Hisanori Umehara

Dual Functions of Fractalkine/CX3C Ligand 1 in Trafficking of Perforin + /Granzyme B + Cytotoxic Effector Lymphocytes That Are Defined by CX3CR1 Expression

Fractalkine/CX3C ligand 1 and its receptor CX3CR1 are known to mediate both cell adhesion and cell migration. Here we show that CX3CR1 defines peripheral blood cytotoxic effector lymphocytes commonly armed with intracellular perforin and granzyme B, which include NK cells, γδ T cells, and terminally differentiated CD8+ T cells. In addition, soluble fractalkine preferentially induced migration of cytotoxic effector lymphocytes. Furthermore, interaction of cytotoxic effector lymphocytes with membrane-bound fractalkine promoted subsequent migration to the secondary chemokines, such as macrophage inflammatory protein-1β/CC ligand 4 or IL-8/CXC ligand 8. Thus, fractalkine expressed on inflamed endothelium may function as a vascular regulator for cytotoxic effector lymphocytes, regardless of their lineage and mode of target cell recognition, through its ability to capture them from blood flow and to promote their emigration in response to other chemokines.

Ceramide-induced Translocation of Protein Kinase C-δ and -ϵ to the Cytosol IMPLICATIONS IN APOPTOSIS

Ceramide is now recognized as an intracellular lipid signal mediator, which induces various kinds of cell functions including apoptosis. Ceramide-induced apoptosis was reported to be blocked by 12-O-tetradecanoylphorbol 13-acetate, a protein kinase C (PKC) activator, but its mechanism remained unclear. Therefore, we investigated whether ceramide has any effects on PKC in the induction of apoptosis. We here report that N-acetylsphingosine (synthetic membrane-permeable ceramide) induced translocation of PKC-δ and -ε isozymes from the membrane to the cytosol within 5 min in human leukemia cell lines. Treatment with sphingomyelinase, tumor necrosis factor-α, or anti-Fas antibody, all of which can induce apoptosis by generating natural ceramide, similarly induced cytosolic translocation of PKC-δ and -ε. In Fas-resistant cells anti-Fas antibody did not induce cytosolic translocation of PKC-δ and -ε because of no generation of ceramide, whereas N-acetylsphingosine induced apoptosis with cytosolic translocation of PKC-δ and -ε. Furthermore, both 12-O-tetradecanoylphorbol 13-acetate and a nonspecific kinase inhibitor, staurosporine, prevented ceramide-induced apoptosis by inhibiting cytosolic translocation of PKC-δ and -ε. These data suggest that cytosolic translocation of PKC-δ and -ε plays an important role in ceramide-mediated apoptosis.

Increase of Nuclear Ceramide through Caspase-3-Dependent Regulation of the “Sphingomyelin Cycle” in Fas-Induced Apoptosis

Regardless of the existence of ceramide-related molecules, such as sphingomyelin (SM), neutral sphingomyelinase (nSMase), and SM synthase, in the nucleus, the regulation of ceramide in the nucleus is poorly understood in stress-induced apoptosis. In Fas-induced Jurkat T-cell apoptosis, we found a time- and dose-dependent increase of ceramide content in the nuclear and microsomal fractions. Fas-induced increase of ceramide content in the nucleus also was detected by confocal microscopy using anticeramide antibody. Activation of nSMase and inhibition of SM synthase were evident in the nuclear fraction after Fas cross-linking, whereas nSMase was activated, but SM synthase was not affected, in the microsomal fraction. Pretreatment with d-609, a putative SM synthase inhibitor, enhanced Fas-induced increase of ceramide in the nucleus and induction of apoptosis along with increase of Fas-induced inhibition of nuclear SM synthase. Fas-induced activation of caspase-3 was detected in the nuclear fraction and in whole cell lysate. A caspase-3 inhibitor, acetyl-Asp-Glu-Val-Asp-chloromethyl ketone, blocked not only Fas-induced increases of apoptosis and ceramide content but also Fas-induced activation of nSMase and inhibition of SM synthase in the nuclear fraction. Taken together, it is suggested that the nucleus is a site for ceramide increase and caspase-3 activation in Fas-induced Jurkat T-cell apoptosis and that caspase-3-dependent regulation of the “SM cycle” consisting of nSMase and SM synthase plays a role in Fas-induced ceramide increase in the nucleus.

Down‐regulation of α6 integrin, an anti‐oncogene product, by functional cooperation of H‐Ras and c‐Myc

The molecular basis of cooperation of H‐Ras and c‐Myc in regulating cellular behaviour, such as cell adhesiveness, is still poorly understood. To investigate the role of H‐Ras and c‐Myc in cell adhesiveness, a constitutively active H‐RasV12 (H‐RasV12) and c‐Myc were stably expressed, singly or in combination in a haematopoietic cell line, and the expression and activity of cell adhesion molecules were monitored.

Differential interaction of Cbl with Grb2 and CrkL in CD2-mediated NK cell activation

Natural killer (NK) cells participate in both innate and adoptive immunity by their prompt secretion of cytokines and by their ability to lyse virally infected cells or tumor cells. CD2 is surface glycoprotein receptors and crucial for NK cell activation. However, molecular events involved in CD2-mediated NK cell activation have not been fully elucidated. Cbl-Grb2 and Cbl-CrkL interactions have been implicated in T cell and B cell receptor, and cytokine receptor signaling. Here we analyzed tyrosine phosphorylation and interactions of Cbl with adapter proteins, Grb2 and CrkL, in NK3.3 cells. CD2 crosslinking results in the marked tyrosine phosphorylation of Cbl in an antibody concentration- and time-dependent manner. Immunodepletion studies reveal that Grb2-associated tyrosine phosphorylated p120 kDa protein is Cbl. In vitro binding studies using GST-fusion proteins demonstrate that Cbl constitutively associates with the SH3 domains of Grb2, with a preference for the amino-terminal domain. In addition, we demonstrate that CrkL associates with a large portion of tyrosine phosphorylated Cbl after CD2 stimulation of NK3.3 cells. In contrast to constitutive Cbl association with Grb2, tyrosine phosphorylated Cbl interacts with CrkL via its SH2 domain only after CD2 stimulation. Although the precise roles of interactions of Cbl with Grb2 and CrkL in NK cell activation remains to be elucidated, their tyrosine phosphorylation, in addition to the multiple protein interactions described here, strongly suggest that interactions of Cbl with Grb2 and CrkL may play pivotal roles in CD2-mediated NK cell activation.

Recurrent ischemic colitis in a patient with malignant rheumatoid arthritis (MRA)

Abstract A 63-year-old male with a 5-year history of malignant rheumatoid arthritis (MRA) developed recurrent massive melena and abdominal pain. Methylprednisolone pulse therapy and high doses of oral prednisolone markedly improved the clinical symptoms and normalized immunological disorders. However, he died of disseminated intra-vascular coagulation secondary to pneumonia caused by methicillin-resistant Staphylococcus aureus. Although a high dose of glucocorticoid therapy is effective for ischemic colitis complicated with MRA, intensive care to avoid any opportunistic infection is required.