Development of an Anti-canine PD-L1 Antibody and Caninized PD-L1 Mouse Model as Translational Research Tools for the Study of Immunotherapy in Humans

Immune checkpoint blockade therapy, one of the most promising cancer immunotherapies, has shown remarkable clinical impact in multiple cancer types. Despite the recent success of immune checkpoint blockade therapy, however, the response rates in patients with cancer are limited (∼20%-40%). To improve the success of immune checkpoint blockade therapy, relevant preclinical animal models are essential for the development and testing of multiple combination approaches and strategies. Companion dogs naturally develop several types of cancer that in many respects resemble clinical cancer in human patients. Therefore, the canine studies of immuno-oncology drugs can generate knowledge that informs and prioritizes new immuno-oncology therapy in humans. The challenge has been, however, that immunotherapeutic antibodies targeting canine immune checkpoint molecules such as canine PD-L1 (cPD-L1) have not been commercially available. Here, we developed a new cPD-L1 antibody as an immuno-oncology drug and characterized its functional and biological properties in multiple assays. We also evaluated the therapeutic efficacy of cPD-L1 antibodies in our unique caninized PD-L1 mice. Together, these in vitro and in vivo data, which include an initial safety profile in laboratory dogs, support development of this cPD-L1 antibody as an immune checkpoint inhibitor for studies in dogs with naturally occurring cancer for translational research. Our new therapeutic antibody and caninized PD-L1 mouse model will be essential translational research tools in raising the success rate of immunotherapy in both dogs and humans.

Significance

Our cPD-L1 antibody and unique caninized mouse model will be critical research tools to improve the efficacy of immune checkpoint blockade therapy in both dogs and humans. Furthermore, these tools will open new perspectives for immunotherapy applications in cancer as well as other autoimmune diseases that could benefit a diverse and broader patient population.

Nuclear export signal mutation of epidermal growth factor receptor enhances malignant phenotypes of cancer cells

Nuclear epidermal growth factor receptor (EGFR) has been shown to be correlated with drug resistance and a poor prognosis in patients with cancer. Previously, we have identified a tripartite nuclear localization signal (NLS) within EGFR. To comprehensively determine the functions and underlying mechanism of nuclear EGFR and its clinical implications, we aimed to explore the nuclear export signal (NES) sequence of EGFR that is responsible for interacting with the exportins. We combined in silico prediction with site-directed mutagenesis approaches and identified a putative NES motif of EGFR, which is located in amino acid residues 736-749. Mutation at leucine 747 (L747) in the EGFR NES led to increased nuclear accumulation of the protein via a less efficient release of the exportin CRM1. Interestingly, L747 with serine (L747S) and with proline (L747P) mutations were found in both tyrosine kinase inhibitor (TKI)-treated and -naïve patients with lung cancer who had acquired or de novo TKI resistance and a poor outcome. Reconstituted expression of the single NES mutant EGFR^L747P or EGFR^L747S, but not the dual mutant along with the internalization-defective or NLS mutation, in lung cancer cells promoted malignant phenotypes, including cell migration, invasiveness, TKI resistance, and tumor initiation, supporting an oncogenic role of nuclear EGFR. Intriguingly, cells with germline expression of the NES L747 mutant developed into B cell lymphoma. Mechanistically, nuclear EGFR signaling is required for sustaining nuclear activated STAT3, but not for Erk. These findings suggest that EGFR functions are compartmentalized and that nuclear EGFR signaling plays a crucial role in tumor malignant phenotypes, leading to tumorigenesis in human cancer.

4-1BB: A promising target for cancer immunotherapy

Immunotherapy, powered by its relative efficacy and safety, has become a prominent therapeutic strategy utilized in the treatment of a wide range of diseases, including cancer. Within this class of therapeutics, there is a variety of drug types such as immune checkpoint blockade therapies, vaccines, and T cell transfer therapies that serve the purpose of harnessing the body’s immune system to combat disease. Of these different types, immune checkpoint blockades that target coinhibitory receptors, which dampen the body’s immune response, have been widely studied and established in clinic. In contrast, however, there remains room for the development and improvement of therapeutics that target costimulatory receptors and enhance the immune response against tumors, one of which being the 4-1BB (CD137/ILA/TNFRSF9) receptor. 4-1BB has been garnering attention as a promising therapeutic target in the setting of cancer, amongst other diseases, due to its broad expression profile and ability to stimulate various signaling pathways involved in the generation of a potent immune response. Since its discovery and demonstration of potential as a clinical target, major progress has been made in the knowledge of 4-1BB and the development of clinical therapeutics that target it. Thus, we seek to summarize and provide a comprehensive update and outlook on those advancements in the context of cancer and immunotherapy.

FBXL20-mediated ubiquitination triggers the proteasomal degradation of 4-1BB

4-1BB [tumor necrosis factor receptor superfamily (TNFRSF9), CD137) is a critical immune stimulator that sustains T cell activity and antitumor immune response. The strategy to eliminate cancers by agonistically targeting 4-1BB is under clinical investigation. As a protein expressed in an inducible manner, 4-1BB is under tight control on both transcription and translation levels to maintain its homeostasis. So far, the mechanisms underlying the transcriptional activation of 4-1BB have been well-interpreted; however, it remains inexplicit how 4-1BB is regulated on the protein level. In this study, we presented experimental evidence supporting that 4-1BB, especially the heavily N-glycosylated (mature) form, is polyubiquitinated and subjected to the ubiquitin-proteasomal system for degradation. By performing proximity-dependent biotin identification screening coupled with biochemical assays, we identified that F-box/LRR-repeat protein 20 acts as the E3 ligase that promotes the polyubiquitination of 4-1BB at the intracellular domain. Our data provided mechanistic insight into 4-1BB regulation on the protein level by unmasking, for the first time, a posttranslational mechanism governing 4-1BB abundance in cells. The findings of this study could potentially guide the development of 4-1BB-targeted therapy for cancers as well as other immune disorders.

