Molecular characterization of IL-32 in human endothelial cells

IL-32 is a newly discovered protein found in human and certain primates, but absent in rodent. Various reports suggest its role as a proinflammatory mediator. Since vascular endothelium is critical in inflammation, we investigate IL-32 in endothelial cells. We found that the gene is expressed in human endothelial cells and Akt strongly induces its expression. Sequence analysis indicates IL-32β as the major isoform in endothelial cells. Surprisingly, we did not detect any secretion of IL-32β in human endothelial cells; instead we observed co-localization of IL-32β with endoplasmic reticulum, suggesting IL-32β is an intracellular protein in these cells. Promoter analysis identified a minimum required region for IL-32 transcription at −0.1 to +0.5 kb around the initially identified transcription start site. We also defined a transcriptional suppressor-binding site at −2.0 to −1.5 kb. Importantly, RNA ligase mediated rapid amplification of cDNA ends in endothelial cells determined the transcription start site at the 328 bp downstream from the original identified site. Finally, we found a positive correlation of IL-32 levels with human breast cancer and glioblastoma multiforme (GBM). These findings improve our understanding of IL-32 in vascular endothelium. IL-32 expression might be valuable as a biomarker for cancer.