Abstract 3044: C. albicans infection mediates upper gastrointestinal tract malignancy independently of Il17a in an APECED-like mouse model

Patients with autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) develop chronic mucocutaneous candidiasis during childhood and about 10% of senior patients develop upper GI tract squamous cell carcinoma (SCC), suggesting that C. albicans infection may be relevant to the cause of SCC development in APECED patients. In this study, we investigated the role of C. albicans infection in upper GI tract SCC development using an APECED-like IKKα kinase-dead (KA/KA) mouse model. We found that KA/KA mice developed upper GI tract SCC after oral infection of WT C. albicans weekly for three months. Interestingly, while upper GI tract SCC development in C. albicans - infected KA/KA mice is IL-17a-independent, EGFR pathway plays an important role in C. albicans infection-mediated tumorigenesis in KA/KA mice, as evidenced by significantly lower SCC incidence in the upper GI tract of KA/KA mice infected with Als3Δ/Δ C. albicans. Moreover, upper GI tract SCCs from WT C. albicans-infected KA/KA mice exhibited robust p-EGFR and Ki67 signals. However, both p-EGFR and Ki67 signals were only mildly increased in upper GI tract of Als3Δ/Δ C. albicans-infected KA/KA mice compared to WT control mice. Meanwhile, EGFR inhibition dramatically reduced C. albicans colonization in upper GI tract and the weight of stomach in KA/KA mice. Furthermore, we found that aberrant infiltrations of neutrophils and macrophages with significant inflammatory signatures were present in the upper GI tract SCCs in KA/KA mice. Interestingly, KA/KA neutrophils exhibited a defect in C. albicans killing capacity due to functional defects in ROS generation, degranulation, NETs formation, and apoptosis. We reasoned that KA/KA neutrophils’ inability in C. albicans killing capacity may further enhance the tumor-promoting microenvironment. Finally, whole genome sequencing data suggested that C. albicans infection may lead to genome instability. Currently we are investigating the role of neutrophil infiltration in C. albicans infection-mediated upper GI tract tumorigenesis.

Citation Format: Feng Zhu, Quynh T. Phan, Elise M. Ferre, Jami Willette-Brown, Rosalba Salcedo, Tsai-Wei Shen, Yu Fan, Yongmei Zhao, Monika Mehta, Daoud Meerzaman, Bao Tran, Giorgio Trinchieri, Michail S. Lionakis, Scott G. Filler, Yinling Hu. C. albicans infection mediates upper gastrointestinal tract malignancy independently of Il17a in an APECED-like mouse model [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 3044.

NLRP3 Inhibition Ameliorates Severe Cutaneous Autoimmune Manifestations in a Mouse Model of Autoimmune Polyendocrinopathy-Candidiasis-Ectodermal Dystrophy-Like Disease

Patients with autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy show diverse endocrine and nonendocrine manifestations initiated by self-reactive T cells because of AIRE mutation-induced defective central tolerance. A large number of American patients with autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy suffer from early-onset cutaneous inflammatory lesions accompanied by an infiltration of T cells and myeloid cells. The role of myeloid cells in this setting remains to be fully investigated. In this study, we characterize the autoinflammatory phenotypes in the skin of both autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy-like kinase-dead Ikkα knockin mice and patients with autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy. We found a marked infiltration of autoreactive CD4 T cells, macrophages, and neutrophils; elevated uric acid; and increased NLRP3, a major inflammasome component. Depleting autoreactive CD4 T cells or ablating Ccl2/Cxcr2 genes significantly attenuated the inflammasome activity, inflammation, and skin phenotypes in kinase-dead Ikkα knockin mice. Importantly, treatment with an NLRP3 inhibitor reduced skin phenotypes and decreased infiltration of CD4 T cells, macrophages, and neutrophils. These results suggest that increased myeloid cell infiltration contributes to autoreactive CD4 T cell-mediated skin autoinflammation. Thus, our findings reveal that the combined infiltration of macrophages and neutrophils is required for autoreactive CD4 T cell-mediated skin disease pathogenesis and that the NLRP3-dependent inflammasome is a potential therapeutic target for the cutaneous manifestations of autoimmune diseases.

C-CBL is required for inhibition of angiogenesis through modulating JAK2/STAT3 activity in ROP development

Purpose:

The incidence of retinopathy of prematurity (ROP) has increased continuously in recent years. However, the therapeutic effects of current treatments still remain undesired. This study aims to investigate the role of C-CBL in retinal angiogenesis in ROP and its potential as a therapeutic target.

Methods:

Mouse retina microvascular endothelial cells (mRMECs) and induced experimental ROP/ oxygen-induced retinopathy (OIR) mice were employed to investigate the role of C-CBL in angiogenesis with combined molecular and cellular approaches, and histopathology methods. OIR mouse pups at postnatal day 12 (P12) were either injected intravitreally with adenovirus overexpressing c-Cbl or c-Cbl siRNA. Retinal neovascularization and avascular status were evaluated by retinal immunofluorescence (IF) staining, whole-mounts and hematoxylin and eosin (H&E) staining.

Results:

C-CBL inhibits neovascularization by negatively regulating JAK2/STAT3/VEGF signaling axis in a ubiquitination-dependent manner. Knockdown of c-Cbl by siRNA reduced ubiquitin-mediated JAK2 degradation and increased levels of p-JAK2, p-STAT3, VEGF, and neovascularization in mRMECs, which can be reversed by JAK2 inhibitor treatment. While knockdown of c-Cbl significantly increased neovascular (NV) zone in the retinas, c-Cbl overexpression inhibited neovascularization in the retinal tissues in OIR mice.

Conclusion:

We found that C-CBL is required for anti-neovascularization process in ROP development by inhibiting JAK2/STAT3-dependent angiogenesis. Thus, our finding strongly suggest that C-CBL may be a potential novel therapeutic target for treating ROP.

Abstract PR10: Candida albicans infection mediates gastrointestinal track malignancy independently of Il17a in an APECED mouse model

The cytokine Il17a plays an important role in protection against fungal infection, yet it also serves as a pathogenic factor in several inflammation-related cancers. Previously we reported that fungal infection promotes the development of esophageal squamous cell carcinoma (ESCC) in the IKKalpha kinase-dead KA knock-in (KA) mice that mimic a human autoimmune disorder, autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED). Our data showed that KA T cells failed to induce Il17a in response to fungal infection. However, the role of Il17a in fungal infection-mediated esophageal carcinogenesis remains to be further determined. In this study, we crossed KA mice with Il17a-/- mice to generate KA;Il17a-/- double mutant mice. We orally inoculated WT, Il17a-/-, KA, and KA;Il17a-/- mice with Candida albicans weekly for 3 months to investigate gastrointestinal (GI) track tumorigenesis, including the SCC development in the oral cavity, esophagus, and forestomach. We found that loss of Il17a leads to much earlier onset of GI track tumors in KA;Il17a-/- mice than that in KA mice. KA;Il17a-/- mice also died much earlier compared to KA mice, which is likely due to increased C. albicans burden in the absence of Il17a. The incidence of GI track tumors is comparable between KA and KA;Il17a-/- mice, suggesting that C. albicans infection-associated GI track tumorigenesis is independent of Il17a in KA mouse model. To further understand the underlying mechanism, we performed single-cell RNA sequencing analysis for CD45+ immune cells isolated from long-term C. alibicans-infected mouse esophagi of WT, Il17a-/-, KA, and KA;Il17a-/- mouse cohorts. Interestingly, the neutrophil population was significantly increased in the esophagi of KA and KA;Il17a-/- mice compared to WT and Il17a-/- mice. However, KA neutrophils exhibited reduced capacity in killing C. albicans with reduced NETs formation compared to WT neutrophils, suggesting that the defect in NETs formation may play a pivotal role in GI track tumorigenesis in the context of fungal infection. We are currently investigating how the interplay between C. albicans infection and host neutrophils regulates Candida infection-associated GI track tumorigenesis.

This abstract is also being presented as Poster B01.

Citation Format: Feng Zhu, Jami Willette-Brown, Trang Phan, Yongmei Zhao, Bao Tran, Scott G. Filler, Mihalis S. Lionakis, Yinling Hu. Candida albicans infection mediates gastrointestinal track malignancy independently of Il17a in an APECED mouse model [abstract]. In: Proceedings of the AACR Special Conference on the Microbiome, Viruses, and Cancer; 2020 Feb 21-24; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2020;80(8 Suppl):Abstract nr PR10.

