IDENTIFICATION AND CHARACTERIZATION OF 2 DISTINCT TRUNCATED FORMS OF GP130 AND A SOLUBLE FORM OF LEUKEMIA INHIBITORY FACTOR-RECEPTOR ALPHA-CHAIN IN NORMAL HUMAN URINE AND PLASMA

Leukemia inhibitory factor (LIF) is a polyfunctional cytokine known to require at least two distinct receptor components (LIF receptor alpha -chain and gp130) in order to form a high affinity, functional recepto r complex. In this report, we present evidence that there are two dist inct truncated forms of gp130 in normal human urine and plasma: a larg e form with a molecular weight of approximately 100,000, which is simi lar to a previously described form of soluble gp130 in human serum, an d a previously undescribed small form with a molecular weight of appro ximately 50,000. Using a panel of monoclonal antibodies raised against the extracellular domain of human gp130, we were able to show that th e small form of the urinary gp130 probably contained only the hemopoie tin domain. Both forms of gp130 bound LIF specifically and were capabl e of forming heterotrimeric complexes with soluble human LIF receptor alpha-chain in the presence of human LIF. In addition to the soluble f orms of gp130, a soluble form of LIF receptor alpha-chain was also det ected in human urine and plasma.