Fas ligand-induced apoptosis of hepatocytes in natural killer cell leukaemia

Stat3 role in the protective effect of FXR Agonist in parenteral nutrition-associated cholestasis

BACKGROUND AND AIMS

Parenteral nutrition (PN) in patients with intestinal failure can lead to cholestasis (PNAC). In a PNAC mouse model, farnesoid X receptor (FXR) agonist (GW4064) treatment alleviated IL-1β-dependent cholestatic liver injury. The objective of this study was to determine whether this hepatic protection of FXR activation is mediated through IL-6-STAT3 signaling.

APPROACH AND RESULTS

Hepatic apoptotic pathways [Fas-associated protein with death domain (Fas) mRNA, caspase 8 protein, and cleaved caspase 3] and IL-6-STAT3 signaling, and expression of its downstream effectors Socs1/3 were all upregulated in the mouse PNAC model (dextran sulfate sodium enterally × 4 d followed by total PN for 14 d). Il1r-/- mice were protected from PNAC in conjunction with suppression of the FAS pathway. GW4064 treatment in the PNAC mouse increased hepatic FXR binding to the Stat3 promoter, further increased STAT3 phosphorylation and upregulated Socs1 and Socs3 mRNA, and prevented cholestasis. In HepG2 cells and primary mouse hepatocytes, IL-1β induced IL-6 mRNA and protein, which were suppressed by GW4064. In IL-1β or phytosterols treated HepG2 and Huh7 cells, siRNA knockdown of STAT3 significantly reduced GW4064-upregulated transcription of hepatoprotective nuclear receptor subfamily 0, group B, member 2 (NR0B2) and ABCG8.

CONCLUSIONS

STAT3 signaling mediated in part the protective effects of GW4064 in the PNAC mouse, and in HepG2 cells and hepatocytes exposed to either IL-1β or phytosterols, 2 factors critical in PNAC pathogenesis. These data demonstrate that FXR agonists may mediate hepatoprotective effects in cholestasis by inducing STAT3 signaling.

Epstein-Barr virus-associated T/natural killer-cell lymphoproliferative disorders

Primary infection with Epstein-Barr virus (EBV) is usually asymptomatic and, in a normal host, EBV remains latent in B cells after primary infection for the remainder of life. Uncommonly, EBV can infect T or natural killer (NK) cells in a person with a defect in innate immunity, and EBV infection can cause unique systemic lymphoproliferative diseases (LPD) of childhood. Primary infection in young children can be complicated by hemophagocytic lymphohistiocytosis or fulminant systemic T-cell LPD of childhood. Uncommonly, patients can develop chronic active EBV (CAEBV) disease-type T/NK LPD, which includes CAEBV infection of the systemic form, hydroa vacciniforme-like T-cell LPD, and mosquito-bite hypersensitivity. The clinical course of CAEBV disease-type T/NK LPD can be smoldering, persistent or progressive, depending on the balance between viral factors and host immunity. Aggressive NK-cell leukemia, hydroa vacciniforme-like T-cell lymphoma, or uncommonly extranodal NK/T-cell lymphoma can develop in children and young adults with CAEBV disease-type T/NK-cell LPD. Extranodal T/NK-cell lymphoma is a disease of adults, and its incidence begins to increase in the third decade and comprises the major subtype of T/NK LPD throughout life. Aggressive NK-cell leukemia and nodal T/NK-cell lymphoma of the elderly are fulminant diseases, and immune senescence may be an important pathogenetic factor. This review describes the current progress in identifying different types of EBV-associated T/NK-cell LPD and includes a brief presentation of data from Korea.