Abstract 2355: IKKa serves as a molecular switch linking miRNA biogenesis and inflammation in skin tumorigenesis

Our previous studies have shown that the absence of tumor suppressor IKKα leads to development of spontaneous mouse squamous cell carcinomas (SCCs) in the skin, lungs, and esophagus, which is partially mediated by aberrant epigenetic alterations and inflammation. However, it remains unknown whether there is a crosstalk between the above-mentioned mechanisms. As a part of the epigenetic machinery, miRNAs regulate many genes post-transcriptionally. Here we show that IKKα deletion in the mouse epidermis results in impaired miRNA processing with markedly reduced expression of ribonuclease Dicer, an enzyme required for miRNA maturation. We found that the lack of IKKα causes Dicer gene silencing through DNA methylation. As a result, the maturation of miR-203-3p, which is the most abundant miRNA in keratinocytes, is blocked in Ikkα-null keratinocytes. Next, we identified Myd88, an important component of innate immunity and inflammation, as one of miR-203-3p targets. The level of Myd88 expression is robustly increased in Ikkα-null keratinocytes due to the lack of miR-203-3p. We also observed increased activity of caspase 1 cleavage, an indicator of inflammasome activation, in Ikkα-null keratinocytes. Interestingly, Myd88 deletion or 5-aza-2’-deoxycytidine (DNA methyltransferase inhibitor) treatment rescued the survival of Ikkαf/f;K5Cre mice, which usually die within three weeks after birth. Ikkαf/f;Myd88f/f;K5Cre mice also develop much fewer spontaneous skin tumors. By analyzing a cohort of human head and neck SCCs from TCGA database, we found that Dicer expression is concurrently downregulated among 32% of patients with low IKKα expression. Taken together, our finding illustrated how IKKα loss mediates Dicer gene silencing, which turns off miRNA processing, including miR-203-3p maturation, and eventually triggers Myd88-dependent inflammation. Thus, our study revealed a novel IKKα/Dicer/miR-203-3p/Myd88 signaling loop, in which IKKα serves as a molecular switch linking microRNA biogenesis and inflammation in skin tumorigenesis.

Citation Format: Feng Zhu, Jian Zhang, Jami Willette-Brown, Ling Su, Xiaolin Wu, Yinling Hu. IKKa serves as a molecular switch linking miRNA biogenesis and inflammation in skin tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2355.

Abstract 5008: Crosstalk between epithelial-IKKα-deletion and symbiotic bacterial-fungal infection in skin carcinogenesis

Bacteria and fungi, two major components of the microbiota, generally share niches and develop both antagonistic and symbiotic relationships, regulating the pathological impacts on the host. The epithelium is where the bacterial-fungal interaction occurs most abundantly, but the relationship between the epithelium, bacteria, and fungi on the pathogenesis of numerous diseases, particularly tumorigenesis, is poorly understood. IKKα is one of the crucial factors regulating the homeostasis of squamous epithelial tissues. Recently, our lab has established a mouse model that develops esophageal squamous cell carcinomas (SCCs) associated with IKKα reduction, inflammation and chronic fungal infection. Cladosporium cladosporioides was a major type of fungi identified in this mouse model. Because IKKα deletion in the keratinocytes causes impaired skin barrier, we hypothesized that loss of epithelial IKKα may control fungal colonization through regulating the barrier integrity and inflammation, resulting in tumor promotion. We thus generated IKKαf/f mice with inducible K15.Cre (IKKαf/f/K15.Cre) which is expressed in skin stem cells, which are important for the epidermal formation and hair follicle development. After ablating IKKα in K15 cells in the oral mucosa and skin, IKKαf/f/K15.Cre mice were orally inoculated with Cladosporium cladosporioides. Loss of epithelial IKKα showed disruption of skin barrier functions and bacterial colonization in the oral mucosa and skin, oral dysplasia and skin SCC development. Interestingly, oral infection with Cladosporium further promoted bacterial colonization as well as skin tumorigenesis in IKKαf/f/K15.Cre mice. This suggests that epithelial IKKα loss can provoke oral bacterial-fungal symbiosis which contributes to tumor promotion. To confirm this hypothesis, we treated Cladosporium-infected IKKαf/f/K15.Cre mice with amoxicillin, an antibiotic, through drinking water. Amoxicillin treatment remarkably reduced skin tumor incidence in fungal-infected IKKαf/f/K15.Cre mice, indicating that oral bacterial-fungal symbiosis indeed promotes skin SCC development driven by epithelial IKKα reduction. We also detected bacterial colonization in human skin SCC tissue array as well as IKKα mutation in 17% of human skin SCC patients from the Cancer Genome Atlas database, supporting that the crosstalk between epithelial IKKα and bacterial-fungal symbiosis in skin SCC promotion is relavent to human diseases. Taken together, our data demonstrate that loss of epithelial IKKα induces the bacterial-fungal symbiosis in oral mucosa, promoting skin tumors. This study will shed light on the importance of the epithelial-bacterial-fungal interaction in the pathogenesis, proposing epithelial IKKα as a novel regulator of the bacterial-fungal interaction.

Citation Format: Na-Young Song, Jami Willette-Brown, Feng Zhu, Yinling Hu. Crosstalk between epithelial-IKKα-deletion and symbiotic bacterial-fungal infection in skin carcinogenesis [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 5008.

IKKα deficiency disrupts the development of marginal zone and follicular B cells

Only few genes have been confidently identified to be involved in the Follicular (FO) and Marginal Zone (MZ) B cell differentiation, migration, and retention in the periphery. Our group previously observed that IKKα kinase inactive mutant mice IKKα^K44A/K44A have significantly lower number of MZ B cells whereas FO B cell numbers appeared relatively normal. Because kinase dead IKKα can retain some of its biological functions that may interfere in revealing its actual role in the MZ and FO B cell differentiation. Therefore, in the current study, we genetically deleted IKKα from the pro-B cell lineage that revealed novel functions of IKKα in the MZ and FO B lymphocyte development. The loss of IKKα produces a significant decline in the percentage of immature B lymphocytes, mature marginal zone B cells, and follicular B cells along with a severe disruption of splenic architecture of marginal and follicular zones. IKKα deficiency affect the recirculation of mature B cells through bone marrow. A transplant of IKKα knockout fetal liver cells into Rag^-/- mice shows a significant reduction compared to control in the B cells recirculating through bone marrow. To reveal the genes important in the B cell migration, a high throughput gene expression analysis was performed on the IKKα deficient recirculating mature B cells (B220⁺IgM^hi). That revealed significant changes in the expression of genes involved in the B lymphocyte survival, homing and migration. And several among those genes identified belong to G protein family. Taken together, this study demonstrates that IKKα forms a vial axis controlling the genes involved in MZ and FO B cell differentiation and migration.

Macrophage inducible nitric oxide synthase circulates inflammation and promotes lung carcinogenesis

Human lung squamous cell carcinoma (SCC) is highly associated with increased pulmonary macrophage infiltration. Previously, we showed that marked pulmonary infiltrating macrophages were required for spontaneous lung SCC development in a mouse model (L-Ikkα^KA/KA, KA/KA) that resembles human lung SCC. Interestingly the lung SCC-associated macrophages specifically express elevated inducible nitric oxide synthase (NOS2). However, the role of macrophage NOS2 in lung carcinogenesis has not been explored. Here, we show that NOS2 ablation inhibits macrophage infiltration, fibrosis, and SCC development in the lungs of KA/KA mice. Macrophage NOS2 was found to circulate inflammation and enhance macrophage migration and survival. NOS2 promotes foamy macrophage formation characterized with impaired lipid metabolism. NOS2 null bone marrow transplantation reduces foamy macrophage numbers and carcinogenesis in KA/KA chimaeras. This finding sheds light on a new mechanism by which macrophage NOS2 increases pulmonary inflammatory responses and macrophage survival and impairs macrophage lipid metabolism, thereby promoting lung SCC formation.

Abstract 1986: Determining the signaling pathway of epithelial-IKKα deletion-mediated symbiotic bacterial and fungal infection in carcinogenesis

Bacteria and fungi, two major components of the microbiota, generally share niches and develop both antagonistic and symbiotic relationships, regulating the pathological impacts on the host. The epithelium is where the bacterial-fungal interaction occurs most abundantly, but the relationship between the epithelium, bacteria, and fungi on the pathogenesis, particularly tumorigenesis, is poorly understood. IKKα is one of the crucial factors regulating the homeostasis of squamous epithelial tissues. Recently, our lab has established a mouse model that develops esophageal squamous cell carcinomas associated with IKKα reduction, inflammation and chronic fungal infection. Cladosporium cladosporioides was a major type of fungi identified in this mouse model. Because IKKα deletion in the keratinocytes causes impaired skin barrier, we hypothesized that loss of epithelial IKKα may control fungal colonization through regulating the barrier integrity and inflammation. We generated IKKαf/f mice with inducible K15.Cre (IKKαf/f/K15.Cre) specifically expressed in keratinocytes in hair follicles which is considered as skin stem cells. After deleting IKKα in K15 cells in oral mucosa and skin, IKKαf/f/K15.Cre mice were orally inoculated with Cladosporium cladosporioides. We found that epithelial IKKα deletion increased bacterial colonization in oral mucosa and skin. Moreover, Cladosporium infection further promoted bacterial and fungal colonization in oral cavity and development of skin tumors. Taken together, our data suggest that loss of epithelial IKKα induces the bacterial-fungal symbiosis in oral mucosa, promoting skin tumors. This study will shed light on the importance of the epithelial-bacterial-fungal interaction in the pathogenesis, proposing epithelial IKKα as a novel regulator of the bacterial-fungal interaction.

