Abstract
The rat Walker 256 carcinoma is an animal model for humoral hypercalcemia of malignancy. This tumor produces and secretes parathyroid hormone (PTH)-related protein (PTHrP), a likely mediator for this syndrome. In this study. we investigated the effect of PTHrP on Walker 256 tumor cell proliferation. We found that [Tyr 36]human (h)PTHrP (1-36)NH 2 and hPTHrP (1-86). unlike hPTHrP (38-64)NH 2, stimulate DNA synthesis dose-dependently in these cells. A similar mitogenic effect was also observed with bovine (b)PTH (1-34) or (Nle 8,18,Tyr 34)bPTH (3-34)NH 2. Moreover, addition of anti-hPTHrP (1-34) neutralizing antibodies decreased tumor cell growth. Conversely. 10 −4M dihutyryl cAMP or Sp-cDBIMPS (a cAMP analogue) inhibited DNA synthesis in these cells, being incompetent at lower doses. PTHrP or PTH failed to stimulate cAMP production, hut they induced a cytosolic calcium transient increase in these cells. These findings support an autocrine role of PTHrP in the regulation of this tumor growth.
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