Identification of hub anoikis-associated genes and risk signature in cutaneous melanoma.

OBJECTIVE: As one of the most lethal and aggressive cutaneous malignancies, cutaneous melanoma (CM) greatly threatens human health and has long challenged clinicians because of its poor therapeutic response. Anoikis is a newly discovered form of apoptosis that was originally identified in the extracellular matrix (ECM). Recent studies have reported that anoikis is central to cancer metastasis. The aim of this study is to explore the role of anoikis-associated genes in CM. MATERIALS AND METHODS: We identified hub anoikis-associated genes in CM and constructed a risk signature for patients with CM. Gene expression from The Cancer Genome Atlas (TCGA) database was used to screen hub anoikis-associated genes connected with CM, and the Gene Expression Omnibus (GEO) dataset was applied to externally validate the identified genes. Weighted gene co-expression network analysis (WGCNA), differential expression, univariate Cox regression, and least absolute shrinkage and selection operator (LASSO) analyses were used to identify hub genes. Immune cell infiltration in CM was also evaluated to explore the association between hub genes and immune heterogeneity. Finally, an anoikis-associated prognostic model was constructed. RESULTS: Following complex analysis, FASLG, SOD2, BST2, PIK3R2, IKZF3, CDK2, and RAC3 were identified as hub anoikis-associated genes. Indeed, Kaplan-Meier and receiver operating characteristic analyses suggested that the expression patterns of hub genes can be used as prognostic factors for CM survival. The expression and survival trends of hub genes were verified in the validation cohort. Immune cell infiltration analysis showed that the number of immune cells varied among patients with CM and identified seven genes. Furthermore, functional analyses indicated that the constructed risk signature was significantly associated with patient survival, age, and tumor growth and could also serve as an independent prognostic factor for patients with CM. CONCLUSIONS: We suggest that the hub genes FASLG, SOD2, BST2, PIK3R2, IKZF3, CDK2, and RAC3 are involved in the anoikis-associated signature. The pattern of hub anoikis-associated genes may have a prognostic potential for CM progression and overall patient survival.

Identification of a pyroptosis-associated long non-coding RNA signature for predicting the immune status and prognosis in skin cutaneous melanoma.

OBJECTIVE: Pyroptosis is correlated with programmed tumor cell death and the tumor microenvironment. However, the prognostic value of pyroptosis-associated long non-coding RNAs (lncRNAs) in skin cutaneous melanoma (SKCM), a malignant tumor with a poor prognosis, has not been established. PATIENTS AND METHODS: In this study, expression profiles and clinical data of patients with SKCM were downloaded from The Cancer Genome Atlas (TCGA) database to identify differentially expressed pyroptosis-related lncRNAs related to overall survival. A lncRNA risk signature was constructed by Cox regression analyses and its prognostic value was evaluated. Associations between the lncRNA signature and immune status, immune microenvironment, tumor stemness, immune checkpoints, and m6A-related genes were further evaluated. RESULTS: Twenty-two pyroptosis-related lncRNAs were identified and incorporated into a prognostic risk signature. The signature was significantly correlated with overall survival, tumor growth, and metastasis in SKCM. The signature demonstrated better diagnostic accuracy than conventional clinicopathological characteristics. A gene set enrichment analysis indicated that the risk signature was enriched in several immune-related pathways. Furthermore, the risk signature was significantly correlated with the immune microenvironment, immune cell infiltration, and immune subtypes, as well as tumor stem cells and some m6A-related genes. The lncRNA expression levels were also significantly related to responses to several anti-tumor drugs. Finally, a nomogram based on the risk score was established. CONCLUSIONS: Overall, a risk signature based on 22 pyroptosis-associated lncRNAs was generated, providing a novel perspective on the determinants of prognosis and survival in SKCM and a basis for the development of individualized treatments.

[DNM1L gene variant caused encephalopathy, lethal, due to defective mitochondrial peroxisomal fission 1: three cases report and literature review].