Citation Format: Na-Young Song, Jami Willette-Brown, Feng Zhu, Yinling Hu. Determining the signaling pathway of epithelial-IKKα deletion-mediated symbiotic bacterial and fungal infection in carcinogenesis [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 1986. doi:10.1158/1538-7445.AM2017-1986

Abstract 4802: Immune dysfunction and fungal infection contribute to esophageal carcinogenesis

Human esophageal cancer is the sixth leading cause of cancer death worldwide. More than 90% of esophageal cancer is esophageal squamous cell carcinoma (ESCC). While the etiological causes remain unclear, esophageal mucosal fungal infection is very common in esophageal cancer patients, including patients with autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED) who have more than 20-fold risk of ESCC when compared to the healthy population. Here, we report that kinase-dead Ikka knock-in mice (hereafter referred to as mutant mice) develop APECED-like autoimmune disease due to developmental defects in thymus and lack of central tolerance. Similar to human APECED patients who develop esophageal mucosal fungal infection on average at the age of five, mutant mice develop fungal infection in oral cavity and esophagus as early as seven weeks old. About 20% of mutant mice develop ESCC during aging, which exhibits specific molecular signatures observed in human ESCC, such as p16 gene silencing, elevated EGFR phosphorylation and PD-L1 expression, etc. Autoreactive T cell depletion, or central tolerance reconstitution and/or normal T cell transfer prevents fungal infection and ESCC development in mutant mice. Importantly, antifungal drug treatment inhibits inflammation and ESCC development in mutant mice. However, oral inoculation of Clasdosporium, one of the major fungal species isolated from mutant mice, increases the tumor incidence from 20% to 63% in mutant mice. These results reveal that immune dysfunction and fungal infection is associated with ESCC development, which sheds new light on ESCC etiological factors, prevention and treatment.

Citation Format: Feng Zhu, Jami Willette-Brown, Na-young Song, Peilin Zhang, Yinling Hu. Immune dysfunction and fungal infection contribute to esophageal carcinogenesis [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 4802. doi:10.1158/1538-7445.AM2017-4802

Autoreactive T Cells and Chronic Fungal Infection Drive Esophageal Carcinogenesis

Humans with autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED), a T cell-driven autoimmune disease caused by impaired central tolerance, are susceptible to chronic fungal infection and esophageal squamous cell carcinoma (ESCC). However, the relationship between autoreactive T cells and chronic fungal infection in ESCC development remains unclear. We find that kinase-dead Ikkα knockin mice develop APECED-like phenotypes, including impaired central tolerance, autoreactive T cells, chronic fungal infection, and ESCCs expressing specific human ESCC markers. Using this model, we investigated the link between ESCC and fungal infection. Autoreactive CD4 T cells permit fungal infection and incite tissue injury and inflammation. Antifungal treatment or autoreactive CD4 T cell depletion rescues, whereas oral fungal administration promotes, ESCC development. Inhibition of inflammation or epidermal growth factor receptor (EGFR) activity decreases fungal burden. Fungal infection is highly associated with ESCCs in non-autoimmune human patients. Therefore, autoreactive T cells and chronic fungal infection, fostered by inflammation and epithelial injury, promote ESCC development.

Abstract 2804: Disrupted integrity in IκB kinase alpha promotes lung adenocarcinoma progression via an oxidative stress-inflammation circuitry

Recent advanced research has highlighted that multiple drivers and somatic aberrations drive intratumor heterogeneity. Multiple hits in different nucleotides of a single critical gene and diverse deregulatory mechanisms in one tumor have challenged to understand how these various forms of a single gene cooperate with other drivers in cancer development. IκB kinase alpha (IKKα) down-or-up-regulation and mutations have been detected in many human cancers; however, the function of IKKα in lung adenocarcinoma (ADC), a major type of human lung cancers, has not been explored. To study how the different mutant forms of IKKα regulate KrasG12D-induced lung ADC development, we crossed KrasG12D mice with Ikkα floxed mice and two Ikkα knock-in mice and found that a lung specific IKKα deletion (IkkαΔLung) and two different IKKα point mutants (IkkαKA/KA: K→A at amino acid 44 and IkkαAA/AA: S→A at amino acids 176 and 180) promote the progression of KrasG12D-induced lung ADCs. The IKKα mutants integrate into the KrasG12D-mediated diverse oncogenic pathways; additionally the mutants increase levels of pulmonary macrophage infiltration, ROS, and DNA damage compared to KrasG12D-induced lung ADCs. IKKα deficiency results in decreased levels of Nrf2, a transcription factor that regulates expression of genes encoding many anti-oxidants, and increased levels of NADPH oxidase 2 (Nox2), which form an oxidative stress-inflammation circuitry partially regulated by a new identified pathway of IKKα, aryl hydrocarbon receptor and Nox2. Treatment with a Nox inhibitor (apocynin) or a ROS scavenger (N-acetyl cysteine), and/or Nox2 null bone marrow transplant inhibits the pathogenesis of ADCs. Also, we observed various aberrations of IKKα in human lung ADCs. The study not only demonstrates that IKKα serves as a gatekeeper to suppress oncogenic oxidative stress in lung ADC development, but also provides an advanced model that explains how the different mutant forms of a signal gene integrate into distinct signalings to enhance the crucial driver KrasG12D-induced lung cancer development.

Citation Format: Na-Young Song, Jami Willette-Brown, Mahesh Dalta, Yinling Hu. Disrupted integrity in IκB kinase alpha promotes lung adenocarcinoma progression via an oxidative stress-inflammation circuitry. [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 2804.

Phospholipid profiling identifies acyl chain elongation as a ubiquitous trait and potential target for the treatment of lung squamous cell carcinoma

Lung cancer is the leading cause of cancer death. Beyond first line treatment, few therapeutic options are available, particularly for squamous cell carcinoma (SCC). Here, we have explored the phospholipidomes of 30 human SCCs and found that they almost invariably (in 96.7% of cases) contain phospholipids with longer acyl chains compared to matched normal tissues. This trait was confirmed using in situ 2D-imaging MS on tissue sections and by phospholipidomics of tumor and normal lung tissue of the L-IkkαKA/KA mouse model of lung SCC. In both human and mouse, the increase in acyl chain length in cancer tissue was accompanied by significant changes in the expression of acyl chain elongases (ELOVLs). Functional screening of differentially expressed ELOVLs by selective gene knockdown in SCC cell lines followed by phospholipidomics revealed ELOVL6 as the main elongation enzyme responsible for acyl chain elongation in cancer cells. Interestingly, inhibition of ELOVL6 drastically reduced colony formation of multiple SCC cell lines in vitro and significantly attenuated their growth as xenografts in vivo in mouse models. These findings identify acyl chain elongation as one of the most common traits of lung SCC discovered so far and pinpoint ELOVL6 as a novel potential target for cancer intervention.

Abstract 801: IKKα at the crossroad between inflammation, oxidative stress and lung carcinogenesis

