Two squamous cell carcinomas not associated with humoral hypercalcemia produce a potent bone resorption-stimulating factor which is interleukin-1 alpha.

Conditioned medium (CM) from two squamous cell carcinoma cell lines, SCC-9 and SCC-13, stimulated bone resorption in neonatal mouse calvariae in organ culture. Enhanced bone resorption induced by CM was associated with an increased production of prostaglandin-E2 (PGE2) by the calvariae. Complete inhibition of stimulated PGE2 synthesis by indomethacin only partially inhibited bone resorption-stimulating activity (BRSA) in the CM. Neither SCC-9 nor SCC-13 CM stimulated cAMP production in rat osteosarcoma cells (ROS 17/2.8). The BRSA in CM was completely inhibited by an antibody to interleukin-1 alpha (IL-1 alpha). Fractionation of SCC-9 CM by gel filtration and HPLC ion exchange chromatography revealed a single peak of BRSA and PGE2 synthesis-stimulating activity at 17-20K (termed SCMII). In mouse calvariae, SCMII increased medium Ca2+ and PGE2 in a dose-dependent manner at concentrations from 20 ng protein/ml to a maximum of 500 ng protein/ml. Preincubation of SCMII with antibody to IL-1 alpha completely inhibited SCMII-induced bone resorption. SCMII also enhanced thymocyte proliferation with activity that was equivalent to 353 U/ml IL-1. Antibodies to IL-1 beta and tumor necrosis factor had no effect on SCMII-induced bone resorption. Using specific enzyme-linked immunosorbent assays for IL-1 alpha and IL-1 beta, IL-1 alpha was measured in high concentrations in both crude and partially purified fractions of SCC-9 and SCC-13 CM. In contrast, IL-1 beta was either undetectable or present in amounts below those that stimulate bone resorption. In addition, SCMII did not enhance cAMP production in bone cells. We conclude that the BRSA produced by the two squamous cell carcinoma cell lines SCC-9 and SCC-13 is IL-1 alpha.