Objective: To investigate the clinical characteristics of R403C variant in DNM1L gene caused encephalopathy, lethal, due to defective mitochondrial peroxisomal fission 1 (EMPF1). Methods: The clinical data of three patients, who carried R403C variant in the DNM1L gene, diagnosed at Xiangya Hospital from February 2018 to February 2020 were retrospectively summarized. Literature reviewing was performed by taking "DNM1L" or "encephalopathy, lethal, due to defective mitochondrial peroxisomal fission 1" as keywords for searching in online Mendelian inheritance in man (OMIM), PubMed, China national knowledge infrastructure (CNKI), and Wanfang data knowledge service platform up to July 2020. And the clinical manifestation, laboratory examination, imaging, treatment, and prognosis were reviewed. Results: Case 1, a 7-year-old boy, developed seizures after a 9-day course of cough without fever. The seizures manifested as generalized tonic-clonic seizures (GTCS) and soon converted to focal status epilepticus (EPC) or focal myoclonus, which were resistant to multi-anti-epileptic drugs combined with sedative drugs. The boy died at the 2nd week after seizure onset. Case 2, also a 7-year-old boy, developed seizures after a 10-day history of amygdalitis. The seizures manifested as focal to generalized tonic-clonic seizure and then converted to EPC or focal myoclonus. And all seizures showed poor responses to multi-anti-epileptic drugs combined with sedative drugs, ketogenic diet, and methylprednisolone treatment. The boy died after 1 month's treatment. Case 3, a 3-year and 5-month old girl, had seizures onset after a 2-week course of viral pneumonia. The seizures onset manifested as focal clonic seizure and converted to EPC, shortly. She was resistant to multi-anti-epiletic drugs combined with sedative drugs and ketogenic treatment. The girl died 3 months afte seizure onset. All of their images showed multifocal T1 low, T2, fluid attenuated inversion recovery, and diffusion-weighted imaging high signal lesions among the brain, and diffuse brain atrophy in case 3. The blood metabolic and cerebrospinal-fluid immunological assays were normal. Genetic analysis suggested a de novo, heterozygous, NM_012062.4: c.1207C>T, p.R403C variant in the DNM1L gene. According to their clinical manifestations, all of them were diagnosed with EMPF1. Literature review included 11 patients carrying this variant in the world. Summarizing the 14 cases, 8 cases had an infectious history before seizure onset, 8 cases had mild or moderate development delay. All of 14 cases had seizures, and the forms mainly included EPC (n=9), focal myoclonus (n=6), GTCS (n=5) and focal clonic seizures (n=4). All of them were refractory, and no effective anti-epileptic drugs were recommended. Early-stage cranial magnetic resonance imaging results showed multiple intracranial focal lesions (n=10), including thalamus (n=7), hippocampus (n=5), basal ganglia (n=4), frontal lobe (n=3), and temporal lobe (n=2). As the disease progressed, the brain manifested as diffused progressive atrophy (n=10). Five of the 14 cases died at reported age. Conclusions: R403C variant in the DNM1L gene can cause mitochondrial fission dysfunction. Patients carrying this variant may manifest as refractory status epilepticus with or without mild-infection indction, development regression and brain atrophy.

Reconstruction of Vehicle-pedestrian Collision Road Traffic Accidents Based on PC-Crash Software.

