SOX11 is a novel binding partner and endogenous inhibitor of SAMHD1 ara-CTPase activity in mantle cell lymphoma.

The sterile alpha motif and histidine-aspartate (HD) domain containing protein 1 (SAMHD1) is a deoxynucleoside triphosphate triphosphohydrolase with ara-CTPase activity that confers cytarabine (ara-C) resistance in several haematological malignancies. Targeting SAMHD1's ara-CTPase activity has recently been demonstrated to enhance ara-C efficacy in acute myeloid leukemia. Here, we identify the transcription factor SRY-related HMG-box containing protein 11 (SOX11) as a novel direct binding partner and first known endogenous inhibitor of SAMHD1. SOX11 is aberrantly expressed not only in mantle cell lymphoma (MCL), but also in some Burkitt lymphomas. Co-immunoprecipitation of SOX11 followed by mass spectrometry in MCL cell lines identified SAMHD1 as the top SOX11 interaction partner which was validated by proximity ligation assay. In vitro, SAMHD1 bound to the HMG box of SOX11 with low-micromolar affinity. In situ crosslinking studies further indicated that SOX11-SAMHD1 binding resulted in a reduced tetramerization of SAMHD1. Functionally, expression of SOX11 inhibited SAMHD1 ara-CTPase activity in a dose-dependent manner resulting in ara-C sensitization in cell lines and in a SOX11-inducible mouse model of MCL. In SOX11-negative MCL, SOX11-mediated ara-CTPase inhibition could be mimicked by adding the recently identified SAMHD1 inhibitor hydroxyurea. Taken together, our results identify SOX11 as a novel SAMHD1 interaction partner and its first known endogenous inhibitor with potentially important implications for clinical therapy stratification.

SOX11 expression is restricted to EBV-negative Burkitt lymphoma and associates with molecular genetic features.

SRY-related HMG-box gene 11 (SOX11) is a transcription factor overexpressed in mantle cell lymphoma (MCL), a subset of Burkitt lymphomas (BL) and precursor lymphoid cell neoplasms but is absent in normal B-cells and other B-cell lymphomas. SOX11 has an oncogenic role in MCL but its contribution to BL pathogenesis remains uncertain. Here, we observed that the presence of Epstein-Barr virus (EBV) and SOX11 expression were mutually exclusive in BL. SOX11 expression in EBV- BL was associated with an IG∷MYC translocation generated by aberrant class switch recombination, while in EBV-/SOX11- tumors the IG∷MYC translocation was mediated by mistaken somatic hypermutations. Interestingly, EBV- SOX11 expressing BL showed higher frequency of SMARCA4 and ID3 mutations compared to EBV-/SOX11- cases. By RNA-sequencing, we identified a SOX11-associated gene expression profile, with functional annotations showing partial overlap with the SOX11 transcriptional program of MCL. Contrary to MCL, no differences on cell migration or BCR signaling were found between SOX11- and SOX11+ BL cells. However, SOX11+ BL showed higher adhesion to VCAM-1 than SOX11- BL cell lines. Here we demonstrate that EBV- BL comprises two subsets of cases based on SOX11 expression. The mutual exclusion of SOX11 and EBV, and the association of SOX11 with a specific genetic landscape suggest a role of SOX11 in the early pathogenesis of BL.

SOX11/PRDX2 axis modulates redox homeostasis and chemoresistance in aggressive mantle cell lymphoma.

