ERK1/2-activated de novo Mapkapk2 synthesis is essential for osteogenic growth peptide mitogenic signaling in osteoblastic cells.
In osteoblasts, the mitogen-activated protein kinases ERK1/2 and p38 as well as the cAMP-response element-binding protein (CREB) have been implicated in the regulation of proliferation and differentiation. The osteogenic growth peptide (OGP) is a 14-mer bone cell mitogen that increases bone formation and trabecular bone density and stimulates fracture healing. OGP-(10-14) is the physiologically active form of OGP. Using gene array analysis, real-time reverse transcription-PCR, and immunoblot and DNA synthesis assays we show here that in MC3T3 E1 and newborn mouse calvarial osteoblastic cultures the OGP-(10-14) mitogenic signaling is critically dependent on de novo synthesis of mitogen-activated protein kinase-activated protein kinase 2 (Mapkapk2) mRNA and protein. The increase in Mapkapk2 occurs following short term (5-60 min) stimulation of ERK1/2 activity by OGP-(10-14); phosphorylation of p38 remains unaffected. Downstream of Mapkapk2, CREB is phosphorylated on Ser(133) leading to its enhanced transcriptional activity. That these events are critical for the OGP-(10-14) mitogenic signaling is demonstrated by blocking the effects of OGP-(10-14) on the ERK1/2 pathway, Mapkapk2, CREB, and DNA synthesis using the MEK inhibitor PD098059. The OGP-(10-14) stimulation of CREB transcriptional activity and DNA synthesis is also blocked by Mapkapk2 siRNA. These data define a novel mitogenic signaling pathway in osteoblasts whereby ERK1/2 stimulation of CREB phosphorylation and transcriptional activity as well as DNA synthesis are critically dependent on de novo Mapkapk2 synthesis.
Miguel
Symone M San
SM
Bone Laboratory, The Hebrew University of Jerusalem, Israel.
Namdar-Attar
Malka
M
Noh
Tommy
T
Frenkel
Baruch
B
Bab
Itai
I
D000818:Animals; D050882:CREB-Binding Protein / Q000235:genetics; D002478:Cells, Cultured; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D020869:Gene Expression Profiling; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D006657:Histones / Q000494:pharmacology*; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D051379:Mice; D008934:Mitogens / Q000494:pharmacology*; D010006:Osteoblasts / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis* / Q000235:genetics; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D000099190:MAP-Kinase-Activated Kinase 2
D050882:CREB-Binding Protein; D048049:Extracellular Signal-Regulated MAP Kinases; D006657:Histones; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008934:Mitogens; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger; D048051:p38 Mitogen-Activated Protein Kinases; D000099190:MAP-Kinase-Activated Kinase 2; C074533:osteogenic growth peptide; C494364:Crebbp protein, mouse