ABSTRACT: Objective To discuss the application value of vehicle-pedestrian collision road traffic accidents reconstruction based on PC-Crash software in forensic identification. Methods A case of vehicle-pedestrian collision was chosen based on a tachograph, then PC-Crash software was applied to construct a vehicle-pedestrian collision model, and reconstruct the vehicle-pedestrian collision road traffic accident. Finally, the process of vehicle-pedestrian collision was reproduced. Results In accident reconstruction, when the car speed was lower than 50km/h, the landing point of the pedestrian after collision was in the front of the car. When the car speed was higher than 50 km/h, after collision, the pedestrian flipped towards the car roof and landed behind the car. With the increase of vehicle speed, throwing distance of the pedestrian increased continuously. When the vehicle collision speed reached 60 km/h, the experimental results in this case were basically consistent with the actual situation of the case. Head acceleration of the pedestrian was at the maximum （1 655.70 m/s2） at 0.080 s. Chest acceleration of the pedestrian increased from 597.63 m/s2 to the peak 675.52 m/s2 at 0.055-0.060 s. Tibia acceleration of the pedestrian increased from 759.26 m/s2 to the first peak 1 367.06 m/s2, then reached the maximum speed （1 718.19 m/s2） at 1.225 s. Conclusion The process of vehicle-pedestrian collision road traffic accidents can be reconstructed based on PC-Crash software under a situation of limited conditions, and can further clarify the speed of the vehicle, the location and degree of human body injury as well as the mechanism of damage of the pedestrian in the accident. Therefore, PC-Crash software has a certain practical value in forensic identification of road traffic accidents.

[Research Progress of Traffic Accident Reconstruction Technology Based on PC-Crash Software].

With the development of the computer simulation technology and the digital simulation technology, the traditional calculation method has been gradually replaced by the digital method to deal the road traffic accident scene and analyse the process. The PC-Crash software simulation system can reconstruct the traffic accidents within 32 vehicles, and the accuracy of reconstruction has been fully verified, which is widely used by the transport police department and the accreditation agency. In this paper, the research of road traffic accident reconstruction using PC-Crash software is reviewed, and the application of road traffic accident reconstruction technology based on PC-Crash software and some existing problems in forensic practice are discussed, which provides reference for the research and identification of road traffic accident simulation and reconstruction and theoretical basis for accident treatment.

[Research Progress of Yunnan Unexplained Sudden Death].

Yunnan unexplained sudden death （YUSD） has obvious spatial and temporal aggregations. With the features of sudden onset and rapid death, its causes remain unclear. However, the onset of YUSD is related to the geological and climatic conditions in specific range of altitude of incidence area, which is also influenced by the existed susceptibility gene loci or several multiple mutations in SNP loci, long-term fatigue, low dietary nutrition, trace element deficiency, poor living condition and hygienic habit, and infection by etiologic microorganism or virus among the residents live in the incidence area of YUSD. Under the continuous influence of factors above, the crowd of incidence area finally occurred unexplained sudden death that prominently shown by myocardial injury. Improvements of public health administration, living conditions, villagers' health, living habits and enhancement of indicator measurement of myocardial enzyme and electrocardiogram for the residents in the incidence area of YUSD are effective measures for prevention of YUSD. Timely identification of cause of death and in-depth genetic research are important ways to explore the causes of YUSD, enhance the effectiveness of treatment and reduce the death rate.

Acute organ failure following the loss of anti-apoptotic cellular FLICE-inhibitory protein involves activation of innate immune receptors.

Apoptosis signaling is involved in both physiological tissue homeostasis and acute and chronic diseases. The role of regulatory apoptosis signaling molecules and their organ-specific functions are less defined. Therefore, we investigated the loss of the anti-apoptotic cellular FLICE-inhibitory protein (cFLIP) and the mechanisms of the resulting lethal organ failure in vivo using inducible knockout mice. These were generated by crossing floxed cFLIP mice to a tamoxifen inducible Rosa26-creERT2 mouse strain. Death following global loss of cFLIP resulted from liver failure, accumulation of M1-polarized macrophages and accompanying hepatic cell death and inflammation. Apoptosis was also prominent in immune cells, the kidney and intestinal epithelial cells (IECs) but not in cardiomyocytes. Cellular injury led to the release of damage-associated molecular patterns (DAMPs) and the induction of innate immune receptors including toll-like receptors (TLRs) 4 and 9, and stimulator of interferon genes (STING). Transplantation of bone marrow with intact cFLIP or depletion of macrophages prevented the phenotype of acute liver failure. Interestingly, compound deletion of cFLIP in bone marrow-derived cells and hepatocytes did not promote organ failure. Thus, cFLIP exerts a critical role in tissue homeostasis by preventing the activation of monocytic cells and innate immunity, which causes cell death and inflammation in susceptible tissues. These results encourage the development of organ-specific anti-apoptotic and anti-inflammatory therapies in acute organ failure.

