PL4. PROTEIN FOLDING: IMPLICATIONS FOR REPRODUCTIVE DISEASES. Conn, P. Michael¹, ¹ Oregon National Primate Research Center, Beaverton, OR
     The GnRH receptor (GnRHR) is a heptahelical G protein coupled receptor (GPCR) found in the plasma membrane of pituitary gonadotropes. GnRHR mutants isolated from patients with hypogonadotropic hypogonadism (HH) are frequently mislocalized proteins; the vast majority of these (12 of the 15 point mutations reported) can be restored to function by peptidomimetic antagonists, acting as pharmacological chaperones or "pharmacoperones." Structure-activity relations have been described for members of three different chemical classes of pharmacoperones. In addition to naturally occurring mutations, "designer" mutants replacing Cys (needed for stabilization of the tertiary structure of the receptor) by Ala, or internal deletions or truncations, can also be rescued by this approach or by alterations in the genetic sequence of the receptor. Non-functional HH mutants also inhibit ligand binding and ligand activated second messenger production by wild type receptor when both are co-expressed in vitro. Confocal microscopy shows that this "dominant-negative effect," (which occurs for human but not for rodent GnRHR), results from wild type receptor retention in the endoplasmic reticulum by mislocalized mutants. Pharmacoperones also rescue the wild type receptor from retention. Because of the large number of human diseases that appear to be caused by defective protein folding and subsequent mislocalization, it is likely that endoplasmic reticulum retention is a common cause of dominant-negative actions for other diseases involving GPCRs, as appears to be the case in HH and for which there exists a potential therapeutic agent. (Supported by: HD-19899, RR-00163, TW/HD-00668 and HD-18185). References: 1. Conn, P.M., Leanos-Miranda, A and Jo Ann Janovick, J. Molecular Interventions 2 (5): 308-316, 2002. 2. Janovick, J., Goulet, M., Bush, E. Greer, J, Wettlauffer, D, and Conn, P.M., J. Pharmacol. Experimental Therapeutics, 305(2): 608-614, 2003 3. Janovick, J.A., Maya-Nunez, G., Conn, P.M. J. Clin. Endocrinol. Metab. 87(7):3255-3262, 2002 4. Leanos-Miranda, A, Janovick, J and Conn, P.M, J. Clin. Endocrinol. Metab. 87(10): 4825-4828 2002. 5. Brothers, S.P. and Conn, P.M., J. Clin. Endocrinol. Metab.88: 6107-6112, 2003. 6. Leanos-Miranda, A, Ulloa Aguirre, A , Ji, T.H., Janovick, J., Conn, P.M., , J Clin Endocrinol Metab 88: 3360-3367, 2003. 7. Janovick, J, Ulloa-Aguirre, A and Conn, PM, Endocrine 22(3):317-328, 2003. 8. Brothers, S.P., Cornea, A, Janovick, J.A. and Conn, P.M., Molecular Endocrinology 18 (7): 1787-1797 (2004), July 2004). 9. Ulloa-Aguirre, A., Janovick, J., Leanos-Miranda, A., Conn, P. M., , Expert Opinion on Therapeutic Targets, 7(2):175-185, 2003. 10. Ulloa-Aguirre, A., Janovick, J.A., Leanos-Miranda, A., and Conn, P.M., Human Reproduction Update, 10 (2): 177-192, 2004, 2004. 11. Ulloa-Aguirre, A., Janovick, J., Brothers, S. and Conn, P.M., Pharmacological Rescue of Conformationally-Defective Proteins: Implications for the Treatment of Human Disease, Traffic 5: 821-837, 2004 published online 8-Oct-2004 (cover image). 12. Castro-Fernandez, C, Maya-Nunez, G and P. Michael Conn, Beyond the Signal Sequence: Protein Routing in Health and Disease, manuscript in press, published online November 8, 2004; Endocrine Reviews, 2005. 13. Leanos-Miranda, A., Ulloa-Aguirre, A., Janovick, J.A. and Conn, P.M., In Vitro Coexpression and Pharmacological Rescue of Mutant GnRH Receptors Causing Hypogonadotropic Hypogonadism in Humans Expressing Compound Heterozygous Alleles. In press, J Clin Endocrinol Metab 2005.