Role of Protein Tyrosine Phosphatase Epsilon (PTPε) in Leukotriene D₄-Induced CXCL8 Expression

Abstract

Phosphorylation on tyrosine residues is recognized as an important mechanism for connecting extracellular stimuli to cellular events and defines a variety of physiologic responses downstream of G protein-coupled receptor (GPCR) activation. To date, few protein tyrosine phosphatases (PTPs) have been shown to associate with GPCRs, and little is known about their role in GPCR signaling. To discover potential cysteinyl-leukotriene receptor (CysLT 1 R)-interacting proteins, we identified protein tyrosine phosphatase « (PTP«) in a yeast two-hybrid assay. Since both proteins are closely linked to asthma, we further investigated their association. Using a human embryonic kidney cell line 293 (HEK-293) cell line stably transfected with the receptor (HEK-LT1), as well as human primary monocytes, we found that PTP« colocalized with CysLT 1 R in both resting and leukotriene D4 (LTD 4 )stimulated cells. Cotransfection of HEK-LT1 with PTP« had no effect on CysLT 1 R expression or LTD 4 -induced internalization, but it inhibited LTD 4 -induced CXC chemokine 8 (CXCL8) promoter transactivation, protein expression, and secretion. Moreover, reduced phosphorylation of extracellular signal regulated kinase 1/2 (ERK1/2), but not of p38 or c-Jun-Nterminal kinase 1 or 2 mitogen-activated protein kinases (MAPKs), was observed upon LTD 4 stimulation of HEK-LT1 coexpressing cytosolic (cyt-) PTP«, but not receptor (R) PTP«. The increased interaction of cyt-PTP« and ERK1/2 after LTD 4 stimulation was shown by coimmunoprecipitation. In addition, enhanced ERK1/2 phosphorylation and CXCL8 secretion were found in LTD 4 -stimulated human monocytes transfected with PTP«-specific siRNAs, adding support to a regulatory/inhibitory role of PTP« in CysLT 1 R signaling. Given that the prevalence of severe asthma is increasing, the identification of PTP« as a new potential therapeutic target may be of interest.

RPTPε promotes M2-polarized macrophage migration through ROCK2 signaling and podosome formation

“…PTPε was of interest here since it is relevant in allergic asthma (Tremblay et al, 2008) and our previous results suggested that it is involved in inflammatory processes modulated by cys-LTs. In addition, whereas previously published data showed that PTPε isoforms were expressed in a non-overlapping expression patterns in murine cell types (Elson and Leder, 1995;Gil-Henn et al, 2000), we showed that both cyt-PTPε and RPTPε were both expressed in human primary monocytes (Lapointe et al, 2019) but their targets were divergent. Thus, the expression pattern and its possible functional significance were the focus of this study.…”

“…3B). Moreover, cyt-PTPεPD1 expression, a splice form of cyt-PTPε, found only in monocytic cells (Wabakken et al, 2002) and previously identified in human monocytes according to its predicted molecular mass (Lapointe et al, 2019), was significantly upregulated in M1-polarized hMDMs (Fig. 3C).…”

“…We have previously shown that cyt-PTPε and RPTPε were involved in LTD 4 -induced CysLT 1 R signaling (Lapointe et al, 2019) with cyt-PTPε having the predominant role in IL-8 production. Here, we first studied the effect of LTD 4 on cyt-PTPε and RPTPε expression.…”

“…cyt-PTPε and RPTPε expression is differentially modulated by cytokines in human primary monocytes Regulation of PTPε expression has not been fully studied in human cells. However, unlike rat and murine cells, human primary monocytes express cyt-PTPε and RPTPε simultaneously (Lapointe et al, 2019). To follow up on this observation, we were interested in examining the modulation of expression of PTPε isoforms in these cells as they are the precursors of hMDMs in vitro and macrophages in vivo.…”

“…In the majority of murine cell types examined, cyt-PTPε and RPTPε expression is mutually exclusive (Elson and Leder, 1995). However, we have previously shown that both isoforms are expressed in human primary monocytes (Lapointe et al, 2019). Their divergent pattern of expression in polarized human monocyte-derived macrophages (hMDMs) is the focus of the present study.…”