the 10 Bcl-2-family members, only the Mcl-1 gene was regulated by IL-6. Upon starvation of IL-6, Mcl-1 gene expression decreased in association with myeloma cell apoptosis and was upregulated after adding IL-6 again in association with myeloma cell survival. A constitutive Mcl-1 expression was induced with an Mcl-1-GFP retrovirus in two IL-6-dependent HMCLs. The Mcl-1 HMCLs have a marked reduced apoptosis upon IL-6 starvation compared to HMCLs transduced with control GFP retrovirus and may grow without adding IL-6. These data emphasize the major role of Mcl-1 antiapoptotic protein in the IL-6-induced survival of human myeloma cells.

Inhibition of STAT3 prevents neointima formation by inhibiting proliferation and promoting apoptosis of neointimal smooth muscle cells

In cultured vascular smooth muscle cells (SMCs), STAT3 mediates proliferation signal by directly activating transcription of early growth response genes. Recently, we have found that balloon injury transiently induces JAK2 and STAT3 expressions and activations with a peak at day 7 in rat carotid artery. However, the specific role of STAT3 in neointima formation remains unknown. Adenoviral vector encoding a dominant negative STAT3 (AxCAdnSTAT3) or beta-galactosidase (control) was overexpressed in a balloon-injured artery to inhibit endogenous STAT3 activation selectively. In controls, neointima became evident after day 4, and reached a maximum at day 14. The number of bromodeoxyuridine (BrdU)-positive proliferating or TUNEL-positive apoptotic neointimal SMCs peaked at day 7, decreasing to lower levels by day 14. AxCAdnSTAT3 not only abrogated STAT3 phosphorylation but also decreased BrdU labeling index by 60% and increased TUNEL index by 35% at day 7 versus controls, resulting in the 40% reduction in the intima/media area ratio at day 14. At day 7, in controls, vascular injury upregulated antiapoptotic mediator Mcl-i and Bcl-xL expression by 8-fold to 5-fold, respectively, versus sham, whereas proapoptotic Bax slightly increased by 1.5-fold versus sham. AxCAdnSTAT3 reversed the upregulated Mcl-1 and Bcl-xL levels by 70% and 37%,respectively, while having no affect on Bax expression. In conclusion, the STAT3-mediated pathway plays an important role in neointima formation through enhanced vascular SMC accumulation by promoting cell proliferation and survival.

Signal transducer and activator of transcription proteins in leukemias

Signal transducer and activator of transcription (STAT) proteins are a 7-member family of cytoplasmic transcription factors that contribute to signal transduction by cytokines, hormones, and growth factors. STAT proteins control fundamental cellular processes, including survival, proliferation, and differentiation. Given the critical roles of STAT proteins, it was hypothesized that inappropriate or aberrant activation of STATs might contribute to cellular transformation and, in particular, leukemogenesis. Constitutive activation of mutated STAT3 has in fact been demonstrated to result in transformation. STAT activation has been extensively studied in leukemias, and mechanisms of STAT activation and the potential role of STAT signaling in leukemogenesis are the focus of this review. A better understanding of mechanisms of dysregulation of STAT signaling pathways may serve as a basis for designing novel therapeutic strategies that target these pathways in leukemia cells.

Interleukin-3 stimulation of mcl-1 gene transcription involves activation of the PU.1 transcription factor through a p38 mitogen-activated protein kinase-dependent pathway

We have previously demonstrated that the antiapoptotic gene mcl-1 is activated by interleukin-3 (IL-3) in Ba/F3 pro-B cells through two promoter elements designated the CRE-2 and SIE motifs. While the CRE-2-binding complex contains the CREB protein and is activated by IL-3 through the phosphatidylinositol 3-kinase/Akt-dependent pathway, the identity and cytokine activation pathway of the SIE-binding complex remains unclear. In this report, we demonstrated that PU.1 is one component of the SIE-binding complex. A chromatin immunoprecipitation assay further confirmed that PU.1 binds to the mcl-1 promoter region containing the SIE motif in vivo. While IL-3 stimulation does not significantly alter the SIE-binding activity of PU.1, it markedly increases PU.1's transactivation activity. The latter effect coincides with the increased phosphorylation of PU.1 following IL-3 activation of a p38 mitogen-activated protein kinase (p38(MAPK))-dependent pathway. A serine-to-alanine substitution at position 142 significantly weakens PU.1's ability to be phosphorylated by the p38(MAPK) immunocomplex. Furthermore, this S142A mutant is impaired in the ability to be further stimulated by IL-3 to transactivate the mcl-1 reporter through the SIE motif. Taken together, our results demonstrate that IL-3 stimulation of mcl-1 gene transcription through the SIE motif involves phosphorylation of PU.1 at serine 142 by a p38(MAPK)-dependent pathway.

