Transactivation by Runt related factor-2 of matrix metalloproteinase-13 in astrocytes.

We have previously shown functional expression by osteoblasts of signaling machineries required for neurotransmission in the brain. In this study, we have evaluated possible functional expression of different osseous genes in the brain. In embryonic and adult mouse brains, mRNA expression was invariably seen for the master regulator of osteoblastic differentiation Runt related factor-2 (Runx2), in addition to the partner protein core binding factor-beta and their targets such as osteopontin (OPN) and matrix metalloproteinase-13 (MMP13), but not for collagen-I or osteocalcin. In pluripotent P19 progenitor cells, Runx2 mRNA expression was drastically increased along with mRNA expression of an astrocytic marker, but not with neuronal marker mRNA expression. Both mRNA and corresponding protein were detected for Runx2 in cultured rat neocortical astrocytes and astrocytic C6 glioma cells. In C6 glioma cells, transient overexpression of Runx2 significantly increased mRNA expression of MMP13, but not of OPN. Moreover, transient overexpression of Runx2 significantly increased luciferase activity in C6 glioma cells transfected with the reporter plasmid linked to a wild-type Runx2 binding element in the MMP13 promoter, but not in cells with a mutated element. These results suggest that Runx2 signal input may lead to transactivation of MMP13 gene without affecting OPN expression in astrocytes.