Participation of c-FLIP in NLRP3 and AIM2 inflammasome activation.

Cellular FLICE-inhibitory protein (c-FLIP) is an inhibitor of caspase-8 and is required for macrophage survival. Recent studies have revealed a selective role of caspase-8 in noncanonical IL-1ß production that is independent of caspase-1 or inflammasome. Here we demonstrated that c-FLIP(L) is an unexpected contributor to canonical inflammasome activation for the generation of caspase-1 and active IL-1ß. Hemizygotic deletion of c-FLIP impaired ATP- and monosodium uric acid (MSU)-induced IL-1ß production in macrophages primed through Toll-like receptors (TLRs). Decreased IL-1ß expression was attributed to a reduced activation of caspase-1 in c-FLIP hemizygotic cells. In contrast, the production of TNF-α was not affected by downregulation in c-FLIP. c-FLIP(L) interacted with NLRP3 or procaspase-1. c-FLIP is required for the full NLRP3 inflammasome assembly and NLRP3 mitochondrial localization, and c-FLIP is associated with NLRP3 inflammasome. c-FLIP downregulation also reduced AIM2 inflammasome activation. In contrast, c-FLIP inhibited SMAC mimetic-, FasL-, or Dectin-1-induced IL-1ß generation that is caspase-8-mediated. Our results demonstrate a prominent role of c-FLIP(L) in the optimal activation of the NLRP3 and AIM2 inflammasomes, and suggest that c-FLIP could be a valid target for treatment of inflammatory diseases caused by over-activation of inflammasomes.

Diabetic liver injury from streptozotocin is regulated through the caspase-8 homolog cFLIP involving activation of JNK2 and intrahepatic immunocompetent cells.

The endemic occurrence of obesity and the associated risk factors that constitute the metabolic syndrome have been predicted to lead to a dramatic increase in chronic liver disease. Non-alcoholic steatohepatitis (NASH) has become the most frequent liver disease in countries with a high prevalence of obesity. In addition, hepatic steatosis and insulin resistance have been implicated in disease progression of other liver diseases, including chronic viral hepatitis and hepatocellular carcinoma. The molecular mechanisms underlying the link between insulin signaling and hepatocellular injury are only partly understood. We have explored the role of the antiapoptotic caspase-8 homolog cellular FLICE-inhibitory protein (cFLIP) on liver cell survival in a diabetic model with hypoinsulinemic diabetes in order to delineate the role of insulin signaling on hepatocellular survival. cFLIP regulates cellular injury from apoptosis signaling pathways, and loss of cFLIP was previously shown to promote injury from activated TNF and CD95/Apo-1 receptors. In mice lacking cFLIP in hepatocytes (flip(-/-)), loss of insulin following streptozotocin treatment resulted in caspase- and c-Jun N-terminal kinase (JNK)-dependent liver injury after 21 days. Substitution of insulin, inhibition of JNK using the SP600125 compound in vivo or genetic deletion of the mitogen-activated protein kinase (MAPK)9 (JNK2) in all tissues abolished the injurious effect. Strikingly, the difference in injury between wild-type and cFLIP-deficient mice occurred only in vivo and was accompanied by liver-infiltrating inflammatory cells with a trend toward increased amounts of NK1.1-positive cells and secretion of proinflammatory cytokines. Transfer of bone marrow from rag-1-deficient mice that are depleted from B and T lymphocytes prevented liver injury in flip(-/-) mice. These findings support a direct role of insulin on cellular survival by alternating the activation of injurious MAPK, caspases and the recruitment of inflammatory cells to the liver. Thus, increasing resistance to insulin signaling pathways in hepatocytes appears to be an important factor in the initiation and progression of chronic liver disease.

