Signaling in human osteoblasts by extracellular nucleotides. Their weak induction of the c-fos proto-oncogene via Ca2+ mobilization is strongly potentiated by a parathyroid hormone/cAMP-dependent protein kinase pathway independently of mitogen-activated protein kinase.
Extracellular nucleotides acting through specific P2 receptors activate intracellular signaling cascades. Consistent with the expression of G protein-coupled P2Y receptors in skeletal tissue, the human osteosarcoma cell line SaOS-2 and primary osteoblasts express P2Y1 and P2Y2 receptors, respectively. Their activation by nucleotide agonists (ADP and ATP for P2Y1; ATP and UTP for P2Y2) elevates [Ca2+]i and moderately induces expression of the c-fos proto-oncogene. A synergistic effect on c-fos induction is observed by combining ATP and parathyroid hormone, a key bone cell regulator. Parathyroid hormone elevates intracellular cAMP levels and correspondingly activates a stably integrated reporter gene driven by the Ca2+/cAMP-responsive element of the human c-fos promoter. Nucleotides have little effect on either cAMP levels or this reporter, instead activating luciferase controlled by the full c-fos promoter. This induction is reproduced by a stably integrated serum response element reporter independently of mitogen-activated protein kinase activation and ternary complex factor phosphorylation. This novel example of synergy between the cAMP-dependent protein kinase/CaCRE signaling module and a non-mitogen-activated protein kinase/ternary complex factor pathway that targets the serum response element shows that extracellular ATP, via P2Y receptors, can potentiate strong responses to ubiquitous growth and differentiative factors.
D000255:Adenosine Triphosphate / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D006801:Humans; D010006:Osteoblasts / Q000201:enzymology / Q000502:physiology*; D010281:Parathyroid Hormone / Q000378:metabolism*; D000090063:Proto-Oncogene Mas; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D018048:Receptors, Purinergic P2 / Q000096:biosynthesis; D058472:Receptors, Purinergic P2Y1; D058473:Receptors, Purinergic P2Y2; D015398:Signal Transduction; D014544:Uridine Triphosphate / Q000378:metabolism