Progress in understanding and managing natural killer-cell malignancies

The World Health Organization classification of haematolymphoid tumours recognizes three categories of natural killer (NK)-cell neoplasms: blastic NK-cell lymphoma, aggressive NK-cell leukaemia, and extranodal NK/T-cell lymphoma, nasal-type. Recent studies indicate that CD4+CD56+ blastic NK-cell lymphoma is of plasmacytoid dendritic cell origin, and true tumours of precursor NK-cell origin may be present mainly in the CD4-CD56+ subset. Myeloid/NK-cell precursor acute leukaemia may also develop from precursor NK cells. However, because the developmental pathway of normal NK cells is not well understood, tumours of precursor NK-cell origin are not clearly identified. Among mature NK-cell tumours, extranodal NK/T-cell lymphoma is relatively common in Asia and Latin America. In localized disease, chemoradiotherapy seems to be promising, and in advanced disease, new combination chemotherapies are under active investigation. Aggressive NK-cell leukaemia is rare and has a poor prognosis. Because NK-cell neoplasms are rare and difficult to manage, rigorous studies are required for their understanding and management.

Cytotoxic granule disruption is a late event in chemotherapy-induced apoptosis in Natural Killer YT cells

Cytotoxic lymphocytes such as Natural Killer (NK) cells can result in leukemias and lymphomas with aggressive clinical course. The cytoplasmic granules of NK cells contain molecules that cause apoptosis of their target cells. In this study, we examined changes of the cytotoxic granules of the Natural Killer cell line YT during Etoposide-induced apoptosis. Etoposide treatment resulted in an early upregulation of Fas and cytoplasmic release of mitochondrial cytochrome c. The cytotoxic granules remain intact in the early stages of apoptosis induction with no significant cytoplasmic release of granzyme B, which is one of the components of the cytotoxic granules. These results suggest that disruption of the cytotoxic granules is not involved in the induction stage of Etoposide-induced apoptosis in the NK cell line YT.

Does CD95 have tumor promoting activities?

CD95 (APO-1/Fas) is an important inducer of the extrinsic apoptosis signaling pathway and therapy induced apoptosis of many tumor cells has been linked to the activity of CD95. Changes in the expression of CD95 and/or its ligand CD95L are frequently found in human cancer. The downregulation or mutation of CD95 has been proposed as a mechanism by which cancer cells avoid destruction by the immune system through reduced apoptosis sensitivity. CD95 has therefore been viewed as a tumor suppressor. Furthermore, increased CD95L concentration in tumor patients has been linked to tumor cells killing infiltrating lymphocytes in a process called "the tumor counter-attack". Recent data have illuminated unknown activities of CD95 in tumor cells with downregulated or mutated CD95 in the presence of increased CD95L. Under these conditions the stimulation of CD95 signals nonapoptotic pathways, activating NF-kappaB and MAP kinases for example, which may result in the induction of tumorigenic or prosurvival genes. A new model of CD95 functions is proposed in which CD95 is converted from a tumor suppressor to a tumor promotor by a single point mutation in one of the CD95 alleles, a situation frequently found in advanced human cancer, resulting in apoptosis resistance and activation of tumorigenic pathways.

Clinical features and treatment strategies of Epstein-Barr virus-associated hemophagocytic lymphohistiocytosis

Epstein-Barr virus (EBV) is the major triggering factor producing hemophagocytic syndrome or hemophagocytic lymphohistiocytosis (HLH). In this review, diagnostic problems, clinical and histopathological features, and treatment strategies of EBV-HLH have been described. In patients with EBV-HLH, the EBV-infected T cells or natural killer (NK) cells are mostly mono- or oligo-clonally proliferating, where hypercytokinemia plays a major role and causes hemophagocytosis, cellular damage and dysfunction of various organs. Although the majority of EBV-HLH cases develop in apparently immunocompetent children and adolescents, it also occurs in association with infectious mononucleosis, chronic active EBV infection, familial HLH, X-linked lymphoproliferative disease, lymphoproliferative disease like peripheral T-cell lymphoma and NK cell leukemia. In terms of treatment, special therapeutic measures are required to control the cytokine storm generated by EBV and to suppress proliferating EBV-genome-containing cells, because the clinical courses are often fulminant and result in a poor outcome.