Consequences of the Lack of CD73 and Prostatic Acid Phosphatase in the Lymphoid Organs

Abstract

CD73, ecto-5′-nucleotidase, is the key enzyme catalyzing the conversion of extracellular AMP to adenosine that controls vascular permeability and immunosuppression. Also prostatic acid phosphatase (PAP) possesses ecto-5′-nucleotidase/AMPase activity and is present in leukocytes. However, its role related to immune system is unknown. Therefore, we analyzed enzymatic activities and leukocyte subtypes of CD73 and PAP knockouts and generated CD73/PAP double knockout mice to elucidate the contribution of CD73 and PAP to immunological parameters. Enzymatic assays confirmed the ability of recombinant human PAP to hydrolyze [3H]AMP, although at much lower rate than human CD73. Nevertheless, 5′-nucleotidase/AMPase activity in splenocytes and lymphocytes from PAP−/− mice tended to be lower than in wild-type controls, suggesting potential contribution of PAP, along with CD73, into lymphoid AMP metabolism ex vivo. Single knockouts had decreased number of CD4+/CD25+/FoxP3 + regulatory T cells in thymus and CD73/PAP double knockouts exhibited reduced percentages of CD4+ cells in spleen, regulatory T cells in lymph nodes and thymus, and CD4+ and CD8+ cells in blood. These findings suggest that PAP has a synergistic role together with CD73 in the immune system by contributing to the balance of leukocyte subpopulations and especially to the number of regulatory T cells in lymph nodes and thymus.

Up-regulated Ectonucleotidases in Fas-Associated Death Domain Protein– and Receptor-Interacting Protein Kinase 1–Deficient Jurkat Leukemia Cells Counteract Extracellular ATP/AMP Accumulation via Pannexin-1 Channels during Chemotherapeutic Drug-Induced Apoptosis

“…Despite its canonical association with the prostate gland, recent studies have indicated that TM-PAP and/or the secreted PAP isoform function as significant ectonucleotidases in multiple tissues and cell types, including saliva (Araujo et al, 2014), dorsal root ganglion neurons that mediate nociception (Street et al, 2011;Zylka et al, 2008), and normal T lymphocytes (Yegutkin et al, 2014). Up-regulated PAP is also used as a biomarker of prostate cancer (Hakalahti et al, 1993), and our observations suggest the possibility that it may also be a marker for some subtypes of leukemias.…”

“…Multiple ACPP splice variants yield a secreted PAP isoform and another with a transmembrane anchor (TM-PAP). Recent studies have indicated that TM-PAP mRNA and enzyme activity is expressed in normal murine and human lymphoid tissues and different T-cell subsets (Quintero et al, 2007;Yegutkin et al, 2014). Notably, inclusion of 10 mM L-tartrate, as a low affinity but high-efficacy inhibitor of PAP isozymes, markedly (∼80%) attenuated the robust «-AMP → «-ADO metabolism by the RIP1-deficient Jurkat cells (Fig.…”

“…Up-regulated PAP is also used as a biomarker of prostate cancer (Hakalahti et al, 1993), and our observations suggest the possibility that it may also be a marker for some subtypes of leukemias. Because selective and well-defined pharmacologic inhibitors of PAP ectonucleotidase activity are not readily available (Larsen et al, 2009;McCoy et al, 2013), most studies have used PAP-knockout mice to define physiologic roles (Zylka et al, 2008;Street et al, 2011;Yegutkin et al, 2014). Studies using siRNA with Jurkat cells and other human leukemia lines would be informative to define roles for TM-PAP in the growth, survival, and immunogenicity of hematopoietic tumors.…”

Purinergic signalling in B cells

“…Traffic of lymphocytes between blood and tissues is essential for propagation of inflammation and purinergic signaling plays an important role in this process through conditioning kinetics of lymphocytes (Henttinen et al, 2003;Yegutkin et al, 2014). Extravasation of leukocytes to target tissue consists of following steps: temporal adhesion of lymphocytes to vascular endothelium, rolling of cells along endothelium, activation resulting in holding of the cells and subsequent transmigration into tissue (Springer, 1994).…”

Adenosine in the Thymus

“…Interestingly, both retinoids ( Mucida et al, 2007 ) and ADO ( Ohta and Sitkovsky, 2014 ) promote the TGF-β-dependent development of T reg cells in the periphery. In CD73/prostatic acid phosphatase double knock out mice, where the extracellular ADO levels are low, the tT reg cell production was found to be impaired ( Yegutkin et al, 2014 ) indicating the involvement of ADO also in the tT reg cell differentiation.…”