Protein kinase C-epsilon (PKC-epsilon) plays a central role in cardiac cell signaling, but mechanisms of translocation and anchoring upon activation are poorly understood. Conventional PKC isoforms rely on a rapid Ca2+-mediated recruitment to cell membranes, but this mechanism cannot be employed by PKC-epsilon or other PKC isoforms lacking a Ca2+-binding domain. In this study, we used recombinant green fluorescent protein (GFP) fusion constructs and confocal microscopy to examine the localization, kinetics, and reversibility of PKC-epsilon anchoring in permeabilized rat cardiac myocytes. PKC-epsilon-GFP bound with a striated pattern that co-localized with alpha-actinin, a marker of the Z-line of the sarcomere. Binding required activation of PKC and occurred slowly but reversibly with apparent rate constants of k(on) = 4.6 +/- 1.2 x 10(3) M(-1) x s(-1) and k(off) = 1.4 +/- 0.5 x 10(-3) s(-1) (t1/2 = 8 min) as determined by fluorescence recovery after photobleaching and by perfusion experiments. A truncated construct composed of the N-terminal 144-amino-acid variable region of PKC-epsilon (epsilonV1-GFP), but not an analogous N-terminal domain of PKC-delta, mimicked the Z-line decoration and slow binding rate of the full-length enzyme. These findings suggest that the epsilonV1 domain is important in determining PKC-epsilon localization and translocation kinetics in cardiac muscle. Moreover, PKC-epsilon translocation is not a diffusion-controlled binding process but instead may be limited by intramolecular conformational changes within the V1 domain. The k(off) for epsilonV1-GFP was two- to threefold faster than for full-length enzyme, indicating that other domains in PKC-epsilon contribute to anchoring by prolonging the bound state.
Endothelin-1 (ET-1) is an autocrine factor in the mammalian heart important in enhancing cardiac performance, protecting against myocardial ischemia, and initiating the development of cardiac hypertrophy. The ET A receptor is a seven-transmembrane G-protein-coupled receptor whose precise subcellular localization in cardiac muscle is unknown. Here we used fluorescein ET-1 and 125 I-ET-1 to provide evidence for ET-1 receptors in cardiac transverse tubules (T-tubules). Moreover, the ET A receptor and downstream effector phospholipase C- 1 were co-localized within T-tubules using standard immunofluorescence techniques, and protein kinase C (PKC)-⑀-enhanced green fluorescent protein bound reversibly to T-tubules upon activation. Localized photorelease of diacylglycerol further suggested compartmentation of PKC signaling, with release at the myocyte "surface" mimicking the negative inotropic effects of bath-applied PKC activators and "deep" release mimicking the positive inotropic effect of ET-1. The functional significance of T-tubular ET-1 receptors was further tested by rendering the T-tubule lumen inaccessible to bath-applied ET-1. Such "detubulated" cardiac myocytes showed no positive inotropic response to 20 nM ET-1, despite retaining both a nearly normal twitch response to field stimulation and a robust positive inotropic response to 20 nM isoproterenol. We propose that ET-1 enhances myocyte contractility by activating ET A receptor-phospholipase C- 1 -PKC-⑀ signaling complexes preferentially localized in cardiac T-tubules. Compartmentation of ET-1 signaling complexes may explain the discordant effects of ET-1 versus bath applied PKC activators and may contribute to both the specificity and diversity of the cardiac actions of ET-1.
The effect of rituximab on malignant B cells and normal circulating B cells has been previously studied. In contrast, data on the degree of depletion of nonneoplastic B cells induced by rituximab in lymph nodes and spleen is limited. For this purpose, clinical charts, autopsy records, lymph node and spleen sections, and immunoperoxidase stains were reviewed from 10 patients who had received 1 to 40 doses of rituximab before death. The percentage of nonneoplastic B cells was lower in the lymph node and spleen in rituximab-treated patients when compared with cyclophosphamide, doxorubicin, vincristine, and prednisone-treated patients and patients without lymphoma. The effect of rituximab on nonneoplastic B cells was observed as soon as 1 month after administration and with as few as 3 doses. Reappearance of normal numbers of B cells was not observed 1 to 12 months after the last dose of rituximab was administered. We conclude that rituximab induces prompt, consistent, profound, and prolonged depletion of B lymphocyte populations in human lymphoid tissue.
Extranodal NK/T cell lymphoma nasal type is an EBV driven non-Hodgkin lymphoma, rare in the United States, with no known satisfactory treatment. Two patients with this entity refractory to CHOP chemotherapy responded to single agent pegaspargase (pegylated L-asparaginase). A 64-year-old Caucasian woman presented with extranodal NK/T lymphoma nasal type on her left buttocks. After initial treatment with loco-regional irradiation and CHOP, she developed extensive lower extremity lesions, and subsequent paranasal sinus involvement. With pegaspargase, she had a dramatic improvement of her skin lesions and proceeded to autologous stem cell transplant. A 48 year old Asian man presented with nasal cavity extranodal NK/T lymphoma which resolved with radiation therapy. Multiple liver lesions which developed while receiving CHOP completely resolved on pegaspargase. L-Asparaginase and its pegylated form have activity in this disease and further exploration alone or in combination is warranted.
Pediatric nodal marginal zone lymphoma (NMZL) is described as a separate variant of NMZL in the most recent WHO classification of tumors of hematologic and lymphoid tissues. It has distinctive morphology and clinical presentation and stands out as an indolent disease with remarkably better overall prognosis compared to classic NMZL. Here we report two adult cases of NMZL with clinical and morphologic features consistent with pediatric NMZL (pNMZL) and review available literature describing the clinical and histologic presentation of pNMZL.. Two men, ages 44 and 18 years, each presented with localized cervical lymphadenopathy that histologically demonstrated florid proliferation of the marginal zone and disruption of reactive germinal centers, progressive transformation of germinal centers (PTGC) -like morphologic features typical for pNMZL and clonal disease with immunophenotype consistent with NMZL. This is the first report of pNMZL in a middle-aged person. Distinct histologic features and characteristic benign clinical course will help to distinguish this rare variant from other NMZL in adults. Clinically, recognition is important to understand the true incidence of this rare form in the adult population and to avoid unnecessary overtreatment of this indolent form.
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