(E)-1-[2-Hy-droxy-4,6-bis-(meth-oxy-meth-oxy)phen-yl]-3-phenyl-prop-2-en-1-one.

The title compound, C19H20O6, consists of a tetra-substituted benzene ring with one substituent being an α,ß-unsaturated cinnamoyl group, which forms an extended conjugated system in the mol-ecule. In addition, two meth-oxy-meth-oxy and one hy-droxy group are bonded to the central benzene ring. The dihedral angle between eh rings is 10.22 (10)°. An intra-molecular hydrogen bond is observed between the hy-droxy group and the carbonyl O atom. One of the meth-oxy-meth-oxy substituents is conformationally disordered over two sets of sites with site-occupation factors of 0.831 (3) and 0.169 (3).

A role for c-FLIP(L) in the regulation of apoptosis, autophagy, and necroptosis in T lymphocytes.

Caspase 8 plays a dual role in the survival of T lymphocytes. Although active caspase 8 mediates apoptosis upon death receptor signaling, the loss of caspase 8 activity leads to receptor-interacting protein (RIP)-1/RIP-3-dependent necrotic cell death (necroptosis) upon TCR activation. The anti-apoptotic protein c-FLIP (cellular caspase 8 (FLICE)-like inhibitory protein) suppresses death receptor-induced caspase 8 activation. Moreover, recent findings suggest that c-FLIP is also involved in inhibiting necroptosis and autophagy. It remains unclear whether c-FLIP protects primary T lymphocytes from necroptosis or regulates the threshold at which autophagy occurs. Here, we used a c-FLIP isoform-specific conditional deletion model to show that c-FLIP(L)-deficient T cells underwent RIP-1-dependent necroptosis upon TCR stimulation. Interestingly, although previous studies have only described necroptosis in the absence of caspase 8 activity, we found that pro-apoptotic caspase 8 activity and apoptosis were also enhanced in c-FLIP(L)-deficient T lymphocytes. Furthermore, c-FLIP(L)-deficient T cells exhibited enhanced autophagy, which served a cytoprotective function. Together, these findings indicate that c-FLIP(L) plays an important antinecroptotic role and is a key regulator of apoptosis, autophagy, and necroptosis in T lymphocytes.

A school outbreak of Shigella sonnei infection in China: clinical features, antibiotic susceptibility and molecular epidemiology.

OBJECTIVE: To describe the clinical features of infection, and the antibiotic susceptibility of epidemic strains, and investigate plasmid maps and integrons of the isolates from an outbreak of Shigella sonnei infection at an elementary school in southwest China. STUDY DESIGN: Cross-sectional study. SETTING: An elementary school and five hospitals in Chengdu in southwest China. RESULTS: There were 1,134 students in the school. 937 (82.6%) students had signs and symptoms. Of the 568 (60.6%, 568/937) hospitalized students, 93.3% 86.8%, 72.4%, and 28.9% of the hospitalized patients had diarrhea, fever, abdominal pain, and vomiting, respectively. S. sonnei strains were isolated from the stool samples of 36.0% (337/937) students. All of the outbreak isolates had the same high-level antimicrobial resistance and plasmid profiles, which were different from that of sporadic strains. All the outbreak S. sonnei isolates were positive for the integrin gene and contained class 2 integron; however, two outbreak isolates contained class 1 and class 2 integrons. CONCLUSIONS: Diarrhea, fever, and abdominal pain were the three most common clinical manifestations observed in patients infected with S. sonnei. High-level antibiotic resistance was observed among Shigella species.

Cytokine-dependent and cytokine-independent roles for Mcl-1: genetic evidence for multiple mechanisms by which Mcl-1 promotes survival in primary T lymphocytes.

