Specific inhibitor of MEK-mediated cross-talk between ERK and p38 MAPK during differentiation of human osteosarcoma cells

Abstract

Osteosarcoma is the most common primary malignant bone tumor, accounting for approximately 20% of all primary sarcomas in bone. Although treatment modalities have been improved over the past decades, it is still a tumor with a high mortality rate in children and young adults. Based on histological considerations, osteosarcoma arises from impaired differentiation of these immature cells into more mature types and that correction of this impairment may reduce malignancy and increase the efficiency of chemotherapy. The purpose of this study was to determine the effect of specific inhibitors of MAPK extracellular signaling-regulated kinase (ERK) kinase (MEK) and p38 on the differentiation of human osteosarcoma cell line SaOS-2 cells. We found that PD98059, a specific inhibitor of MEK, inhibited the serum-stimulated proliferation of SaOS-2 cells; whereas SB203580, a specific inhibitor of p38 MAPK, had little effect on it. SB203580 suppressed ALPase activity, gene expression of type I collagen, and expression of ALP and BMP-2 mRNAs; whereas PD98059 upregulated them dose dependently. In addition, immunoblot and immunostaining analysis revealed that phosphorylation of ERK was increased by treatment with SB203580; whereas PD98059 increased the phosphorylation of p38, which implies a seesaw-like balance between ERK and p38 phosphorylation. We suggest that osteosarcoma cell differentiation is regulated by the balance between the activities of the ERK and p38 pathways and that the MEK/ERK pathway negatively regulates osteosarcoma cell differentiation, whereas the p38 pathway does so positively. MEK inhibitor may thus be a good candidate for altering the expression of the osteosarcoma malignant phenotype.

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

“…SaOS-2 cells pretreated with PD98059, which inhibits ERK1/2 phosphorylation by preventing MEK1 activation [28], contained much more Dlx5 mRNA than untreated cells. These results agree well with those of Shimo et al [49], who showed that adding PD98059 promotes the early stages of SaOS-2 cell differentiation induced by serum. Further, SaOS-2 cells pretreated with PD98059 and then with BMP-2 also contained more Osx transcripts than did similar cells incubated with BMP-9 alone.…”

“…There have been several reports that state that p38 is also involved in osteoblast differentiation [35,49]. Shimo et al [49] showed that SaOS-2 cells in a medium containing 10% FBS contained fewer type I collagen and fewer ALP transcripts when treated with a p38 inhibitor than did untreated cells.…”

Logic Modeling in Quantitative Systems Pharmacology

“…We note that the inhibition of p38 is predicted to increase survival, consistent with experimental observations 57, 76, 77. However, the observation that Erk and Stat3 have an important role in LNCaP cells57 is not verified, as it has no influence on survival in the model.…”

Signaling through the P38 and ERK pathways: a common link between HIV replication and the immune response

“…P38 is frequently linked to inflammation and apoptosis, while ERK often plays a role in survival and proliferation [11,13]. Although the P38 and ERK pathways may appear to play opposing roles, many researchers have shown that there is a substantial amount of crosstalk between these pathways [14,15]. It is the balance between ERK and P38 activation that helps a cell decide between cell division or cell cycle arrest, to promote or inhibit inflammation, and life or death.…”