c-CBL E3 ubiquitin ligase is overexpressed in cutaneous T-cell lymphoma: its inhibition promotes activation-induced cell death

Siah2-GRP78 interaction regulates ROS and provides a proliferative advantage to Helicobacter pylori-infected gastric epithelial cancer cells

Helicobacter pylori-mediated gastric carcinogenesis involves upregulation of the E3 ubiquitin ligase Siah2 and its phosphorylation-mediated stabilization. This study elucidates a novel mechanism of oxidative stress regulation by phosphorylated Siah2 in H. pylori-infected gastric epithelial cancer cells (GECs). We identify that H. pylori-mediated Siah2 phosphorylation at the 6th serine residue (P-S6-Siah2) enhances proteasomal degradation of the 78-kDa glucose-regulated protein (GRP78) possessing antioxidant functions. S6 phosphorylation stabilizes Siah2 and P-S6-Siah2 potentiates H. pylori-mediated reactive oxygen species (ROS) generation. However, infected S6A phospho-null Siah2-expressing cells have decreased cellular GRP78 level as surprisingly these cells release GRP78 to a higher extent and accumulate significantly higher ROS than the wild type (WT) Siah2 construct-expressing cells. Ectopic expression of GRP78 prevents the loss of mitochondrial membrane potential and cellular ROS accumulation caused by H. pylori. H. pylori-induced mitochondrial damage and mitochondrial membrane potential loss are potentiated in Siah2-overexpressing cells but these effects are further enhanced in S6A-expressing cells. This study also confirms that while phosphorylation-mediated Siah2 stabilization optimally upregulates aggresome accumulation, it suppresses autophagosome formation, thus decreasing the dependency on the latter mechanism in regulating cellular protein abundance. Disruption of the phospho-Siah2-mediated aggresome formation impairs proliferation of infected GECs. Thus, Siah2 phosphorylation has diagnostic and therapeutic significance in H. pylori-mediated gastric cancer (GC).

Epigenetics of Cutaneous T-Cell Lymphomas

Epigenetic modifications rarely occur in isolation (as single “epigenetic modifications”). They usually appear together and form a network to control the epigenetic system. Cutaneous malignancies are usually affected by epigenetic changes. However, there is limited knowledge regarding the epigenetic changes associated with cutaneous lymphomas. In this review, we focused on cutaneous T-cell lymphomas such as mycosis fungoides, Sézary syndrome, and anaplastic large cell lymphoma. With regard to epigenetic changes, we summarize the detailed chemical modifications categorized into DNA methylation and histone acetylation and methylation. We also summarize the epigenetic modifications and characteristics of the drug for cutaneous T-cell lymphoma (CTCL). Furthermore, we discuss current research on epigenetic-targeted therapy against cutaneous T-cell lymphomas. Although the current method of treatment with histone deacetylase inhibitors does not exhibit sufficient therapeutic benefits in all cases of CTCL, epigenetic-targeted combination therapy might overcome this limitation for patients with CTCL.

Eimeria acervulina Microneme Protein 3 Inhibits Apoptosis of the Chicken Duodenal Epithelial Cell by Targeting the Casitas B-Lineage Lymphoma Protein

Eimeria acervulina (E. acervulina) causes coccidiosis in poultry which persists as economic pain worldwide. Most damage to the intestinal mucosa results from apoptosis of the infected intestinal epithelial cells. The Microneme protein 3 (MIC3) protein is a key virulence factor in some parasites involved in host cell apoptosis inhibition. Here, we studied whether and how MIC3 affects the apoptosis in E. acervulina infected chicken duodenal epithelial cells. Through flow cytometry (FCM), we found that the presence of merozoites and the overexpression of MIC3 significantly decreased apoptosis and the activity of caspase-3 in chicken duodenal epithelial cells at 4, 6, and 8 h post merozoite infection (P < 0.01). Silencing the Casitas B-lineage lymphoma (CBL) protein, a host receptor for MIC3 with shRNA was shown to promote apoptosis in the chicken duodenal epithelial cells. The early apoptotic rate of host cells in the lentiviral-MIC3 group was significantly lower than that in the lentiviral-MIC3 + shRNA CBL group at 4 h after MIC3 expression (P < 0.01), and it was moderately decreased in the lentiviral-MIC3 + shRNA CBL group compared with that in the shRNA CBL group. Our data indicated that MIC3 inhibited early apoptosis of E. acervulina infected chicken duodenal epithelial cells by targeting host receptor-CBL protein. These findings unveiled one of the mechanisms of how intracellular parasites affect the apoptosis of infected host cells, which provided a deeper understanding of their pathogenesis.