Inhibition of STAT3 signaling induces apoptosis and decreases survivin expression in primary effusion lymphoma

Despite some exciting new leads in molecular pathogenesis, AIDS-defining primary effusion lymphoma (PEL) remains a fatal malignancy. The lack of substantial progress in the management of PEL demands innovative treatment approaches. Targeting intracellular molecules critical to cell survival is one unexplored strategy for treating PEL. Here we show that inhibition of signal transducer and activator of transcription-3 (STAT3) leads to apoptosis in PEL cells. STAT3 is constitutively phosphorylated in PEL cell lines BC-1, BCBL-1, and VG-1. Transduction of dominant-negative STAT3 and pharmacological STAT3 inhibition caused caspase-dependent cell death. Although STAT3 activation is known to induce expression of Bcl-2 family proteins, PEL cell apoptosis was independent of Bcl-2, Bcl-X(L), or Mcl-1 protein expression. Instead, STAT3 inhibition induced transcriptional repression of survivin, a recently identified inhibitor of apoptosis. Forced overexpression of survivin rescued VG-1 cells from apoptosis induced by STAT3 inhibition. Our findings suggest that activated STAT3 signaling directly contributes to malignant progression of PEL by preventing apoptosis, acting through the prosurvival protein survivin. Since constitutive STAT3 activation and survivin expression have been widely documented in different types of cancers, their linkage may extend to many malignancies and be critical to their pathogenesis.

Cloning and characterization of a functional promoter of the human SOCS-3 gene

SOCS-3 is a member of a newly discovered protein family that inhibits LIF-activated Janus kinase (JAK)-signal transducers and activators of transcription (STAT) signaling in a negative auto-regulatory manner. In this study, we have cloned and characterized the promoter region of the human SOCS-3 gene. This region is approximately 1.1 kbp in length and consists of two putative STAT-binding elements, a G-rich element, and a putative TATA box. These elements are highly conserved in both murine and rat SOCS-3 promoters. Functional analysis of this region shows that the whole fragment (approximately 1.1 kbp) has high basal promoter activity and is responsive to growth factors. We also found that the wild type SOCS-3 promoter construct has significantly greater activity in non-small-cell lung cancer cell lines than in normal cells in accordance with STAT3 disregulation in these cells. Cloning of the human SOCS-3 promoter should help uncover mechanisms of regulation of the JAK-STAT pathway in human cancer.

Expression of Mcl-1 in mantle cell lymphoma is associated with high-grade morphology, a high proliferative state, and p53 overexpression

Mantle cell lymphoma (MCL) is a distinct type of B-cell non-Hodgkin's lymphoma characterized by the t(11;14)(q13;q32) and cyclin D1 overexpression. Defects in apoptosis may contribute to pathogenesis. This study evaluated the expression of the anti-apoptotic protein Mcl-1 in two MCL cell lines and five frozen MCL tumours (four small-cell, one blastoid/large-cell) using western blot analysis. Mcl-1 expression was also assessed in 36 formalin-fixed, paraffin wax-embedded MCL tumours (24 small-cell, 12 blastoid/large-cell) by immunohistochemistry. Western blot analysis revealed the expected 37 kD protein product in both MCL cell lines and in five frozen tumours, with the blastoid case having the highest expression level. Using a cut-off of >10% immunolabelled cells for Mcl-1, it was found that 12 of 36 MCL tumours were positive. Mcl-1-positive tumours had a higher frequency of blastoid/large-cell morphology (8/12 versus 4/24, p = 0.009), p53 overexpression (3/10 versus 1/23, p = 0.04), and higher Ki67 immuno-labelling (p = 0.002). It is concluded that expression of Mcl-1 in MCL is heterogeneous. A relatively high level of Mcl-1 expression correlates with high-grade morphology, a high proliferative state, and p53 overexpression.

