Expression and signaling of parathyroid hormone-related protein in cultured podocytes.
Podocyte function appears to be regulated by vasoactive factors. In vivo podocytes express parathyroid hormone-related protein (PTHrP), the N-terminal fragment of which has vasoactive properties. Since the signaling pathway(s) of PTHrP(1-36) are unknown in podocytes, differentiated cells of a conditionally immortalized mouse podocyte cell line were studied. Gene expression of PTHrP and the PTH/PTHrP receptor was investigated by RT-PCR; protein distribution of PTHrP was examined by immunofluorescence. Accumulation of cAMP was determined by an enzyme immunoassay; [Ca2+]i was measured by fura-2 ratio imaging. PTHrP and PTH/PTHrP receptor mRNA was detected in differentiated podocytes. Immunoreactive PTHrP exhibited a granular distribution in the cytoplasm of differentiated podocytes. With regard to the signaling pathway(s) of PTHrP(1-36), a concentration-dependent increase of cAMP levels with an EC50 value of 4 +/- 2 nM was found. PTHrP(1-36) (1 microM) increased cAMP levels 5.5 +/- 1.1-fold above baseline as compared with a 25.4 +/- 4.2-fold increase in response to forskolin (10 microM). The PTH/PTHrP receptor antagonist PTHrP(7-34) significantly diminished the PTHrP(1-36)-induced cAMP increase. While superfusion of podocytes with bradykinin (100 nM) increased [Ca2+]i, PTHrP(1-36) (100 nM) was without effect on [Ca2+]i. However, PTHrP(1-36) attenuated the bradykinin-induced increase in [Ca2+]i. Our results suggest that PTHrP is an autocrine hormone in podocytes, which selectively activates the cAMP pathway through the PTH/PTHrP receptor.
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Institute of Anatomy and Cell Biology, University of Heidelberg, Germany. karlhans.endlich@urz.uni-heidelberg.de
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D000818:Animals; D002118:Calcium / Q000378:metabolism; D002461:Cell Line, Transformed; D000242:Cyclic AMP / Q000037:antagonists & inhibitors / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D007124:Immunoenzyme Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D007678:Kidney Glomerulus / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D009994:Osmolar Concentration; D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments / Q000494:pharmacology / Q000502:physiology; D011506:Proteins / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D044168:Receptor, Parathyroid Hormone, Type 1; D018016:Receptors, Parathyroid Hormone / Q000378:metabolism; D015398:Signal Transduction; D014018:Tissue Distribution
D044162:Parathyroid Hormone-Related Protein; D010446:Peptide Fragments; D011506:Proteins; D044168:Receptor, Parathyroid Hormone, Type 1; D018016:Receptors, Parathyroid Hormone; C079957:parathyroid hormone-related peptide (1-36); C431128:parathyroid hormone-related protein (7-34); D000242:Cyclic AMP; D002118:Calcium