NELL-1-dependent mineralisation of Saos-2 human osteosarcoma cells is mediated via c-Jun N-terminal kinase pathway activation

Abstract

Purpose 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 mitogenactivated 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.

NELL-1 expression in benign and malignant bone tumors

“…More study both isolating tumor-derived NELL-1 protein and supplementing NELL-1 in OS cells in culture is needed to answer these questions. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 Prior studies in the Saos2 osteosarcoma cell line do suggest that recombinant NELL-1 protein does induce osteogenic differentiation in this cell line via potentiation of MAPK signaling [27]. However, clear variability exists between OS cell lines in their responsiveness to osteoinductive protein stimuli, such as with BMPs (Bone Morphogenetic Proteins) [28].…”

Nell-1 Enhances Osteogenic Differentiation of Pre-Osteoblasts on Titanium Surfaces via the MAPK-ERK Signaling Pathway

“…It is noteworthy that OPN production could be reduced by the siRNA-mediated degradation of Ras through the inhibition of the ERK pathway [26]. Moreover, the JNK inhibitor SP600125 suppresses Nell-1-induced mineralization and intracellular phosphate accumulation in Saos-2 cells, while ERK1/2 and P38 inhibitors have no effect [48]. In this study, the expression of a series of osteogenic proteins and genes in pre-osteoblasts was significantly decreased by co-treatment with the ERK inhibitor U0126 and Nell-1.…”

NELL-1 Injection Maintains Long-Bone Quantity and Quality in an Ovariectomy-Induced Osteoporotic Senile Rat Model

“…After attachment, the medium was replaced with an osteogenic differentiation medium (ODM). The medium was supplemented with either (rh)NELL-1 at 300 ng/mL [29][30][31][32][33] or control PBS. The ODM was replaced every third day.…”