Lung cancer is a leading cause of cancer mortality worldwide. We previously demonstrated that IKKα kinase dead knock-in (IkkαK44A/K44A, KA) mice spontaneously develop lung SCCs, which is associated with IKKα reduction and increased inflammation. Currently, lung adenocarcinoma (ADC) has surpassed SCC. Although downregulation of IKKα has been reported in lung ADCs, the role of IKKα is not clarified yet. Here, we attempted to verify whether IKKα inactivation plays a role in development of lung adenocarcinomas (ADCs). K-rasG12D (Kras) mice are a well-established lung ADC model. Thus, we generated K-rasG12D;IkkαK44A/K44A (Kras;KA) and K-rasG12D;Ikkαf/f (Kras;FF) mice and activated oncogenic K-rasG12D with intratracheal injection of adenovirus carrying the cre recombinase gene in these mice. At 4∼4.5 months after treatment, both Kras;KA and Kras;FF mice showed enhanced bronchial hyperproliferation and increased number of lung tumors than Kras mice. The histology showed that lung tumors from both mice can be classified into ADCs, while no SCCs were found in Kras;KA and Kras;FF mice. Finally, Kras;FF mice had shorter life span due to labored breathing than Kras mice. Thus, IKKα plays an important role in lung ADCs as well as SCCs. It is well known that the oncogene activation such as Kras can induce a senescence program to suppress the progression of benign tumors. We found that IKKα loss diminished Kras-induced senescence, given the results from senescence-associated β-gal assay and Ki67 staining. We previously reported that inflammation is required for development of lung SCCs in KA mice. Macrophages were significantly accumulated in the lung of Kras;FF mice as well. In general, inflammation can cause oxidative stress. In line with this notion, the microarray analysis revealed that several antioxidant genes were markedly downregulated, while expression of some reactive oxygen species (ROS)-generating genes was increased in the lung tissues from Kras;FF mice compared to Kras mice. In consistent, IKKα depletion was correlated with increased level of ROS in lung tumors, which resulted in further oxidative DNA damage. Interestingly, tumors from Kras mice also showed IKKα reduction compared to WT lungs. Taken together, these findings suggest that IKKα reduction can promote Kras-driven lung tumorigenesis through its interplay between inflammation and oxidative stress. Inflammation and oxidative stress can sustain and exacerbate each other, leading to a vicious cycle of tumor-prone microenvironment. It is evident that IKKα plays a crucial role in inflammation from massive investigations. The role of IKKα in oxidative stress, however, is not clarified yet. Thus, our investigation of the role of IKKα on lung ADC development in the context of modulating oxidative stress will provide better strategies to break the vicious cycle between inflammation, oxidative stress and lung tumorigenesis and noble therapeutic targets for treatment.

Citation Format: Na-Young Song, Jami Willette-Brown, Mahesh Dalta, Yinling Hu. IKKα at the crossroad between inflammation, oxidative stress and lung carcinogenesis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 801. doi:10.1158/1538-7445.AM2015-801

IKKα is required for the homeostasis of regulatory T cells and for the expansion of both regulatory and effector CD4 T cells

It was reported that TNF receptor type II signaling, which has the capacity to stimulate CD4+ forkhead box P3+ (Foxp3+) regulatory T cells (Tregs), activated the noncanonical NF-κB pathway in an IKKα-dependent manner. Therefore, we studied the role of IKKα in the homeostasis of Treg population. To this end, we generated a mouse strain with conditional knockout of IKKα in CD4 cells (Ikkα(f/f):CD4.Cre) that showed a >60% reduction in the number of Tregs in the thymus and peripheral lymphoid tissues, whereas the number of Foxp3- effector T cells (Teffs) remained at a normal level. The function of Tregs deficient in IKKα was examined using Rag1(-/-) mice cotransferred with naive CD4 cells (nCD4s). Although wild-type (WT) Tregs inhibited colitis induced by transfer of WT nCD4s, IKKα-deficient Tregs failed to do so, which was associated with their inability to reconstitute Rag1(-/-) mice. Furthermore, nCD4s deficient in IKKα also failed to reconstitute Rag1(-/-) mice and were defective in proliferative responses in vitro and in vivo. Thus, our study reveals a novel role of IKKα in the maintenance of a normal Treg population and in the control of expansion of CD4 T cells. These properties of IKKα may be exploited as therapeutic strategies in the treatment of major human diseases.

Abstract 931: Role of IKKα in K-ras-driven lung carcinogenesis

IKKα, one of subunits of the IKK complex, is required for the epidermal homeostasis. We previously demonstrated that keratin 5-specific deletion of IKKα induces spontaneous skin squamous cell carcinomas (SCCs) in mice. Interestingly, IKKα kinase dead knockin (IKKαK44A/K44A, KA) mice spontaneously develop lung SCCs which is associated with increased inflammation and IKKα reduction. Thus, IKKα downregulation is crucial for the SCC formation in skin and lung. Here, we attempted to verify whether IKKα inactivation plays a role in the development of lung adenocarcinomas (ADCs) as well. We have crossed between KA mice and K-rasG12D oncogenic mutant (Kras) mice. Then, these IKKαK44A/K44A;K-rasG12D (KA;Kras) mice were intratracheally treated with adenovirus carrying the cre recombinase gene to activate K-ras oncogene. At 4.5 months after intratracheal injection, the lung weight was significantly increased in KA;Kras compared to Kras mice. Moreover, the lungs of KA;Kras mice showed increased bronchial epithelial cells and Ki67-positive cells in the bronchial regions. At 7 months after treatment, lung tumors in KA;Kras mice were larger compared to tumors in Kras mice. Finally, KA;Kras mice had shorter life span due to breathing problems. KA;Kras mice started to die at around 20 weeks after injection, while KR mice started to die from around 30 weeks. To confirm whether IKKα reduction promotes K-ras-driven lung carcinogenesis, we generated IKKαf/f (FF) mice crossed with Kras (FF;Kras) mice. Similar to KA;Kras, FF;Kras mice showed significant increase of lung weight, hyperproliferative bronchial abnormalities, Ki-67-positive cells in the bronchial regions and the number of large tumors at 4 months following treatment compared with Kras only group. Taken together, these data suggest that IKKα downregulation promotes K-ras-driven lung tumorigenesis and plays an important role in lung ADCs as well as in SCCs. The underlying molecular mechanism needs to be further investigated.

Citation Format: Na-Young Song, Jami Willette-Brown, Mahesh Dalta, Yinling Hu. Role of IKKα in K-ras-driven lung carcinogenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 931. doi:10.1158/1538-7445.AM2014-931

Abstract 3618: Ikkα modulates primary sclerosing cholangitis and intrahepatic cholangiocarcinoma

Intrahepatic cholangiocarcinoma (ICC) is the second most common primary liver cancer after hepatocellular carcinoma (HCC). The risk of ICC is higher in patients with primary sclerosing cholangitis (PSC). To date, the cellular and molecular mechanism underlying the pathological progression of PSC and ICC is poorly understood. IKKα is part of the IκB kinase (IKK) complex, which plays an important role in regulating inflammation- associated carcinogenesis through both NF-κB-dependent and independent pathways. Here, we show that IKKα mutant mice developed very serious PSC as early as four weeks of age. The ALT/AST and bilirubin levels were significantly increased in the serum of IKKα mutant mice along with lymphocytic and eosinophilic infiltration into the liver. Liver inflammation in the IKKα mutant mice, mediated by macrophages, neutrophils and CD4+ T cells, was associated with the death of cholangiocytes and hepatocytes, and obstruction of intrahepatic and extrahepatic bile ducts, which impeded bile flow and ultimately led to biliary fibrosis and cirrhosis. Additionally, upon activation of NOTCH signaling in the liver via hydrodynamic shear, we observed that NOTCH-induced ICC, with the PSC, developed significantly faster in IKKα mutant mice. To identify whether intrinsic IKKα dysfunction in hepatocytes promotes the NOTCH-induced ICC in IKKα mutant mice, we generated IKKα hep KO mice, in which IKKα is conditionally knocked out in hepatocytes. No biliary disease or liver injury was observed in these mice. We then established an accelerated ICC model utilizing hydrodynamic delivery of NICD and AKT expression vectors. Unexpectedly, ICC development was remarkably slower in the IKKα hep KO mice compared to the IKKα floxed control mice, and this delayed ICC development was associated with reduced activation or levels of AKT, NOTCH, MAPK/ERK and c-Myc. These data suggest that IKKα may play a protective role in PSC, while promote ICC derived from hepatocytes. In contrast to ICC, we also established the cMET/β-catenin-induced HCC model in the IKKα hep KO mice, which did not reveal any difference in tumor development between IKKα hep KO and control mice. Taken together, our findings suggest that IKKα plays complicated and important roles in PSC and ICC pathological progression.

Citation Format: Qun Jiang, Zuoxiang Xiao, Timothy Back, Anthony Scarzello, Scott Roan, Jami Willette-Brown, Feng Zhu, Yinling Hu, Robert H. Wiltrout. Ikkα modulates primary sclerosing cholangitis and intrahepatic cholangiocarcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3618. doi:10.1158/1538-7445.AM2014-3618

An IKKα-nucleophosmin axis utilizes inflammatory signaling to promote genome integrity

The inflammatory microenvironment promotes skin tumorigenesis. However, the mechanisms by which cells protect themselves from inflammatory signals are unknown. Downregulation of IKKα promotes skin tumor progression from papillomas to squamous cell carcinomas, which is frequently accompanied by genomic instability, including aneuploid chromosomes and extra centrosomes. In this study, we found that IKKα promoted oligomerization of nucleophosmin (NPM), a negative centrosome duplication regulator, which further enhanced NPM and centrosome association, inhibited centrosome amplification, and maintained genome integrity. Levels of NPM hexamers and IKKα were conversely associated with skin tumor progression. Importantly, proinflammatory cytokine-induced IKKα activation promoted the formation of NPM oligomers and reduced centrosome numbers in mouse and human cells, whereas kinase-dead IKKα blocked this connection. Therefore, our findings suggest a mechanism in which an IKKα-NPM axis may use inflammatory signals to suppress centrosome amplification, promote genomic integrity, and prevent tumor progression.