Myeloid cell leukemia sequence-1 (Mcl-1) is a critical anti-apoptotic factor in T lymphocytes. However, in spite of the many pro-apoptotic proteins with proposed binding to Mcl-1, the specific interactions by which Mcl-1 regulates primary T-cell survival under different conditions have not been fully explored. Further, how different trophic cytokines modulate the specific role(s) of Mcl-1 is unknown. Here, we use genetic mouse models to dissect the roles of Mcl-1 in primary T lymphocytes. Using the inducible Mcl-1-floxed estrogen receptor-Cre fusion protein (Mcl-1(f/f)ERCre) deletion system in combination with genetic modification of other B-cell lymphoma 2 (Bcl-2) family members, we show that loss of pro-apoptotic Bcl-2 homologous antagonist/killer (Bak) rescues the survival of Mcl-1-deficient T cells in the presence of IL-7. Without IL-7, the survival of Mcl-1-deficient cells cannot be rescued by loss of Bak, but is partially rescued by overexpression of Bcl-2 or loss of Bcl-2-interacting mediator of cell death (Bim). Thus, Mcl-1 and Bcl-2 have a shared role, the inhibition of Bim, in promoting T-cell survival during cytokine withdrawal. Finally, we show that other common gamma-chain (γc) cytokines differentially modulate the roles of Mcl-1. IL-15 has effects similar to those of IL-7 in memory T cells and naïve CD8(+) cells, but not naïve CD4(+) cells. However, IL-4 maintains Mcl-1 and Bcl-2 but also upregulates Bim and Bcl-2-associated X protein (Bax), thus altering the cell's dependence on Mcl-1.

Autophagy is essential to suppress cell stress and to allow BCR-Abl-mediated leukemogenesis.

Hematopoietic cells normally require cell extrinsic signals to maintain metabolism and survival. In contrast, cancer cells can express constitutively active oncogenic kinases such as BCR-Abl that promote these processes independent of extrinsic growth factors. When cells receive insufficient growth signals or when oncogenic kinases are inhibited, glucose metabolism decreases and the self-digestive process of autophagy is elevated to degrade bulk cytoplasm and organelles. Although autophagy has been proposed to provide a cell-intrinsic nutrient supply for mitochondrial oxidative metabolism and to maintain cellular homeostasis through degradation of damaged organelles or protein aggregates, its acute role in growth factor deprivation or inhibition of oncogenic kinases remains poorly understood. We therefore developed a growth factor-dependent hematopoietic cell culture model in which autophagy can be acutely disrupted through conditional Cre-mediated excision of the autophagy-essential gene Atg3. Treated cells rapidly lost their ability to perform autophagy and underwent cell cycle arrest and apoptosis. Although Atg3 was essential for optimal upregulation of mitochondrial oxidative pathways in growth factor withdrawal, this metabolic contribution of autophagy did not appear critical for cell survival, as provision of exogenous pyruvate or lipids could not completely rescue Atg3 deficiency. Instead, autophagy suppressed a stress response that otherwise led to p53 phosphorylation and upregulation of p21 and the pro-apoptotic Bcl-2 family protein Puma. Importantly, BCR-Abl-expressing cells had low basal levels of autophagy, but were highly dependent on this process, and rapidly underwent apoptosis upon disruption of autophagy through Atg3 deletion or treatment with chemical autophagy inhibitors. This dependence on autophagy extended in vivo, as Atg3 deletion also prevented BCR-Abl-mediated leukemogenesis in a cell transfer model. Together these data demonstrate a critical role for autophagy to mitigate cell stress, and that cells expressing the oncogenic kinase BCR-Abl appear particularly dependent on autophagy for cell survival and leukemogenesis.

Mcl-1 promotes survival of thymocytes by inhibition of Bak in a pathway separate from Bcl-2.