Common expression of an unusual CD45 isoform on T cells from patients with large granular lymphocyte leukaemia and autoimmune lymphoproliferative syndrome

Patients with T-cell large granular lymphocyte (T-LGL) leukaemia and autoimmune lymphoproliferative syndrome (ALPS) share many features, including autoimmunity and an expansion of (cytotoxic) T cells, which in ALPS patients express an unusual (B220) isoform of CD45, corresponding to an altered O-glycosylation profile. Here we showed that T-LGL leukaemia cells also expressed this B220 isoform. We hypothesize that B220+ T cells constitute proliferating T cells that have become competent to undergo apoptosis, but that constitutive (ALPS) or functional (T-LGL) defects prevent this process. Altered O-glycosylation of the extracellular domains of CD45 may have consequences for this tyrosine phosphatase as a regulator of cell proliferation and survival.

Inhibition of Bcr-Abl kinase activity by PD180970 blocks constitutive activation of Stat5 and growth of CML cells

Chronic myelogenous leukemia (CML) is a myeloproliferative disease characterized by the BCR-ABL genetic translocation and constitutive activation of the Abl tyrosine kinase. Among members of the Signal Transducers and Activators of Transcription (STAT) family of transcription factors, Stat5 is activated by the Bcr-Abl kinase and is implicated in the pathogenesis of CML. We recently identified PD180970 as a new and highly potent inhibitor of Bcr-Abl kinase. In this study, we show that blocking Bcr-Abl kinase activity using PD180970 in the human K562 CML cell line resulted in inhibition of Stat5 DNA-binding activity with an IC(50) of 5 nM. Furthermore, abrogation of Abl kinase-mediated Stat5 activation suppressed cell proliferation and induced apoptosis in K562 cells, but not in the Bcr-Abl-negative myeloid cell lines, HEL 92.1.7 and HL-60. Dominant-negative Stat5 protein expressed from a vaccinia virus vector also induced apoptosis of K562 cells, consistent with earlier studies that demonstrated an essential role of Stat5 signaling in growth and survival of CML cells. RNA and protein analyses revealed several candidate target genes of Stat5, including Bcl-x, Mcl-1, c-Myc and cyclin D2, which were down-regulated after treatment with PD180970. In addition, PD180970 inhibited Stat5 DNA-binding activity in cultured primary leukemic cells derived from CML patients. To detect activated Stat5 in CML patient specimens, we developed an immunocytochemical assay that can be used as a molecular end-point assay to monitor inhibition of Bcr-Abl signaling. Moreover, PD180970 blocked Stat5 signaling and induced apoptosis of STI-571 (Gleevec, Imatinib)-resistant Bcr-Abl-positive cells. Together, these results suggest that the mechanism of action of PD180970 involves inhibition of Bcr-Abl-mediated Stat5 signaling and provide further evidence that compounds in this structural class may represent potential therapeutic agents for CML.

Inhibition of constitutively active Stat3 suppresses proliferation and induces apoptosis in glioblastoma multiforme cells

Glioblastoma multiforme (GBM), the most common and malignant central nervous system tumor in humans, is highly proliferative and resistant to apoptosis. Stat3, a latent transcription factor being activated by aberrant cytokine or growth factor signaling, acts as a suppressor of apoptosis in a number of cancer cells. Here we report that GBM tumors and cell lines contain high levels of constitutively activated Stat3 when compared with normal human astrocytes, white matter, and normal tissue adjacent to tumor. The persistent activation of Stat3 is in part, attributable to an autocrine action of interleukin-6 in the GBM cell line U251. Janus kinase inhibitor AG490 inhibits Stat3 activation with a concomitant reduction in steady-state levels of Bcl-X(L), Bcl-2 and Mcl-1 proteins and induces apoptosis in U251 cells as revealed by Poly (ADP-ribose) polymerase cleavage and Annexin-V staining. Expression of a dominant negative mutant Stat3 protein or treatment with AG490 markedly reduces the proliferation of U251 cells by inhibiting the constitutive activation of Stat3. These results provide evidence that constitutive activation of Stat3 contributes to the pathogenesis of glioblastoma by promoting both proliferation and survival of GBM cells. Therefore, targeting Stat3 signaling may provide a potential therapeutic intervention for GBM.

