Both retinoids and the mannose 6-phosphate/insulin-like growth factor-II (M6P/IGF2) receptor have been shown to play fundamental roles in the control of cell growth in development and oncogenesis. Recent work has discovered that retinoic acid (RA) binds to the M6P/IGF2 receptor with high affinity, leading to alteration of the primary functions of the receptor and suppression of cell growth. These findings suggest that M6P/IGF2 receptor mediates a novel RA response pathway that may be important in cell growth regulation. However, the molecular mechanism underlying this pathway remains largely unknown. Thus, the overall goal of this proposal is to understand how RA interacts with the M6P/IGF2 receptor and the role of this interaction in cell growth regulation. The key questions that we wish to address are: 1) Where is the functional domain of the receptor protein responsible for retinoid binding? 2) What is the authentic biological consequence of the interaction? and 3) How do they work? Accordingly, the specific aims of this application are: (1) To identify the retinoid binding site of the M6P/IGF2 receptor; (2) To extend the understanding of the biological consequence of the RA-M6P/IGF2R interaction. (3) To identify the biochemical processes responsible for the biological effect of RA-M6P/IGF2R interaction. Our general approach is to create a mutant M6P/IGF2R that fails to bind RA and then assess differences of functional responses to RA between the cells expressing wild-type M6P/IGF2R and those with the mutant receptor. The principal methods to be used include protein mutagenesis, photoaffinity labeling, amino acid sequence analysis, ligand binding assay, immuno-detection, enzymatic assay and morphological analysis. Significance This project will provide fundamental information about how retinoids interact with the M6P/IGF2 receptor and shed light on the role of this novel retinoid-response pathway in regulation of cell growth. This knowledge may lead to novel or more effective therapeutic and preventive approaches for cancer and developmental defects.
