Abstract 4209: CD38KO K-NK cells prevent NK cell fratricide effect and improve isatuximab-mediated cytotoxicity against multiple myeloma cells

Multiple myeloma (MM) is a plasma cell malignancy characterized by clonal accumulation of malignant plasma cells in the bone marrow. CD38 is highly expressed on MM cells, and antibodies targeting CD38 (such as Isatuximab and Daratumumab) induce MM cell killing though several mechanisms, particularly by NK cell-mediated antibody dependent cellular cytotoxicity (ADCC). However, NK cells also express CD38 and treatment with anti-CD38 antibodies results in a rapid decrease of NK cells presumably due to fratricide, which may potentially limit NK cell mediated ADCC and reduce the efficacy of anti-CD38 antibody treatment. NK cells lacking CD38 in combination with Daratumumab have been shown to be resistant to NK cell fratricide and have improved ADCC. Here, we investigated the effect of knocking out CD38 in K-NK cells (CD38KO K-NK) in combination with Isatuximab. Peripheral blood NK cells were isolated from healthy donors and expanded using Kiadis PM21 particle technology (Oyer et al, Cytotherapy 2016) to produce highly activated K-NK cells. To produce CD38KO K-NK cells, CRISPR gene editing was applied during NK cell expansion by electroporating with Cas9/RNP complexes targeting CD38, and successful deletion of CD38 was confirmed by flow cytometry analysis. Analysis of key NK cell receptors by flow cytometry evidenced very similar receptor profiles between WT and CD38KO K-NK cells, suggesting that CD38 deletion does not affect the potent activation state of the K-NK cells. Importantly, CD38KO K-NK cells were found to be resistant to Isatuximab-induced fratricide. The cytotoxic activity of CD38KO K-NK cells in combination with Isatuximab against LP-1 and H929 MM cell lines was also measured. Calcein release assay and Incucyte based analysis revealed that cytotoxicity of CD38KO K-NK cells is enhanced in presence of Isatuximab, and that CD38KO K-NK cells are more cytotoxic than WT when combined with Isatuximab. Furthermore, the effect of Isatuximab/CD38KO K-NK cells combination also in association with SAR444245 (also termed THOR-707; Ptacin et al, Nat Commun 2021), an engineered non-α binding IL-2 that promotes NK cell activation and proliferation, was tested. Cytotoxicity of WT or CD38KO NK cells is enhanced in the presence of SAR444245. Indeed, addition of SAR444245 was found to further enhance the cytotoxic activity of CD38KO K-NK cells against LP-1 MM cells when combined with Isatuximab, resulting in an overall superior and sustained cytotoxicity. These data suggest that deletion of CD38 mitigates NK cell fratricide and improves Isatuximab-mediated ADCC against MM cells, and provide evidence for the therapeutic potential of the triple combination CD38KO NK cells, Isatuximab and SAR444245 in the setting of MM.

Citation Format: Marco Meloni, Pauline Perrin, Erik Slinger, Chrissta Maracle, Alain Fournier, Nicole Acuff, Jill Mooney, Robert Y. Igarashi, Angela Virone-Oddos, Marielle Chiron. CD38KO K-NK cells prevent NK cell fratricide effect and improve isatuximab-mediated cytotoxicity against multiple myeloma cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4209.

The human cytomegalovirus-encoded G protein-coupled receptor UL33 exhibits oncomodulatory properties

