Expression of the murine interleukin 6 receptor in hepatoma cells: the intracytoplasmic domain is not required for interleukin 6 signal transduction

This paper reports on cDNA coding for the 80-kDa murine IL 6 receptor (mIL 6R) that was cloned from a mouse liver cDNA library. Human hepatoma Hep3B cells transfected transiently or stably with an expression vector carrying the entire coding region for mIL6R become responsive to mouse IL 6 (mIL 6). We monitored response to the cytokine through the transcriptional activation of a co-transfected IL 6-inducible human C-reactive protein (CRP) promoter; response to mIL 6 is lost upon treatment of the cells with increasing amounts of a monoclonal antibody to mIL 6R. mIL 6R mutants have been generated in the carboxy-terminal portion of the molecule. Their functional analysis in hepatoma cells shows that the intracytoplasmic domain of the receptor is not absolutely essential to IL 6 signal transduction (i.e. CRP promoter activation), but that the last 40 amino acids contribute to maximal IL 6 response in these cells.