Leucocyte-specific protein (LSP1) in malignant lymphoma and Hodgkin's disease

Lymphocyte-Specific Protein 1 Regulates Expression and Stability of Endothelial Nitric Oxide Synthase

Nitric oxide (NO), synthesized by endothelial nitric oxide synthase (eNOS), plays a critical role in blood pressure regulation. Genome-wide association studies have identified genetic susceptibility loci for hypertension in human lymphocyte-specific protein 1 (LSP1) gene. LSP1 is recognized as modulator of leukocyte extravasation, and endothelial permeability, however, the role of LSP1 in regulation of NO signaling within endothelial cells (ECs) remains unknown. The present study investigated the role of LSP1 in the regulation of eNOS expression and activity utilizing human macrovascular ECs in vitro and LSP1 knockout (KO) mice. In ECs, specific CRISPR-Cas9 genomic editing deleted LSP1 and caused downregulation of eNOS expression. LSP1 gain-of-function through adenovirus-mediated gene transfer was associated with enhanced expression of eNOS. Co-immunoprecipitation and confocal fluorescence microscopy revealed that eNOS and LSP1 formed a protein complex under basal conditions in ECs. Furthermore, LSP1 deficiency in mice promoted significant upregulation and instability of eNOS. Utilizing a mass-spectrometry-based bottom-up proteomics approach, we identified novel truncated forms of eNOS in immunoprecipitates from LSP1 KO aortae. Our experimental data suggest an important role of endothelial LSP1 in regulation of eNOS expression and activity within human ECs and murine vascular tissues.

Elevated lymphocyte specific protein 1 expression is involved in the regulation of leukocyte migration and immunosuppressive microenvironment in glioblastoma

Immune cell infiltration mediates therapeutic response to immune therapies. The investigation on the genes regulating leukocyte migration may help us to understand the mechanisms regulating immune cell infiltration in tumor microenvironment. Here, we collected the data from Chinese Glioma Genome Atlas (CGGA) and The Cancer Genome Atlas (TCGA) to analyze the expression of leukocyte migration related genes in glioblastoma (GBM). Lymphocyte specific protein 1 (LSP1) was identified as the only gene in this family which not only has an elevated expression, but also serve as an independent predictive factor for progressive malignancy in glioma. We further confirmed these results in clinical glioma samples by quantitative PCR, immunofluorescence, immunohistochemistry, and western blot. Moreover, LSP1 expression was closely related to the response to radio- and chemotherapy in GBM, and positively correlated with immunosuppressive cell populations, including M2 macrophages, neutrophil, and regulatory T cell. Additionally, elevated LSP-1 expression enhanced the expression of immunosuppression related genes like programmed cell death 1 (PD1) and leukocyte associated immunoglobulin like receptor 1 (LAIR1) in macrophages. LSP1 also promoted the migration of macrophages. Together, our study suggests a novel role of LSP1 contributing to immunosuppressive microenvironment in GBM and serving as a potential therapeutic target for it.

Temporal regulation of Lsp1 O-GlcNAcylation and phosphorylation during apoptosis of activated B cells

Crosslinking of B-cell receptor (BCR) sets off an apoptosis programme, but the underlying pathways remain obscure. Here we decipher the molecular mechanisms bridging B-cell activation and apoptosis mediated by post-translational modification (PTM). We find that O-GlcNAcase inhibition enhances B-cell activation and apoptosis induced by BCR crosslinking. This proteome-scale analysis of the functional interplay between protein O-GlcNAcylation and phosphorylation in stimulated mouse primary B cells identifies 313 O-GlcNAcylation-dependent phosphosites on 224 phosphoproteins. Among these phosphoproteins, temporal regulation of the O-GlcNAcylation and phosphorylation of lymphocyte-specific protein-1 (Lsp1) is a key switch that triggers apoptosis in activated B cells. O-GlcNAcylation at S209 of Lsp1 is a prerequisite for the recruitment of its kinase, PKC-β1, to induce S243 phosphorylation, leading to ERK activation and downregulation of BCL-2 and BCL-xL. Thus, we demonstrate the critical PTM interplay of Lsp1 that transmits signals for initiating apoptosis after BCR ligation.

B cell receptor (BCR) activation can trigger signalling causing apoptosis in order to eliminate auto-reactive B cells. Here the authors show that the O-GlcNAcylation and phosphorylation of lymphocyte-specific protein-1 are involved in a switch that regulates the initiation of apoptosis induced by BCR cross-linking.