Herpesviruses can rewire cellular signaling in host cells by expressing viral G protein-coupled receptors (GPCRs). These viral receptors exhibit homology to human chemokine receptors, but some display constitutive activity and promiscuous G protein coupling. Human cytomegalovirus (HCMV) has been detected in multiple cancers, including glioblastoma, and its genome encodes four GPCRs. One of these receptors, US28, is expressed in glioblastoma and possesses constitutive activity and oncomodulatory properties. UL33, another HCMV-encoded GPCR, also displays constitutive signaling via Gα_q, Gα_i, and Gα_s proteins. However, little is known about the nature and functional effects of UL33-driven signaling. Here, we assessed UL33's signaling repertoire and oncomodulatory potential. UL33 activated multiple proliferative, angiogenic, and inflammatory signaling pathways in HEK293T and U251 glioblastoma cells. Notably, upon infection, UL33 contributed to HCMV-mediated STAT3 activation. Moreover, UL33 increased spheroid growth in vitro and accelerated tumor growth in different in vivo tumor models, including an orthotopic glioblastoma xenograft model. UL33-mediated signaling was similar to that stimulated by US28; however, UL33-induced tumor growth was delayed. Additionally, the spatiotemporal expression of the two receptors only partially overlapped in HCMV-infected glioblastoma cells. In conclusion, our results unveil that UL33 has broad signaling capacity and provide mechanistic insight into its functional effects. UL33, like US28, exhibits oncomodulatory properties, elicited via constitutive activation of multiple signaling pathways. UL33 and US28 might contribute to HCMV's oncomodulatory effects through complementing and converging cellular signaling, and hence UL33 may represent a promising drug target in HCMV-associated malignancies.

CD40 signaling instructs chronic lymphocytic leukemia cells to attract monocytes via the CCR2 axis

Chronic lymphocytic leukemia (CLL) cells are provided with essential survival and proliferative signals in the lymph node microenvironment. Here, CLL cells engage in various interactions with bystander cells such as T cells and macrophages. Phenotypically distinct types of tumor infiltrating macrophages can either be tumor supportive (M2) or play a role in tumor immune surveillance (M1). Although recent in vitro findings suggest a protective role for macrophages in CLL, the actual balance between these macrophage subsets in CLL lymphoid tissue is still unclear. Furthermore, the mechanism of recruitment of monocytes towards the CLL lymph node is currently unknown. Both questions are addressed in this paper. Immunofluorescence staining of lymph node samples showed macrophage skewing towards an M2 tumor-promoting phenotype. This polarization likely results from CLL-secreted soluble factors, as both patient serum and CLL-conditioned medium recapitulated the skewing effect. Considering that CLL cell cytokine secretion is affected by adjacent T cells, we next studied CLL-mediated monocyte recruitment in the presence or absence of T-cell signals. While unstimulated CLL cells were inactive, T cell-stimulated CLL cells actively recruited monocytes. This correlated with secretion of various chemokines such as C-C-motif-ligand-2,3,4,5,7,24, C-X-C-motif-ligand-5,10, and Interleukin-10. We also identified CD40L as the responsible T-cell factor that mediated recruitment, and showed that recruitment critically depended on the C-C-motif-chemokine-receptor-2 axis. These studies show that the shaping of a tumor supportive microenvironment depends on cytokinome alterations (including C-C-motif-ligand-2) that occur after interactions between CLL, T cells and monocytes. Therefore, targeted inhibition of CD40L or C-C-motif-chemokine-receptor-2 may be relevant therapeutic options.

Cell lines generated from a chronic lymphocytic leukemia mouse model exhibit constitutive Btk and Akt signaling

Chronic lymphocytic leukemia (CLL) is characterized by the accumulation of mature CD5⁺ B cells in blood. Spontaneous apoptosis of CLL cells in vitro has hampered in-depth investigation of CLL pathogenesis. Here we describe the generation of three monoclonal mouse cell lines, EMC2, EMC4 and EMC6, from the IgH.TEμ CLL mouse model based on sporadic expression of SV40 large T antigen. The cell lines exhibit a stable CD5⁺CD43⁺IgM⁺CD19⁺ CLL phenotype in culture and can be adoptively transferred into Rag1^−/− mice. RNA-seq analysis revealed only minor differences between the cell lines and their primary tumors and suggested that NF-κB and mTOR signaling pathways were involved in cell line outgrowth. In vitro survival and proliferation was dependent on constitutive phosphorylation of Bruton's tyrosine kinase (Btk) at Y551/Y223, and Akt(S473). Treatment of the cell lines with small molecule inhibitors specific for Btk (ibrutinib) or PI3K (idelalisib), which is upstream of Akt, resulted in reduced viability, proliferation and fibronectin-dependent cell adhesion. Treatment of cell line-engrafted Rag1^−/− mice with ibrutinib was associated with transient lymphocytosis, reduced splenomegaly and increased overall survival. Thus, by generating stable cell lines we established a novel platform for in vitro and in vivo investigation of CLL signal transduction and treatment modalities.

