Human mesothelioma cells produce factors that stimulate the production of hyaluronan by mesothelial cells and fibroblasts.

The hyaluronan production by three human malignant mesothelioma cell lines and nine primary human mesothelial cell types was determined. The mesothelioma cell lines produced only minute amounts of hyaluronan (less than 0.1 microgram/10(6) cells/48 h) whereas mesothelial cells synthesized large quantities of hyaluronan (10-72 micrograms/10(6) cells/48 h). Conditioned media from the mesothelioma cell lines were investigated for their ability to stimulate hyaluronan production by fibroblasts and mesothelial cells in vitro, and in all cases stimulatory effects were found. The factor(s) in the conditioned medium of the mesothelioma cell line Mero-25 that were responsible for hyaluronan stimulation were heat stable and partially trypsin resistant. The stimulatory activity was partially inhibited by an antiserum against platelet-derived growth factor and basic fibroblast growth factor. Our data suggest that the increased hyaluronan synthesis seen in patients with mesothelioma is due to the release of factors from mesothelioma cells that stimulate other cells to produce hyaluronan.