A receptor subunit that combines with cytokine receptor gp130 to form the dual specificity receptor for leukemia inhibitory factor and oncostatin m. The subunit is also a component of the ciliary neurotrophic factor RECEPTOR. Both membrane-bound and secreted isoforms of the receptor subunit exist due to alternative splicing of its mRNA. The secreted isoform is believed to act as an inhibitory receptor, while the membrane-bound form is a signaling receptor.