Targeting antigen-independent proliferation in chronic lymphocytic leukemia through differential kinase inhibition

The clinical success of B-cell receptor (BCR) signaling pathway inhibitors in chronic lymphocytic leukemia (CLL) is attributed to inhibition of adhesion in and migration towards the lymph node. Proliferation of CLL cells is restricted to this protective niche, but the underlying mechanism(s) is/are not known. Treatment with BCR pathway inhibitors results in rapid reductions of total clone size, while CLL cell survival is not affected, which points towards inhibition of proliferation. In vitro, BCR stimulation does not induce proliferation of CLL, but triggering via Toll-like receptor, tumor necrosis factor or cytokine receptors does. Here, we investigated the effects of clinically applied inhibitors that target BCR signaling, in the context of proliferation triggered either via CD40L/IL-21 or after CpG stimulation. CD40L/IL-21-induced proliferation could be inhibited by idelalisib and ibrutinib. We demonstrate this was due to blockade of CD40L-induced ERK-signaling. Targeting JAKs, but not SYK, blocked CD40L/IL-21-induced proliferation. In contrast, PI3K, BTK as well as SYK inhibition prevented CpG-induced proliferation. Knockdown experiments showed that CD40L/IL-21 did not co-opt upstream BCR components such as CD79A, in contrast to CpG-induced proliferation. Our data indicate that currently applied BTK/PI3K inhibitors target antigen-independent proliferation in CLL, and suggest that targeting of JAK and/or SYK might be clinically useful.

Macrophages confer survival signals via CCR1-dependent translational MCL-1 induction in chronic lymphocytic leukemia

Protective interactions with bystander cells in micro-environmental niches, such as lymph nodes (LNs), contribute to survival and therapy resistance of chronic lymphocytic leukemia (CLL) cells. This is caused by a shift in expression of B-cell lymphoma 2 (BCL-2) family members. Pro-survival proteins B-cell lymphoma-extra large (BCL-X_L), BCL-2-related protein A1 (BFL-1) and myeloid leukemia cell differentiation protein 1 (MCL-1) are upregulated by LN-residing T cells through CD40L interaction, presumably via nuclear factor (NF)-κB signaling. Macrophages (Mφs) also reside in the LN, and are assumed to provide important supportive functions for CLL cells. However, if and how Mφs are able to induce survival is incompletely known. We first established that Mφs induced survival because of an exclusive upregulation of MCL-1. Next, we investigated the mechanism underlying MCL-1 induction by Mφs in comparison with CD40L. Genome-wide expression profiling of in vitro Mφ- and CD40L-stimulated CLL cells indicated activation of the phosphoinositide 3-kinase (PI3K)-V-Akt murine thymoma viral oncogene homolog (AKT)-mammalian target of rapamycin (mTOR) pathway, which was confirmed in ex vivo CLL LN material. Inhibition of PI3K-AKT-mTOR signaling abrogated MCL-1 upregulation and survival by Mφs, as well as CD40 stimulation. MCL-1 can be regulated at multiple levels, and we established that AKT leads to increased MCL-1 translation, but does not affect MCL-1 transcription or protein stabilization. Furthermore, among Mφ-secreted factors that could activate AKT, we found that induction of MCL-1 and survival critically depended on C-C motif chemokine receptor-1 (CCR1). In conclusion, this study indicates that two distinct micro-environmental factors, CD40L and Mφs, signal via CCR1 to induce AKT activation resulting in translational stabilization of MCL-1, and hence can contribute to CLL cell survival.

