ALTERED CELL-SURFACE EXPRESSION AND SIGNALING OF LEPTIN RECEPTORS CONTAINING THE FATTY MUTATION

Leptin and the leptin receptor are key players in the regulation of bo dy weight. In an attempt to dissect the molecular mechanism of the Zuc ker fatty rat leptin receptor mutation (Gln(269) --> Pro) we analyzed the effects of this mutation on leptin receptor signaling and expressi on in three different expression systems: 1) 32D cells expressing lept in/erythropoietin receptor chimeras, 2) COS-7 cells expressing a lepti n receptor short form, and 3) 293 cells expressing soluble receptor fo rms. To determine if the Gln(269) --> Pro mutation is critical for the observed phenotype, we made a similar Gln --> Pro mutation at a vicin al residue two amino acids upstream of the fatty mutation to see if it would have similar effects. Incorporation of either of the Gln --> Pr o mutations into wild type receptor forms did not interfere with lepti n binding, but it resulted in a signaling-incompetent receptor. In add ition, the majority of the mutant receptor protein was localized intra cellularly. Our results suggest that the obese phenotype resulting fro m the Gln(269) --> Pro mutation in the leptin receptor of the Zucker f atty rat may be due not only to a reduced cell surface expression of t his form of the leptin receptor, but also to a post-leptin binding mal function of the receptor that interferes with subsequent signal transd uction.