NELL-1-dependent mineralisation of Saos-2 human osteosarcoma cells is mediated via c-Jun N-terminal kinase pathway activation.
OBJECTIVE
NELL-1 is a novel osteoinductive growth factor that has shown promising results for the regeneration of bone. Moreover, NELL-1 has been used successfully in bone regeneration in the axial, appendicular and calvarial skeleton of both small and large animal models. Despite increasing evidence of NELL-1 efficacy and future usefulness as an alternative to traditional bone graft substitutes, much has yet to be understood regarding the mechanisms of action of this novel protein. The activation of the mitogen-activated protein kinase (MAPK) pathway has been well studied in the setting of growth factor-mediated changes in osteogenic differentiation.


METHODS
In this study, we provide evidence of the involvement of MAPK signalling pathways in NELL-1-induced terminal osteogenic differentiation of Saos-2 human osteosarcoma cells. Activation of extracellular signal-regulated kinase (ERK1/2), P38 and c-Jun N-terminal kinase (JNK) pathways were screened with MAPK signalling protein array after recombinant human (rh)NELL-1 treatment. Next, the mineralisation and intracellular phosphate levels after rhNELL-1 stimulation were assessed in the presence or absence of specific MAPK inhibitors.


RESULTS
Results showed that rhNELL-1 predominantly increased JNK pathway activation. Moreover, the specific JNK inhibitor SP600125 blocked rhNELL-1-induced mineralisation and intracellular phosphate accumulation, whereas ERK1/2 and P38 inhibitors showed no effect.


CONCLUSIONS
Thus, activation of the JNK pathway is necessary to mediate terminal osteogenic differentiation of Saos-2 osteosarcoma cells by rhNELL-1. Future studies will extend these in vitro mechanisms to the in vivo effects of NELL-1 in dealing with orthopaedic defects caused by skeletal malignancies or other aetiologies.
Dental and Craniofacial Research Institute and Section of Orthodontics, School of Dentistry, University of California, Los Angeles, 10833 Le Conte Ave, CHS 30-117, Los Angeles, CA 90095, USA.
Feng
F
Chen
Ben
B
Walder
Aaron W
AW
James
Donnalisa E
DE
Soofer
Chia
C
Soo
Kang
K
Ting
Xinli
X
Zhang
D000873:Anthracenes / Q000494:pharmacology; D001859:Bone Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D002113:Calcification, Physiologic / Q000187:drug effects; D002130:Calcium Phosphates / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D002135:Calcium-Binding Proteins; D002454:Cell Differentiation / Q000187:drug effects; D045744:Cell Line, Tumor; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D009419:Nerve Tissue Proteins / Q000378:metabolism / Q000494:pharmacology*; D010011:Osteocytes / Q000187:drug effects / Q000378:metabolism; D012516:Osteosarcoma / Q000188:drug therapy* / Q000378:metabolism; D011994:Recombinant Proteins
D000873:Anthracenes; D002130:Calcium Phosphates; D002135:Calcium-Binding Proteins; D004791:Enzyme Inhibitors; C104144:NELL1 protein, human; D009419:Nerve Tissue Proteins; D011994:Recombinant Proteins; C432165:pyrazolanthrone; C020243:calcium phosphate; D048031:JNK Mitogen-Activated Protein Kinases