Preventing MEK1 activation influences the responses of human osteosarcoma cells to bone morphogenetic proteins 2 and 9

Abstract

It was recently suggested that bone morphogenetic protein (BMP)-2 may be useful for treating osteosarcoma cells. BMP-9, which has been patented to treat breast and prostate cancers, has a higher osteoinductive potential than BMP-2. Peptides derived from the knuckle epitope of BMPs (pBMPs) also induced osteogenic differentiation. However, the effect of BMP-9 and pBMPs on osteosarcoma cells is unclear. We analyzed the effects of BMP-2, BMP-9, pBMP-2, and pBMP-9 on the behavior of human MG-63 and SaOS-2 osteosarcoma cells. An inhibitor of MEK1 activation (PD98059) that prevents downstream extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation and a specific inhibitor of p38 were also used as mitogen activated protein kinase-targeting therapy is being investigated as a treatment modality for osteosarcoma. BMP-2 and BMP-9 (1.92 nmol/l) induced the phosphorylation of Smad1/5/8 in both osteosarcoma cells within 1 h but had different effects on mitogen activated protein kinase pathways. Whereas BMP-2 mainly activated ERK1/2, BMP-9 phosphorylated p38 within 1 h. pBMP-2 did not activate either the Smad or ERK/p38, whereas pBMP-9, like BMP-9, induced both Smad1/5/8 and p38 phosphorylation. p38 activation by BMP-9 or pBMP-9 was also enhanced by PD98059. However, BMP-2 or BMP-9 increased the amounts of distal-less homeobox 5 and Osterix mRNAs in SaOS-2 cells within 6 h, whereas pBMP-9 had no effect. PD98059 promoted the highest level of Osterix mRNA in SaOS-2 cells incubated with BMP-2 or BMP-9, whereas p38 inhibitor had no effect. Furthermore, PD98059 induced the lowest proliferation of MG-63 cells incubated with BMP-2, whereas p38 inhibitor did not affect the proliferation of either osteosarcoma cell line. Therefore a combination of BMP-2 or BMP-9 and an inhibitor of MEK1 may be a promising tool for regulating osteosarcoma cell behavior.

Potential Roles of Bone Morphogenetic Protein (BMP)-9 in Human Liver Diseases

“…Whether the effects observed in BMP-9-mediated osteogenic differentiation by ERK and p38 inhibition are the result of Smad signaling modulation or a direct effect of the MAPKs on this process is not known. Along these lines, p38 activation induced by BMP-9 has been documented in other cell types such as osteosarcoma cells [51], human osteoclasts derived from cord blood monocytes [52] and dental follicle stem cells [53]. In the former case, together with p38 activation, downregulation of phospho-ERK was achieved upon BMP-9 treatment.…”

“…Interestingly, Cox2 seems to directly modulate Smad1,5,8 signaling and Smad dependent gene expression in MPC [57]. Along these lines, the transcription factor Runx2, which is central for osteoblast differentiation by directly stimulating the expression of most of the well established bone markers (among them alkaline phosphatase and osteopontin), has been shown to be a target gene of BMP-9 in several cellular models like MPCs, osteosarcoma and dedifferentiated fat cells [51,56,58]. It is worth mentioning that the hypoxia inducible factor, Hif1α, has been recently described as a target of BMP-9 in MSC.…”

From skeletal to non skeletal: The intriguing roles of BMP-9: A literature review

“…Recent studies analyzed the effect of BMP9 (rhBMP9 or AdBMP9) in different human osteosarcoma cell lines such as MG-63 cells [80,81]. For example, BMP9 expression was obtained through infection of human osteosarcoma MG-63 and 143B cells by a BMP9 expressing adenovirus [82].…”

Superior bone‐inducing potential of rhBMP9 compared to rhBMP2

“…It has been hypothesized that the attractive osteogenic potential of BMP9 might be attributed to the differences in canonical BMP signaling pathways . Both BMP‐2 and −9 have been shown to activate SMAD pathways through the phosphorylation of the transcription factors Smad1/5/8 by type I receptors in osteoblast cells . Noggin is a well‐known BMP antagonist, which binds with carrying affinities and blocks SMAD‐dependent signaling.…”

“…7 Both BMP-2 and 29 have been shown to activate SMAD pathways through the phosphorylation of the transcription factors Smad1/5/8 by type I receptors in osteoblast cells. 34,35 Noggin is a wellknown BMP antagonist, which binds with carrying affinities and blocks SMAD-dependent signaling. Endogenous noggin also binds to BMP2 and inhibits its action whereas, previous reports have shown that BMP9 stimulation also leads to noggin expression, however SMAD phosphorylation by BMP9 is not inhibited.…”