Role of Protein Tyrosine Phosphatase Epsilon (PTPϵ) in LTD4-Induced CXCL8 Expression

Phosphorylation on tyrosine residues is recognized as an important mechanism for connecting extracellular stimuli to cellular events and defines a variety of physiological responses downstream of G protein-coupled receptor (GPCR) activation. To date, very few protein tyrosine phosphatases (PTPs) have been shown to associate with GPCRs and little is known about their role in GPCR signaling. In an attempt to discover potential cysteinyl-leukotriene receptor (CysLT1R)-interacting proteins, we identified protein tyrosine phosphatase epsilon (PTPϵ) in a yeast two-hybrid assay. Since both proteins are closely linked to asthma, their association was further investigated. Using a HEK-293 cell line stably transfected with the receptor (HEK-LT1) as well as human primary monocytes, we found that PTPϵ co-localized with CysLT1R in both resting and leukotriene D4 (LTD4)-stimulated cells. Co-transfection of HEK-LT1 with PTPϵ had no effect on CysLT1R expression or LTD4-induced internalisation, but inhibited LTD4-induced CXC chemokine 8 (CXCL8) promoter transactivation, protein expression and secretion. Moreover, reduced phosphorylation of ERK1/2, but not of p38 or JNK1/2 MAPKs, was observed upon LTD4 stimulation of HEK-LT1 co-expressing cytosolic (cyt-) PTPϵ, but not receptor (R) PTPϵ. The increased interaction of cyt-PTPϵ and ERK1/2 after LTD4 stimulation was shown by co-immunoprecipitation. In addition, enhanced ERK1/2 phosphorylation and CXCL8 secretion were found in LTD4-stimulated human monocytes transfected with PTPϵ-specific siRNAs adding support to a regulatory/inhibitory role of PTPϵ in CysLT1R signaling. Given that the prevalence of severe asthma is increasing, the identification of PTPϵ as a new potential therapeutic target may be of interest.