| G.R. Sharpe, J.P. Dillon, J.A. Gallagher and W.D. Fraser
(1998) Human keratinocytes express transcripts for three isoforms of
parathyroid hormone-related protein (PTHrP), but not for the parathyroid hormone/PTHrP
receptor: effects of 1,25(OH)(2), vitamin D-3. Brit. J.
Dermatol. 138: 944-951 Parathyroid hormone-related protein (PTHrP) is strongly expressed in the epidermis and has been implicated in the regulation of growth and differentiation of keratinocytes. PTHrP has N-terminaI sequence homology with parathyroid hormone (PTH) and binds to the type I PTH/PTHrP receptor, but earlier reports suggest that keratinocytes do not possess this cell surface receptor: In order to determine which PTHrP mRNA isoforms are expressed by keratinocytes and whether the type I receptor mRNA is present, we designed specific primers for reverse transcriptase-polymerase chain reaction, The interaction of PTHrP with other promoters of keratinocyte differentiation is unclear In particular, 1,25(OH)(2)D-3 is also fundamental in calcium homeostasis and induces changes in intracellular calcium. We therefore investigated the effect of 1.25(OH)(2)D-3 on 10(-10)-10(-6) mol/L. expression and protein production in cultured human keratinocytes. Cells were incubated for 3 days at concentrations of 1,25(OH)(2)D-3 of 10(-10)-10(-6) mol/L. PTHrP in culture supernatant, measured by two site immunoradiometric assay, was 915 +/- 98 PTHrP fmol/mg of cell layer protein in untreated cultures decreasing to 570 +/- 113 with 10(-8) mol/L and 402 +/- 24 with 10(-6) mol/L 1,25(OH)(2)D-3 (mean +/- SEM, P < 0.01, n = 6). Transcripts for all three PTHrP isoforms (139, 141 and 173 amino acids) were detectable in keratinocyte mRNA. Corresponding to the decrease in PTHrP protein we demonstrated a reduction in all three PTHrP mRNA transcripts after 3 days' incubation with 1,25(OH)(2)D-3 over a concentration range 10(-10)-10-(6) mol/L. Repeated studies failed to detect type I PTH/PTHrP receptor mRNA in human keratinocytes, either in control cultures or in the presence of 1,25(OH)(2)D-3. We have shown that keratinocytes produce abundant PTHrP and that this is modulated by 1,25(OH)(2)D-3, suggesting a physiological role. Further studies are required to investigate the relative expression of PTHrP isoforms, their role in keratinocyte signalling and the receptors involved. |