Rheumatoid arthritis synoviocyte survival is dependent on Stat3

Rheumatoid arthritis (RA) synovial fibroblasts (SFs) are relatively resistant to apoptosis and exhibit dysregulated growth secondary to production of autocrine-acting growth factors and the accumulation of cell-autonomous defects. Many of the cytokines and growth factors expressed during RA synovitis, including IL-6, epidermal growth factor (EGF), and platelet-derived growth factor, activate the transcription factor Stat3 that has been implicated in promoting cell growth and survival. We analyzed the role of Stat3 in mediating the abnormal growth and survival properties of RA synoviocytes using retroviral-mediated gene transfer of a dominant negative mutant of Stat3, termed Stat3-YF. Approximately 3- to 5-fold overexpression of Stat3-YF effectively blocked endogenous Stat3 activation and Stat3-dependent gene expression, including expression of the socs3 and myc genes. Stat3-YF-transduced RA synoviocytes failed to grow in culture, exhibited markedly diminished [(3)H]thymidine incorporation (>90% decreased), and died spontaneously. Cell death occurred by apoptosis, as confirmed by annexin V staining, propidium iodide exclusion, and identification of cells with subdiploid levels of DNA. In marked contrast to control cells, EGF accelerated death of Stat3-YF-transduced SFs, such that >90% of cells were dead within 24-48 h of transduction. These results indicate that ablation of Stat3 function converts EGF from a growth/survival factor for RA synoviocytes to a death factor. Stat3-YF also induced apoptosis in osteoarthritis synoviocytes, and levels of apoptosis were increased by exogenous EGF. Apoptosis in Stat3-YF-transduced osteoarthritis synoviocytes was suppressed when Stat1 activity was blocked using a dominant negative Stat1 mutant. Our results identify Stat3 as an important molecule for RA SF survival, and suggest that Stat3 may represent a good target for gene therapy.

Roles of activated Src and Stat3 signaling in melanoma tumor cell growth

Activation of protein tyrosine kinases is prevalent in human cancers and previous studies have demonstrated that Stat3 signaling is a point of convergence for many of these tyrosine kinases. Moreover, a critical role for constitutive activation of Stat3 in tumor cell proliferation and survival has been established in diverse cancers. However, the oncogenic signaling pathways in melanoma cells remain to be fully defined. In this study, we demonstrate that Stat3 is constitutively activated in a majority of human melanoma cell lines and tumor specimens examined. Blocking Src tyrosine kinase activity, but not EGF receptor or JAK family kinases, leads to inhibition of Stat3 signaling in melanoma cell lines. Consistent with a role of Src in the pathogenesis of melanoma, we show that c-Src tyrosine kinase is activated in melanoma cell lines. Significantly, melanoma cells undergo apoptosis when either Src kinase activity or Stat3 signaling is inhibited. Blockade of Src or Stat3 is also accompanied by down-regulation of expression of the anti-apoptotic genes, Bcl-x(L) and Mcl-1. These findings demonstrate that Src-activated Stat3 signaling is important for the growth and survival of melanoma tumor cells.

Blockade of Fas-dependent apoptosis by soluble Fas in LGL leukemia

Altered expression of the Fas-Fas ligand apoptotic pathway leads to lymphoproliferative and autoimmune diseases. Inlpr/lpr mice and children with autoimmune lymphoproliferative syndrome, defective apoptosis is due to Fas mutations. Large granular lymphocyte (LGL) leukemia is a clonal lymphoproliferative disorder associated with rheumatoid arthritis. Leukemic LGLs are resistant to Fas-dependent apoptosis despite expressing high levels of Fas. Such resistance can be overcome by activating leukemic LGLs in vitro, suggesting inhibition of Fas signaling in leukemic cells. We report that sera from patients with LGL leukemia contain high levels of soluble Fas. Ten of these 33 patients with LGL leukemia also had rheumatoid arthritis. Cloning and sequencing revealed expression of multiple Fas messenger RNA variants in leukemic LGL. These Fas variants, including 3 newly described here, encode soluble Fas molecules. Supernatants from cells transfected with these Fas variants blocked Fas-dependent apoptosis of leukemic LGLs. These results suggest that blockade of Fas-signaling by soluble Fas may be a mechanism leading to apoptosis resistance in leukemic LGLs.

