Constitutive and activation-dependent phosphorylation of lymphocyte phosphatase-associated phosphoprotein (LPAP)

Abstract

Lymphocyte phosphatase-associated phosphoprotein (LPAP) is a small transmembrane protein expressed exclusively in lymphocytes. LPAP is a component of a supramolecular complex composed of the phosphatase CD45, the co-receptor CD4, and the kinase Lck. In contrast to its immunologically important partners, the function of LPAP is unknown. We hypothesized that the biological role of LPAP may be determined by analyzing LPAP phosphorylation. In the present study, we identified LPAP phosphorylation sites by site-directed mutagenesis, phospho-specific antibodies, and protein immunoprecipitation coupled to mass spectrometry analysis. Our results confirmed previous reports that Ser-99, Ser-153, and Ser-163 are phosphorylated, as well as provided evidence for the phosphorylation of Ser-172. Using various SDS-PAGE techniques, we detected and quantified a set of LPAP phosphoforms that were assigned to a combination of particular phosphorylation events. The phosphorylation of LPAP appears to be a tightly regulated process. Our results support the model: following phorbol 12-myristate 13-acetate (PMA) or TCR/CD3 activation of T cells, LPAP is rapidly dephosphorylated at Ser-99 and Ser-172 and slowly phosphorylated at Ser-163. Ser-153 exhibited a high basal level of phosphorylation in both resting and activated cells. Therefore, we suggest that LPAP may function as a co-regulator of T-cell signaling.

Single‐cell RNA sequencing reveals localized tumour ablation and intratumoural immunostimulant delivery potentiate T cell mediated tumour killing

“…For example, LAIT promoted the expression of Gimap transcripts, Dusp1 (MKP‐1), Isg15 , and Ptprc , which are involved in T cell survival, activation, and death (Figure S2D). 39–42 LAIT also induced the expression of Fos, Jun, Ptprcap , and Lcp1 (Figure 2E), which are associated with T cell receptor (TCR) signaling, 43–45 indicating that T cells in LAIT‐treated tumours are responding to their cognate antigens. LAIT also initiated changes in several other genes with less known functions in T cells, as listed in Table S1.…”

Proteogenomic Characterization Reveals Therapeutic Vulnerabilities in Lung Adenocarcinoma

“…ANK1 knockdown affects cancer-relevant pathways; furthermore, miR-486-3p and miR-486-5p, both strongly associated with lung adenocarcinoma oncogenesis, are located within ANK1 introns and are co-expressed with their host gene. PTPRCAP (CD45-associated protein), together with the three other members of its supramolecular complex, PTPRC (phosphatase CD45), co-receptor CD4, and kinase LCK, is implicated in regulation of lymphocyte function (Kruglova et al, 2017;Matsuda et al, 1998). Although methylation probe positions did not allow us to determine whether the complex partners of PTPRCAP are regulated by methylation, the partners showed coordinated expression at the protein level (Figure 3G).…”

ScRNA-seq reveals tumor microenvironment remodeling induced by local intervention-based immunotherapy

“…For example, LIT promoted the expression of Gimap proteins, Dusp1 (MKP-1), Isg15 , and Ptprc , which are involved in T cell survival, activation/function, and death (Figure S3F) (25-28). LIT also induced the expression of Fos, Jun, Ptprcap , and Lcp1 (Figure 3E), which are associated with T cell receptor (TCR) signaling (29-31), indicating that T cells in LIT-treated tumors are responding to their cognate antigens. LIT also initiated changes in several other genes with less known functions in T cells, as listed in Table S1.…”