Significance of N-terminal proteolysis of CCL14a to activity on the chemokine receptors CCR1 and CCR5 and the human cytomegalovirus-encoded chemokine receptor US28.
J Immunol, 183 (2):
1229-37 (2009)Abstract
The CC chemokine CCL14a is constitutively expressed in a large variety of tissues and its inactive proform CCL14a(1–74) circulates in high concentrations in plasma. CCL14a(1–74) is converted into CCL14a(9–74) by the proteases urokinase-type plasminogen activator and plasmin and is a highly active agonist for the chemokine receptors CCR1 and CCR5. In this study, a new CCL14a analog, CCL14a(12–74), was isolated from blood filtrate. To elucidate the functional role of the N terminus, a panel of N-terminally truncated CCL14a analogs were tested on the receptors CCR1 to CCR5 and on the human cytomegalovirus (HCMV)-encoded chemokine receptor US28. The rank order of binding affinity to these receptors and of the activation of CCR1 and CCR5-mediated intracellular Ca2+ concentration mobilization is CCL14a(6–74)<(7–74)<(8–74)<<(9–74) = (10–74)>>(11–74)>>(12–74). The almost identical affinities of CCL14a(7–74), CCL14a(9–74), and CCL14a(10–74) for the US28 receptor and the inhibition of US28-mediated HIV infection of 293T cells by all of the N-terminally truncated CCL14a analogs support the promiscuous nature of the viral chemokine receptor US28. In high concentrations, CCL14a(12–74) did reveal antagonistic activity on intracellular Ca2+ concentration mobilization in CCR1- and CCR5-transfected cells, which suggests that truncation of Tyr11 might be of significance for an efficient inactivation of CCL14a. A putative inactivation pathway of CCL14a(9–74) to CCL14a(12–74) may involve the dipeptidase CD26/dipeptidyl peptidase IV (DPPIV), which generates CCL14a(11–74), and the metalloprotease aminopeptidase N (CD13), which displays the capacity to generate CCL14a(12–74) from CCL14a(11–74). Our results suggest that the activity of CCL14a might be regulated by stringent proteolytic activation and inactivation steps.