Protein phosphorylation and dephosphorylation are complex enzymatic reactions. Protein phosphorylation plays an important role in several cellular processes, including differentiation, cell growth, adhesion, motility, and apoptosis. Moreover, the actions of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs) regulate tyrosine phosphorylation. Crucially, PTPs are emerging as a unique class of tumor suppressors that utilize proteins as substrates. In this study, researchers searched a library of 80,000 small molecule inhibitors of PTPs and identified DJ001. Especially, DJ001 is a highly specific inhibitor of PTPσ and has the potential to bind to PTPσ.
DJ001 displays high specificity for PTPσ and antagonizes PTPσ via unique non-competitive, allosteric binding. Mechanistically, DJ001 suppresses radiation-induced HSC apoptosis via activation of the RhoGTPase, RAC1, and induction of BCL-XL. Researchers tested the inhibitory activity of DJ001 in a direct PTPσ enzymatic assay. As a result, DJ001 displays strong inhibitory activity against PTPσ, with an IC50 of 1.5 μM. While, DJ001 displays no inhibitory activity against 20 other phosphatases, with only modest inhibitory activity against protein phosphatase 5. Treatment with DJ001 (10–1000 ng/mL; 7 days) increases the percentages and numbers of BM KSL cells in culture compared with control cultures. In addition, DJ001 treatment also significantly increases the numbers of colony-forming cells (CFCs) in the 3-day culture of BM KSL cells.
DJ001 promotes HSC regeneration in vivo. Administration of DJ001 to irradiated mice promotes HSC regeneration, accelerates hematologic recovery, and improves survival. Similarly, DJ001 administration accelerates hematologic recovery in mice treated with 5-fluorouracil chemotherapy. Furthermore, the treatment of irradiated human HSCs with DJ001 promotes the regeneration of human HSCs capable of multilineage in vivo repopulation.
Above all, DJ001 is a selective, small-molecule PTPσ inhibitor for human hematopoietic regeneration.