Mantle cell lymphoma (MCL) is an incurable B-cell neoplasm characterized by an aggressive behavior, short responses to conventional therapies and SOX11 overexpression, which is associated with aggressive disease features and inferior clinical outcome of patients. Oxidative stress is known to induce tumorigenesis and tumor progression, whereas high expression levels of antioxidant genes have been associated with chemoresistance in different cancers. However, the role of oxidative stress in MCL pathogenesis and the involvement of SOX11 regulating redox homeostasis in MCL cells are largely unknown. Here, by integrating gene set enrichment analysis of two independent series of MCL, we observed that SOX11+ MCL had higher reactive oxygen species (ROS) levels compared to SOX11- MCL primary tumors and increased expression of Peredoxine2 (PRDX2), which upregulation significantly correlated with SOX11 overexpression, higher ROS production and worse overall survival of patients. SOX11 knockout (SOX11KO) significantly reduced PRDX2 expression, and SOX11KO and PRDX2 knockdown (PRDX2KD) had increased ROS levels and ROS-mediated tumor cell death upon treatment with drugs, compared to control MCL cell lines. Our results suggest an aberrant redox homeostasis associated with chemoresistance in aggressive MCL through SOX11-mediated PRDX2 upregulation, highlighting PRDX2 as promising target for new therapeutic strategies to overcome chemoresistance in aggressive MCLs.

SOX11 is a novel binding partner and endogenous inhibitor of SAMHD1 ara-CTPase activity in mantle cell lymphoma.

ABSTRACT: Sterile alpha motif and histidine-aspartate (HD) domain-containing protein 1 (SAMHD1) is a deoxynucleoside triphosphate triphosphohydrolase with ara-CTPase activity that confers cytarabine (ara-C) resistance in several hematological malignancies. Targeting SAMHD1's ara-CTPase activity has recently been demonstrated to enhance ara-C efficacy in acute myeloid leukemia. Here, we identify the transcription factor SRY-related HMG-box containing protein 11 (SOX11) as a novel direct binding partner and first known endogenous inhibitor of SAMHD1. SOX11 is aberrantly expressed not only in mantle cell lymphoma (MCL), but also in some Burkitt lymphomas. Coimmunoprecipitation of SOX11 followed by mass spectrometry in MCL cell lines identified SAMHD1 as the top SOX11 interaction partner, which was validated by proximity ligation assay. In vitro, SAMHD1 bound to the HMG box of SOX11 with low-micromolar affinity. In situ crosslinking studies further indicated that SOX11-SAMHD1 binding resulted in a reduced tetramerization of SAMHD1. Functionally, expression of SOX11 inhibited SAMHD1 ara-CTPase activity in a dose-dependent manner resulting in ara-C sensitization in cell lines and in a SOX11-inducible mouse model of MCL. In SOX11-negative MCL, SOX11-mediated ara-CTPase inhibition could be mimicked by adding the recently identified SAMHD1 inhibitor hydroxyurea. Taken together, our results identify SOX11 as a novel SAMHD1 interaction partner and its first known endogenous inhibitor with potentially important implications for clinical therapy stratification.

Tumorigenic role of Musashi-2 in aggressive mantle cell lymphoma.

SOX11 overexpression has been associated with aggressive behavior of mantle cell lymphomas (MCL). SOX11 is overexpressed in embryonic and cancer stem cells (CSC) of some tumors. Although CSC have been isolated from primary MCL, their relationship to SOX11 expression and contribution to MCL pathogenesis and clinical evolution remain unknown. Here, we observed enrichment in leukemic and hematopoietic stem cells gene signatures in SOX11+ compared to SOX11- MCL primary cases. Musashi-2 (MSI2) emerged as one of the most significant upregulated stem cell-related genes in SOX11+ MCLs. SOX11 is directly bound to the MSI2 promoter upregulating its expression in vitro. MSI2 intronic enhancers were strongly activated in SOX11+ MCL cell lines and primary cases. MSI2 upregulation was significantly associated with poor overall survival independently of other high-risk features of MCL. MSI2 knockdown decreased the expression of genes related to apoptosis and stem cell features and significantly reduced clonogenic growth, tumor cell survival and chemoresistance in MCL cells. MSI2-knockdown cells had reduced tumorigenic engraftment into mice bone marrow and spleen compared to control cells in xenotransplanted mouse models. Our results suggest that MSI2 might play a key role in sustaining stemness and tumor cell survival, representing a possible novel target for therapeutic interventions in MCL.

