Differential expression of calcitonin and parathyroid hormone/parathyroid hormone-related protein receptors in P19 embryonic carcinoma cells treated with retinoic acid.

Mouse embryonic carcinoma P19 cell aggregates treated with retinoic acid (RA) sequentially differentiate into neurons and astrocytes, whereas attached cells develop a mesodermal phenotype. The expression of calcitonin (CT) and PTH/PTH-related protein (PTHrP) receptors was investigated in embryonic cells, and during neural and mesodermal differentiation. In embryonic P19 cells, specific binding of [I-125]salmon (s) CT(1-32) ([I-125]sCT(1-32)) was 56 fmol/mg protein, and of [I-125]chicken (ch) [Tyr(36)]PTHrP(1-36) amide ([I-125]- chPTHrP(1-36)) < 0.5 fmol/mg protein. Correspondingly, cAMP was maximally stimulated 47-fold by sCT(1-32) (EC50 0.05 nM) and 3-fold by chPTHrP(1-36) (EC50 1.3 nM). Receptor autoradiography revealed specific binding of [I-125]sCT(1-32) to the undifferentiated P19 cells, but not to RA induced neurons and astrocytes. At the same time, [I-125]sCT(1-32) binding and cAMP accumulation by sCT were gradually decreased. But, specific binding of [I-125]chPTHrP(1-36) was raised at least B-fold compared with embryonic cells to 3 fmol/mg protein, in parallel with a 10-fold higher maximal cAMP accumulation. A similar, but delayed suppression of CT and stimulation of PTH/PTHrP receptor expression was observed during mesodermal cell differentiation. The results indicate-that CT receptors are associated with undifferentiated P19 cells, whereas PTH/PTHrP receptors are expressed in RA induced neural and mesodermal cells.