SOX11 and HIG-2 are cross-regulated and affect growth in mantle cell lymphoma.

The transcriptional factor SOX11 is a disease-defining antigen in mantle cell lymphoma (MCL) and absent in most non-malignant tissues. To explore the role of SOX11-related cell signaling, and potentially take benefit from these for targeted therapy, associated networks and proteins need to be defined. In this study, we used an inducible SOX11 knock-down system followed by gene expression analysis to identify co-regulated genes and associated signaling pathways. A limited number (n = 27) of significantly co-regulated genes were identified, including SETMAR, HIG-2, and CD24. Further analysis confirmed co-regulation of SOX11 with HIG-2 and CD24 at the protein level. Of major interest, knock-down of HIG-2 reduced SOX11 levels and increased proliferation, the proteins are thus cross-regulated. HIG-2 was localized at the plasma cell membrane in both cell lines and primary MCL cells, and could potentially be of interest for targeted therapy.

DNA methylation and histone modifications regulate SOX11 expression in lymphoid and solid cancer cells.

BACKGROUND: The neural transcription factor SOX11 is present at specific stages during embryo development with a very restricted expression in adult tissue, indicating precise regulation of transcription. SOX11 is strongly up-regulated in some malignancies and have a functional role in tumorgenesis. With the aim to explore differences in epigenetic regulation of SOX11 expression in normal versus neoplastic cells, we investigated methylation and histone modifications related to the SOX11 promoter and the possibility to induce re-expression using histone deacetylase (HDAC) or EZH2 inhibitors. METHODS: The epigenetic regulation of SOX11 was investigated in distinct non-malignant cell populations (n = 7) and neoplastic cell-lines (n = 42) of different cellular origins. DNA methylation was assessed using bisulfite sequencing, methylation-specific melting curve analysis, MethyLight and pyrosequencing. The presence of H3K27me3 was assessed using ChIP-qPCR. The HDAC inhibitors Vorinostat and trichostatin A were used to induce SOX11 in cell lines with no endogenous expression. RESULTS: The SOX11 promoter shows a low degree of methylation and strong enrichment of H3K27me3 in non-malignant differentiated cells, independent of cellular origin. Cancers of the B-cell lineage are strongly marked by de novo methylation at the SOX11 promoter in SOX11 non-expressing cells, while solid cancer entities display a more varying degree of SOX11 promoter methylation. The silencing mark H3K27me3 was generally present at the SOX11 promoter in non-expressing cells, and an increased enrichment was observed in cancer cells with a low degree of SOX11 methylation compared to cells with dense methylation. Finally, we demonstrate that the HDAC inhibitors (vorinostat and trichostatin A) induce SOX11 expression in cancer cells with low levels of SOX11 methylation. CONCLUSIONS: We show that SOX11 is strongly marked by repressive histone marks in non-malignant cells. In contrast, SOX11 regulation in neoplastic tissues is more complex involving both DNA methylation and histone modifications. The possibility to re-express SOX11 in non-methylated tissue is of clinical relevance, and was successfully achieved in cell lines with low levels of SOX11 methylation. In breast cancer patients, methylation of the SOX11 promoter was shown to correlate with estrogen receptor status, suggesting that SOX11 may be functionally re-expressed during treatment with HDAC inhibitors in specific patient subgroups.

Knock-down of SOX11 induces autotaxin-dependent increase in proliferation in vitro and more aggressive tumors in vivo.

The transcription factor SOX11 is a novel diagnostic marker for mantle cell lymphoma (MCL), distinguishing this aggressive tumor from potential simulators. Recent data also show that the level of SOX11 correlates to in vitro growth properties in MCL, as well as the clinical progression. We have previously shown that MCL-associated pathways, such as Rb-E2F, are dysregulated leading to decreased proliferation upon overexpression of SOX11, emphasizing the impact of SOX11 on MCL-specific gene expression and growth control. However, it remains to be determined which growth regulatory pathways that are induced upon SOX11 knock-down, leading to an increased cellular growth. Consequently, we established a model cell line with constitutive down-regulation of SOX11. The highly proliferative features of this cell line were investigated by gene expression analysis, proliferation assay, cell cycle distribution and potential to induce tumors in NOD-SCID mice. Our in vitro studies demonstrated a SOX11-dependent regulation of MCL-specific gene expression. In addition, we identified autotaxin (ATX) to be regulated by SOX11. Our results clearly showed a correlation between SOX11 level and cellular growth rate, which was dependent on ATX, as well as a direct relation between the level of SOX11 in tumorigenic cells and the growth rate of these tumors in NOD-SCID mice.