Structural Basis for the SUMO2 Isoform Specificity of SENP7.

SUMO proteases or deSUMOylases regulate the lifetime of SUMO-conjugated targets in the cell by cleaving off the isopetidic bond between the substrate and the SUMO modifier, thus reversing the conjugation activity of the SUMO E3 ligases. In humans the deSUMOylating activity is mainly conducted by the SENP/ULP protease family, which is constituted of six members sharing a homologous catalytic globular domain. SENP6 and SENP7 are the most divergent members of the family and they show a unique SUMO2/3 isoform preference and a particular activity for dismantling polySUMO2 chains. Here, we present the crystal structure of the catalytic domain of human SENP7 bound to SUMO2, revealing structural key elements for the SUMO2 isoform specificity of SENP7. In particular, we describe the specific contacts between SUMO2 and a unique insertion in SENP7 (named Loop1) that is responsible for the SUMO2 isoform specificity. All the other interface contacts between SENP7 and SUMO2, including the SUMO2 C-terminal tail interaction, are conserved among members of the SENP/ULP family. Our data give insight into an evolutionary adaptation to restrict the deSUMOylating activity in SENP6 and SENP7 for the SUMO2/3 isoforms.

Expression of obesity- and type-2 diabetes-associated genes in omental adipose tissue of individuals with obesity.

AIMS: Obesity and type 2 diabetes mellitus are two pathologies that share metabolic abnormalities in most of the cases; however, there are differences as well. Some studies have reported that approximately 30% of obese patients have normal glucose and lipid levels in blood despite an accumulation of abdominal adipose tissue. Here, we compare the gene expression in adipose tissue of several genes associated with obesity and/or diabetes between obese patients without T2D and obese patients with T2D. METHODS: Omental adipose tissue was collected during the patients elective bariatric surgery. Gene expression was determined by real-time PCR. Phenotypic variables were correlated with gene expression and 2^-ΔΔCt relative expression analysis between groups was performed. RESULTS: The stronger correlations in the obese without T2D or reference group was between ICAM1 and HbA1c; HP and TC and LDL while in the obese with diabetes or case group the correlation occurred between CSF1 and BMI. A correlation between HP and TC was found in the case group as well. The expression of VEGFA, CCND2, IL1R1 and PTEN was downregulated in the obese with T2D group. CONCLUSIONS: This study identified genes whose expression is different between obese subjects with and without diabetes. Those genes are related to inflammation, cholesterol transport, adipocyte differentiation/expansion and browning.

SOX11, CD70, and Treg cells configure the tumor-immune microenvironment of aggressive mantle cell lymphoma.

Mantle cell lymphoma (MCL) is a mature B-cell neoplasm with a heterogeneous clinical and biological behavior. SOX11 oncogenic expression contributes to the aggressiveness of these tumors by different mechanisms, including tumor and stromal cell interactions. However, the precise composition of the immune cell microenvironment of MCL, its possible relationship to SOX11 expression, and how it may contribute to tumor behavior is not well known. Here, we performed an integrative transcriptome analysis of 730 immune-related genes combined with the immune cell phenotype analysis by immunohistochemistry in SOX11+ and SOX11- primary nodal MCL cases and non-neoplastic reactive lymph nodes. SOX11+ MCL had a significant lower T-cell intratumoral infiltration compared with negative cases. A reduced expression of MHCI/II-like and T-cell costimulation and signaling activation related transcripts was significantly associated with poor clinical outcome. Moreover, we identified CD70 as a SOX11 direct target gene, whose overexpression was induced in SOX11+, but not SOX11- tumor cells by CD40L in vitro. CD70 was overexpressed in primary SOX11+ MCL and it was associated with an immune unbalance of the tumor microenvironment characterized by increased number of effector regulatory t (Treg) cell infiltration, higher proliferation, and aggressive clinical course. CD27 was expressed with moderate to strong intensity in 76% of cases. Overall, our results suggest that SOX11 expression in MCL is associated with an immunosuppressive microenvironment characterized by CD70 overexpression in tumor cells, increased Treg cell infiltration and downmodulation of antigen processing, and presentation and T-cell activation that could promote MCL progression and represent a potential target for tailored therapies.

