Phosphorylation of human gp130 at Ser-782 adjacent to the di-leucine internalization motif - Effects on expression and signaling

The receptor for leukemia inhibitory factor (LIF) consists of two polypepti des, the LIF receptor and gp130. Agonist stimulation has been shown previou sly to cause phosphorylation of gp130 on serine, threonine, and tyrosine re sidues. We found that gp130 fusion proteins were phosphorylated exclusively on Ser-782 by LIF- and growth factor-stimulated 3T3-L1 cell extracts. Ser- 780 was required for phosphorylation of Ser-782 but was not itself phosphor ylated. Ser-782 is located immediately N-terminal to the di-leucine motif o f gp130, which regulates internalization of the receptor. Transient express ion of chimeric granulocyte colony-stimulating factor receptor (G-CSFR)-gp1 30(S782A) receptors resulted in increased cell surface expression in COS-7 cells and increased ability to induce vasoactive intestinal peptide gene ex pression in IMR-32 neuroblastoma cells when compared with expression of chi meric receptors containing wild-type gp130 cytoplasmic domains. These resul ts identify Ser-782 as the major phosphorylated serine residue in human gp1 30 and indicate that this site regulates cell surface expression of the rec eptor polypeptide.