Analysis of the Effect of Gentian Violet on Apoptosis and Proliferation in Cutaneous T-Cell Lymphoma in an In Vitro Study

Importance

Triggering the extrinsic apoptotic pathway is an effective way to kill cutaneous T-cell lymphoma (CTCL) cells in vitro and ex vivo.

Objective

To compare small molecules that induce extrinsic apoptosis in CTCL to identify and analyze compounds that induce high levels of tumor cell death and block tumor cell growth.

Design, Setting, and Participants

From November 5, 2014, to January 30, 2018, this study performed high-throughput small molecule screening of 1710 compounds followed by detailed analysis of the ability of gentian violet (GV) to promote apoptosis and inhibit proliferation of CTCL cells.

Exposures

In vitro and ex vivo analyses using enzyme-linked immunosorbent assays, flow cytometry, and immunoblotting.

Main Outcomes and Measures

Apoptosis, cleaved caspases, extrinsic apoptotic death receptors and ligands, cell proliferation, nuclear factor-κB expression, and other factors.

Results

This study used high-throughput screening to detect cleaved caspase 8 induced in CTCL cells by 1710 unique compounds. The nonprescription, topical antimicrobial remedy GV induced more total apoptosis than did nitrogen mustard (mechlorethamine). Furthermore, GV induced 4 to 6 times greater apoptosis in CTCL lines than in normal keratinocytes, suggesting a favorable topical toxicity profile. In addition to increasing caspase 8, GV also upregulated death receptors 4 and 5, tumor necrosis factor (TNF)-related apoptosis-inducing ligand, and Fas ligand but not the Fas receptor, TNF receptor, or TNF-α ligand. These results are consistent with induction of extrinsic apoptosis via the Fas and TNF-related apoptosis-inducing ligand pathways. Increased phosphorylation of phospholipase C-γ1, Ca2+ influx, and reactive oxygen species were also detected, indicating that the mechanism of Fas ligand upregulation involves key elements of the activation-induced cell death pathway. In ex vivo studies, 1-μmol/L GV induced up to 90% CTCL apoptosis in Sézary blood cells. In addition, GV reduced expression of antiapoptotic myeloid cell leukemia 1 and proproliferative nuclear factor-κB components and increased inhibitory κB levels. This finding was associated with cell cycle arrest and reduced CTCL tumor cell proliferation. Furthermore, the CTCL killing associated with GV was augmented when used in combination with methotrexate.

Conclusions and Relevance

This study found that GV attacked tumor viability and growth in CTCL. Although purple at neutral pH, GV can be rendered colorless by altering its pH. These preclinical findings may help to broaden knowledge of the antineoplastic features of GV and provide a rationale for clinical studies of its use as a novel, inexpensive, topical therapy for CTCL that is available worldwide.

Ubiquitin Ligases in Cancer Immunotherapy - Balancing Antitumor and Autoimmunity

Considerable progress has been made in understanding the contribution of E3 ubiquitin ligases to health and disease, including the pathogenesis of immunological disorders. Ubiquitin ligases exert exquisite spatial and temporal control over protein stability and function, and are thus crucial for the regulation of both innate and adaptive immunity. Given that immune responses can be both detrimental (autoimmunity) and beneficial (antitumor immunity), it is vital to understand how ubiquitin ligases maintain immunological homeostasis. Such knowledge could reveal novel mechanisms underlying immune regulation and identify new therapeutic approaches to enhance antitumor immunity and safeguard against autoimmunity.

