Ascites sarcoma 180, a tumor associated with hypercalcemia, secretes potent bone-resorbing factors including transforming growth factor α, interleukin-1α and interleukin-6

Abstract

Ascites sarcoma 180 (S180A) is a transplantable tumor which causes hypercalcemia in tumor-bearing mice, and stimulates bone resorption without parathyroid hormone-like activity. In the present study, parathyroid hormone-related protein (PTHrP) mRNA could not be detected in total RNA from S180A cells. Bone-resorbing activity (BRA) derived from serum-free conditioned medium of S180A cells (S180A-CM) was coeluted with either transforming growth factor α (TGFα) activity (peak A, approximate M_r 29 kDa) or lymphocyte-activating factor (LAF) activity (peak B, M_r, 20.1–24 kDa) in Bio-Gel P-100 column chromatography. Fractions in peak A and B contained IL-6 but not tumor necrosis factor α (TNFα). Subsequent separation of peak A by reverse-phase high performance liquid chromatography produced a single fraction which contained both BRA and TGFα activity. Recombinant human TGFα-induced bone resorption was completely inhibited by indomethacin. The BRA in peak A was partially inhibited by indomethacin and almost completely inhibited by simultaneous treatment of indomethacin and anti-IL-6 antibody. The BRA in peak B was partially inhibited by neutralization with anti-IL-1α antibody and was completely inhibited by simultaneous treatment with anti-IL-1α and anti-IL-6 antibody in the absence of indomethacin. Bone resorption induced by S180A-CM was associated with an increased production of prostaglandin E₂ (PGE₂) by cal varia. The BRA in S180A-CM, however, was not completely abolished by the simultaneous addition of indomethacin and anti-IL-1α, anti-IL-1β and anti-IL-6 antibodies. Our findings indicate that (1) BRA derived from S180A cells includes TGFα, IL-1α, IL-6 and some other unknown factor(s), distinct from PTHrP, IL-1β and TNFα, and (2) these unknown factors resorb bone in part via a PGE₂-independent pathway.