Lipoxygenase metabolites are mediators of PTH-dependent human osteoblast growth.
PTH-induced osteoblast proliferation may contribute to its anabolic effects in bone. Since PTH-dependent osteoblast-like cell (Ob) growth is mediated via protein kinase C (PKC) and MAP kinase-kinase (MEK) and since lipoxygenase (LO) products activate PKC in a number of cell types, we assessed the expression of LO pathways in primary human cultured Ob. Ob from pre- or post-menopausal women were cultured and were treated with PTH and assayed for the expression of 12-LO and both type I and type II 15-LO mRNA and for the release their enzymatic products, 12- and 15-hydroxyeicosatetraenoic acid (HETE). Cells were also treated with PTH for stimulation DNA synthesis. First, Ob express platelet type- 12-LO and both type I and type II 15-LO mRNA and release their enzymatic products, 12- and 15-hydroxyeicosatetraenoic acid (HETE). Second, in female Ob, PTH induced a rapid increase in 12-HETE (50 fold increase) and 15-HETE (80 fold increase) and increased the expression of 12-LO mRNA but not of the two isoforms of 15-LO. PTH as well as 12 and 15-HETE stimulated DNA synthesis in Ob. The LO inhibitor baicalein inhibited PTH-stimulated DNA synthesis, which was reversed in the presence of either 12- or 15-HETE. A PKC inhibitor (bisindolylmaleimide I) as well as a MEK inhibitor (PD 98059) completely inhibited the stimulation of DNA synthesis by PTH, 12-HETE and the combination of PTH and 12-HETE. In contrast, 15-HETE-induced DNA synthesis was not abolished by these inhibitors. Further, 15-HETE partially restored the stimulatory effect of PTH on DNA synthesis in cells treated with PKC or MEK inhibitors. Finally, PTH- induced ERK1/2 phosphorylation, was blocked by a MEK inhibitor. These results demonstrate a novel mechanism of PTH-induced human bone cell proliferation operating through LO enzymes.
Somjen
Dalia
D
Institute of Endocrinology, Metabolism and Hypertension, Tel-Aviv Sourasky Medical Center, Tel-Aviv University, Tel-Aviv 64239, Israel.
Tordjman
Karen
K
Katzburg
Sara
S
Knoll
Esther
E
Sharon
Orli
O
Limor
Rona
R
Naidich
Michal
M
Naor
Zvi
Z
Hendel
David
D
Stern
Naftali
N
D019377:12-Hydroxy-5,8,10,14-eicosatetraenoic Acid / Q000378:metabolism*; D001092:Arachidonate 12-Lipoxygenase / Q000235:genetics / Q000378:metabolism*; D001093:Arachidonate 15-Lipoxygenase / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D004791:Enzyme Inhibitors / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D006801:Humans; D006893:Hydroxyeicosatetraenoic Acids / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D010006:Osteoblasts / Q000166:cytology / Q000502:physiology*; D010281:Parathyroid Hormone / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism
D004791:Enzyme Inhibitors; D006893:Hydroxyeicosatetraenoic Acids; D007527:Isoenzymes; C470125:PTH protein, human; D010281:Parathyroid Hormone; D019377:12-Hydroxy-5,8,10,14-eicosatetraenoic Acid; C025984:15-hydroxy-5,8,11,13-eicosatetraenoic acid; D004247:DNA; D001092:Arachidonate 12-Lipoxygenase; D001093:Arachidonate 15-Lipoxygenase; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases; D048369:MAP Kinase Kinase 1