IKKalpha is critical for the maintenance of a normal pool of regulatory T cells and for the expansion of both regulatory and effector T cells (P1095)

Our previous studies show that TNF activates and expands Tregs through TNFR2. It was reported that TNF-TNFR2 interaction results in the activation of alternative NFκB pathway through p100 processing, in IKKα-dependent manner. We therefore hypothesize that IKKα may play an important role in determining the size of Treg pool. To this end, we generated a mouse strain with conditional KO of IKKα in CD4 cells (CD4-IKKα-/-) which showed a marked reduction in the number of Tregs and in the proportion of Tregs in CD4 cells, indicating that IKKα KO had more profound impact on Tregs than Teffs. In vitro, naïve CD4 cells deficient in IKKα could be differentiated as usual into Foxp3-expressing cells by TGFβ, suggesting that reduction of Tregs in CD4-IKKα-/- mice was likely due to a defect in the maintenance of the Treg pool, rather than a malfunction in the induction of Foxp3 expression. The function of Tregs deficient in IKKα was examined by co-transfer to Rag1-/- mice together with naïve CD4 cells. Although WT Tregs was able to inhibit colitis induced by transfer of WT naïve CD4 cells, IKKα-deficient Tregs failed to inhibit colitis which was associated with their incapacity to reconstitute in Rag1-/- mice. Nevertheless, naïve CD4 cells deficient in IKKα also failed to reconstitute Rag1-/- mice. Therefore, our study indicate that IKKα is important for the maintenance of normal Treg pool and is critical for the expansion of Treg cells as well as Teff cells.

The pivotal role of IKKα in the development of spontaneous lung squamous cell carcinomas

Here, we report that kinase-dead IKKα knockin mice develop spontaneous lung squamous cell carcinomas (SCCs) associated with IKKα downregulation and marked pulmonary inflammation. IKKα reduction upregulated the expression of p63, Trim29, and keratin 5 (K5), which serve as diagnostic markers for human lung SCCs. IKKα(low)K5(+)p63(hi) cell expansion and SCC formation were accompanied by inflammation-associated deregulation of oncogenes, tumor suppressors, and stem cell regulators. Reintroducing transgenic K5.IKKα, depleting macrophages, and reconstituting irradiated mutant animals with wild-type bone marrow (BM) prevented SCC development, suggesting that BM-derived IKKα mutant macrophages promote the transition of IKKα(low)K5(+)p63(hi) cells to tumor cells. This mouse model resembles human lung SCCs, sheds light on the mechanisms underlying lung malignancy development, and identifies targets for therapy of lung SCCs.

Abstract 2560: IKKα inactivation predisposes to spontaneous lung squamous cell carcinomas

Lung cancer is the leading cause of cancer deaths worldwide. To advance the understanding of this disease, various genetically engineered and chemical induced mouse models have been established. However, most animal models resemble human lung adenocarcinoma, and spontaneous lung squamous cell carcinomas (SCCs) mouse models are very rare. Here, we generated Ikkα-KA/KA knock-in mice (KA/KA) in which an ATP binding site of IKKα, Lys 44 was replaced by alanine. The knock-in mice develop severe skin lesions and begin to die after 6 months. We found lung SCCs in some of the mice. To study lung SCC development, we decided to stabilize the skin condition by reintroducing transgenic IKKα by crossing KA/KA with Lori.IKKα transgenic mice to generate KA/KA/Lori.IKKα (KA/KAL) mice. Almost all the KA/KAL (100%) mice at 4 to 6 months of age developed spontaneous lethal lung SCCs. The endogenous IKKα protein level generally markedly declined in an age dependent manner in these IKKα mutant mice. Progenitor cell related markers Sox2, OCT3/4 and Nanog were only increased in the lung SCC tissue but not in the tumor adjacent tissues, implying the involvement of cancer stem cells in lung SCC. Furthermore, we detected substantial increases in Ras and CyclinD1 levels and EGFR, ERK and p38 activities in lung SCCs. On the other hand, we detected reduction in tumor suppressor gene Rb and IαBβ accompanying with reduced IKKα levels in KA/KAL lungs as well as in lung SCCs. Importantly, we observed a similar alteration pattern in mouse and human lung SCCs. Finally, reintroducing IKKα into lung epithelial cells prevented lung SCC development in mice. Collectively, our study supports the tumor suppressing role of IKKα in lung tumorigenesis. This novel lung SCC mouse model may facilitate investigations in pathogenesis, diagnosis, and treatment of human lung SCC disease.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2560. doi:1538-7445.AM2012-2560

Abstract 2561: IKKα links inflammation and tumorigenesis in a mouse model of lung squamous cell carcinoma

NF-kB plays critical roles in linking inflammation and carcinogenesis. The activation of NF-kB is regulated by the IkB Kinase Complex (IKK), composed of IKKα, IKKα, and NF-κB essential modulator (NEMO). We have established a mouse model of lung squamous cell carcinoma (SCC) by inactivating IKKα in vivo. However, IKKα's attributes relating to linkage between inflammation and lung SCC have not yet been well-defined. We now show that inactivation of IKKα in mice causes systemic chronic inflammation, which consequently promotes lung SCC initiation and progression. In mice with mutated IKKα, CD4 T cells, dendritic cells, and macrophages are all significantly increased in the spleen and lung. Proinflammatory cytokines and chemokines are also remarkably elevated in the lungs of these mice. An M2 macrophage phenotype is observed only in the lungs of old IKKα mutant mice, not in younger mice, suggesting the M1/M2 polarization may be driven by the proinflammatory microenvironment in these mice. Production of Th2 cytokines and IL-10 are elevated in CD4 T cells from the lungs of mice with mutated IKKα, and may contribute to M2 polarization during the chronic inflammation. In addition, depletion of macrophages in these mice can significantly reduce Th2 cytokine production, oxidative DNA damage, and shut down SCC development in the lungs, suggesting their important roles in inflammation-associated lung carcinogenesis. Together, our data suggest that IKKα may play important roles in linking inflammation and lung SCC tumorigenesis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2561. doi:1538-7445.AM2012-2561

IKKα represses a network of inflammation and proliferation pathways and elevates c-Myc antagonists and differentiation in a dose-dependent manner in the skin

Inhibitor of nuclear factor κB kinase-α (IKKα) is required for maintaining skin homeostasis and preventing skin tumorigenesis. However, its signaling has not been extensively investigated. In the present study, we generated two mouse lines that expressed different levels of transgenic IKKα in the basal epidermis under the control of keratin-5 promoter and further evaluated their effects on the major pathways of inflammation, proliferation, and differentiation in the skin. Regardless of the transgenic IKKα levels, the mice develop normally. Because IKKα deletion in keratinocytes blocks terminal differentiation and induces epidermal hyperplasia and skin inflammation, we depleted the endogenous IKKα in these transgenic mice and found that the transgenic IKKα represses epidermal thickness and induces terminal differentiation in a dose-dependent manner. Also, transgenic IKKα was found to elevate expression of Max dimer protein 1 (Mad1) and ovo-like 1, c-Myc antagonists, but repress activities of epidermal growth factor receptor (EGFR), extracellular signal-regulated kinase (ERK), Jun-amino-terminal kinases, c-Jun, signal transducer and activator of transcription 3 (Stat3), and growth factor levels in a dose-dependent fashion in the skin. Moreover, EGFR reduction represses IKKα deletion-induced excessive ERK, Stat3 and c-Jun activities, and skin inflammation. These new findings indicate that elevated IKKα expression not only represses epidermal thickness and induces terminal differentiation, but also suppresses skin inflammation by an integrated loop. Thus, IKKα maintains skin homeostasis through a broad range of signaling pathways.

Reduction of IKKalpha expression promotes chronic ultraviolet B exposure-induced skin inflammation and carcinogenesis

Ultraviolet B light (UVB) is a common cause of human skin cancer. UVB irradiation induces mutations in the tumor suppressor p53 gene as well as chronic inflammation, which are both essential for UVB carcinogenesis. Inhibitor of nuclear factor kappaB kinase-alpha (IKKalpha) plays an important role in maintaining skin homeostasis, and expression of IKKalpha was found to be down-regulated in human and murine skin squamous cell carcinomas. However, the role of IKKalpha in UVB skin carcinogenesis has not been investigated. Thus, here we performed UVB carcinogenesis experiments on Ikkalpha(+/+) and Ikkalpha(+/-) mice. Ikkalpha(+/-) mice were found to develop a twofold greater number of skin tumors than Ikkalpha(+/+) mice after chronic UVB irradiation. In addition, tumor latency was significantly shorter and tumors were bigger in Ikkalpha(+/-) than in Ikkalpha(+/+) mice. At an early stage of carcinogenesis, an increase in UVB-induced p53 mutations as well as macrophage recruitment and mitogenic activity, and a decrease in UVB-induced apoptosis, were detected in Ikkalpha(+/-) compared with those in Ikkalpha(+/+) skin. Also, reduction of IKKalpha levels in keratinocytes up-regulated the expression of monocyte chemoattractant protein-1 (MCP-1/CCL2), TNFalpha, IL-1, and IL-6, and elevated macrophage migration, which might promote macrophage recruitment and inflammation. Therefore, these findings suggest that reduction of IKKalpha expression orchestrates UVB carcinogen, accelerating tumorigenesis.