Impaired ribosome biogenesis checkpoint activation induces p53-dependent MCL-1 degradation and MYC-driven lymphoma death.

MYC-driven B-cell lymphomas are addicted to increased levels of ribosome biogenesis (RiBi), offering the potential for therapeutic intervention. However, it is unclear whether inhibition of RiBi suppresses lymphomagenesis by decreasing translational capacity and/or by p53 activation mediated by the impaired RiBi checkpoint (IRBC). Here we generated Eµ-Myc lymphoma cells expressing inducible short hairpin RNAs to either ribosomal protein L7a (RPL7a) or RPL11, the latter an essential component of the IRBC. The loss of either protein reduced RiBi, protein synthesis, and cell proliferation to similar extents. However, only RPL7a depletion induced p53-mediated apoptosis through the selective proteasomal degradation of antiapoptotic MCL-1, indicating the critical role of the IRBC in this mechanism. Strikingly, low concentrations of the US Food and Drug Administration-approved anticancer RNA polymerase I inhibitor Actinomycin D (ActD) dramatically prolonged the survival of mice harboring Trp53+/+;Eµ-Myc but not Trp53-/-;Eµ-Myc lymphomas, which provides a rationale for treating MYC-driven B-cell lymphomas with ActD. Importantly, the molecular effects of ActD on Eµ-Myc cells were recapitulated in human B-cell lymphoma cell lines, highlighting the potential for ActD as a therapeutic avenue for p53 wild-type lymphoma.

Increased tumour angiogenesis in SOX11-positive mantle cell lymphoma.

AIMS: Mantle cell lymphoma (MCL) is a heterogeneous disease with an aggressive behaviour in most cases, which is associated with expression of sex determining region-Y-box11 (SOX11). Experimental studies have shown that SOX11 expression is associated with an angiogenic switch characterised by increased expression of angiogenic-related signatures and vascularisation of murine tumours. However, the relationship between angiogenesis and SOX11 expression in primary tumours is not well understood. Therefore, the aim of this study was to evaluate the development of microvascular angiogenesis in primary MCL in relation to SOX11 expression and its potential prognostic value. METHODS AND RESULTS: Fifty-six patients diagnosed with MCL, 38 SOX11-positive and 18 SOX11-negative, were studied. The relative intratumoral microvascular area (MVA) and microvessel density (MVD) (number of intratumoral microvessels/µm2 ) were measured on CD34-stained slides using a computerised image analysis system. SOX11-positive MCL showed a significant higher microvascular development than negative tumours (median MVA = 14.5 × 10-3 versus 5.0 × 10-3 P < 0.001; median MVD = 18.6/µm2 versus 14.2/µm2 , P = 0.021). Analysing the MVA and MVD as continuous variables, a high MVD was associated with shorter overall survival (P = 0.004), and a similar tendency was observed for high MVA (P = 0.064). The microvascular development was not related to the Ki-67 proliferative index or 17p/TP53, 9p or 11q alterations. CONCLUSIONS: These findings suggest that SOX11 promotes an angiogenic phenotype in primary MCL, which may contribute to the more aggressive behaviour of these tumours.

Selective BTK inhibition improves bendamustine therapy response and normalizes immune effector functions in chronic lymphocytic leukemia.

