ИСТИНА

Background: LPAP (Lymphocyte Phosphatase-Associated Phosphoprotein) is a transmembrane protein with unknown function that is tightly associated with the phosphatase CD45. There is evidence that phosphorylation status of LPAP undergoes changes after lymphocyte activation. This indicates that LPAP may be involved in the regulation of immune response. However, the information about the identities of LPAP phosphorylation sites is limited. Our aim was to investigate LPAP phosphorylation in rested and activated lymphocytes, identify individual LPAP phosphoforms, and determine possible transitions between them. Results: 2D electrophoresis showed that in CEM cells at least five different phosphoforms existed. Using NetPhos software, we predicted 11 the most probable sites of LPAP phosphorylation. These sites were mutated to alanin in order to determine their impact on protein phosphorylation. LPAP transiently transfected in HEK293T cells was phosphorylated only on Ser153, whereas LPAP in CEM cells was phosphorylated on additional sites, Ser99 and Thr113. The phosphorylation of Ser99 was decreased after cell activation.