Parathyroid hormone regulation of proline uptake by cultured neonatal mouse osteoblastlike cells

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Abstract
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.
Funding Information
  • National Institute on Aging (AG-02731)