Ephrin receptor A10 monoclonal antibodies and the derived chimeric antigen receptor T cells exert an antitumor response in mouse models of triple-negative breast cancer

Expression of the receptor tyrosine kinase ephrin receptor A10 (EphA10), which is undetectable in most normal tissues except for the male testis, has been shown to correlate with tumor progression and poor prognosis in several malignancies, including triple-negative breast cancer (TNBC). Therefore, EphA10 could be a potential therapeutic target, likely with minimal adverse effects. However, no effective clinical drugs against EphA10 are currently available. Here, we report high expression levels of EphA10 in tumor regions of breast, lung, and ovarian cancers as well as in immunosuppressive myeloid cells in the tumor microenvironment. Furthermore, we developed anti-EphA10 monoclonal antibodies (mAbs) that specifically recognize cell surface EphA10, but not other EphA family isoforms, and target tumor regions precisely in vivo with no apparent accumulation in other organs. In syngeneic TNBC mouse models, we found that anti-EphA10 mAb clone #4 enhanced tumor regression, therapeutic response rate, and T cell–mediated antitumor immunity. Notably, the chimeric antigen receptor T cells derived from clone #4 significantly inhibited TNBC cell viability in vitro and tumor growth in vivo. Together, our findings suggest that targeting EphA10 via EphA10 mAbs and EphA10-specific chimeric antigen receptor–T cell therapy may represent a promising strategy for patients with EphA10-positive tumors.

N-Glycosylation Facilitates 4-1BB Membrane Localization by Avoiding Its Multimerization

Leveraging the T cell immunity against tumors represents a revolutionary type of cancer therapy. 4-1BB is a well-characterized costimulatory immune receptor existing on activated T cells and mediating their proliferation and cytotoxicity under infectious diseases and cancers. Despite the accumulating interest in implementing 4-1BB as a therapeutic target for immune-related disorders, less is known about the pattern of its intracellular behaviors and regulations. It has been previously demonstrated that 4-1BB is heavily modified by N-glycosylation; however, the biological importance of this modification lacks detailed elucidation. Through biochemical, biophysical, and cell-biological approaches, we systematically evaluated the impact of N-glycosylation on the ligand interaction, stability, and localization of 4-1BB. We hereby highlighted that N-glycan functions by preventing the oligomerization of 4-1BB, thus permitting its membrane transportation and fast turn-over. Without N-glycosylation, 4-1BB could be aberrantly accumulated intracellularly and fail to be sufficiently inserted in the membrane. The N-glycosylation-guided intracellular processing of 4-1BB serves as the potential mechanism explicitly modulating the “on” and “off” of 4-1BB through the control of protein abundance. Our study will further solidify the understanding of the biological properties of 4-1BB and facilitate the clinical practice against this promising therapeutic target.

Abstract P063: Tumor cell-derived lactic acid inhibit anti-tumor immunity in the immune checkpoint blockade resistant tumor

Immune checkpoint blockade therapy targeting the PD-1/PD-L1 axis, one of the most promising cancer immunotherapies, has shown remarkable clinical impact in multiple cancer types. Despite the recent success of PD-1/PD-L1 blockade therapy, acquired resistance, emerging as late relapses or recurrences, has been reported in the long-term follow-up of clinical trials. However, the resistance mechanisms of PD-1/PD-L1 blockade therapy are still unclear. Here we found that tumor cell-derived lactate rendered the immunosuppressive tumor microenvironment in the PD-1/PD-L1 blockade resistant tumors. Interestingly, increased lactate in the PD-1/PD-L1 blockade resistant tumors enhanced PD-1/PD-L1 interaction. Furthermore, combining a PD-L1-antibody-drug conjugate (ADC) with AZD3965, a MCT inhibitor eradicated the resistant tumor cells synergistically in 4T1 syngeneic murine models. Together, our results suggest a new combination treatment strategy to improve the therapeutic efficacy of immune checkpoint blockade therapies.

Citation Format: Wonkyung Oh, Alyssa Min Jung Kim, Ruoxuan Sun, Seung-Oe Lim. Tumor cell-derived lactic acid inhibit anti-tumor immunity in the immune checkpoint blockade resistant tumor [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P063.

TYRO3 induces anti-PD-1/PD-L1 therapy resistance by limiting innate immunity and tumoral ferroptosis

Immune checkpoint blockade therapy has demonstrated promising clinical outcomes for multiple cancer types. However, the emergence of resistance as well as inadequate biomarkers for patient stratification have largely limited the clinical benefits. Here, we showed that tumors with high TYRO3 expression exhibited anti-programmed cell death protein 1/programmed death ligand 1 (anti-PD-1/PD-L1) resistance in a syngeneic mouse model and in patients who received anti-PD-1/PD-L1 therapy. Mechanistically, TYRO3 inhibited tumor cell ferroptosis triggered by anti-PD-1/PD-L1 and facilitated the development of a protumor microenvironment by reducing the M1/M2 macrophage ratio, resulting in resistance to anti-PD-1/PD-L1 therapy. Inhibition of TYRO3 promoted tumor ferroptosis and sensitized resistant tumors to anti-PD-1 therapy. Collectively, our findings suggest that TYRO3 could serve as a predictive biomarker for patient selection and a promising therapeutic target to overcome anti-PD-1/PD-L1 resistance.

Abstract A16: Metformin is a potential nontoxic adjuvant to enhance the efficacy of non-PDL1/PD-1 targeting immune therapies

Investigations into various immunotherapies combined with conventional anticancer drugs are ongoing to increase therapeutic efficacy. However, combination therapy generally increases the risk of side effects. To achieve high efficacy with minimal side effects, nontoxic adjuvants should be identified and appropriate combinations should be designed based on the functional mechanism. In this regard, metformin can be an attractive candidate for immunotherapeutic adjuvants. Metformin is a widely used oral medication for type 2 diabetes (T2D) and has been recognized as a safe and well-tolerated drug through several decades of clinical experience. Interestingly, metformin also exhibits antitumor effects as several case-control studies for T2D patients indicated that metformin reduces the incidence of various cancer types. However, the functions and the detailed mechanism of metformin related to cancer immunity are not fully understood. In this study, we investigated the antitumor effects of metformin in relation to cancer immunity in the tumor microenvironment. Our data showed that AMPK activated by metformin decreases the expression of PD-L1 in the cancer cells, blocking PD-L1’s ability to aid cancer cells in escaping immune surveillance. This is caused by the mechanism in which phosphorylation of PD-L1 at S195 induces an abnormal glycan structure that leads to endoplasmic reticulum-associated degradation. In addition, we have obtained human breast tumor tissues from a previous clinical trial investigating metformin as treatment for breast cancer patients. The data from human tumor tissues also provided strong support to our current conclusion, namely AMPK activated by metformin reduces the level of PD-L1. On the basis of these results, we validated the possibility of metformin as an adjuvant to boost the efficacy of previous immunotherapy without toxicity. Our findings suggest that metformin has strong potential to be used as an adjuvant for immunotherapy. Metformin is expected to have synergistic effect with various non-PDL1/PD-1 targeting immune therapies without additional toxicity.

