HD-PTP is a 1,636 amino acid protein encoded by the human gene PTPN23. HD-PTP belongs to the protein-tyrosine phosphatase family, non-receptor class subfamily. It contains one BRO1 domain, two TPR repeats and one tyrosine-protein phosphatase domain. The C-terminal region contains the PTP-like domain, whereas the N-terminal region contains the two TPR regions. These regions are homologous to the yeast protein, BRO1, which is involved in the mitogen-activated protein kinase signaling pathway. Similarly, HD-PTP is believed to act as a negative regulator of Ras-mediated mitogenic activity and is phosphorylated upon DNA damage, probably by ATM or ATR. HD-PTP protein is differentially modulated by two angiogenic growth factors. While Vascular Endothelial Growth Factor (VEGF) has no affect on protein levels, Fibroblast Growth Factor-2 (FGF-2) induces HD-PTP degradation via the proteasome system.