COMPLEX OF THE SOLUBLE IL-11 RECEPTOR AND IL-11 ACTS AS IL-6-TYPE CYTOKINE IN HEPATIC AND NONHEPATIC CELLS

The signaling functions of the membrane and soluble form of the mouse IL-11 receptor (mIL-11R) were compared in rat and human hepatoma cells , which have a low endogenous IL-11 response. The expression vectors e ncoding either the full length or a secretory form of the ligand bindi ng subunit of mIL-11R together with IL-6-responsive reporter gene cons tructs were transiently transfected into the H-35 and HepG2, cells. An IL-11-specific stimulation of transcription was detected that was qua litatively similar to that mediated by the endogenous IL-6R. HepG2 cel ls were noted to synthesize constitutively IL-11, resulting in an auto crine stimulation of gene expression. Addition of COS cell-derived sol uble mIL-11R to the hepatoma cell cultures prominently enhanced IL-11 regulation of transfected reporter gene constructs and expression of e ndogenous acute phase plasma protein genes. Similarly, the complex of soluble mIL-11R and IL-11 was capable of mediating an IL-6-type signal ing in cells that are naturally deficient in It-ii response as shown b y the activation of STAT1 and STAT3 in mouse embryonal carcinoma cells and human T cells. The results indicate that the IL-11R can serve as a substitute to IL-6R in activating gene expression in target cells th at are devoid of the appropriate ligand-binding receptor subunits.