Citation Format: Jong-Ho Cha, Wen-Hao Yang, Weiya Xia, Yongkun Wei, Li-Chuan Chan, Seung-Oe Lim, Chia-Wei Li, Jennifer Hsu, Hung-Ling Wang, Chu-Wei Kuo, Wei-Chao Chang, Sirwan Hadad, Colin Purdie, Aaron McCoy, Jennifer Litton, Elizabeth Mittendorf, Stacy Moulder, William Symmans, Alastair M Thompson, Helen Piwnica-Worms, Chung-Hsuan Chen, Kay-Hooi Khoo, Mien-Chie Hung. Metformin is a potential nontoxic adjuvant to enhance the efficacy of non-PDL1/PD-1 targeting immune therapies [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr A16.

Oncogenic signaling pathways associated with immune evasion and resistance to immune checkpoint inhibitors in cancer

Immune checkpoint inhibitors (ICIs) are novel class of anti-cancer drugs that exhibit significant therapeutic effects even in patients with advanced-stage cancer. However, the efficacy of ICIs is limited due to resistance. Therefore, appropriate biomarkers to select patients who are likely to respond to these drugs as well as combination therapy to overcome the resistance are urgently necessary. Cancer is caused by various genetic alterations that lead to abnormalities in oncogenic signaling pathways. The aberrant oncogenic signaling pathways serve as not only prognostic and predictive biomarkers, but also targets for molecularly targeted therapy. Growing evidence shows that the aberrant oncogenic signaling pathways in cancer cells facilitate the resistance to ICIs by modulating the regulation of immune checkpoint and cancer immune surveillance. Indeed, it has been demonstrated that some molecular targeted therapies significantly improve the efficacy of ICIs in preclinical and clinical studies. In this review, we highlighted several oncogenic signaling pathways including receptor tyrosine kinases (RTKs), MAPK, PI3K-AKT-mTOR, JAK-STAT, Hippo, and Wnt pathways, and summarized the recent findings of the mechanisms underlying the regulation of cancer immunity and the ICI resistance induced by these aberrant oncogenic signaling pathways in cancer cells. Moreover, we discussed potential combination therapies with ICIs and molecularly targeted drugs to overcome the resistance and increase the efficacy of ICIs.

Disruption of tumour-associated macrophage trafficking by the osteopontin-induced colony-stimulating factor-1 signalling sensitises hepatocellular carcinoma to anti-PD-L1 blockade

OBJECTIVE

In the tumour microenvironment, critical drivers of immune escape include the oncogenic activity of the tumour cell-intrinsic osteopontin (OPN), the expression of programmed death ligand 1 (PD-L1) and the expansion of tumour-associated macrophages (TAMs). We investigated the feasibility of targeting these pathways as a therapeutic option in hepatocellular carcinoma (HCC) mouse models.

DESIGN

We analysed the number of tumour-infiltrating immune cells and the inflammatory immune profiles in chemically induced liver tumour isolated from wild-type and OPNknockout (KO) mice. In vitro cell cocultures were further conducted to investigate the crosstalk between TAMs and HCC cells mediated by OPN, colony stimulating factor-1 (CSF1) and CSF1 receptor (CSF1R). The in vivo efficacy of anti-PD-L1 and CSF1/CSF1R inhibition was evaluated in OPN overexpressing subcutaneous or orthotopic mouse model of HCC.

RESULTS

The numbers of TAMs, as well as the expression levels of M2 macrophage markers and PD-L1 were significantly decreased, but the levels of cytokines produced by T-helper 1 (Th1) cells were upregulated in tumour tissues from OPN KO mice compared with that from the controls. In addition, we observed a positive association between the OPN and PD-L1 expression, and OPN expression and TAM infiltration in tumour tissues from patients with HCC. We further demonstrated that OPN facilitates chemotactic migration, and alternative activation of macrophages, and promotes the PD-L1 expression in HCC via activation of the CSF1-CSF1R pathway in macrophages. Combining anti-PD-L1 and CSF1R inhibition elicited potent antitumour activity and prolonged survival of OPN^high tumour-bearing mice. Histological, flow cytometric and ELISA revealed increased CD8⁺ T cell infiltration, reduced TAMs and enhanced Th1/Th2 cytokine balance in multiple mouse models of HCC.

CONCLUSIONS

OPN/CSF1/CSF1R axis plays a critical role in the immunosuppressive nature of the HCC microenvironment. Blocking CSF1/CSF1R prevents TAM trafficking and thereby enhances the efficacy of immune checkpoint inhibitors for the treatment of HCC.

IL-6/JAK1 pathway drives PD-L1 Y112 phosphorylation to promote cancer immune evasion

Glycosylation of immune receptors and ligands, such as T cell receptor and coinhibitory molecules, regulates immune signaling activation and immune surveillance. However, how oncogenic signaling initiates glycosylation of coinhibitory molecules to induce immunosuppression remains unclear. Here we show that IL-6-activated JAK1 phosphorylates programmed death-ligand 1 (PD-L1) Tyr112, which recruits the endoplasmic reticulum-associated N-glycosyltransferase STT3A to catalyze PD-L1 glycosylation and maintain PD-L1 stability. Targeting of IL-6 by IL-6 antibody induced synergistic T cell killing effects when combined with anti-T cell immunoglobulin mucin-3 (anti-Tim-3) therapy in animal models. A positive correlation between IL-6 and PD-L1 expression was also observed in hepatocellular carcinoma patient tumor tissues. These results identify a mechanism regulating PD-L1 glycosylation initiation and suggest the combination of anti-IL-6 and anti-Tim-3 as an effective marker-guided therapeutic strategy.

Metformin Promotes Antitumor Immunity via Endoplasmic-Reticulum-Associated Degradation of PD-L1

Metformin has been reported to possess antitumor activity and maintain high cytotoxic T lymphocyte (CTL) immune surveillance. However, the functions and detailed mechanisms of metformin's role in cancer immunity are not fully understood. Here, we show that metformin increases CTL activity by reducing the stability and membrane localization of programmed death ligand-1 (PD-L1). Furthermore, we discover that AMP-activated protein kinase (AMPK) activated by metformin directly phosphorylates S195 of PD-L1. S195 phosphorylation induces abnormal PD-L1 glycosylation, resulting in its ER accumulation and ER-associated protein degradation (ERAD). Consistently, tumor tissues from metformin-treated breast cancer patients exhibit reduced PD-L1 levels with AMPK activation. Blocking the inhibitory signal of PD-L1 by metformin enhances CTL activity against cancer cells. Our findings identify a new regulatory mechanism of PD-L1 expression through the ERAD pathway and suggest that the metformin-CTLA4 blockade combination has the potential to increase the efficacy of immunotherapy.