Preclinical Studies Support Combined Inhibition of BET Family Proteins and Histone Deacetylases as Epigenetic Therapy for Cutaneous T-Cell Lymphoma

Advanced-stage cutaneous T-cell lymphoma (CTCL) is usually a fatal malignancy despite optimal use of currently available treatments. In this preclinical study of novel CTCL therapy, we performed in vitro and ex vivo experiments to determine the efficacy of combination treatment with a panel of BET bromodomain inhibitors (BETi) (JQ1, OTX015, CPI-0610, I-BET762) and HDAC inhibitors (HDACi) (SAHA/Vorinostat, Romidepsin). BETi/HDACi combinations were synergistic (combination index <1) against cell viability and induced G0/G1 cell cycle arrest. Apoptosis was uniformly enhanced. From a mechanistic standpoint, proliferative drivers c-Myc, Cyclin D1, NFkB, and IL-15Rα were reduced. Inhibitory CDKN1A was increased. CDKN1B, IL-7R, IL-17Rα, STAT3, and STAT5 alterations varied. There were significant increases in extrinsic apoptotic pathway death receptors and ligands (FasL, DR4, DR5, TRAIL, and TNFR1). At clinically tolerable levels of single agents, Romidepsin (1 nM) + OTX015 (125 nM) induced the greatest apoptosis (60%_80%) at 96 hours. Ex vivo studies of leukemic CTCL cells obtained from patients with Sezary syndrome also showed higher levels of apoptosis (about 60%-90%) in response to combination treatments relative to single agents. In contrast, combination treatment of normal CD4+ T cells induced only minimal apoptosis (<10%). Our findings show that the mechanism of action of BETi/HDACi therapy in CTCL involves induction of both cell cycle arrest and apoptosis with reduced proliferative drivers and enhanced expression of apoptotic extrinsic pathway death receptors and ligands. Relative to single agents, the superior anti-CTCL effects of BETi/HDACi combinations in vitro and ex vivo provide a rationale for clinical trials exploring their efficacy as therapy for CTCL.

Src-family kinase-Cbl axis negatively regulates NLRP3 inflammasome activation

Activation of the NLRP3 inflammasome is crucial for immune defense, but improper and excessive activation causes inflammatory diseases. We previously reported that Pyk2 is essential for NLRP3 inflammasome activation. Here we show that the Src-family kinases (SFKs)-Cbl axis plays a pivotal role in suppressing NLRP3 inflammasome activation in response to stimulation by nigericin or ATP, as assessed using gene knockout and gene knockdown cells, dominant active/negative mutants, and pharmacological inhibition. We reveal that the phosphorylation of Cbl is regulated by SFKs, and that phosphorylation of Cbl at Tyr371 suppresses NLRP3 inflammasome activation. Mechanistically, Cbl decreases the level of phosphorylated Pyk2 (p-Pyk2) through ubiquitination-mediated proteasomal degradation and reduces mitochondrial ROS (mtROS) production by contributing to the maintenance of mitochondrial size. The lower levels of p-Pyk2 and mtROS dampen NLRP3 inflammasome activation. In vivo, inhibition of Cbl with an analgesic drug, hydrocotarnine, increases inflammasome-mediated IL-18 secretion in the colon, and protects mice from dextran sulphate sodium-induced colitis. Together, our novel findings provide new insights into the role of the SFK-Cbl axis in suppressing NLRP3 inflammasome activation and identify a novel clinical utility of hydrocortanine for disease treatment.

c-CBL E3 Ubiquitin Ligase Expression Increases Across the Spectrum of Benign and Malignant T-Cell Skin Diseases

Prolonged survival of lesional T cells plays a central role in the pathogenesis of T-cell-mediated dermatoses. We have recently shown that the ubiquitin ligase c-CBL is highly expressed in cutaneous T-cell lymphoma (CTCL) and that its knockdown increases activation-induced cell death, a key pathway for T-cell apoptosis. Here, we extend our work on c-CBL expression in malignant T cells to their nonneoplastic counterparts in benign inflammatory dermatoses. Immunohistochemical staining with anti-c-CBL antibody was performed on lesional biopsies from a total of 65 patients with atopic dermatitis, allergic contact dermatitis, pityriasis rosea, psoriasis vulgaris, lichen planus, mycosis fungoides (MF)/Sézary syndrome (SS) as well as on tonsil tissue from 5 individuals and on 5 human CTCL cell lines. Protein levels were measured in situ using multispectral image analysis, a quantitative method that is ×5 more sensitive than standard immunohistology for antigen detection. There was a significant (P < 0.05) and progressive increase of mean c-CBL expression across the spectrum of inflammatory dermatoses (2-fold), MF/SS (3-fold), and lymphoma cell lines (4-fold) as compared with tonsillar T lymphocytes. A subset of MF/SS cases expressed mean c-CBL levels above the ranges observed in inflammatory dermatoses. Given our prior finding that c-CBL inhibits activation-induced cell death, c-CBL might play a role in the pathogenesis of inflammatory dermatoses and CTCL.

