Effects of transmembrane and juxtamembrane domains on proliferative ability of TSLP receptor

Thymic stromal lymphopoietin (TSLP) is an IL-7-like cytokine that requires a heterodimeric receptor complex composed of the interleukin-7 receptor alpha chain and the TSLP receptor, which is related to the common gamma chain. TSLP has been shown to play an important role in the development of allergic inflammation, such as asthma and atopic dermatitis. Chimeric receptors composed of the cytoplasmic region of the TSLP receptor fused to the extracellular regions of homodimeric receptors, such as erythropoietin (Epo) receptor and thrombopoietin receptor have been used to dissect signaling events induced by the TSLP receptor. Intriguingly, studies using such chimeric TSLP receptors revealed that the human, but not mouse, TSLP receptor cytoplasmic domain can support proliferation of growth factor-dependent cells after homodimerization. Here, we used a systematic approach to investigate the mechanistic basis of this difference. Our studies revealed that induced homodimerization of receptor chimeras containing the transmembrane and cytoplasmic domains of both human and mouse TSLP receptors is not sufficient for driving cell proliferation. However, chimeric receptors with the transmembrane and juxtamembrane domains of Epo receptor fused to the cytoplasmic domain of human TSLP receptor signal like the Epo receptor and induce the activation of Jak2. Site-directed mutagenesis showed that the lone tyrosine residue in human TSLP receptor is not required for transmitting proliferative signals in receptor chimeras, which is consistent with the observation that none of the tyrosine residues are required for Epo receptor to support proliferation. Our data suggests that in the chimeric receptor context, the transmembrane and juxtamembrane domains of mouse Epo receptor are essential for the cytoplasmic domain of human TSLPR to achieve the strong proliferative ability and can modulate signaling pathway transmitted by the cytoplasmic domains of these chimeras.