Several cultured human squamous cell carcinoma cell lines (SCC-4, SCC-12B2, SCC-12F2, EC-GI-10, and BEN) and one normal keratinocyte line (Epy-1) were investigated for the production of bone resorption-stimulating activity (BRSA). Conditioned medium (CM) from each of the six cell lines stimulated bone resorption in neonatal mouse calvariae in culture. The BRSA of SCC-12F2 and EC-GI-10 was inhibited completely by antibody to interleukin-la (IL-1α), whereas the BRSA in CM from the BEN, SCC-4, SCC-12B2, and Epy-1 cell lines was only partially inhibited by anti-IL-la. Addition of indomethacin to the calvarial cultures also partially inhibited the BRSA from EC-GI-10, SCC-4, SCC-12B2, and Epy-1 cells; the BRSA from BEN and SCC-12F2 cells was inhibited completely by indomethacin. cAMP production by calvariae was determined after a 60-min incubation with CM. CM from ECGI- 10, BEN, SCC-4, and Epy-1 stimulated cAMP production by bone. Preincubation of CM from BEN, EC-GI-10, SCC-4, and Epy-1 cells with two antisera against PTH-related protein [PTHrP; one specific for two PTHrP-(l-141), the other recognizing both PTHrP-(l-40) and PTHrP-(l-141)] completely inhibited the cAMP-stimulating activity. Using specific enzymelinked immunosorbent assays for IL-la and IL-1β, IL-1α was measured in CM of the SCC-4, SCC-12B2, SCC-12F2, and Epy- 1 cell lines. IL-1β was undetectable (<0.1 ng/ml) in CM from all cell lines. Our findings indicate that the BRSA secreted by SCC- 12F2 cells can be accounted for largely or entirely by IL-1α, while the activity produced by SCC-12B2 includes IL-1α and another unknown factor(s). The BRSA produced by EC-GI-10, BEN, SCC-4, and Epy-1 cells includes both IL-1α and PTHrP. We conclude that IL-1α may be a more prevalent and biologically significant component of the BRSA produced by SCCs than previously recognized.
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