The Bruton's tyrosine kinase (BTK) inhibitor ibrutinib has been shown to be highly effective in patients with chronic lymphocytic leukemia (CLL) and is approved for CLL treatment. Unfortunately, resistance and intolerance to ibrutinib has been observed in several studies, opening the door for more specific BTK inhibitors. CC-292 (spebrutinib) is a BTK inhibitor with increased specificity for BTK and less inhibition of other kinases. Our in vitro studies showed that CC-292 potently inhibited B-cell receptor signaling, activation, proliferation and chemotaxis of CLL cells. In in vivo studies using the adoptive transfer TCL1 mouse model of CLL, CC-292 reduced tumor load and normalized tumor-associated expansion of T cells and monocytes, while not affecting T cell function. Importantly, the combination of CC-292 and bendamustine impaired CLL cell proliferation in vivo and enhanced the control of CLL progression. Our results demonstrate that CC-292 is a specific BTK inhibitor with promising performance in combination with bendamustine in CLL. Further clinical trials are warranted to investigate the therapeutic efficacy of this combination regimen.

A quaternary tetramer assembly inhibits the deubiquitinating activity of USP25.

USP25 deubiquitinating enzyme is a key member of the ubiquitin system, which acts as a positive regulator of the Wnt/ß-catenin signaling by promoting the deubiquitination and stabilization of tankyrases. USP25 is characterized by the presence of a long insertion in the middle of the conserved catalytic domain. The crystal structure of USP25 displays an unexpected homotetrameric quaternary assembly that is directly involved in the inhibition of its enzymatic activity. The tetramer is assembled by the association of two dimers and includes contacts between the coiled-coil insertion domain and the ubiquitin-binding pocket at the catalytic domain, revealing a distinctive autoinhibitory mechanism. Biochemical and kinetic assays with dimer, tetramer and truncation constructs of USP25 support this mechanism, displaying higher catalytic activity in the dimer assembly. Moreover, the high stabilization of tankyrases in cultured cells by ectopic expression of a constitutive dimer of USP25 supports a biological relevance of this tetramerization/inhibition mechanism.

SOX11, a key oncogenic factor in mantle cell lymphoma.

PURPOSE OF REVIEW: SOX11 has emerged as a key transcription factor in the pathogenesis of mantle cell lymphoma (MCL) whereas it is not expressed in normal B cells or virtually in any other mature B-cell neoplasm. This review will examine the role of SOX11 as a biomarker in MCL, the new information on its transcriptional targets, and the mechanisms regulating its expression in MCL. RECENT FINDINGS: SOX11 is highly expressed in conventional MCL, including cyclin D1-negative cases, but it is not expressed in the indolent leukemic nonnodal MCL subtype. These two MCL subtypes also differ in their cell-of-origin, IGHV mutational status and genomic instability. SOX11 promotes tumor growth of MCL cells in vivo and regulates a broad transcriptional program that includes B-cell differentiation pathways and tumor-microenvironment interactions, among others. The mechanisms upregulating SOX11 in MCL are not well understood but are mediated in part by the three-dimensional reconfiguration of the DNA, bringing together a distant enhancer region and the SOX11 promoter. SUMMARY: SOX11 is a relevant element in the pathogenesis of MCL and has been instrumental to identify two distinct clinicobiological subtypes of this tumor. Further studies should clarify the mechanisms mediating its oncogenic potential and leading to its intriguing expression in these tumors.

Role of SOX11 and Genetic Events Cooperating with Cyclin D1 in Mantle Cell Lymphoma.

Mantle cell lymphoma (MCL) is an aggressive lymphoid neoplasm, incurable with current therapies. The t(11;14)(q13;q32) involving cyclin D1 is considered the first oncogenic hit found in virtually all MCLs. However, additional secondary genomic alterations are essential for complete transformation. MCLs are genetically very unstable with several genetic alterations associated with its high proliferative behavior involving several oncogenic pathways. Furthermore, SOX11 is overexpressed in the majority of conventional MCLs (cMCL), including cyclin D1-negative cases, but absent in non-nodal leukemic MCL with indolent clinical behavior (nnMCL). Recent data have revealed the potential oncogenic role of SOX11 in MCL biology, highlighting its implication in tumor aggressiveness and progression. This review addresses the implication of SOX11 overexpression and frequent genetic lesions, cooperating with cyclin D1 underlying the pathogenesis of this aggressive disease.