Leukocyte-specific protein 1 links TNF receptor-associated factor 1 to survival signaling downstream of 4-1BB in T cells

4-1BB is a member of the TNFR superfamily, which contributes to the activation of signaling pathways required for the survival of activated and memory T cells. We have shown previously that TRAF1, an adaptor protein recruited to 4-1BB, is required for 4-1BB-mediated CD8 T cell survival in vivo. With the use of a proteomics approach in primary T cells, we have identified LSP1 as a novel protein recruited to the 4-1BB signaling complex in a TRAF1-dependent manner. Further characterization of the interaction between TRAF1 and LSP1 revealed that LSP1 requires the TRAF-N domain of TRAF1 for direct association. Similarly to TRAF1(-/-) T cells, LSP1(-/-) T cells exhibit impaired ERK activation following stimulation through 4-1BB and consequently, are unable to down-modulate expression of the proapoptotic Bcl-2 family member Bim. Moreover, we demonstrate that the absence of LSP1 expression leads to defective expansion and survival of T cells in response to 4-1BB stimulation. Thus, we have identified LSP1 as a new mediator involved in 4-1BB signaling and T cell survival. Collectively, our work shows that TRAF1 and LSP1 cooperate downstream of 4-1BB to activate ERK signaling and down-modulate the levels of Bim leading to enhanced T cell survival.

Pathobiology of anaplastic large cell lymphoma

The authors revise the concept of anaplastic large cell lymphoma (ALCL) in the light of the recently updated WHO classification of Tumors of Hematopoietic and Lymphoid Tissues both on biological and clinical grounds. The main histological findings are illustrated with special reference to the cytological spectrum that is indeed characteristic of the tumor. The phenotype is reported in detail: the expression of the ALK protein as well as the chromosomal abnormalities is discussed with their potential pathogenetic implications. The clinical features of ALCL are presented by underlining the difference in terms of response to therapy and survival between the ALK-positive and ALK-negative forms. Finally, the biological rationale for potential innovative targeted therapies is presented.

Genetic susceptibility loci for breast cancer by estrogen receptor status

Breast cancer is a heterogeneous disease, and risk factors could be differentially associated with the development of distinct tumor subtypes that manifest different biological behavior and progression. In support of this view, there is growing evidence that known breast cancer risk factors vary by hormone receptor status and perhaps other pathologic characteristics of disease. Recent work from large consortial studies has led to the discovery of novel breast cancer susceptibility loci in genic (CASP8, FGFR2, TNRC9, MAP3K1, LSP1) and nongenic regions (8q24, 2q35, 5p12) of the genome, and to the finding of substantial heterogeneity by tumor characteristics. In particular, susceptibility loci in FGFR2, TNRC9, 8q24, 2q35, and 5p12 have stronger associations for estrogen receptor-positive (ER+) disease than estrogen receptor-negative (ER -) disease. These findings suggest that common genetic variants can influence the pathologic subtype of breast cancer, and provide further support for the hypothesis that ER+ and ER(-) disease result from different etiologic pathways. Current studies had limited power to detect susceptibility loci for less common tumor subtypes, such as ER(-) disease including triple-negative and basal-like tumors. Ongoing work targeting uncommon subtypes is likely to identify additional tumor-specific susceptibility loci in the near future. Characterization of etiologic heterogeneity of breast cancer may lead to improvements in the understanding of the biological mechanisms for breast cancer, and ultimately result in improvements in prevention, early detection, and treatment.

Leukocyte-specific protein 1 targets the ERK/MAP kinase scaffold protein KSR and MEK1 and ERK2 to the actin cytoskeleton

The identification and characterization of scaffold and targeting proteins of the ERK/MAP kinase pathway is important to understand the function and intracellular organization of this pathway. The F-actin binding protein leukocyte-specific protein 1 (LSP1) binds to PKCβI and expression of B-LSP1, an LSP1 truncate containing the PKCβI binding residues, inhibits anti-IgM-induced translocation of PKCβI to the plasma membrane and anti-IgM-induced activation of ERK2. To understand the role of LSP1 in the regulation of PKCβI-dependent ERK2 activation, we investigated whether LSP1 interacts with ERK/MAP kinase pathway components and targets these proteins to the actin cytoskeleton. We show that LSP1 associates with the ERK scaffold protein KSR and with MEK1 and ERK2. LSP1-associated MEK1 is activated by anti-IgM treatment and this activation is inhibited by expression of B-LSP1, suggesting that the activation of LSP1-associated MEK1 is PKCβI dependent. Confocal microscopy showed that LSP1 targets KSR, MEK1 and ERK2 to peripheral actin filaments. Thus our data show that LSP1 is a cytoskeletal targeting protein for the ERK/MAP kinase pathway and support a model in which MEK1 and ERK2 are organized in a cytoskeletal signaling complex together with KSR, PKCβI and LSP1 and are activated by anti-IgM in a PKCβI-dependent manner.