Epigenetically Enhanced PDT Induces Significantly Higher Levels of Multiple Extrinsic Pathway Apoptotic Factors than Standard PDT, Resulting in Greater Extrinsic and Overall Apoptosis of Cutaneous T-cell Lymphoma

Aminolevulinate-based photodynamic therapy (ALA-PDT) selectively eliminates diseased tissues primarily through the induction of intrinsic apoptotic pathway. ALA-PDT is a first-line therapy for actinic keratosis, however, it is less effective for cutaneous T-cell lymphoma (CTCL). We have previously demonstrated that the resistance of CTCL to apoptosis correlates with decreased expression of death receptors such as FAS, and that methotrexate functions as an epigenetic regulator that reestablishes the susceptibility of CTCL to extrinsic pathway apoptosis. We showed previously that MTX augments the effectiveness of PDT by sensitizing cells to apoptosis by induction of apoptotic factors, a process we call "epigenetically enhanced" PDT (ePDT). Here, in CTCL cell lines, leukemic CTCL cells, and normal blood T cells, we analyzed multiple components of the FAS, TRAIL, and TNF families using multispectral imaging of immunostained cytopreparations, a quantitative technique with five-fold greater sensitivity than standard immunocytology. ePDT induced significantly greater FAS, FASL, TRAIL-R1 & -R2, and TNFα levels than standard PDT. This correlated with significantly greater induction of extrinsic pathway apoptosis and/or overall apoptosis in all CTCL samples. There was no appreciable effect on normal T cells. These data set the stage for clinical trials of ePDT as a novel localized treatment of CTCL.

c-CBL regulates melanoma proliferation, migration, invasion and the FAK-SRC-GRB2 nexus

Melanoma is one of the most aggressive and lethal forms of skin cancer. Despite recent improvements in targeted therapies, many patients with advanced disease fail to achieve lasting tumor regression. Therefore, it is important to develop novel druggable targets that can be exploited to improve clinical outcome. Here, we studied the role of Casitas B-lineage lymphoma (c-CBL), an E3 ubiquitin ligase, in human melanoma. Employing quantitative real-time PCR and Western blot analysis in a panel of human melanoma cell lines (A375, G361, Hs-294T, SK-Mel-2, SK-Mel-28 and 451Lu), we found that c-CBL is strongly expressed in human melanoma cells at the mRNA and protein levels. Further, we determined c-CBL levels in clinical samples of melanomas and benign melanocytic nevi, using quantitative Nuance multispectral imaging. Compared to benign nevi, melanomas showed an overlapping range of c-CBL immunoreactivity. Small interfering RNA (siRNA)-mediated knockdown of c-CBL resulted in decreased proliferation, clonogenic survival and migration of melanoma cells. Furthermore, it also resulted in decreased cellular invasion in a 3D spheroid assay system. C-CBL and FAK are regulated by SRC, and FAK binds SRC and GRB2. C-CBL E3 ligase domain regulates receptor tyrosine kinase internalization through ubiquitination and its ring finger domain stabilizes the FAK-SRC-actin cytoskeleton thereby promoting cellular motility. C-CBL knockdown was associated with decreased protein and/or mRNA levels of SRC, FAK and GRB2. Taken together, we have provided evidence that c-CBL plays a role in melanoma cell proliferation, migration and invasion as well as inhibition of the FAK-GRB2-SRC nexus. Our findings indicate that additional studies are warranted to further dissect the role of c-CBL in melanoma and determine the therapeutic potential of its inhibition.