Deglycosylation of PD-L1 by 2-deoxyglucose reverses PARP inhibitor-induced immunosuppression in triple-negative breast cancer

Triple-negative breast cancer (TNBC), the most difficult-to-treat breast cancer subtype, lacks well-defined molecular targets. TNBC has increased programmed death-ligand 1 (PD-L1) expression, and its immunosuppressive nature makes it suitable for immune checkpoint blockade therapy. However, the response rate of TNBC to anti-PD-L1 or anti-programmed cell death protein 1 (PD-1) therapy remains unsatisfactory, as only 10-20% of TNBC patients have a partial response. Glycosylated PD-L1, the functional form of PD-L1, is required for PD-L1-PD-1 interaction. TNBC cells have significantly higher levels of glycosylated PD-L1 than non-TNBC cells do. In a screening of glucose analogs to block PD-L1 glycosylation, we found that 2-deoxyglucose (2-DG) can act as a glucose analog to decrease PD-L1 glycosylation. Because PARP inhibition upregulates PD-L1, 2-DG reduced PARP inhibition-mediated expression of glycosylated PD-L1. The combination of PARP inhibition and 2-DG had potent anti-tumor activity. Together, our results provide a strong rationale for investigating the targeting of PD-L1 glycosylation in TNBC further.

Rational combination of immunotherapy for triple negative breast cancer treatment

Recent evidence indicates that tumor infiltrating lymphocytes (TILs), including cytotoxic T cells, are present in the tumor microenvironment of triple-negative breast cancers (TNBC). Despite the presence of cytotoxic T cells, these tumors still develop, progress, and metastasize, suggesting evasion of immune response. One mechanism of immunosuppression is the presence of the T cell inhibitory molecule, programmed death protein 1 (PD-1), on infiltrating T cells and its cognate ligand programmed death ligand 1 (PD-L1) on tumor cells, myeloid dendritic cells (DCs), and macrophages, in the tumor microenvironment. Because TNBC is immunologically insensitive, combinatorial strategies may be ideal to increase both anti-proliferation activity and cytotoxic T cells activity in TNBC. On the basis of two recently discovered regulatory mechanisms of PD-L1, we discuss the potential interactions to boost anti-tumor immunity against TNBC in this review and propose therapeutic strategies that could reduce PD-L1 expression by chemotherapeutic drugs or targeted therapies and sensitize TNBC to immunotherapies.

Abstract 5606: Eradication of triple-negative breast cancer cells by targeting glycosylated PD-L1

EGF signaling inhibits GSK3β-β-TrCP-mediated degradation of N-linked glycosylated programmed death ligand-1 (PD-L1), resulting in PD-L1 protein destabilization and enhanced immune checkpoint blockade efficacy. Here we show that EGF also mediates PD-L1 and receptor programmed cell death protein-1 (PD-1) interaction, requiring β-1,3-N-acetylglucosaminyl transferase (B3GNT3) expression in triple-negative breast cancer cells. Downregulation of B3GNT3 enhances cytotoxic T cell-mediated anti-tumor immunity. A monoclonal antibody targeting glycosylated PD-L1 (gPD-L1) blocks PD-L1/PD-1 interaction and promotes PD-L1 internalization and degradation. In addition to immune reactivation, drug-conjugated gPD-L1 antibody induces potent cell-killing effect as well as bystander-killing effect on adjacent cancer cells without PD-L1 expression with virtually no detectable toxicities. Our work suggests targeting protein glycosylation as a potential strategy to enhance immune checkpoint therapy.

Citation Format: Seung-Oe Lim, Chia-Wei Li, Mien-Chie Hung. Eradication of triple-negative breast cancer cells by targeting glycosylated PD-L1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5606.

Stress hormones promote EGFR inhibitor resistance in NSCLC: Implications for combinations with β-blockers

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) resistance mediated by T790M-independent mechanisms remains a major challenge in the treatment of non-small cell lung cancer (NSCLC). We identified a targetable mechanism of EGFR inhibitor resistance whereby stress hormones activate β₂-adrenergic receptors (β₂-ARs) on NSCLC cells, which cooperatively signal with mutant EGFR, resulting in the inactivation of the tumor suppressor, liver kinase B1 (LKB1), and subsequently induce interleukin-6 (IL-6) expression. We show that stress and β₂-AR activation promote tumor growth and EGFR inhibitor resistance, which can be abrogated with β-blockers or IL-6 inhibition. IL-6 was associated with a worse outcome in EGFR TKI-treated NSCLC patients, and β-blocker use was associated with lower IL-6 concentrations and improved benefit from EGFR inhibitors. These findings provide evidence that chronic stress hormones promote EGFR TKI resistance via β₂-AR signaling by an LKB1/CREB (cyclic adenosine 3',5'-monophosphate response element-binding protein)/IL-6-dependent mechanism and suggest that combinations of β-blockers with EGFR TKIs merit further investigation as a strategy to abrogate resistance.

Angiogenin/Ribonuclease 5 Is an EGFR Ligand and a Serum Biomarker for Erlotinib Sensitivity in Pancreatic Cancer

Pancreatic ribonuclease (RNase) is a secreted enzyme critical for host defense. We discover an intrinsic RNase function, serving as a ligand for epidermal growth factor receptor (EGFR), a member of receptor tyrosine kinase (RTK), in pancreatic ductal adenocarcinoma (PDAC). The closely related bovine RNase A and human RNase 5 (angiogenin [ANG]) can trigger oncogenic transformation independently of their catalytic activities via direct association with EGFR. Notably, high plasma ANG level in PDAC patients is positively associated with response to EGFR inhibitor erlotinib treatment. These results identify a role of ANG as a serum biomarker that may be used to stratify patients for EGFR-targeted therapies, and offer insights into the ligand-receptor relationship between RNase and RTK families.