Development of regulatory T cells requires IL-7Ralpha stimulation by IL-7 or TSLP

Interleukin-7 (IL-7), a cytokine produced by stromal cells, is required for thymic development and peripheral homeostasis of most major subsets of T cells. We examined whether regulatory T (Treg) cells also required the IL-7 pathway by analyzing IL-7Ralpha(-/-) mice. We observed a striking reduction in cells with the Treg surface phenotype (CD4, CD25, GITR (glucocorticoid-induced tumor necrosis factor [TNF]-like receptor), CD45RB, CD62L, CD103) or intracellular markers (cytotoxic T-lymphocyte-associated antigen-4, CTLA-4, and forkhead box transcription factor 3, Foxp3). Foxp3 transcripts were virtually absent in IL-7Ralpha(-/-) lymphoid tissues, and no Treg cell suppressive activity could be detected. There are 2 known ligands for IL-7Ralpha: IL-7 itself and thymic stromal lymphopoietin (TSLP). Surprisingly, mice deficient in IL-7 or the other chain of the TSLP receptor (TSLPR) developed relatively normal numbers of Treg cells. Combined deletion of IL-7 and TSLP receptor greatly reduced Treg cell development in the thymus but was not required for survival of mature peripheral Treg cells. We conclude that Treg cells, like other T cells, require signals from the IL-7 receptor, but unlike other T cells, do not require IL-7 itself because of at least partially overlapping actions of IL-7 and TSLP for development of Treg cells.

The influence of IL-2 family cytokines on activation and function of naturally occurring regulatory T cells

IL-2 is essential for CD4+CD25+forkhead box P3+ (FoxP3+) naturally occurring regulatory T cell (Treg) homeostasis and activation. Binding of IL-2 to its receptor leads to phosphorylation of STAT5, and binding of phosphorylated STAT5 to the foxp3 promoter increases foxp3 transcription, resulting in elevated levels of FoxP3 protein in Tregs. Transcriptional regulation by the elevated levels of FoxP3 is thought to be essential for the strong suppressor function seen in activated Tregs. IL-2 belongs to a family cytokines, which all depend on the common gamma-receptor chain (gammac). Given the well-documented effects of IL-2 on Treg function, the effect of other IL-2 family cytokines (IL-7, -15, and -21) on Tregs was examined. We observed that IL-7 and IL-15 induce STAT5 phosphorylation and up-regulation of FoxP3 in Tregs. STAT5 activation correlated with enhanced viability. However, only in the presence of IL-2 did Tregs acquire potent suppressor function. This finding is surprising, as IL-15 as well as IL-2 use the same IL-2R betac and gammac for signaling. In contrast, IL-21 activated STAT3 but did not activate STAT5 and had no effect on Treg viability, activation, or function. We therefore conclude that phosphorylation of STAT5, mediated through the IL-2Rgamma, promotes Treg survival in a resting and activated state. However, activation of STAT5 alone in conjunction with TCR signaling is not sufficient for the induction of potent suppressor function in Tregs, as IL-7 and IL-15 are not capable of inducing potent Treg suppressor function.

Modulation of lymphocyte function with inhibitory CD2: loss of NK and NKT cells

Analysis of the NK cell developmental pathway suggests that CD2 expression may be important in regulating NK maturation. To test this hypothesis, we developed mice containing only an inhibitory CD2 molecule by linking the extracellular domain of CD2 to an intracellular immunoreceptor tyrosine-based inhibitory motif (ITIM) motif. Mice containing the CD2 Tg(ITIM) transgene, introduced into a CD2 KO background, have no morphologically detectable lymph nodes, although development of the thymus appears normal. In addition, these mice had major loss of both NK and NKT subsets in peripheral organs, while T and B cell frequencies were intact. Expression of CD2 was low on T cells and lacking on B cells and functional defects were observed in these populations. NKT cells expressing CD4 were absent, while the CD8+ and double negative NKT cells were retained. Small subsets of NK cells were detected but expression of CD2 on these cells was very low or absent, and their maturation was impaired. Based on the phenotype described here, we believe that these mice represent a unique model to study lymphoid organ and lymphocyte development.

Regulation of Ly49D/DAP12 Signal Transduction by Src-Family Kinases and CD45

Activating, DAP12-coupled members of the Ly-49 family of NK cell receptors help control viral infections in mice. However, the kinases and/or phosphatases mediating tyrosine phosphorylation of Ly-49D-associated DAP12 have not been elucidated. In this study, we show for the first time that Src family tyrosine kinases are physically and functionally associated with Ly-49D/DAP12 signaling in murine NK cells. Specifically, we demonstrate the following: 1) inhibition of Src family kinases suppresses DAP12 phosphorylation and downstream DAP12 signals; 2) both Fyn and Lck are capable of phosphorylating DAP12; and 3) both kinases coimmunoprecipitate with the Ly-49D/DAP12 complex in NK cells. Although we detect enhanced phosphorylation of Fyn upon Ly-49D cross-linking in NK cells, Ly-49D-mediated events in both Fyn-/- and Fyn/Lck-/- mice appear normal, reinforcing the theme of redundancy in the ability of Src family kinases to initiate activation events. In contrast to disruption of specific Src family enzymes, Ly-49D/DAP12-mediated calcium mobilization and cytokine production by CD45 null NK cells are defective. Although others have ascribed the effects of CD45 mutation solely on the suppression of Src family activity, we demonstrate in this study that DAP12 is hyperphosphorylated in CD45 null NK cells, resulting in uncoordinated tyrosine-mediated signaling upon Ly-49D ligation. Therefore, although our data are consistent with a Src kinase activity proximally within DAP12 signaling, DAP12 also appears to be a substrate of CD45, suggesting a more complex role for this phosphatase than has been reported previously.

Receptor glycosylation regulates Ly-49 binding to MHC class I

Murine NK cells express the Ly-49 family of class I MHC-binding receptors that control their ability to lyse tumor or virally infected host target cells. X-ray crystallography studies have identified two predominant contact sites (sites 1 and 2) that are involved in the binding of the inhibitory receptor, Ly-49A, to H-2D(d). Ly-49G2 (inhibitory) and Ly-49D (activating) are highly homologous to Ly-49A and also recognize H-2D(d). However, the binding of Ly-49D and G(2) to H-2D(d) is of lower affinity than Ly-49A. All Ly-49s contain N-glycosylation motifs; however, the importance of receptor glycosylation in Ly-49-class I interactions has not been determined. Ly-49D and G(2) contain a glycosylation motif (NTT (221-223)), absent in Ly-49A, adjacent to one of the proposed binding sites for H-2D(d) (site 2). The presence of a complex carbohydrate group at this critical site could interfere with class I binding. In this study, we are able to demonstrate for the first time that Ly-49D binds H-2D(d) in the presence of mouse beta(2)-microglobulin. We also demonstrate that glycosylation of the NTT (221-23) motif of Ly-49D inteferes with recognition of H-2D(d). Alteration of the Ly-49D-NTT (221-23) motif to abolish glycosylation at this site resulted in enhanced H-2D(d) binding and receptor activation. Furthermore, glycosylation of Ly-49G2 at NTT (221-23) also reduces receptor binding to H-2D(d) tetramers. Therefore, the addition of complex carbohydrates to the Ly-49 family of receptors may represent a mechanism by which NK cells regulate affinity for host class I ligands.

Interaction of Ly-49D+ NK cells with H-2Dd target cells leads to Dap-12 phosphorylation and IFN-gamma secretion

Murine Ly-49D augments NK cell function upon recognition of target cells expressing H-2Dd. Ly-49D activation is mediated by the immunoreceptor tyrosine-based activation motif-containing signaling moiety Dap-12. In this report we demonstrate that Ly-49D receptor ligation can lead to the rapid and potent secretion of IFN-gamma. Cytokine secretion can be induced from Ly-49D+ NK cells after receptor ligation with Ab or after interaction with target cells expressing their H-2Dd ligand. Consistent with the dominant inhibitory function of Ly-49G, NK cells coexpressing Ly-49D and Ly-49G show a profound reduction in IFN-gamma secretion after interaction with targets expressing their common ligand, H-2Dd. Importantly, we are able to demonstrate for the first time that effector/target cell interactions using Ly-49D+ NK cells and H-2Dd targets result in the rapid phosphorylation of Dap-12. However, Dap-12 is not phosphorylated when Ly-49D+ NK cells coexpress the inhibitory receptor, Ly-49G. These studies are novel in describing Ly-49 activation vs inhibition, where two Ly-49 receptors recognize the same class I ligand, with the dominant inhibitory receptor down-regulating phosphorylation of Dap-12, cytokine secretion, and cytotoxicity in NK cells.

