Parathyroid hormone regulation of proline uptake by cultured neonatal mouse osteoblastlike cells.
Regulation of proline uptake by the synthetic amino-terminal fragment of bovine parathyroid hormone [bPTH-(1-34)] has been studied in confluent primary cultures of osteoblastlike cells isolated from neonatal mouse calvaria. The initial velocity of proline transport was increased by 85% in cultures treated with 24 nM bPTH-(1-34) for 6 h. Cycloheximide, at a concentration that inhibited protein synthesis by 97%, did not prevent this effect. However, adding the inhibitor during the first 1-2 h of hormone treatment did significantly reduce its magnitude. Exposure of cells to the inhibitor alone caused a time-dependent decrease in the basal rate of proline uptake. In the absence of protein synthesis, the maximal velocity (Vmax) of transport was 60% greater in cultures treated with 24 nM bPTH-(1-34) than in controls. The concentration of proline at which half-maximal transport occurred (Km) was unchanged. In cultures treated with cycloheximide alone, proline transport decreased as a first-order exponential with a half-life of 250-280 min. Parathyroid hormone significantly reduced this decline, increasing the half-life of proline transport activity about fourfold. These effects were duplicated by 1 mM DBcAMP. It is concluded that bPTH-(1-34) increases proline transport in osteoblastlike cells by decreasing the degradation of amino acid transport system A proteins. The hormone may also affect the synthesis of these molecules. These effects appear to be mediated by cAMP.
Yee
J A
JA
Department of Cell Biology and Anatomy, Texas Tech University Health Sciences Center, Lubbock 79430.
Sutton
J K
JK
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D003994:Bucladesine / Q000494:pharmacology; D002417:Cattle; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D010281:Parathyroid Hormone / Q000502:physiology*; D011392:Proline / Q000378:metabolism*; D014176:Protein Biosynthesis
D010281:Parathyroid Hormone; D003994:Bucladesine; D003513:Cycloheximide; D011392:Proline