Eradication of Triple-Negative Breast Cancer Cells by Targeting Glycosylated PD-L1

Protein glycosylation provides proteomic diversity in regulating protein localization, stability, and activity; it remains largely unknown whether the sugar moiety contributes to immunosuppression. In the study of immune receptor glycosylation, we showed that EGF induces programmed death ligand 1 (PD-L1) and receptor programmed cell death protein 1 (PD-1) interaction, requiring β-1,3-N-acetylglucosaminyl transferase (B3GNT3) expression in triple-negative breast cancer. Downregulation of B3GNT3 enhances cytotoxic T cell-mediated anti-tumor immunity. A monoclonal antibody targeting glycosylated PD-L1 (gPD-L1) blocks PD-L1/PD-1 interaction and promotes PD-L1 internalization and degradation. In addition to immune reactivation, drug-conjugated gPD-L1 antibody induces a potent cell-killing effect as well as a bystander-killing effect on adjacent cancer cells lacking PD-L1 expression without any detectable toxicity. Our work suggests targeting protein glycosylation as a potential strategy to enhance immune checkpoint therapy.

Abstract 4713: Deubiquitination and stabilization of programmed cell death-ligand 1 by CSN5

Chronic inflammation in cancer is often associated with disease aggressiveness. Pro-inflammatory cytokines produced in the tumor microenvironment lead to eradication of antitumor immunity and enhanced tumor cell survival. In the current study, we identified TNFα as a major factor triggering cancer cell immunosuppression against T cell surveillance via stabilization of programmed cell death-ligand 1 (PD-L1). We demonstrated that COP9 signalosome 5 (CSN5), induced by NF-κB p65, is required for TNFα-mediated PD-L1 stabilization in cancer cells. CSN5 inhibits the ubiquitination and degradation of PD-L1. The role of CSN5 in modulating PD-L1 stabilization prompted us to use CSN5 inhibitor, curcumin, to show that it could destabilize PD-L1. Curcumin reduced CSN5 activity to attenuate TNFα-mediated PD-L1 stabilization and enhanced anti-tumor immunity. Preclinical data demonstrated inhibition of CSN5 sensitized cancer cells to anti-CTLA4 therapy, suggesting CSN5 inhibitor may be a useful adjuvant to enhance immune-based therapies.

Note: This abstract was not presented at the meeting.

Citation Format: Seung-Oe Lim, Chia-Wei Li, Mien-Chie Hung. Deubiquitination and stabilization of programmed cell death-ligand 1 by CSN5 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4713. doi:10.1158/1538-7445.AM2017-4713

Abstract B47: Stabilization of programmed death ligand-1 by epidermal growth factor enhances cancer cell immune escape

Extracellular interaction between programmed death ligand-1 (PD-L1) and programmed cell death protein-1 (PD-1) leads to tumor-associated immune escape. Despite efforts to limit the interaction between cancer cells and immune cells, the molecular mechanism by which cancer cells initiate immune escape is less understood. Here, we show that the immunosuppression activity of PD-L1 is stringently modulated by the spatial competition between ubiquitination and N-glycosylation. We identified glycogen synthase kinase 3β (GSK3β) as a novel protein that interacts with PD-L1 and can induce phosphorylation-dependent proteasome degradation by β-TrCP. In depth analysis of PD-L1 N192, N200, and N219 glycosylation suggests glycosylation antagonizes GSK3β binding. In this regard, only non-glycosylated PD-L1 forms a complex with GSK3β and β-TrCP. We also demonstrate that epidermal growth factor (EGF) stabilizes PD-L1 via GSK3β inactivation in basal-like breast cancer (BLBC). Inhibition of EGF signaling by gefitinib destabilizes PD-L1, enhances antitumor T cell immunity, and sensitizes BLBC cells to PD-1 blockade. Together, our results link ubiquitination and glycosylation pathways with stringent regulation of PD-L1, which could open new therapeutic strategies to enhance cancer immune therapy efficacy.

Citation Format: Seung-Oe Lim, Chia-Wei Li, Mien-Chie Hung. Stabilization of programmed death ligand-1 by epidermal growth factor enhances cancer cell immune escape. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr B47.

PARP Inhibitor Upregulates PD-L1 Expression and Enhances Cancer-Associated Immunosuppression

Purpose: To explore whether a cross-talk exists between PARP inhibition and PD-L1/PD-1 immune checkpoint axis, and determine whether blockade of PD-L1/PD-1 potentiates PARP inhibitor (PARPi) in tumor suppression.Experimental Design: Breast cancer cell lines, xenograft tumors, and syngeneic tumors treated with PARPi were assessed for PD-L1 expression by immunoblotting, IHC, and FACS analyses. The phospho-kinase antibody array screen was used to explore the underlying mechanism of PARPi-induced PD-L1 upregulation. The therapeutic efficacy of PARPi alone, PD-L1 blockade alone, or their combination was tested in a syngeneic tumor model. The tumor-infiltrating lymphocytes and tumor cells isolated from syngeneic tumors were analyzed by CyTOF and FACS to evaluate the activity of antitumor immunity in the tumor microenvironment.Results: PARPi upregulated PD-L1 expression in breast cancer cell lines and animal models. Mechanistically, PARPi inactivated GSK3β, which in turn enhanced PARPi-mediated PD-L1 upregulation. PARPi attenuated anticancer immunity via upregulation of PD-L1, and blockade of PD-L1 resensitized PARPi-treated cancer cells to T-cell killing. The combination of PARPi and anti-PD-L1 therapy compared with each agent alone significantly increased the therapeutic efficacy in vivoConclusions: Our study demonstrates a cross-talk between PARPi and tumor-associated immunosuppression and provides evidence to support the combination of PARPi and PD-L1 or PD-1 immune checkpoint blockade as a potential therapeutic approach to treat breast cancer. Clin Cancer Res; 23(14); 3711-20. ©2017 AACR.

Deubiquitination and Stabilization of PD-L1 by CSN5

Pro-inflammatory cytokines produced in the tumor microenvironment lead to eradication of anti-tumor immunity and enhanced tumor cell survival. In the current study, we identified tumor necrosis factor alpha (TNF-α) as a major factor triggering cancer cell immunosuppression against T cell surveillance via stabilization of programmed cell death-ligand 1 (PD-L1). We demonstrated that COP9 signalosome 5 (CSN5), induced by NF-κB p65, is required for TNF-α-mediated PD-L1 stabilization in cancer cells. CSN5 inhibits the ubiquitination and degradation of PD-L1. Inhibition of CSN5 by curcumin diminished cancer cell PD-L1 expression and sensitized cancer cells to anti-CTLA4 therapy.

