Characterization and comparison of the intronic promoter of murine osteoclastic protein-tyrosine phosphatase, PTP-oc, with the human PTP-oc promoter.

This study characterized the murine osteoclastic protein-tyrosine phosphatase (PTP-oc) promoter located within intron 12 of the Glepp1 gene. A 2-kb DNA fragment containing the putative intronic promoter showed strong promoter activity in pre-osteoclastic RAW264.7 and U937 cells, but not in non-osteoclastic cells. Deletion analyses identified a proximal region with elements required for basal activity, and upstream repressor and enhancer elements. The cell-type-specificity of the promoter was conferred by upstream domains. At least nine conserved response elements, with potential transcription factor binding sites, were identified in both human and murine promoters. EMSA and ChIP indicate the presence of occupied binding sites for Pit-1a, Ikaros-1/2, and D1DR transcription factors in the murine promoter. Site-directed mutagenesis of response elements resulted in down- or up-regulation of promoter activity: some of the effects were different between the murine and human promoter, suggesting that there may be inter-species differences in the regulation of the PTP-oc promoter.

Targeted deletion of the osteoclast protein-tyrosine phosphatase (PTP-oc) promoter prevents RANKL-mediated osteoclastic differentiation of RAW264.7 cells.

An osteoclastic protein-tyrosine phosphatase, PTP-oc, shares the same gene with a renal PTP, Glepp1. This study demonstrated that targeted deletion of PTP-oc promoter by homologous recombination in RAW264.7 cells completely abolished PTP-oc expression without affecting Glepp1 expression. This strategy to inhibit PTP-oc function has three advantages over commonly used gene knock down strategies (e.g., small interference RNA). This strategy: (1) yielded cells completely devoid of PTP-oc, (2) had no off-target gene silencing effects, and (3) did not affect Glepp1 expression. The inability of PTP-oc-deficient RAW264.7 cells to undergo RANKL-mediated osteoclastic differentiation confirmed a regulatory role for PTP-oc in RANKL-mediated osteoclast differentiation.