DNA microarray analysis of T cell-type lymphoproliferative disease of granular lymphocytes

Lymphoproliferative disease of granular lymphocytes (LDGL) is characterized by the clonal proliferation of large granular lymphocytes of either T- or natural killer cell origin. To better understand the nature of T cell-type LDGL, we purified the CD4-CD8+ proliferative fractions from LDGL patients (n=4) and the surface marker-matched T cells isolated from healthy volunteers (n=4), and compared the expression profiles of 3456 genes using DNA microarray. Through this analysis, we identified a total of six genes whose expression was active in the LDGL T cells, but silent in the normal ones. Interestingly, expression of the gene for interleukin (IL) 1beta was specific to LDGL T cells, which was further confirmed by the examination of the serum level of IL-1beta protein. Given its important role in inflammatory reactions, the disease-specific expression of IL-1beta may have a causative relationship with the LDGL-associated rheumatoid arthritis. Spectratyping analysis of the T-cell receptor repertoire also proved the monoclonal or oligoclonal nature of LDGL cells. These data have shown that microarray analysis with a purified T-cell subset is an efficient approach to investigate the pathological condition of Tcell-type LDGL.

MCL1 provides a window on the role of the BCL2 family in cell proliferation, differentiation and tumorigenesis

The MCL1 gene (myeloid cell leukemia-1) was discovered serendipitously about a decade ago and proved to be a member of the emerging BCL2 gene family. Ongoing studies of this gene provide an interesting perspective on the role of the BCL2 family in transitions in cell phenotype. Specifically, gene products that influence cell viability as a major effect (eg MCL1, BCL2 and other family members) can act as key determinants in cell proliferation, differentiation and tumorigenesis. Although they do not have a direct role in proliferation/differentiation programs, these genes can either permit these programs to proceed or prevent them. Through such effects, the BCL2 family regulates the normal flow of cells through cycles of proliferation and along various pathways of differentiation. A model is presented suggesting that this is accomplished by sustaining or inhibiting viability at critical points in the cell lifecycle. These critical points represent windows of time during which cell fate transitions are effected. They can also be visualized as windows that open or close to promote or prevent continued progression along various cell fate pathways. The pattern of BCL2 family expression at these points allows for the proliferation differentiation, and continued viability of cell types that are needed, while aborting these processes for cells that are overabundant or no longer needed. The combined action of the various family members can therefore control the fate of cells, tissues and even the organism. This mechanism involving apoptosis-related genes is readily executable, and is poised to respond to external signals through the differential regulation of BCL2 family members. As such, it plays an important role in the maintenance of tissue homeostasis and function. Alterations that affect the BCL2 family impair the capacity to control the flow of cells through these critical points, and thereby 'leave the window open' for cell immortalization and cancer. Targeting this family may thus provide a means of inhibiting cancer development and inducing apoptosis in tumor cells.

The role of hepatocyte growth factor (scatter factor) in epithelial-mesenchymal transition and breast cancer

North American women have a one in eight lifetime risk of developing breast cancer, and approximately one in three women with breast cancer will die of metastases. We, and others, have recently shown that high levels of expression of hepatocyte growth factor (HGF) and its receptor Met are associated with invasive human breast cancer and may be causally linked to metastasis. This high level of HGF and Met expression has been considered as a possible indicator of earlier recurrence and shortened survival in breast cancer patients. In contrast, HGF expression (but not Met) is strongly suppressed in normal breast epithelial cells. HGF and Met are therefore candidate targets for therapeutic intervention in the treatment of breast cancer. We have recently demonstrated that sustained activation or hyper-activation of c-Src and Stat3, which occurs in invasive breast cancer, can stimulate strong expression of HGF in carcinoma cells. In contrast, transient induction of Stat3 occurs in normal epithelium and promotes mammary tubulogenesis. We hypothesize that increased autocrine HGF-Met signaling is a critical downstream function of c-Src-Stat3 activation in mammary tumorigenesis. Future studies will identify novel Stat3 consensus sites that regulate HGF promoter activity and HGF expression preferentially in carcinoma cells and could lead to novel therapeutic drugs that specifically block HGF expression in mammary carcinoma cells, and which could be used in combined treatments to abrogate metastasis.