Glycosylation and stabilization of programmed death ligand-1 suppresses T-cell activity

Extracellular interaction between programmed death ligand-1 (PD-L1) and programmed cell death protein-1 (PD-1) leads to tumour-associated immune escape. Here we show that the immunosuppression activity of PD-L1 is stringently modulated by ubiquitination and N-glycosylation. We show that glycogen synthase kinase 3β (GSK3β) interacts with PD-L1 and induces phosphorylation-dependent proteasome degradation of PD-L1 by β-TrCP. In-depth analysis of PD-L1 N192, N200 and N219 glycosylation suggests that glycosylation antagonizes GSK3β binding. In this regard, only non-glycosylated PD-L1 forms a complex with GSK3β and β-TrCP. We also demonstrate that epidermal growth factor (EGF) stabilizes PD-L1 via GSK3β inactivation in basal-like breast cancer. Inhibition of EGF signalling by gefitinib destabilizes PD-L1, enhances antitumour T-cell immunity and therapeutic efficacy of PD-1 blockade in syngeneic mouse models. Together, our results link ubiquitination and glycosylation pathways to the stringent regulation of PD-L1, which could lead to potential therapeutic strategies to enhance cancer immune therapy efficacy.

Extracellular PKM2 induces cancer proliferation by activating the EGFR signaling pathway

Pyruvate kinase is a key enzyme in the glycolytic pathway that converts phosphoenolpyruvate to pyruvate, and the M2 isoform of pyruvate kinase (PKM2) is associated with cancer. PKM2 has been reported to function independently of its pyruvate kinase activity, which is crucial for cancer cell proliferation. Moreover, there is growing evidence indicating that dimeric PKM2 is released from tumor cells into the circulation of cancer patients. However, the role of secreted PKM2 in cancer is not well understood. Here, we found that the phosphorylation level of epidermal growth factor receptor (EGFR) significantly increased upon the exposure of cells to the recombinant PKM2 protein. In addition, secreted PKM2 induces EGFR phosphorylation and activates the EGFR downstream signaling in triple-negative breast cancer cells. In contrast, knocking down PKM2 decreased EGFR phosphorylation. Moreover, expression of R399E mutant PKM2, which has been reported to preferentially form a dimer, enhanced EGFR phosphorylation, cellular transformation, and cell proliferation more strongly than the wild-type PKM2. Thus, our study revealed a novel function of extracellular PKM2 in the promoting cancer cell proliferation through EGFR activation.

AKT1 Inhibits Epithelial-to-Mesenchymal Transition in Breast Cancer through Phosphorylation-Dependent Twist1 Degradation

Epithelial-to-mesenchymal transition (EMT) is an essential physiologic process that promotes cancer cell migration, invasion, and metastasis. Several lines of evidence from both cellular and genetic studies suggest that AKT1/PKBα, but not AKT2 or AKT3, serves as a negative regulator of EMT and breast cancer metastasis. However, the underlying mechanism by which AKT1 suppresses EMT remains poorly defined. Here, we demonstrate that phosphorylation of Twist1 by AKT1 is required for β-TrCP-mediated Twist1 ubiquitination and degradation. The clinically used AKT inhibitor MK-2206, which possesses higher specificity toward AKT1, stabilized Twist1 and enhanced EMT in breast cancer cells. However, we discovered that resveratrol, a naturally occurring compound, induced β-TrCP-mediated Twist1 degradation to attenuate MK-2206-induced EMT in breast cancer cells. Taken together, our findings demonstrate that resveratrol counteracts the unexpected metastatic potential induced by anti-AKT therapy and therefore suggest that the addition of resveratrol to an anti-AKT therapeutic regimen may provide extra support for limiting EMT.

EGFR Signaling Enhances Aerobic Glycolysis in Triple-Negative Breast Cancer Cells to Promote Tumor Growth and Immune Escape

Oncogenic signaling reprograms cancer cell metabolism to augment the production of glycolytic metabolites in favor of tumor growth. The ability of cancer cells to evade immunosurveillance and the role of metabolic regulators in T-cell functions suggest that oncogene-induced metabolic reprogramming may be linked to immune escape. EGF signaling, frequently dysregulated in triple-negative breast cancer (TNBC), is also associated with increased glycolysis. Here, we demonstrated in TNBC cells that EGF signaling activates the first step in glycolysis, but impedes the last step, leading to an accumulation of metabolic intermediates in this pathway. Furthermore, we showed that one of these intermediates, fructose 1,6 bisphosphate (F1,6BP), directly binds to and enhances the activity of the EGFR, thereby increasing lactate excretion, which leads to inhibition of local cytotoxic T-cell activity. Notably, combining the glycolysis inhibitor 2-deoxy-d-glucose with the EGFR inhibitor gefitinib effectively suppressed TNBC cell proliferation and tumor growth. Our results illustrate how jointly targeting the EGFR/F1,6BP signaling axis may offer an immediately applicable therapeutic strategy to treat TNBC.

EGFR modulates microRNA maturation in response to hypoxia through phosphorylation of AGO2

MicroRNAs (miRNAs) are generated by two-step processing to yield small RNAs that negatively regulate target gene expression at the post-transcriptional level. Deregulation of miRNAs has been linked to diverse pathological processes, including cancer. Recent studies have also implicated miRNAs in the regulation of cellular response to a spectrum of stresses, such as hypoxia, which is frequently encountered in the poorly angiogenic core of a solid tumour. However, the upstream regulators of miRNA biogenesis machineries remain obscure, raising the question of how tumour cells efficiently coordinate and impose specificity on miRNA expression and function in response to stresses. Here we show that epidermal growth factor receptor (EGFR), which is the product of a well-characterized oncogene in human cancers, suppresses the maturation of specific tumour-suppressor-like miRNAs in response to hypoxic stress through phosphorylation of argonaute 2 (AGO2) at Tyr 393. The association between EGFR and AGO2 is enhanced by hypoxia, leading to elevated AGO2-Y393 phosphorylation, which in turn reduces the binding of Dicer to AGO2 and inhibits miRNA processing from precursor miRNAs to mature miRNAs. We also identify a long-loop structure in precursor miRNAs as a critical regulatory element in phospho-Y393-AGO2-mediated miRNA maturation. Furthermore, AGO2-Y393 phosphorylation mediates EGFR-enhanced cell survival and invasiveness under hypoxia, and correlates with poorer overall survival in breast cancer patients. Our study reveals a previously unrecognized function of EGFR in miRNA maturation and demonstrates how EGFR is likely to function as a regulator of AGO2 through novel post-translational modification. These findings suggest that modulation of miRNA biogenesis is important for stress response in tumour cells and has potential clinical implications.