Antigen-affinity controls pre-germinal center B cell selection by promoting Mcl-1 induction through BAFF receptor signaling

Upon antigen encounter, the responsive B cell pool undergoes stringent selection which eliminates cells with low B cell receptor (BCR) affinity. Already before formation of the germinal center, activated B cells of low-affinity are negatively selected in a process that is molecularly not well understood. In this study, we investigated the mechanism behind pre-GC affinity-mediated B cell selection. We applied affinity mutants of HEL antigen and found that rapidly after activation B cells become highly dependent on the cytokine BAFF. Moreover, expression of BAFF receptor CD268 is regulated in a BCR-affinity dependent fashion. High affinity responses via BAFF correlated with PI3K activation, which controlled expression of the pro-survival protein Mcl-1, and thereby increased survival. In the presence of excess BAFF, or in absence of the Mcl-1 antagonist Noxa, more low-affinity B cells survived the first two days after antigen encounter. This resulted in increased numbers of antigen-specific B cells of low affinity upon immunization and reduced the overall affinity of cells that contributed to the germinal center reaction. Our findings elucidate a crucial molecular pathway of B cell selection in the earliest phases of activation by identifying a novel link between BCR affinity and BAFF-R signaling towards Mcl-1.

Functional disparities among BCL-2 members in tonsillar and leukemic B-cell subsets assessed by BH3-mimetic profiling

For successful treatment of malignant B-cells it is crucial to understand intrinsic survival requirements in relation to their normal progenitors. Long-lived humoral immunity as well as most B-cell malignancies, originate in the germinal center (GC). Murine GC B-cells depend on pro-survival protein MCL-1, but not BCL-XL. In contrast, naive and memory B-cells depend on BCL-2, but not BCL-XL or MCL-1. For human B-cell subsets, the functional relationships among BCL-2 members are unclear, and also if and how they shift after malignant transformation. We here dissect these aspects in human tonsil and primary leukemia (CLL) cells by single and combined treatment with novel, highly specific BH3-mimetics. We found that MCL-1 expression in GC B-cells is regulated post-translationally and its importance is highlighted by preferential binding to pro-apoptotic BIM. In contrast, BCL-XL is transcriptionally induced and binds solely to weak sensitizer BIK, potentially explaining why BCL-XL is not required for GC B-cell survival. Using novel BH3-mimetics, we found that naive and memory B-cells depend on BCL-2, GC cells predominantly on MCL-1, whereas plasma cells need both BCL-XL and MCL-1 for survival. CLL cells switch from highly sensitive for BCL-2 inhibition to resistant after CD40-stimulation. However, combined inhibition of BCL-2, plus BCL-XL or MCL-1 effectively kills these cells, thus exposing a weakness that may be therapeutically useful. These general principles offer important clues for designing treatment strategies for B-cell malignancies.

Abstract 3554: Functional disparity among BCL-2 members in tonsillar and leukemic B cell subsets probed by next generation BH3 mimetic profiling

Introduction and aim. Long-lived humoral immunity, in the form of plasma cells (PC) and memory B cells, as well as most B cell malignancies, originate in the germinal center (GC). For successful therapies against malignant B cells it is crucial to understand their survival requirements in relation to their normal counterparts. It was previously shown that murine GC B cells depend on pro-survival protein MCL-1, but not BCL-XL, although both are expressed. In contrast, naïve and memory B cells express BCL-2, and as a consequence, they are sensitive to the BH3 mimetic ABT-737, which blocks both BCL-2 and BCL-XL but not MCL-1. The divergent roles of MCL-1 and BCL-XL in GC B cells still remain unexplained, and it is unknown if this also holds for human B cells. We here dissect these aspects in human tonsillar B subsets and in chronic lymphocytic leukemia (CLL) cells, a B cell cancer where expression of BCL-2 members is influenced by signals that also occur in the normal GC.