Structure/function relationship of activating Ly-49D and inhibitory Ly-49G2 NK receptors

Murine NK cells express Ly-49 family receptors capable of either inhibiting or activating lytic function. The overlapping patterns of expression of the various receptors have complicated their precise biochemical characterization. Here we describe the use of the Jurkat T cell line as the model for the study of Ly-49s. We demonstrate that Ly-49D is capable of delivering activation signals to Jurkat T cells even in the absence of the recently described Ly-49D-associated chain, DAP-12. Ly-49D signaling in Jurkat leads to tyrosine phosphorylation of TCRzeta and requires Syk/Zap70 family kinases and arginine 54 of Ly-49D, suggesting that Ly-49D signals via association with TCRzeta. Coexpression studies in 293-T cells confirmed the ability of Ly-49D to associate with TCRzeta. In addition, we have used this model to study the functional interactions between an inhibitory Ly-49 (Ly-49G2) and an activating Ly-49 (Ly-49D). Ly-49G2 blocks activation mediated by Ly-49D in an immunoreceptor tyrosine-based inhibitory motif (ITIM)-dependent manner. In contrast, Ly-49G2 was incapable of inhibiting activation by the TCR even though human killer cell inhibitory receptor (KIR) (KIR3DL2(GL183)) effectively inhibits TCR. Both the ability of Ly-49G2 to block Ly-49D activation and the failure of Ly-49G2 to inhibit TCR signaling were confirmed in primary murine NK cells and NK/T cells, respectively. These data demonstrate the dominant effects of the inhibitory receptors over those that activate and suggest an inability of the Ly-49 type II inhibitory receptors to efficiently inhibit type I transmembrane receptor signaling in T cells and NK cells.

Structure/Function Relationship of Activating Ly-49D and Inhibitory Ly-49G2 NK Receptors

Murine NK cells express Ly-49 family receptors capable of either inhibiting or activating lytic function. The overlapping patterns of expression of the various receptors have complicated their precise biochemical characterization. Here we describe the use of the Jurkat T cell line as the model for the study of Ly-49s. We demonstrate that Ly-49D is capable of delivering activation signals to Jurkat T cells even in the absence of the recently described Ly-49D-associated chain, DAP-12. Ly-49D signaling in Jurkat leads to tyrosine phosphorylation of TCRζ and requires Syk/Zap70 family kinases and arginine 54 of Ly-49D, suggesting that Ly-49D signals via association with TCRζ. Coexpression studies in 293-T cells confirmed the ability of Ly-49D to associate with TCRζ. In addition, we have used this model to study the functional interactions between an inhibitory Ly-49 (Ly-49G2) and an activating Ly-49 (Ly-49D). Ly-49G2 blocks activation mediated by Ly-49D in an immunoreceptor tyrosine-based inhibitory motif (ITIM)-dependent manner. In contrast, Ly-49G2 was incapable of inhibiting activation by the TCR even though human killer cell inhibitory receptor (KIR) (KIR3DL2(GL183)) effectively inhibits TCR. Both the ability of Ly-49G2 to block Ly-49D activation and the failure of Ly-49G2 to inhibit TCR signaling were confirmed in primary murine NK cells and NK/T cells, respectively. These data demonstrate the dominant effects of the inhibitory receptors over those that activate and suggest an inability of the Ly-49 type II inhibitory receptors to efficiently inhibit type I transmembrane receptor signaling in T cells and NK cells.

Induction of DAP12 phosphorylation, calcium mobilization, and cytokine secretion by Ly49H

The ability of several Ly49 family members to inhibit natural killer (NK) cell functions through recruitment of SHP-1 phosphatase has been reported. In contrast, the mechanisms underlying the activating signal generated by Ly49D are poorly understood. A homodimeric phosphoprotein (pp16) that physically and functionally associates with Ly49D has been described. In this study, a rabbit anti-mouse pp16 antiserum was generated and used to demonstrate that pp16 corresponds to the recently described DAP12 molecule. In addition, we show that a second Ly49 family member that lacks an immunoreceptor tyrosine-based inhibitory motif and contains a charged residue in the transmembrane domain, Ly49H, also associates with DAP12. Furthermore, we show that engagement of the Ly49H/DAP12 complex results in phosphorylation of DAP12, intracellular calcium mobilization, and tumor necrosis factor secretion in transfected cells. These results thus provide evidence that Ly49H is an activating receptor that associates with DAP12, previously described as a pp16 component of the Ly49D receptor complex.

DAP12-mediated signal transduction in natural killer cells. A dominant role for the Syk protein-tyrosine kinase

The murine Ly49 family contains nine genes in two subgroups: the inhibitory receptors (Ly49A, B, C, E, F, G2, and I) and the noninhibitory receptors (Ly49D and H). Unlike their inhibitory counterparts, Ly49D and H do not contain immunoreceptor tyrosine-based inhibitory motifs but associate with a recently described co-receptor, DAP12, to transmit positive signals to natural killer (NK) cells. DAP12 is also expressed in myeloid cells, but the receptors coupled to it there are unknown. Here we document the signaling pathways of the Ly49D/DAP12 complex in NK cells. We show that ligation of Ly49D results in 1) tyrosine phosphorylation of several substrates, including phospholipase Cgamma1, Cbl, and p44/p42 mitogen-activated protein kinase, and 2) calcium mobilization. Moreover, we demonstrate that although human DAP12 reportedly binds the SH2 domains of both Syk and Zap-70, ligation of Ly49D leads to activation of Syk but not Zap-70. Consistent with this observation, Ly49D/DAP12-mediated calcium mobilization is blocked by dominant negative Syk but not by catalytically inactive Zap-70. These data demonstrate the dependence of DAP12-coupled receptors on Syk and suggest that the outcome of Ly49D/DAP12 engagement will be regulated by Cbl and culminate in the activation of transcription factors.

Characterization of an associated 16-kDa tyrosine phosphoprotein required for Ly-49D signal transduction

Ly-49D is an activating receptor on NK cells that does not become tyrosine phosphorylated upon activation. This report demonstrates that immunoprecipitation of Ly-49D, following pervanadate treatment or specific Ab cross-linking, coprecipitates a 16-kDa tyrosine-phosphorylated protein (pp16). Immunoblotting experiments and data from TCR-zeta/Fc epsilonRIgamma double knockout mice confirm that pp16 is not TCR-zeta, TCR-eta, or Fc epsilonRIgamma. Association of pp16 with Ly-49D involves a transmembrane arginine since mutation to leucine (Ly-49D[R54L]) abolishes association with pp16 in transfected P815 cells. In addition, Ly-49D(R54L) transfectants fail to mediate Ca2+ mobilization following Ab cross-linking. Therefore, signaling through Ly49D on NK cells depends on association with a distinct tyrosine phosphoprotein (pp16) in a manner analogous to that of TCR and FcR. Expression of this novel signaling peptide in both the NK and myeloid lineages indicates that pp16 is likely involved in the signal transduction cascade of additional receptor families.

Cutting Edge: Characterization of an Associated 16-kDa Tyrosine Phosphoprotein Required for Ly-49D Signal Transduction

Ly-49D is an activating receptor on NK cells that does not become tyrosine phosphorylated upon activation. This report demonstrates that immunoprecipitation of Ly-49D, following pervanadate treatment or specific Ab cross-linking, coprecipitates a 16-kDa tyrosine-phosphorylated protein (pp16). Immunoblotting experiments and data from TCR-ζ/FcεRIγ double knockout mice confirm that pp16 is not TCR-ζ, TCR-η, or FcεRIγ. Association of pp16 with Ly-49D involves a transmembrane arginine since mutation to leucine (Ly-49DR54L) abolishes association with pp16 in transfected P815 cells. In addition, Ly-49DR54L transfectants fail to mediate Ca2+ mobilization following Ab cross-linking. Therefore, signaling through Ly-49D on NK cells depends on association with a distinct tyrosine phosphoprotein (pp16) in a manner analogous to that of TCR and FcR. Expression of this novel signaling peptide in both the NK and myeloid lineages indicates that pp16 is likely involved in the signal transduction cascade of additional receptor families.

