Parathyroid hormone-related protein binding to human T-cell lymphotropic virus type I-infected lymphocytes.

An HTLV-I-infected human lymphocyte line (MT-2) was evaluated for 1) the presence of receptors for PTH-related protein (PTHrP), 2) cell proliferation in response to PTHrP, and 3) adrenylate cyclase and intracellular calcium response to PTHrP. PTHrP-(1-36) was labeled with 125I, purified, and used to detect binding to MT-2 cells. Specific binding ranged between 4-9% of the total radioactivity. Specific binding increased with increasing cell number, was maximal within 30-60 min, and was highest at 37 C. Scatchard analysis revealed a one-binding site fit, with a Kd of 14.5 nM. Binding was not competed for by calcitonin, calcitonin gene-related peptide, or interleukin-1 beta. PTHrP at 1.0 and 0.1 microM inhibited proliferation in MT-2 cells. PTHrP did not alter adenylate cyclase stimulation in MT-2 cells, but did cause an increase in intracellular calcium. These findings indicate that MT-2 cells have receptors for PTHrP and are consistent with a potential autocrine role of PTHrP in HTLV-I-infected lymphoid cells.