Targeting apoptosis in cancer chemotherapy

The aim of cancer biology is for a better understanding of the molecular basis of cancer, with the expectation that this will result in therapeutic advances and improved outcomes for patients. The discovery of apoptosis has contributed much to our understanding of the mechanisms of cell death, in both normal and neoplastic cells, and it has led to changes in the way that chemotherapy has been viewed. It is now increasingly accepted that part of the efficacy of conventional chemotherapeutic drugs is due to their ability to induce apoptosis, although this area is not without controversy. This has allowed advances in the fundamental understanding of apoptosis to have similar impacts upon cancer biology. It is now possible to construct a framework where cellular decisions about life and death can be seen as the result of a balance of pro- and anti-apoptotic signals, enacted by protein members of the Bcl-2 family, controlling mitochondrial cytochrome c release. This framework has allowed the importance of providing death signals and abrogating survival signals to both be appreciated. A range of novel approaches to the induction of apoptosis by downregulating survival signalling are described. In addition, many alternative strategies aimed at targeting particular molecular abnormalities of neoplastic cells as a means of inducing apoptosis are also under investigation and several of these are discussed. The mechanistic understanding of cell death will have profound impacts upon the practice of oncology and outlook for many patients.

Effects of the Bcr/abl kinase inhibitors STI571 and adaphostin (NSC 680410) on chronic myelogenous leukemia cells in vitro

The adenosine triphosphate binding-site-directed agent STI571 and the tyrphostin adaphostin are undergoing evaluation as bcr/abl kinase inhibitors. The current study compared the effects of these agents on the survival of K562 cells, bcr/abl-transduced FDC-P1 cells, and myeloid progenitors from patients with chronic myelogenous leukemia (CML) compared with healthy donors. Treatment of K562 cells with 10 microM adaphostin resulted in decreased p210(bcr/abl) polypeptide levels in the first 6 hours, followed by caspase activation and accumulation of apoptotic cells in less than 12 hours. By 24 hours, 90% of the cells were apoptotic and unable to form colonies. In contrast, 20 microM STI571 caused rapid inhibition of bcr/abl autophosphorylation without p210(bcr/abl) degradation. Although this was followed by the inhibition of Stat5 phosphorylation and the down-regulation of Bcl-x(L) and Mcl-1, only 7% +/- 3% and 25% +/- 9% of cells were apoptotic at 16 and 24 hours, respectively. Instead, the cytotoxic effects of STI571 became more pronounced with prolonged exposure, with IC90 values greater than 20 microM and 1.0 +/- 0.6 microM after 24 and 48 hours, respectively. Consistent with these results, 24-hour adaphostin exposure inhibited CML granulocyte colony-forming units (CFU-G) (median IC50, 12 microM) but not normal CFU-G (median IC50, greater than 20 microM), whereas 24-hour STI571 treatment had no effect on CML or normal CFU-G. Additional experiments revealed that STI571-resistant K562 cells remained sensitive to adaphostin. Moreover, the combination of STI571 + adaphostin induced more cytotoxicity in K562 cells and in CML CFU-G than either agent alone did. Collectively, these results identify adaphostin as a mechanistically distinct CML-selective agent that retains activity in STI571-resistant cell lines.

8p12 stem cell myeloproliferative disorder: the FOP-fibroblast growth factor receptor 1 fusion protein of the t(6;8) translocation induces cell survival mediated by mitogen-activated protein kinase and phosphatidylinositol 3-kinase/Akt/mTOR pathways

The FOP-fibroblast growth factor receptor 1 (FGFR1) fusion protein is expressed as a consequence of a t(6;8) (q27;p12) translocation associated with a stem cell myeloproliferative disorder with lymphoma, myeloid hyperplasia and eosinophilia. In the present report, we show that the fusion of the leucine-rich N-terminal region of FOP to the catalytic domain of FGFR1 results in conversion of murine hematopoietic cell line Ba/F3 to factor-independent cell survival via an antiapoptotic effect. This survival effect is dependent upon the constitutive tyrosine phosphorylation of FOP-FGFR1. Phosphorylation of STAT1 and of STAT3, but not STAT5, is observed in cells expressing FOP-FGFR1. The survival function of FOP-FGFR1 is abrogated by mutation of the phospholipase C gamma binding site. Mitogen-activated protein kinase (MAPK) is also activated in FOP-FGFR1-expressing cells and confers cytokine-independent survival to hematopoietic cells. These results demonstrate that FOP-FGFR1 is capable of protecting cells from apoptosis by using the same effectors as the wild-type FGFR1. Furthermore, we show that FOP-FGFR1 phosphorylates phosphatidylinositol 3 (PI3)-kinase and AKT and that specific inhibitors of PI3-kinase impair its ability to promote cell survival. In addition, FOP-FGFR1-expressing cells show constitutive phosphorylation of the positive regulator of translation p70S6 kinase; this phosphorylation is inhibited by PI3-kinase and mTOR (mammalian target of rapamycin) inhibitors. These results indicate that translation control is important to mediate the cell survival effect induced by FOP-FGFR1. Finally, FOP-FGFR1 protects cells from apoptosis by survival signals including BCL2 overexpression and inactivation of caspase-9 activity. Elucidation of signaling events downstream of FOP-FGFR1 constitutive activation provides insight into the mechanism of leukemogenesis mediated by this oncogenic fusion protein.