Experimental procedures. We used FACS sorting of tonsil B subsets, mRNA and protein profiling, co-culture of CLL cells, co-IP of BCL-2 members, cell death assays with next generation BH3 mimetics specific for BCL-2, BCL-XL or MCL-1 (ABT-199, WEHI-539, A-1210477).

Results. Naive and memory B cells are mainly sensitive to specific inhibition of BCL-2 by ABT-199. In contrast, GC B cells and tonsil PC are insensitive to ABT-199, but undergo apoptosis when MCL-1 is inhibited. Tonsil PC display yet another profile and are remarkably sensitive to inhibition of BCL-XL. MCL-1 expression in GC B cells is regulated post-translationally and its physiological importance is highlighted by exclusive binding to pro-apoptotic BIM. In contrast, BCL-XL is transcriptionally induced in the GC-light zone, and is solely bound to the weak BH3-only sensitizer BIK, which may explain why BCL-XL is not required for GC B cell survival.

These approaches were extended to primary CLL cells either resting or stimulated via CD40, as model for circulating and lymph node resident cells. We showed recently that CD40 stimulation strongly induces MCL-1, BCL-XL and BFL-1, similar to the pattern in healthy GC B cells, and confers complete resistance to ABT-199, whereas untreated CLL cells are highly sensitive. We now demonstrate that dual or triple BH3 mimetic combinations are effective in killing CD40-stimulated CLL. In contrast to GC B cells, BIK is absent in CLL cells while NOXA is highly expressed and, like BIM, is bound to MCL-1. This may account for differential sensitivity to (combinations of) BH3 mimetics.

Conclusion. Using novel BH3 mimetics and interaction profiles, we were able to probe the contribution of individual BCL-2 members in survival of normal and malignant B cells. Our findings provide clues to determine therapeutic windows in novel treatment strategies in B cell and other malignancies.

Citation Format: Victor Peperzak, Rachel Thijssen, Hanneke ter Burg, Erik Slinger, Arnon P. Kater, Eric Eldering. Functional disparity among BCL-2 members in tonsillar and leukemic B cell subsets probed by next generation BH3 mimetic profiling. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3554.

IL-23 activates innate lymphoid cells to promote neonatal intestinal pathology

Interleukin-23 (IL-23) responsive group 3 innate lymphoid cells (ILC3s) have been implicated in immune homeostasis and pathogenesis in the adult, but little is known about their roles in the newborn. Here we show that IL-23 promotes conversion of embryonic intestinal Lin(-)IL-23R(+)Thy1(+) cells into IL-22-producing Thy1(+)Sca-1(hi) ILC3s in vitro. Gut-specific expression of IL-23 also activated and expanded Thy1(+)Sca-1(hi) ILC3s, which produced IL-22, IL-17, interferon gamma (IFN-γ), and granulocyte-macrophage colony-stimulating factor (GM-CSF) and were distinct from canonical CD4(+) lymphoid tissue inducer (LTi) cells. These ILC3s accumulated under the epithelium in intercellular adhesion molecule (ICAM)-1-positive cell aggregates together with neutrophils that disrupted the epithelium, leading to the formation of discrete intestinal erosions, bleeding, and neonatal death. Genetic and antibody depletion of ILC3s rescued the mice from neonatal death. Antibiotic treatment of pregnant mothers and offspring prolonged survival of IL-23 transgenic mice, suggesting a role for the commensal flora on ILC3-induced pathogenesis. Our results reveal a novel role for the IL-23-ILC3s axis in the pathogenesis of neonatal intestinal inflammation.

