Parathyroid hormone down-regulates the epidermal growth factor receptors in clonal osteoblastic mouse calvarial cells, MC3T3-E1: possible mediation by adenosine 3'5'-cyclic monophosphate.
The effects of PTH on the binding and mitogenic activity of epidermal growth factor (EGF) were studied in clonal, PTH- and EGF-responsive mouse osteoblastic cell line, MC3T3-E1. Treatment of cells with synthetic rat PTH-(1-34) at 10(-10)-10(-8) M resulted in a dose-related decrease (maximally 30% relative to the control value) in the specific binding of a biologically active, 125I-iodolabeled derivative of recombinant human EGF ([125I]iodo-EGF). The PTH-induced decrease in EGF binding was time dependent, requiring at least 4 h of PTH treatment at 37 C for a maximal effect, completely reversible after cessation of PTH exposure and specific only to biologically active PTH. Scatchard analysis of saturation binding data revealed that the PTH-induced reduction of EGF binding was accounted for by a proportional decrease in the available EGF-binding sites without an alteration in binding affinity (Kd = 0.7-0.8 nM). PTH treatment resulted ina concomitant decrease in mitotic responsiveness to EGF (maximally 40-50% of control). Both of these down-regulatory effects of PTH were closely mimicked by forskolin, cholera toxin, or (Bu)2cAMP. Addition of either colchicine or cytochalasin-B during PTH treatment completely abolished the PTH-induced reduction of EGF binding. These data indicate that PTH down-regulates EGF receptors and reduces the mitotic responsiveness to EGF, probably via a cAMP-dependent cytoskeleton-mediated mechanism(s) in osteoblastic MC3T3-E1 cells.
Ohta
S
S
Department of Orthopedic Surgery, Kyoto University School of Medicine, Japan.
Shigeno
C
C
Yamamoto
I
I
Okumura
H
H
Lee
K
K
Uneno
S
S
Konishi
J
J
Yamamuro
T
T
D000818:Animals; D002999:Clone Cells; D000242:Cyclic AMP / Q000502:physiology*; D004815:Epidermal Growth Factor / Q000378:metabolism / Q000494:pharmacology; D066246:ErbB Receptors / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008938:Mitosis / Q000187:drug effects; D010006:Osteoblasts / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000494:pharmacology*; D012886:Skull / Q000166:cytology*
D010281:Parathyroid Hormone; D004815:Epidermal Growth Factor; D000242:Cyclic AMP; D066246:ErbB Receptors