AP-1 in mechanically-stressed hPDLF cells

We investigated the involvement of the immediate-early gene products Jun and Kos (AP-1 ) in the response of human periodontal ligament fibroblast (hPDLF) cells to physiological mechanical stress. For this purpose, the ability of kinasrs targeting Jun and Fos to phosphorylate these transcription factors and induce specific TRE-binding activity after mechanical perturbation (stretching) of hPDLF cells was explored. Cultured hPDLF cells (cells bearing an osteogenic potential) were subjected to short-term mechanical stretching under previously established conditions. After 7-30 min, extracts were prepared from stretched and control cultures. Their kinase activity against Jun and Fos was tested in an in-gel kinase assay while their TRE-binding capacity was assessed in KMS and SW assays. These analyses revealed that specific kinases, with apparent MW in the range of well-characterized Jun/Fos targeting enzymes, were gradually induced in mechanically-stretched hPDLF cells and augmented the basal-level phosphorylation of both substrates. This effect was in concert with enhanced. c-Jun-containing DNA-binding activity of extracts obtained from stretched hPDlF cell cultures on the L/B/K alkaline phosphatase (AP) gene .V-TRK, and increased activity of the corresponding enzyme in these extracts. Because elevated expression of the L/B/K AP gene is linked to the onset of the osteobîast phenotype, we suggest that mechanical stimulation may signal the differentiation pathway of hPDLF cells with Jun and Fos acting as downstream molecular effectors of mechanotransductiou.