Dasatinib in combination with fludarabine in patients with refractory chronic lymphocytic leukemia: a multicenter phase 2 study

Resistance to chemotherapy-induced apoptosis in CLL is associated with overexpression of antiapoptotic proteins induced by signals from the microenvironment. In vitro, dasatinib effectively inhibits expression of anti-apoptotic regulators and restores fludarabine sensitivity in activated CLL. The aim of this study was to evaluate efficacy of one cycle of dasatinib monotherapy (100mg/day, days 1-28) followed by combination of dasatinib with fludarabine (40mg/m²/day, days 1-3 every 28 day) for a total of 6 cycles in fludarabine-refractory CLL. The primary endpoint was overall response rate according to the IWCLL'08 criteria. 20 patients were enrolled: 18 completed at least one cycle of treatment of which 67% finished at least 2 cycles of combination treatment. 3 of these 18 patients reached a formal PR (16.7%). Majority of patients obtained some reduction in lymph node (LN) size. Most frequent toxicity was related to myelosuppression. NF-κB RNA expression levels of circulating CLL cells decreased whereas the levels of pro-apoptotic NOXA increased during treatment. In conclusion, dasatinib/fludarabine combination has modest clinical efficacy in fludarabine-refractory patients.

Constitutive β-catenin signaling by the viral chemokine receptor US28

Chronic activation of Wnt/ß-catenin signaling is found in a variety of human malignancies including melanoma, colorectal and hepatocellular carcinomas. Interestingly, expression of the HCMV-encoded chemokine receptor US28 in intestinal epithelial cells promotes intestinal neoplasia in transgenic mice, which is associated with increased nuclear accumulation of ß-catenin. In this study we show that this viral receptor constitutively activates ß-catenin and enhances ß-catenin-dependent transcription. Our data illustrate that this viral receptor does not activate ß-catenin via the classical Wnt/Frizzled signaling pathway. Analysis of US28 mediated signaling indicates the involvement of the Rho-Rho kinase (ROCK) pathway in the activation of ß-catenin. Moreover, cells infected with HCMV show significant increases in ß-catenin stabilization and signaling, which is mediated to a large extent by expression of US28. The modulation of the ß-catenin signal transduction pathway by a viral chemokine receptor provides alternative regulation of this pathway, with potential relevance for the development of colon cancer and virus-associated diseases.

A role for the epidermal growth factor receptor signaling in development of intestinal serrated polyps in mice and humans

BACKGROUND & AIMS

Epithelial cancers can be initiated by activating mutations in components of the mitogen-activated protein kinase signaling pathway such as v-raf murine sarcoma viral oncogene homolog B1 (BRAF), v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS), or epidermal growth factor receptor (EGFR). Human intestinal serrated polyps are a heterogeneous group of benign lesions, but some progress to colorectal cancer. Tumors that arise from these polyps frequently contain activating mutations in BRAF or KRAS, but little is known about the role of EGFR activation in their development.

METHODS

Polyp samples were obtained from adults during screening colonoscopies at Mount Sinai Hospital in New York. We measured levels of EGFR protein and phosphorylation in human serrated polyps by immunohistochemical and immunoblot analyses. We generated transgenic mice that express the ligand for EGFR, Heparin-binding EGF-like growth factor (HB-EGF), in the intestine.

RESULTS

EGFR and the extracellular-regulated kinases (ERK)1/2 were phosphorylated in serrated areas of human hyperplastic polyps (HPPs), sessile serrated adenomas, and traditional serrated adenomas. EGFR and ERK1/2 were phosphorylated in the absence of KRAS or BRAF activating mutations in a subset of HPP. Transgenic expression of the EGFR ligand HB-EGF in the intestines of mice promoted development of small cecal serrated polyps. Mice that expressed a combination of HB-EGF and US28 (a constitutively active, G-protein-coupled receptor that increases processing of HB-EGF from the membrane) rapidly developed large cecal serrated polyps. These polyps were similar to HPPs and had increased phosphorylation of EGFR and ERK1/2 within the serrated epithelium. Administration of pharmacologic inhibitors of EGFR or MAPK to these transgenic mice significantly reduced polyp development.

CONCLUSIONS

Activation of EGFR signaling in the intestine of mice promotes development of serrated polyps. EGFR signaling also is activated in human HPPs, sessile serrated adenomas, and traditional serrated adenomas.