Acute and chronic neutropenias. What is new?

Recently, some of the mechanisms and consequences in the severe chronic neutropenias (e.g. the neutrophil elastase gene mutations and the risk to progress to myelodysplasia and acute leukaemia) and in drug-induced agranulocytosis (e.g. the apoptosis-inducing ability of metabolites of clozapine) have been elucidated, and new aspects of autoimmune and the large granular lymphocyte syndrome were described (e.g. aberrant elaboration of Fas-ligand causing neutrophil apoptosis). Investigations of the mild to moderate chronic neutropenias have shown the significance of interactions between the myeloid development and the immune network (e.g. relations to immunoglobulin aberrations). Granulocyte-colony stimulation factor (G-CSF) is widely used in patients with severe chronic neutropenia, however, its use in other conditions is mostly based on anecdotal evidence. In addition, immune modulating regimens, such as metothrexate, ciclosporine and monoclonal antibodies, are increasingly employed for the autoimmune neutropenias.

Phosphotyrosyl peptides block Stat3-mediated DNA binding activity, gene regulation, and cell transformation

Signal transducers and activators of transcription (STATs) comprise a family of cytoplasmic signaling proteins that participates in normal cellular responses to cytokines and growth factors. Frequently, however, constitutive activation of certain STAT family members, particularly Stat3, has accompanied a wide variety of human malignancies. To identify small molecule inhibitors of Stat3, we investigated the ability of the Stat3 SH2 domain-binding peptide, PY*LKTK (where Y* represents phosphotyrosine), to disrupt Stat3 activity in vitro. The presence of PY*LKTK, but not PYLKTK or PFLKTK, in nuclear extracts results in significant reduction in the levels of DNA binding activities of Stat3, to a lesser extent of Stat1, and with no effect on that of Stat5. Analyses of alanine scanning mutagenesis and deletion derivatives of PY*LKTK reveal that the Leu residue at the Y+1 position and a substituent at the Y-1 position (but not necessarily Pro) are essential for the disruption of active Stat3, thereby mapping the minimum active sequence to the tripeptide, XY*L. Studies involving bead-coupled PY*LKTK peptide demonstrate that this phosphopeptide directly complexes with Stat3 monomers in vitro, suggesting that PY*LKTK disrupts Stat3:Stat3 dimers. As evidence for the functional importance of peptide-directed inhibition of Stat3, PY*LKTK-mts (mts, membrane translocating sequence) selectively inhibits constitutive and ligand-induced Stat3 activation in vivo. Furthermore, PY*LKTK-mts suppresses transformation by the Src oncoprotein, which has been shown previously to require constitutive Stat3 activation. Altogether, we have identified a minimal peptide that inhibits Stat3 signaling and provides the conceptual basis for use of this peptide as a lead for novel peptidomimetic drug design.

Inhibition of constitutively active Stat3 suppresses growth of human ovarian and breast cancer cells

Signal transducers and activators of transcription (STATs) are transcription factors activated in response to cytokines and growth factors. Constitutively active Stat3 has been shown to mediate oncogenic transformation in cultured cells and induce tumor formation in mice. An increasing number of tumor-derived cell lines as well as samples from human cancer have been reported to express constitutively active Stat3 protein. We previously demonstrated that ovarian cancer cell lines express high levels of constitutively active Stat3. In this study, we show that inhibition of the Stat3 signaling pathway using the Janus Kinase-selective inhibitor, AG490, and a dominant negative Stat3 (Stat3beta) significantly suppresses the growth of ovarian and breast cancer cell lines harboring constitutively active Stat3. In the ovarian cancer cell lines, AG490 also diminished the phosphorylation of Stat3, Stat3 DNA binding activity, and the expression of Bcl-x(L). Further, AG490 induced significant apoptosis in ovarian and breast cancer cell lines expressing high levels of constitutively active Stat3 but had a less profound effect on normal cells lacking constitutively active Stat3. AG490 also enhanced apoptosis induced by cisplatin in ovarian cancer cells. These results suggest that inhibition of Stat3 signaling may provide a potential therapeutic approach for treating ovarian and breast cancers.