Abstract 3027: A novel function of EGFR in epigenetic modulation via hMOF in breast cancer

The epidermal growth factor receptor (EGFR) is aberrantly active in breast cancer, initiates and drives tumorigenic pathways, and has been implicated in multiple tumorigenic processes including hyperplasia, chemo-resistance and metastasis. Histone lysine modifications directly influence activation and repression of transcription. MYST family acetyltransferase, human males absent on the first (hMOF), plays an important role in transcription activity through histone H4K16 acetylation. Loss of hMOF and subsequently the absence of H4K16 acetylation have been shown to be a common feature in human cancer including breast cancer. However, the regulation of hMOF remains largely unknown. Recently, we have discovered the acetylation of EGFR in human breast cancer cells. Thus, we screened a set of EGFR-interacting acetyltransferases using co-immunoprecipitation analysis and ingenuity pathway analysis (IPA). Here, we found that EGFR directly interacts with and phosphorylates hMOF. EGFR-induced phosphorylation hMOF was significantly reduced in the hMOF YF mutant. Indeed, hMOF YF mutant showed a higher histone acetyltransferase (HAT) activity compare to wild type hMOF. In addition, tyrosine kinase inhibitor (TKI) also enhanced the HAT activity of wild type hMOF. Furthermore, we found that EGFR modulates acetylation status of histone H4K16 via phosphorylating hMOF. We anticipate our study of EGFR and hMOF to be of therapeutic relevance, possibly leading to novel discovery in drug development targeting the receptor tyrosine kinase and the acetylation process.

Citation Format: Seung-Oe Lim, Chia-Wei Li, Shih-Shin Chang, Jia Shen, Mien-Chie Hung. A novel function of EGFR in epigenetic modulation via hMOF in breast cancer . [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3027. doi:10.1158/1538-7445.AM2013-3027

Snail inhibits Notch1 intracellular domain mediated transcriptional activation via competing with MAML1

Notch1 intracellular domain (NICD) is the transcription factor which controls cell fate and differentiation in embryonic and tumor cells. Snail has a critical role which increases invasion and metastasis of cancer cell as a transcription factor and epigenetic regulator. Recently, we discovered NICD induced Snail degradation by direct binding interaction with Snail. In this experiment, we found that Snail suppressed transcriptional activity of the protein complex formed with NICD and RBPJk in nucleus. Moreover, Snail decreased transcription of NICD target genes via competing with MAML1, co-activator, in NICD complex. In conclusion, Snail inhibited NICD-mediated transcriptional activation of target genes by physical interaction with NICD.

Epithelial-mesenchymal transition induced by TNF-α requires NF-κB-mediated transcriptional upregulation of Twist1

Proinflammatory cytokines produced in the tumor microenvironment facilitate tumor development and metastatic progression. In particular, TNF-α promotes cancer invasion and angiogenesis associated with epithelial-mesenchymal transition (EMT); however, the mechanisms underlying its induction of EMT in cancer cells remain unclear. Here we show that EMT and cancer stemness properties induced by chronic treatment with TNF-α are mediated by the upregulation of the transcriptional repressor Twist1. Exposure to TNF-α rapidly induced Twist1 mRNA and protein expression in normal breast epithelial and breast cancer cells. Both IKK-β and NF-κB p65 were required for TNF-α-induced expression of Twist1, suggesting the involvement of canonical NF-κB signaling. In support of this likelihood, we defined a functional NF-κB-binding site in the Twist1 promoter, and overexpression of p65 was sufficient to induce transcriptional upregulation of Twist1 along with EMT in mammary epithelial cells. Conversely, suppressing Twist1 expression abrogated p65-induced cell migration, invasion, EMT, and stemness properties, establishing that Twist1 is required for NF-κB to induce these aggressive phenotypes in breast cancer cells. Taken together, our results establish a signaling axis through which the tumor microenvironment elicits Twist1 expression to promote cancer metastasis. We suggest that targeting NF-κB-mediated Twist1 upregulation may offer an effective a therapeutic strategy for breast cancer treatment.

Notch1 binds and induces degradation of Snail in hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is a common, highly invasive malignant tumor associated with a high mortality rate. We previously reported that the aberrant expression of Snail via activation of reactive oxygen species contributes to the invasive property of HCC, in part by downregulation of E-cadherin through both transcriptional repression and epigenetic modification of the E-cadherin promoter. Having demonstrated the ability of Snail to bind and recruit histone deacetylase 1 and DNA methyltransferase 1 in this context, we set out to look for other interactions that could affect its ability to promote oncogenic transformation and cancer cell invasion.

RESULTS

Using cells that stably expressed Snail, we characterized Snail protein interactors by tandem affinity purification and mass spectrometry. Immunoprecipitation and subcellular colocalization studies were performed to confirm our identification of the Notch1 intracellular domain (NICD) as a novel Snail-binding partner. NICD interaction with Snail was found to induce ubiquitination and MDM2-dependent degradation of Snail. Interestingly, NICD inhibited Snail-dependent invasive properties in both HCC cells and mouse embryonic fibroblasts.

CONCLUSIONS

Our study demonstrates that NICD can oppose Snail-dependent HCC cell invasion by binding and inducing proteolytic degradation of Snail. Although Notch signaling and Snail are both widely considered tumor-promoting factors, our findings indicate that the individual oncogenic contribution of Notch1 and Snail in malignant systems should be interpreted carefully, particularly when they are conjointly expressed.

Reactive oxygen species downregulate catalase expression via methylation of a CpG island in the Oct-1 promoter

Reactive oxygen species (ROS) caused oxidative stress plays a key role in carcinogenesis. The POU domain transcription factor Oct-1 and catalase is closely associated with ROS. However, a correlation between these two key proteins has not been demonstrated before. In this report, we show that Oct-1 acts as an activator of catalase, by binding to the catalase promoter in hepatocellular carcinoma (HCC) cell lines. In addition, we suggest that Oct-1 is downregulated by ROS via CpG island methylation in its promoter. These findings contribute to a better understanding of the epigenetic changes induced by ROS in the process of carcinogenesis.

Notch1 differentially regulates oncogenesis by wildtype p53 overexpression and p53 mutation in grade III hepatocellular carcinoma

The tumor suppressor p53 is a key prognostic factor in hepatocellular carcinoma (HCC), yet only 35% of grade III tumors exhibit mutation of p53. Several other pathways have been implicated in HCC and, among these, the role of the Notch1/Snail pathway remains unclear. Therefore, we investigated the expression of p53, Notch1, and Snail proteins in HCC with regard to both clinical grade and p53 mutational status. Immunoblotting for p53 revealed that, whereas in many tumors increased p53 was a result of p53 mutation, wildtype p53 (p53WT) expression was also frequently elevated in HCCs. Coordinated evaluation of p53, Notch1, and Snail expression suggests that grade III HCC can be subdivided based on the expression of these three proteins. We found that Notch1 expression in HCC tissues and cell lines is differentially affected by p53WT and mutant p53 (p53Mut). Notch1 expression was correlated with p53 expression in cells expressing p53WT, but was not elevated in p53Mut-expressing cells. Virally mediated expression or silencing of p53WT or p53Mut confirmed that p53WT overexpression causes Notch1 up-regulation in HCC. Surprisingly, the consequence of Notch1 overexpression for the proliferative and invasive capacity of HCC cells depends on both the p53 mutational status and activation of the Snail pathway.

