The cytoplasmic tyrosine motifs is full-length glycoprotein 130 have different roles in IL-6 signal transduction

The function of the signal-transducing receptor subunit glycoprotein 130 (g p130) in the IL-6-receptor complex has previously been studied using carbox yl-terminal deletion mutants or a truncated molecule of similar to 60 membr ane-proximal amino acids (containing box 1 and box 2) linked to the individ ual gp130 tyrosine moths, However, the redundancy of the tyrosine moths wit hin the cytoplasmic part of gp130 has been neglected, Here we describe the analysis of the function of the individual cytoplasmic tyrosine residues of gp130 in the context of the full-length receptor protein in IL-6 signaling as measured by STAT activation, acute phase protein induction, and stimula tion of proliferation. Add-back receptor mutants containing only one cytopl asmic tyrosine have been generated and tested for their efficiency in IL-6 signal transduction, Our studies revealed that tyrosine motifs which have b een described to recruit STAT proteins are not equivalent with respect to t heir potential to activate STAT factors and acute phase protein gene promot ers: the two distal tyrosines, Tyr(905) and Tyr(915), Of gp130 were more pa tent than Tyr(767) and Tyr(814), Surprisingly, Tyr(405) and Tyr(915) mediat e acute phase protein gene promoter activation stronger than the wild-type receptor containing all six cytoplasmic tyrosine residues. In contrast, Ba/ F3 cells stably transfected with add-back receptors containing Tyr(767) Or. Tyr(905) were more sensitive to IL-6-induced proliferation than cells expr essing the other add-back receptor mutants. Thus, the tyrosine residues in the cytoplasmic part of gp130 were found to contribute differentially to IL -6 signal transduction in the full-length gp130 protein.