Herpesvirus-encoded GPCRs rewire cellular signaling

Viral G-protein-coupled receptors (vGPCRs) are chemokine receptor homologues encoded by the Herpes- and Capripoxviridae. They are thought to have been hijacked from the host genome during the course of evolution. These vGPCRs play different roles in the viral lifecycle and associated pathologies. Three members of the Herpesviridae, Kaposi sarcoma-associated herpesvirus (KSHV), Epstein-Barr virus (EBV) and human cytomegalovirus (HCMV) are capable of setting up persistent latent infections in humans. Two of the herpesviruses, KSHV and EBV, are associated with cancer, while HCMV may have an oncomodulary effect. The vGPCRs may contribute to the escape of immune surveillance and (constitutively) activate signaling pathways linked to proliferation and inflammation. Some vGPCRs induce activation of autocrine and paracrine signaling, resulting in secretion of growth factors and/or cytokines. As a result, vGPCRs effectively rewire cellular signaling networks. Delineating the cellular signaling networks modulated by these vGPCRs will be crucial for treatment of virus-associated pathologies.

HCMV-encoded chemokine receptor US28 mediates proliferative signaling through the IL-6-STAT3 axis

US28 is a viral G protein (heterotrimeric guanosine triphosphate-binding protein)-coupled receptor encoded by the human cytomegalovirus (HCMV). In addition to binding and internalizing chemokines, US28 constitutively activates signaling pathways linked to cell proliferation. Here, we show increased concentrations of vascular endothelial growth factor and interleukin-6 (IL-6) in supernatants of US28-expressing NIH 3T3 cells. Increased IL-6 was associated with increased activation of the signal transducer and activator of transcription 3 (STAT3) through upstream activation of the Janus-activated kinase JAK1. We used conditioned growth medium, IL-6-neutralizing antibodies, an inhibitor of the IL-6 receptor, and short hairpin RNA targeting IL-6 to show that US28 activates the IL-6-JAK1-STAT3 signaling axis through activation of the transcription factor nuclear factor kappaB and the consequent production of IL-6. Treatment of cells with a specific inhibitor of STAT3 inhibited US28-dependent [(3)H]thymidine incorporation and foci formation, suggesting a key role for STAT3 in the US28-mediated proliferative phenotype. US28 also elicited STAT3 activation and IL-6 secretion in HCMV-infected cells. Analyses of tumor specimens from glioblastoma patients demonstrated colocalization of US28 and phosphorylated STAT3 in the vascular niche of these tumors. Moreover, increased phospho-STAT3 abundance correlated with poor patient outcome. We propose that US28 induces proliferation in HCMV-infected tumors by establishing a positive feedback loop through activation of the IL-6-STAT3 signaling axis.

The human cytomegalovirus-encoded chemokine receptor US28 promotes angiogenesis and tumor formation via cyclooxygenase-2

The human cytomegalovirus (HCMV), potentially associated with the development of malignancies, encodes the constitutively active chemokine receptor US28. Previously, we have shown that US28 expression induces an oncogenic phenotype both in vitro and in vivo. Microarray analysis revealed differential expression of genes involved in oncogenic signaling in US28-expressing NIH-3T3 cells. In particular, the expression of cyclooxygenase-2 (COX-2), a key mediator of inflammatory diseases and major determinant in several forms of cancer, was highly up-regulated. US28 induced increases in COX-2 expression via activation of nuclear factor-kappaB, driving the production of vascular endothelial growth factor. Also, in HCMV-infected cells, US28 contributed to the viral induction of COX-2. Finally, the involvement of COX-2 in US28-mediated tumor formation was evaluated using the COX-2 selective inhibitor Celecoxib. Targeting COX-2 in vivo with Celecoxib led to a marked delay in the onset of tumor formation in nude mice injected with US28-transfected NIH-3T3 cells and a reduction of subsequent growth by repressing the US28-induced angiogenic activity. Hence, the development of HCMV-related proliferative diseases may partially be ascribed to the ability of US28 to activate COX-2.