CONCLUSION

In the presence of p53WT, Snail/Notch1 activation increased the invasiveness of HCC cells. In contrast, in the absence of p53WT, Notch1 decreased the invasiveness of HCC. Taken together, these findings shed new light on the complex role of the Notch1/Snail axis in HCC and provide a framework for further classifying HCC based on the expression and mutational status of p53 and the expression of Notch1 and Snail.

Epigenetic changes induced by reactive oxygen species in hepatocellular carcinoma: methylation of the E-cadherin promoter

BACKGROUND & AIMS

In addition to genetic alterations, epigenetic changes underlie tumor progression and metastasis. Promoter methylation can silence tumor suppressor genes, and reactive oxygen species (ROS) promote DNA damage, although the relationship between ROS and epigenetic changes in cancer cells is not clear. We sought to determine whether ROS promote hypermethylation of the promoter region of E-cadherin, a regulator of the epithelial-to-mesenchymal transition, in hepatocellular carcinoma (HCC) cells.

METHODS

HCC cells were exposed to H(2)O(2) or stably transfected to express Snail, a transcription factor that down-regulates E-cadherin expression. E-cadherin and Snail expression levels were examined by real-time reverse-transcriptase polymerase chain reaction and immunoblot analyses. The methylation status of E-cadherin was examined by methyl-specific polymerase chain reaction, bisulfite sequencing, and chromatin immunoprecipitation. The interactions between Snail, histone deacetylase 1, and DNA methyltransferase 1 were assessed by immunoprecipitation/immunoblot and immunofluorescence analyses. ROS-induced stress, E-cadherin expression, Snail expression, and E-cadherin promoter methylation were confirmed in HCC tissues by immunoblot, immunohistochemistry, and methyl-specific polymerase chain reaction analyses.

RESULTS

We demonstrated that ROS induce hypermethylation of the E-cadherin promoter by increasing Snail expression. Snail induced DNA methylation of the E-cadherin promoter by recruiting histone deacetylase 1 and DNA methyltransferase 1. In human HCC tissues, we observed a correlation among ROS induction, E-cadherin down-regulation, Snail up-regulation, and E-cadherin promoter methylation.

CONCLUSIONS

These findings provide novel mechanistic insights into epigenetic modulations induced by ROS in the process of carcinogenesis. They are potentially relevant to understanding the activity of ROS in silencing various tumor suppressor genes and in subsequent tumor progression and metastasis.

Expression of heat shock proteins (HSP27, HSP60, HSP70, HSP90, GRP78, GRP94) in hepatitis B virus-related hepatocellular carcinomas and dysplastic nodules

AIM: Expression of heat shock proteins (HSPs) is frequently up-regulated in hepatocellular carcinoma (HCC), which evolves from dysplastic nodule (DN) and early HCC to advanced HCC. However, little is known about the differential expression of HSPs in multistep hepatocarcinogenesis. It was the purpose of this study to monitor the expression of HSPs in multistep hepatocarcinogenesis and to evaluate their prognostic significance in hepatitis B virus (HBV)-related HCC.

METHODS: Thirty-eight HCC and 19 DN samples were obtained from 52 hepatitis B surface antigen-positive Korean patients. Immunohistochemical and dot immunoblot analyses of HSP27, HSP60, HSP70, HSP90, glucose regulated protein (GRP)78, and GRP94 were performed and their expression at different stages of HCC development was statistically analyzed.

RESULTS: Expression of HSP27, HSP70, HSP90, GRP78, and GRP94 increased along with the stepwise progression of hepatocarcinogenesis. Strong correlation was found only in GRP78 (Spearman’s r = 0.802). There was a positive correlation between the expressions of GRP78, GRP94, HSP90, or HSP70 and prognostic factors of HCC. Specifically, the expression of GRP78, GRP94, or HSP90 was associated significantly with vascular invasion and intrahepatic metastasis.

CONCLUSION: The expressions of HSPs are commonly up-regulated in HBV-related HCCs and GRP78 might play an important role in the stepwise progression of HBV-related hepatocarcinogenesis. GRP78, GRP94, and HSP90 may be important prognostic markers of HBV-related HCC, strongly suggesting vascular invasion and intrahepatic metastasis.

Reduction in cyclin D1/Cdk4/retinoblastoma protein signaling by CRE-decoy oligonucleotide

We have previously demonstrated that the activation of p53 signaling may contribute to tumor growth inhibition by the CRE-decoy oligonucleotide containing CRE sequence (5'-TGACGTCA-3') (Lee et al., Biochemistry 39, 4863-4868, 2000). However, growth inhibition by CRE-decoy treatment was also observed in tumor cells containing a mutant p53 (Park et al., J. Biol. Chem. 274, 1573-1580, 1999). To understand additional mechanisms of the decoy oligonucleotide, we investigated the effect on cyclin D1 expression and a cyclin D1/Cdk4/retinoblastoma protein (pRB) signaling pathway. Here we show that in MCF7 breast cancer cells the CRE-decoy competed with cyclin D1-CRE (5'-TAACGTCA-3') for binding transcription factors and reduced cyclin D1 gene expression (in reporter gene assay, Northern blotting and Western blotting) to modulate cyclin D1/Cdk4/pRB signaling and G1-S progression in a steady state and/or under estrogen stimulation. Decrease of cyclin D1 protein level by CRE-decoy treatment was also observed in p53-mutated cancer cells. Cyclin D1 expression was also diminished in MCF7 cells stably expressing dominant negative mutant CREB indicating that the nonspecific effect of oligonucleotide or its degradation products could be excluded. These data suggest that inhibition of cyclin D1 expression contributes to the growth inhibition induced by the decoy oligonucleotide in MCF7 cells through a cyclin D1/Cdk4/pRB signaling pathway. Downregulation of cyclin D1 expression also provides a mechanism of CRE-decoy-induced growth inhibition in tumor cells having p53 mutation.