SOX11 promotes tumor protective microenvironment interactions through CXCR4 and FAK regulation in mantle cell lymphoma.

SOX11 overexpression in mantle cell lymphoma (MCL) has been associated with more aggressive behavior and worse outcome. However, SOX11 oncogenic pathways driving MCL tumor progression are poorly understood. Here, we demonstrate that SOX11 binds to regulatory regions of 2 important genes for microenvironment signals in cancer: (C-X-C motif) chemokine receptor 4 (CXCR4) and PTK2 (encoding for focal adhesion kinase [FAK]). Moreover, SOX11+ xenograft and human primary MCL tumors overexpress cell migration and stromal stimulation gene signatures compared with their SOX11- counterparts. We show that SOX11 directly upregulates CXCR4 and FAK expression, activating PI3K/AKT and ERK1/2 FAK-downstream pathways in MCL. Concordantly, SOX11+ MCL cells have higher cell migration, transmigration through endothelial cells, adhesion to stromal cells, and cell proliferation and display an increased resistance to conventional drug therapies compared with SOX11- MCL cells. Specific FAK inhibition blocks downstream PI3K/AKT- and ERK1/2-mediated phosphorylation. Additionally, specific FAK and PI3K inhibitors reduce SOX11-enhanced MCL cell migration and stromal interactions and revert cell adhesion-mediated drug resistance (CAM-DR) to the same levels as SOX11- MCL cells. In intravenous MCL xenograft models, SOX11+ MCL cells display higher cell migration, invasion, and growth compared with SOX11-knockdown cells, and specific FAK and CXCR4 inhibitors impair SOX11-enhanced MCL engraftment in bone marrow. Overall, our results suggest that SOX11 promotes MCL homing and invasion and increases CAM-DR through the direct regulation of CXCR4 and FAK expression and FAK/PI3K/AKT pathway activation, contributing to a more aggressive phenotype. Inhibition of this pathway may represent an efficient strategy to overcome stromal-mediated chemotherapy refractoriness in aggressive MCL.

Plasma cell and terminal B-cell differentiation in mantle cell lymphoma mainly occur in the SOX11-negative subtype.

Mantle cell lymphoma is a mature lymphoid neoplasm characterized by the t(11;14)(q13;q32) and cyclin D1 overexpression. SOX11 is a transcription factor commonly overexpressed in these tumors but absent in most other mature B-cell lymphomas whose function is not well understood. Experimental studies have shown that silencing of SOX11 in mantle cell lymphoma cells promotes the shift from a mature B cell into an early plasmacytic differentiation phenotype, suggesting that SOX11 may contribute to tumor development by blocking the B-cell differentiation program. The relationship between SOX11 expression and terminal B-cell differentiation in primary mantle cell lymphoma and its relationship to the plasmacytic differentiation observed in occasional cases is not known. In this study we have investigated the terminal B-cell differentiation phenotype in 60 mantle cell lymphomas, 41 SOX11-positive and 19 SOX11-negative. Monotypic plasma cells and lymphoid cells with plasmacytic differentiation expressing cyclin D1 were observed in 7 (37%) SOX11-negative but in none of 41 SOX11-positive mantle cell lymphomas (P<0.001). Intense cytoplasmic expression of a restricted immunoglobulin light chain was significantly more frequent in SOX11-negative than -positive tumors (58 vs 13%) (P=0.001). Similarly, BLIMP1 and XBP1 expression was also significantly more frequent in SOX11-negative than in -positive cases (83 vs 34% and 75 vs 11%, respectively) (P=0.001). However, no differences in the expression of IRF4/MUM1 were observed among these subtypes of mantle cell lymphoma. In conclusion, these results indicate that SOX11-negative mantle cell lymphoma may be a particular subtype of this tumor characterized by more frequent morphological and immunophenotypic terminal B-cell differentiation features that may be facilitated by the absence of SOX11 transcription factor.

