CLL-162 PTX3 is Constitutively Active in CLL Cells

The pentraxin-related PTX3, commonly produced by myeloid and endothelial cells, is a humoral pattern-recognition protein of the innate immune system. Because CLL patients' PTX3 plasma levels are high and most circulating cells in patients with chronic lymphocytic leukemia (CLL) are CLL cells, we reasoned that CLL cells produce PTX3. Western immunoblotting revealed that low-density cells from 7 out of 7 CLL patients produce high levels of PTX3, flow cytometry analysis revealed that the PTX3-producing cells are B lymphocytes co-expressing CD19 and CD5, and confocal microscopy demonstrated that PTX3 co-localized with STAT3. Because signal transducer and activator of transcription (STAT)-3 is constitutively activated in CLL cells and we identified putative STAT3 binding sites within the PTX3 gene promoter, we postulated that phosphorylated STAT3 triggers transcriptional activation of PTX3. Immunoprecipitation analysis of CLL cells' chromatin fragments showed that STAT3 antibodies precipitated PTX3 DNA. STAT3 knockdown induced a marked reduction in PTX3 expression, indicating a STAT3-induced transcriptional activation of the PTX3 gene in CLL cells. Using an electromobility shift assay that we established and a dual-reporter luciferase assay, we confirmed that STAT3 binds the PTX3 gene promoter. Downregulation of PTX3 induced apoptotic disassembly of CLL cells, suggesting that inhibition of PTX3 might benefit patients with CLL.