The antiapoptotic proteins Mcl-1 and Bcl-2 have been shown to be critical in T-cell development and homeostasis, but the precise mechanism by which these proteins function in T cells and other cells of the body is unclear. Potential mechanisms have allowed both for overlapping and unique roles for these proteins because of their abilities to bind different proapoptotic Bcl-2 family members, but it is unclear which of these mechanisms are important in an in vivo context. By generation of various genetic mouse models, we found that Mcl-1-deficient thymocytes die largely by a Bak-specific mechanism. In vivo deletion of Bak rescued the survival and developmental blocks of Mcl-1-deficient thymocytes at the double-negative and single-positive stages. Transgenic overexpression of Bcl-2 and in vivo deletion of Bax or Bim were unable to rescue Mcl-1-deficient thymocytes. Thus, Mcl-1 functions in a unique pathway from Bcl-2 in T lymphocytes, likely because of its specific ability to bind and sequester proapoptotic Bak. Together, these data provide an in vivo model for Mcl-1 activity and present us with a greater understanding of the pathways that promote thymocyte survival.

Down-regulation of the orphan nuclear receptor ROR gamma t is essential for T lymphocyte maturation.

Thymocyte development is a tightly regulated process. CD4+CD8+ double-positive (DP) immature thymocytes exhibit distinct phenotypic features from mature T cells; they express only 10% of surface TCR that are found on mature T cells and do not proliferate and produce IL-2 in response to stimulation. In this report we show that transgenic expression of the orphan nuclear receptor ROR gamma t in mature T cells down-regulates their surface TCR expression. The ROR gamma t transgene inhibits IL-2 production by mature T cells, and this inhibition may be partially due to the inhibitory effect of ROR gamma t on c-Rel transcription. Furthermore, ectopic expression of ROR gamma t inhibits the proliferation of mature and immature T cells. These results, together with its predominant expression in DP thymocytes, suggest that ROR gamma t controls these distinct phenotypic features of DP thymocytes. Our data suggest that down-regulation of ROR gamma t expression in thymocytes is essential for their maturation.

The role of orphan nuclear receptor in thymocyte differentiation and lymphoid organ development.

T lymphocytes differentiate in the thymus through several phenotypically distinct stages that are tightly regulated by multiple nuclear transcription factors. Immature CD4+CD8+ double positive (DP) thymocytes make up a majority of the population in the thymus, and exhibit several phenotypic features distinct from mature T cells. DP thymocytes express only about 10% of surface TCR that are found on mature T cells and do not proliferate and produce IL-2 in response to stimulation. Several critical events of T lymphocyte maturation such as TCRalpha gene recombination, positive and negative selection, and CD4/CD8 lineage commitment occur around the DP stage. Recent studies from our group and others on the orphan nuclear receptor RORgamma and its thymus-specific isoform RORgammat support a critical role for this nuclear receptor in the regulation of DP thymocyte function. In addition, RORgamma is required for the development of lymph nodes and Peyer's patches.

High level expression of CD43 inhibits T cell receptor/CD3-mediated apoptosis.

In a screen designed to identify genes that regulate T cell receptor (TCR)/CD3-mediated apoptosis, we found that high level expression of CD43 protected T cell hybridomas from activation-induced cell death. The protection appears to result from its capacity to block Fas-mediated death signals rather than from inhibition of the upregulation of Fas and/or Fas ligand after T cell stimulation. We found that peripheral CD4(+) T cells can be divided into two subsets based on the level of CD43 surface expression. The CD4(+)CD43(low) subset exhibits a naive T cell phenotype, being CD62L(high)CD45RB(high)CD44(low), whereas CD4(+)CD43(high) cells exhibit a memory phenotype, being CD62L(low)CD45RB(low)CD44(high). Recent studies have demonstrated that engagement of TCR and Fas induces naive CD4(+) T cells to undergo apoptosis, and the same treatment enhances the proliferation of memory CD4(+) T cells. We confirm here that peripheral CD4(+)CD43(high) T cells are resistant to TCR/CD3-mediated cell death. These results suggest that the expression levels of CD43 on naive and memory CD4(+) T cells determine their susceptibility to Fas-dependent cell death and that high level expression of CD43 may be used as a marker to define CD4(+) memory T cells. Expression of CD43 provides a novel mechanism by which tumor cells expressing abnormally high levels of CD43 may escape Fas-mediated killing.