Update on the molecular pathogenesis and targeted approaches of mantle cell lymphoma: summary of the 12th annual conference of the European Mantle Cell Lymphoma Network.

Mantle cell lymphoma (MCL) is a distinct subtype of malignant lymphoma which is characterized by the chromosomal translocation t(11;14)(q13;q32) resulting in constitutional overexpression of cyclin D1 and cell cycle dysregulation in almost all cases. Clinically, MCL shows an aggressive clinical course with a continuous relapse pattern and a median survival of only 3-5 years. However, recently a subset of 15% long-term survivors has been identified with a rather indolent clinical course. Targeted strategies include the proteasome inhibitors, immune modulatory drugs (IMiDs), mammalian target of rapamycin (mTOR) inhibitors and especially inhibitors of the B-cell receptor pathway. Our recent annual conference focused on the molecular pathogenesis of the disease and how these underlying molecular alterations may guide the selection and integration of innovative approaches for therapy. This review of the meeting covers in particular the identification of indolent cases, and deals with the role of the B-cell receptor pathway in MCL, as well as the detection of minimal residual disease and implementation of molecular approaches in current clinical trials.

SOX11 promotes tumor angiogenesis through transcriptional regulation of PDGFA in mantle cell lymphoma.

SOX11 is overexpressed in several solid tumors and in the vast majority of aggressive mantle cell lymphomas (MCLs). We have recently proven that SOX11 silencing reduces tumor growth in a MCL xenograft model, consistent with the indolent clinical course of the human SOX11-negative mantle cell lymphoma (MCL). However, the direct oncogenic mechanisms and downstream effector pathways implicated in SOX11-driven transformation remain poorly understood. Here, we observed that SOX11-positive xenograft and human primary MCL tumors overexpressed angiogenic gene signatures and had a higher microvascular density compared with their SOX11-negative counterparts. Conditioned media of SOX11-positive MCL cell lines induced in vitro endothelial cell proliferation, migration, tube formation, and activation of downstream angiogenic pathways. We identified PDGFA as a SOX11 direct target gene upregulated in MCL cells whose inhibition impaired SOX11-enhanced in vitro angiogenic effects on endothelial cells. In addition, platelet-derived growth factor A (PDGFA) was overexpressed in SOX11-positive but not in SOX11-negative MCL. In vivo, imatinib impaired tumor angiogenesis and lymphoma growth in SOX11-positive MCL xenograft tumors. Overall, our results demonstrate a prominent role for SOX11 as a driver of proangiogenic signals in MCL, and highlight the SOX11-PDGFA axis as a potential therapeutic target for the treatment of this aggressive disease.

Assessment of SOX11 expression in routine lymphoma tissue sections: characterization of new monoclonal antibodies for diagnosis of mantle cell lymphoma.

The diagnosis of mantle cell lymphoma (MCL) can be difficult, especially when no t(11;14) translocation and cyclin D1 overexpression can be detected. In such cases, the transcription factor SOX11 represents an important diagnostic marker, as it is expressed in most MCLs and, in particular, in all cyclin D1-negative MCLs reported so far. A reliable anti-SOX11 antibody is therefore a very useful tool for routine diagnosis. Here, we characterize the new monoclonal anti-SOX11 antibodies, suitable for Western blot assay and immunohistochemistry (IHC) on formalin-fixed paraffin-embedded tissue; we tested them on a large series of primary lymphoid tumors and compared these results with those of other routinely used antibodies. Moreover, we show that IHC results depend on transcription levels of SOX11, which suggests that posttranscriptional and posttranslational modifications do not significantly affect cutoff levels for IHC detection of SOX11.