Enhancing Effect of Interleukin‐2 on Production of Parathyroid Hormone‐related Protein by Adult T‐Cell Leukemia Cells

Leukemic cells from patients with adult T‐cell leukemia (ATL) can produce a calcium‐regulating protein, parathyroid hormone‐related protein (PTHrP). Moreover, it has been reported that ATL cells produce some cytokines besides PTHrP and that these cells respond to the T‐cell growth factors, interleukin‐2 (IL‐2) and interIenkin‐4 (IL‐4). To elucidate whether PTHrP produced by ATL cells is regulated by IL‐2 or IL‐4, we investigated the in vitro effects of IL‐2 and IL‐4 on the release of PTHrP. IL‐2 increased the release of PTHrP into the conditioned medium from leukemic cells in some, but not all, ATL patients; however, IL‐4 did not affect the PTHrP release. PTHrP messenger RNA (mRNA) levels were increased in ATL cells cultured in the presence of IL‐2. These data suggest that IL‐2 plays a role in the regulation of hypercalcemia by enhancing the production of PTHrP in ATL patients.