How melanoma cells evade trail-induced apoptosis

At the doses used clinically, chemotherapy is believed to kill melanoma by a final common 'mitochondrial' pathway that leads to apoptosis. Similarly, several natural defence mechanisms kill melanoma by the same pathways. A corollary to the latter is that survival of melanoma in the host is due to the development of anti-apoptotic mechanisms in melanoma cells. What are these mechanisms? And how might we bypass them to improve the treatment of melanoma?

Apoptosis and the response to anticancer therapy

Apoptosis is a distinctive form of cell death that reflects cleavage of a subset of intracellular polypeptides by proteases known as caspases. Two major intracellular caspase cascades, one activated predominantly by death receptor ligands and the other triggered by various cellular stresses, including DNA damage and microtubule disruption, have been delineated. Activation of these protease cascades is tightly regulated by a number of polypeptides, including Bcl-2 family members, inhibitor of apoptosis proteins, and several protein kinases. The demonstration that many antineoplastic agents induce apoptosis in susceptible cells raises the possibility that factors affecting caspase activation and activity might be important determinants of anticancer drug sensitivity. Here, we review recent studies describing the regulation of apoptotic pathways and identify potential implications of these findings for resistance to antineoplastic agents.

CD95 antigen mutations in hematopoietic malignancies

The CD95 receptor, also known as Fas/Apo-1, is a member of the Tumor Necrosis Factor receptor (TNF-R) family of death receptors. Apoptosis mediated by CD95 plays a central role in maintaining homeostasis of the immune system. Dysregulation of the CD95 apoptotic pathway has been proposed as a mechanism of oncogenesis by providing a survival advantage to potentially malignant cells. This extended lifespan could allow the accumulation of further mutations leading to malignant transformation. Several mechanisms of resistance to CD95 mediated apoptosis have been identified, including reduced surface expression of the receptor, overexpression of anti-apoptotic molecules, and loss of function mutations. This review will focus on the potential role of the CD95-CD95 ligand system in the pathogenesis of hematological malignancies, with particular emphasis on recent work from our laboratory examining the expression of CD95 in B cell lymphomas. We demonstrate that CD95 mutations occur at low frequency in NHL tumors, however, surface expression of the CD95 protein varies with the subtype of lymphoma. Loss of surface CD95 is more likely to occur in lymphomas of aggressive histology, and is unrelated to the detection of CD95 mutations.

T Cell and NK Cell Lymphoproliferative Disorders

This review covers the diagnosis and management of natural killer and peripheral T-cell lymphomas (PTCL). Problems with PTCL include their rarity, representing usually 10-15% of non-Hodgkin's lymphomas in the Western Hemisphere, morphologic heterogeneity, and lack of immunophenotypic markers for clonality. Additionally, their clinical behavior is variable and may not correlate with morphology.

Dr. Kinney gives a general overview of the diagnosis of PTCL and NK cell neoplasms. Emphasis will be placed on extranodal T cell and natural killer (NK) cell lymphomas such as hepatosplenic lymphoma, subcutaneous panniculitis-like lymphoma and nasal/nasal type T/NK-cell lymphoma. The use of ALK gene regulation in the classification of anaplastic large cell lymphoma is also reviewed.

Dr. Loughran describes current understanding of the pathogenesis of large granular lymphocyte (LGL) leukemia. The discussion focuses on LGL leukemia as an instructive model of dysregulated apoptosis causing both malignant and autoimmune disease. Current management options and mechanisms of therapeutic response are also described.

Dr. Greer addresses whether PTCL should be treated differently from the more common diffuse large B cell lymphomas. He discusses the therapeutic options for anaplastic large cell lymphoma (ALCL), from a conservative approach for primary cutaneous ALCL to combination chemotherapy for the highly chemosensitive ALCL expressing anaplastic lymphoma kinase. He reviews therapy options for the extranodal subtypes of PTCL by drawing from series in adults, pediatrics, dermatology, and the Far East.