CSF-1 RECEPTOR INSULIN-RECEPTOR CHIMERA PERMITS CSF-1-DEPENDENT DIFFERENTIATION OF 3T3-L1 PREADIPOCYTES

A chimeric growth factor receptor (CSF1R/IR) was constructed by splici ng cDNA sequences encoding the extracellular ligand binding domain of the human colony stimulating factor-1 (CSF-1) receptor to sequences en coding the transmembrane and cytoplasmic domains of the human insulin receptor. The addition of CSF-1 to cells transfected with the CSF1R/IR chimera cDNA stimulated the tyrosine phosphorylation of a protein tha t was immunoprecipitated by an antibody directed against the carboxyl terminus of the insulin receptor. Phosphopeptide maps of the P-32-labe led CSF1R/IR protein revealed the same pattern of phosphorylation ob s erved in P-32-labeled insulin receptor beta subunits. CSF-1 stimulated the tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1) and Shc in cells expressing the CSF1R/IR chimera. Lipid accumulation a nd the expression of a differentiation specific marker demonstrated th at 3T3-L1 preadipocytes undergo CSF-1-dependent differentiation when t ransfected with the CSF1R/IR chimera cDNA but not when transfected wit h the expression vector alone. A 12-amino acid deletion within the jux tamembrane region of the CSF1R/IR (CSF1R/IR Delta 960) blocked CSF-1-s timulated phosphorylation of IRS-1 and She but did not inhibit CSF-1-m ediated differentiation of 3T3-L1 preadipocytes. These observations in dicate that adipocyte differentiation can be initiated by intracellula r pathways that do not require tyrosine phosphorylation of IRS-1 or Sh c.