A conformational rearrangement upon binding of IgE to its high affinity receptor

One of the critical steps in the allergic reaction is the binding of immunoglobulin E (IgE) to its high affinity receptor (FcepsilonRI). FcepsilonRI is a tetrameric complex composed of an alpha-chain, a beta-chain, and a dimeric gamma-chain. The extracellular portion of the alpha-chain (alpha-t) is sufficient for the binding of IgE. The Fc portion of IgE contains two copies of the FcepsilonRI binding sites. In contrast, the binding stoichiometry is 1:1. Previously, it was hypothesized that the binding of FcepsilonRI to IgE results in a conformational change in IgE that precludes the binding of a second molecule (Presta, L., Shields, R., O'Connel, L., Lahr, S., Porter, J. , Gorman, C., and Jardieu, P.(1994) J. Biol. Chem. 269, 26368-26373). Here we characterize the secondary structure of IgE and alpha-t and analyze their interaction by circular dichroism spectroscopy. Binding experiments show that when IgE interacts with alpha-t there is a 15-26% decrease of the negative ellipticity at 217 nm. Together, the absence of an alpha-helix element in alpha-t and the small contribution of alpha-t to the spectra of the complex indicate that upon binding, a major conformational rearrangement must occur on IgE. In addition, we analyze the thermal unfolding of alpha-t, IgE, and their complex. Despite the several domains that constitute IgE and alpha-t, these molecules unfold cooperatively with two-state kinetics.

Glycosylation of human truncated Fc epsilon RI alpha chain is necessary for efficient folding in the endoplasmic reticulum

The high affinity immunoglobulin E (IgE) receptor is an alpha beta gamma 2 tetrameric complex. The truncated extracellular segment (alpha t) of the heavily glycosylated alpha chain is sufficient for high affinity binding of IgE. Here we have expressed various alpha t mutants in eukaryotic and prokaryotic cells to analyze the role of glycosylation in the folding, stability, and secretion of alpha t. All seven N-linked glycosylation sites in alpha t are glycosylated and their mutations have an additive effect on the folding and secretion of alpha t. Mutation of the seven N-glycosylation sites (delta 1-7 alpha t) induces misfolding and retention of alpha t in the endoplasmic reticulum. Similarly, tunicamycin treatment reduces substantially the folding efficiency of wild-type alpha t. In contrast, no difference in folding efficiency is detected between wild-type alpha t and delta 1-7 alpha t expressed in Escherichia coli. In addition, maturation of N-linked oligosaccharides and addition of O-linked carbohydrates are not required for either the transport or the IgE-binding function of alpha t. Furthermore, complete enzymatic deglycosylation does not affect the stability and the IgE-binding capacity of alpha t. Therefore, glycosylation is not intrinsically necessary for proper folding of alpha t but is required for folding in the endoplasmic reticulum. Our data are compatible with the concept that specific interactions between N-linked oligosaccharides and the folding machinery of the endoplasmic reticulum are necessary for efficient folding of alpha t in eukaryotic cells.

Regulation of c-myc and ornithine decarboxylase expression by distinct protein kinase systems in IL-3-dependent myeloid cells

We have investigated whether PK-C-regulated events are independent of those biochemical events related to IL-3-induced tyrosine kinase activation by 32Dcl cells. The depletion of functional PK-C isoform activity by prolonged PMA treatment reduced the proliferative response to IL-3 by half that of untreated control cells. PK-C-deficient 32Dcl cells were unable to respond to PMA for the induction of c-myc and ODC mRNA accumulation. PK-C down-regulation did not affect IL-3-induced tyrosine phosphorylation and inhibited IL-3-regulated c-myc and ODC mRNA expression by only 30%. However, PK-C down-regulation had a pronounced inhibitory effect on IL-3 regulation of ODC enzymatic activity. While a PK-C-dependent and -independent pathway for the regulation of c-myc and ODC mRNA expression could be demonstrated, the regulation of ODC enzymatic activity appeared to require an intact PK-C system. The data suggest that the optimum biological and biochemical responses to IL-3 requires both pathways intact, however, tyrosine kinase activation and significant increases in gene products associated with proliferation can be achieved in the absence of a functional PK-C system.

IL-2 regulation of tyrosine kinase activity is mediated through the p70-75 beta-subunit of the IL-2 receptor

The stimulation of activated human T lymphocytes with IL-2 results in increased tyrosine kinase activity. IL-2 treatment of Tac+ T cells stimulates the rapid phosphorylation of multiple protein substrates at M of 116, 100, 92, 70 to 75, 60, 56, 55, 33, and 32 kDa. Phosphorylation on tyrosine residues was detected by immunoaffinity purification of protein substrates with Sepharose linked antiphosphotyrosine mAb, 1G2. Although phorbol ester stimulated serine phosphorylation of the IL-2R alpha (p55) subunit recognized by alpha TAC mAb, IL-2 did not stimulate any detectable phosphorylation of IL-2R alpha or associated coimmune precipitated proteins. In fact, the tyrosine phosphorylated proteins did not coprecipitate with alpha Tac antibody and similar phosphoproteins were stimulated by IL-2 in IL-2R alpha- human large granular lymphocytes which express only the 70 to 75 kDa IL-2R beta subunit of the high affinity IL-2R. Anti-Tac mAb could inhibit IL-2-stimulated tyrosine phosphorylation in activated T cells, which express both IL-2R subunits that together form the high affinity receptor complex, but not in large granular lymphocytes expressing only the IL-2R beta subunit. The data suggest that IL-2 stimulation of tyrosine kinase activities requires only the IL-2R beta subunit.

IL-2 regulation of tyrosine kinase activity is mediated through the p70-75 beta-subunit of the IL-2 receptor

The stimulation of activated human T lymphocytes with IL-2 results in increased tyrosine kinase activity. IL-2 treatment of Tac+ T cells stimulates the rapid phosphorylation of multiple protein substrates at M of 116, 100, 92, 70 to 75, 60, 56, 55, 33, and 32 kDa. Phosphorylation on tyrosine residues was detected by immunoaffinity purification of protein substrates with Sepharose linked antiphosphotyrosine mAb, 1G2. Although phorbol ester stimulated serine phosphorylation of the IL-2R alpha (p55) subunit recognized by alpha TAC mAb, IL-2 did not stimulate any detectable phosphorylation of IL-2R alpha or associated coimmune precipitated proteins. In fact, the tyrosine phosphorylated proteins did not coprecipitate with alpha Tac antibody and similar phosphoproteins were stimulated by IL-2 in IL-2R alpha- human large granular lymphocytes which express only the 70 to 75 kDa IL-2R beta subunit of the high affinity IL-2R. Anti-Tac mAb could inhibit IL-2-stimulated tyrosine phosphorylation in activated T cells, which express both IL-2R subunits that together form the high affinity receptor complex, but not in large granular lymphocytes expressing only the IL-2R beta subunit. The data suggest that IL-2 stimulation of tyrosine kinase activities requires only the IL-2R beta subunit.

Detection of low and high affinity binding sites with fluoresceinated human recombinant interleukin-2

In this study, we describe a new methodology to detect and quantify lymphokine receptors, using interleukin-2 as a prototype. Human recombinant interleukin-2 (IL-2) was conjugated to fluorescein isothiocyanate. Binding of fluoresceinated IL-2 to different cell types was assessed by flow cytometry analysis, on a FACS 440 calibrated using fluoresceinated Sephadex G-25 beads. This calibration procedure allowed us to quantify the actual number of binding sites for IL-2. Fluoresceinated IL-2 did not bind to normal resting T cells, whereas a highly significant binding was observed on PHA-activated human T cells. The binding was inhibited by an excess of unlabeled IL-2 and by an excess of anti-IL-2 receptor p55 antibodies (anti-TAC). Dose curves of IL-2 showed a two plateau saturation, the first plateau corresponding to the saturation of high affinity binding sites, as assessed by correlation with the biological activity on IL-2-dependent T cells. Among the cell types tested, fluoresceinated IL-2 bound to IL-2-dependent mouse T cells (the binding in that case was not inhibited by anti-IL-2 receptor p55 antibodies), and to different p70 expressing cell lines or normal cells (MLA 144, normal large granular lymphocytes). Taken together, these results indicate that fluoresceinated IL-2 can be used to detect high as well as low affinity IL-2 binding sites.

Interleukin 3 and phorbol ester stimulate tyrosine phosphorylation of overlapping substrate proteins

FDC-P1 is a murine myeloid cell line that requires interleukin 3 (IL3) for survival and proliferation. While the biological effects of IL3 have been well described, the biochemical mechanisms of IL3 actions have only recently been examined. We have investigated whether IL3 or PMA stimulates phosphorylation of proteins on tyrosine as well as on serine/threonine residues as previously described [(1986) Blood 68, 906-913; (1987) Biochem. J. 244, 683-691]. Here we report that both IL3 and PMA stimulate the tyrosine phosphorylation of at least two proteins: pp70 and pp50 in FDC-P1 cells.