Why do male mice spit soluble enzymes that hydrolyze extracellular nucleotides? Focus on 'Prostatic acid phosphatase is the main acid phosphatase with 5'-ectonucleotidase activity in the male mouse saliva and regulates salivation'

摘要

the 5'-ectonucleotidases found on the surface of most mammalian cells and in blood serum serve as a source of adenosine derived from extracellular nucleotide degradation (11). The 5'-ectonucleotidases are phosphatases whose substrate is extracellular adenosine 5'-monophosphate (AMP) generated from adenosine 5'-tri- and diphosphates (ATP and ADP) released from injured tissues to stimulate cellular responses via P2 purinergic receptors (7). A recent study by Quintero et al. (10) investigated prostatic acid phosphatase (PAP), a 5'-ectonucleotidase that plays a role in the development of adenocar-cinoma of the prostate gland. These authors showed that PAP exists as two alternative splice variants, a transmembrane prostatic acid phosphatase (TMPAP) and secreted PAP (sPAP). TMPAP and sPAP are distinguished functionally from other 5'-nucleotidases through inhibition by L-(+)-tartrate, ability to cleave phosphomonoesters besides AMP, and activity over a wide pH range (i.e., 3-8). TMPAP activation inhibits endocytosis/exocytosis through interaction with snapin (10), a soluble N-ethylmaleimide-sensitive-factor attachment protein receptor (SNARE)-associated protein (5) that negatively regulates secretory vesicle docking and fusion with plasma- membranes (Fig. 1). In addition, adenosine generated by PAP is an agonist for G protein-coupled A1 adenosine receptors (A_1R) that counteract the nociceptive (i.e., pain-producing) effects of ATP (4) occurring through activation of P2X receptor ATP-gated ion channels (2; Fig. 1). However, little information is available concerning physiological roles of sPAP in biological fluids.