B-non-Hodgkin lymphomas (B-NHLs IntroductionHuman lymphomas develop mainly from B lymphocytes after chromosomal translocations involving the IgH promoter and an oncogene, 1,2 but the type-specific molecular basis for lymphoma cell proliferation remains largely unknown. 1 It was recently suggested that, in B-cell lymphomas, CD40 and its ligand CD154 were coexpressed and associated in a raft-based signalosome leading to constitutive expression of Considering that the Lyn Src-family kinase and the Cbp/PAG adaptor are the major phosphotyrosylated proteins of lymphoma rafts, 4,5 and therefore components of a proximal signaling platform, 6 we set out to investigate their membrane organization and oncogenic potential in a panel of human B/T non-Hodgkin and Hodgkin lymphoma cell lines and tissues.In normal lymphocytes, the Csk-binding protein (Cbp)/ phosphoprotein associated with glycosphingolipid-enriched microdomains (PAG) adaptor 7-9 is a major phosphotyrosylated protein involved in the negative regulation of signaling in murine T lymphocytes [10][11][12][13] and mast cells. 14 Cbp/PAG (hereafter PAG), phosphorylated at tyrosine 317, was shown to bind Csk 15 and allow phosphorylation of the Src-kinase C-terminal regulatory tyrosine and inactivation of the Src kinase. 16,17 PAG is tyrosine phosphorylated in resting T lymphocytes and rapidly dephosphorylated upon activation. 10,11,16,17 Likewise, tyrosine phosphorylated PAG associated with Csk was shown to inhibit bovine B lymphocyte proliferation. 18 In contrast, several human B-non-Hodgkin lymphoma (B-NHL) cell lines proliferate with a tyrosine phosphorylated PAG adaptor, 4 suggesting that, in lymphoma cells, this form of PAG rather promotes proliferation.PAG is a 432-amino acid protein localized in sphingolipidenriched membrane microdomains. 19 The cytoplasmic portion of the PAG single transmembrane protein contains 10 phosphorylatable tyrosines and 2 proline-rich domains (residues 131-138 and 257-263), to potentially interact with SH2 and SH3 domains, respectively. Palmitoylation facilitates PAG association with rafts 8 and contributes to the formation of a "lipid shell" around PAG in sphingolipid and cholesterol-rich domains. 20 We investigated how PAG, Lyn, and Csk interact within membrane microdomains in B-NHLs (Burkitt, follicular, mantle cell, and diffuse large B-cell lymphomas of both germinal centerand activated B cell-type), anaplastic large cell T lymphomas (ALCLs) expressing the nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) fusion protein (ALK ϩ lymphomas) and Hodgkin lymphoma-derived cell lines and tissues. The PAG protein was expressed in all those cells, but only in B-NHL lines did the phosphorylated PAG protein associate with sphingolipid-enriched membrane domains (or rafts) and strongly interact with Lyn. The phosphorylated signal transducer and activator of transcription 3 (STAT3) was also part of the Lyn/PAG raft complex in B-NHL lines and tissues and may modulate gene expression under the control of the Lyn/PAG signalosome. The online versio...

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Activation of metabotropic glutamate receptor (mGluR) subtypes can prevent neuronal injury through the signal transduction pathways of nitric oxide (NO). It is this link to NO free radical injury and subsequent DNA damage that is the most intriguing. We therefore examined whether neuronal protection through mGluR activation was dependent on the molecular mechanisms of programmed cell death (PCD). The NO generators sodium nitroprusside and 3-morpholino-sydnonimine were administered to induce NO toxicity in primary hippocampal neurons. PCD was documented by hematoxylin and eosin nuclear staining, DNA gel electrophoresis, transmission electron microscopy, and protein synthesis assays. Following NO exposure, PCD induction was rapid and robust in approximately 70% of the neuronal population. Activation of specific mGluR subtypes with 1S,3R-ACPD and L-AP4, agents that are neuroprotective against NO, significantly limited the progression of PCD. In contrast, antagonism of mGluRs with L-AP3 did not prevent the development of PCD. Induction of new protein synthesis, a common requisite for PCD, was evident following NO exposure, but did not appear to represent a principal pathway of modulation by the mGluR agonists. Our studies suggest that mGluR modulation of NO-induced PCD represents a primary molecular pathway responsible for neuronal survival. Further elucidation of the molecular mGluR signaling pathways may yield new insight into specific genetic regulatory mechanisms responsible for neuronal injury.