Intrahepatic Xenograft of Cutaneous T-Cell Lymphoma Cell Lines: A Useful Model for Rapid Biological and Therapeutic Evaluation

Cutaneous T-cell lymphomas (CTCLs) are a heterogeneous group of diseases primarily involving the skin that could have an aggressive course with circulating blood cells, especially in Sézary syndrome and transformed mycosis fungoides. So far, few CTCL cell lines have been adapted for in vivo experiments and their tumorigenicity has not been adequately assessed, hampering the use of a reproducible model for CTCL biological evaluation. In fact, both patient-derived xenografts and cell line xenografts at subcutaneous sites failed to provide a robust tool, because engraftment was dependent on mice strain and cell line subtype. Herein, we describe an original method of intrahepatic injection into adult NOD.Cg-Prkdc(scid)Il2rg(tm1Wjl)/SzJ mice liver of both aggressive (My-La, HUT78, HH, MAC2A, and MAC2B) and indolent (FE-PD and MAC1) CTCL cell lines. Six of the seven CTCL cell lines were grafted with a high rate of success (80%). Moreover, this model provided a quick (15 days) and robust assay for in vivo evaluation of CTCL cell lines tumorigenicity and therapeutic response in preclinical studies. Such a reproducible model can be therefore used for further functional studies and in vivo drug testing.

Epigenetically Enhanced Photodynamic Therapy (ePDT) is Superior to Conventional Photodynamic Therapy for Inducing Apoptosis in Cutaneous T-Cell Lymphoma

Conventional photodynamic therapy with aminolevulinate (ALA-PDT) selectively induces apoptosis in diseased cells and is highly effective for treating actinic keratoses. However, similar results are achieved only in a subset of patients with cutaneous T-cell lymphoma (CTCL). Our previous work shows that the apoptotic resistance of CTCL correlates with low expression of death receptors like Fas cell surface death receptor (FAS), and that methotrexate upregulates FAS by inhibiting the methylation of its promoter, acting as an epigenetic derepressor that restores the susceptibility of FAS-low CTCL to caspase-8-mediated apoptosis. Here, we demonstrate that methotrexate increases the response of CTCL to ALA-PDT, a concept we refer to as epigenetically enhanced PDT (ePDT). Multiple CTCL cell lines were subjected to conventional PDT versus ePDT. Apoptotic biomarkers were analyzed in situ with multispectral imaging analysis of immunostained cells, a method that is quantitative and 5× more sensitive than standard immunohistology for antigen detection. Compared to conventional PDT or methotrexate alone, ePDT led to significantly greater cell death in all CTCL cell lines tested by inducing greater activation of caspase-8-mediated extrinsic apoptosis. Upregulation of FAS and/or tumor necrosis factor-related apoptosis-inducing ligand pathway components was observed in different CTCL cell lines. These findings provide a rationale for clinical trials of ePDT for CTCL.

Methotrexate and Pralatrexate

This article reviews methotrexate and the more potent, related compound, pralatrexate, for the treatment of cutaneous T-cell lymphomas, including mycosis fungoides, Sézary syndrome, and CD30+ lymphoproliferative disorders. Although these folate antagonists are traditionally viewed as antiproliferative cell cycle inhibitors, it is recognized that they inhibit DNA methylation, providing a rationale for their use as epigenetic regulators and cell proliferation inhibitors. The underlying mechanisms are outlined, key supporting data presented, followed by brief mention of recent mathematical modeling supporting the general superiority of combination therapy. Several novel examples involving folate antagonists are proposed.

Silencing autocrine death: a ubiquitin ligase that blocks activation-induced cell death in cutaneous T-cell lymphoma

Cutaneous T-cell lymphoma (CTCL) tumor cells lack the ability of activated T cells to undergo TCR/CD3-mediated activation-induced cell death (AICD). In this issue, the study reported by Wu et al. demonstrates that c-CBL (Casitas B-lineage Lymphoma proto-oncogene) is overexpressed in CTCL. When CTCL cells lose c-CBL, AICD is enhanced. Furthermore, combination therapy with methotrexate (a known demethylating agent for the CD95 gene) in combination with the loss of c-CBL increases CTCL cell death. Therefore, inhibition of c-CBL could represent a method of sensitizing lymphoma cells to enhance AICD. Armed with their novel data, the investigators envision combination therapies that target c-CBL to reactivate AICD in the malignant T cells whenever responsiveness to TCR/CD3 signaling is retained.