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 IL6 receptor (mIL6R) 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 IL6 (mIL6). We monitored response to the cytokine through the transcriptional activation of a co-transfected IL6-inducible human C-reactive protein (CRP) promoter; response to mIL6 is lost upon treatment of the cells with increasing amounts of a monoclonal antibody to mIL6R. mIL6R 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 IL6 signal transduction (i.e. CRP promoter activation), but that the last 40 amino acids contribute to maximal IL6 response in these cells.