RET Receptor Ashley Bass

What is RET? 10q11.2 21 exons Transmembrane Receptor Tyrosine Kinase Oncogene Identified in 1985 after transfection into NIH3T3 cells of DNA derived from a human T-cell lymphoma. REarranged during Transfection http://ghr.nlm.nih.gov

RET Schematic Three isoforms – Ret 9 and Ret 51 most important (highly conserved between species) – different and tissue specific effects on embryogenesis and tumorigenesis, activate different neurons 9-kidney & ENS development and postnatal life 51-excretory and ens development; dispensible in development Four tandemly repeated cadherin like domains in extracellular domain Protein – N-terminal signal peptide, cadherin like motif, cysteine rich extracellular domain, transmembrane domain, and a tyrosine kinase domain De Groot et al. 2006

What does it do? Important in kidney and neural development Expressed in neural crest cells Proliferation, differentiation, growth and cell survival via RAS and PIK3 pathways

Activation of RET Ligand-induced receptor oligomerization which results in tyrosine autophosphorylation of receptor intracellular domain. Binding of ligand -> RET dimerization and transphosphorylatioon on specific tyrosine residues LIPID RAFTS – shingolipids and cholesterol within membrane; crucial for an abundant biological events including growth factor-receptor signaling. Co-receptors are anchored to the PM and localized to lipid rafts. GFR-a is more widely expressed than RET in neuronal tissues Inactive RET is outside rafts and is recruited by GFR-a1 upon stimulation of GDNF De Groot et al. 2006

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GDNF – 1, NTN – 2, PSP – 3, Artemin – 4 LIGAND: GFL’s Co receptor – GFR-α GDNF – 1, NTN – 2, PSP – 3, Artemin – 4 Multiple docking sites for phosphorylation – activates many pathways Y1062 very important (main dock) Mutation of tyrosine 1062 did not completely get rid of activation of RAS/ERK and PI3K/AKT pathways (alternative signaling pathways) De Groot et al. 2006

GDNF – 1, NTN – 2, PSP – 3, Artemin – 4 LIGAND: GFL’s Co receptor – GFR-α GDNF – 1, NTN – 2, PSP – 3, Artemin – 4 Multiple docking sites for phosphorylation – activates many pathways Y1062 very important (main dock) Mutation of tyrosine 1062 did not completely get rid of activation of RAS/ERK and PI3K/AKT pathways (alternative signaling pathways) De Groot et al. 2006

GDNF – 1, NTN – 2, PSP – 3, Artemin – 4 LIGAND: GFL’s Co receptor – GFR-α GDNF – 1, NTN – 2, PSP – 3, Artemin – 4 Multiple docking sites for phosphorylation – activates many pathways Y1062 very important (main dock) Mutation of tyrosine 1062 did not completely get rid of activation of RAS/ERK and PI3K/AKT pathways (alternative signaling pathways) De Groot et al. 2006

Knock Out Mice Die shortly after birth Renal agenesis or severe dysgenesis Absence of enteric neurons *Essential component of the signaling pathway required for renal and enteric nervous system development *Heterozygotes are normal -homozygotes died between 16 and 24 hours after birth -dysgenesis – severe dysplasia, reduced numbers of recognizeable nephric elements, and no recognizeable medulla, cortex, or nephrogenic zone, regions of undifferentiated mesenchyme Undifferentiated!! Unilateral or bilateral Ret receptor normally transduces a mesenchyme-derived signal that stimulates the formation, growth, and branching of the ureteric bud (renal system precursor)

Kidney Defects in RET Mutant Mice *Most common – no kidneys or ureters A – Wild type male a = adrenal k = kidney B = bladder u = ureter Schuchardt et al. 1994

RET & Human Disease Loss of Function Hirschprung’s Disease Homozygous RET mutants are useful animal models for the study of developmental defects underlying HSCR

Hirschprung’s Disease Absence of enteric neurons No peristalsis in GI tract Missense/nonsense mutation 1/5,000 live births Inherited and sporadic Treatment Most cases are sporadic – 15-20% familial cases; mutations found in RET pathway Can result from RET induced apoptosis in the absence of ligand Congenital – first noticed in newborns with swollen bellies More frequent in males (5X) Associated with other congenital diseases like Down Syndrome, thyroid cancer, neuroblastoma Inherited as autosomal dominant Surgical treatment – remove nonfunctional function of bowel

RET & Human Disease Loss of Function Chromosomal Rearrangements Hirschprung’s Disease Chromosomal Rearrangements Germline Mutations Gain of Function Multiple Endocrine Neoplasia Type II Familial Medullary Thyroid Carcinoma Chromosomal rearrangements – Papillary Thyroid Carcinoma due to radiation RET is constitutively active

Multiple Endocrine Neoplasia Type II Affects thyroid, parathyroid, and adrenal glands Autosomal Dominant 70% Penetrant 1/30,000 affected Point mutations in germline Treatment – removal of thyroid Good prognosis with early diagnosis and intervention Usually germine mutations result in the formation of inactive and recessive alleles at the cellular level. Mutant constitutively active oncogenes cannot be tolerated in the germline because they function as dominant alleles in cells and are therefore highly disruptive of normal embryonic development. Expression of cancer-inducing phenotype is delayed until late development. Diagnosed at any age and affects males and females equally. Signs and tests: blood test, physical exam 70% penetrant by age 70

MEN Type IIA vs. IIB Type IIA Type IIB Tumor Formation –parathyroid Hyperparathyroidism Mutation in cysteine region Later onset Less severe Type IIB Tumor Formation –mucosal neuromas Oral cavity, GI tract Mutation in tyrosine kinase domain Earlier onset More aggressive More rare BOTH – Medullary thyroid carcinoma, pheochromocytomas (adrenal glands) IIA – thyroidectomy around 6 years IIB- one year

Mucosal Neuromas Point Mutation: caused by a substitution in the tryosine kinase domain of the receptor Mutation alters substrate specificity of RET TK Thyroidectomy as early as one year www.valleyhealth.com

Familial Medullary Thyroid Carcinoma Extracellular or TK domain mutations Results in lower transforming activity Predisposition to FMTC instead of MEN 2A Benign Tumors of adrenal glands and parathyroid Usually cysteine substitutions Intracellular domain – infrequent and only small numbers of families with this mutation Some mutations also found in MEN 2A Lower transforming activity – predisposition to FMTC and not MEN 2A

Summary of RET Receptor Transmembrane receptor tyrosine kinase Involved in renal and neural development Thyroid Carcinoma Multiple Endocrine Neoplasia Type II Familial Medullary Thyroid Carcinoma **Involved in many pathways so it can cause different diseases. Disease depends on where mutation occurs in pathway

References Alberti et al. “RET and NTRK1 proto-oncogenes in human diseases.” Jour. of Cellular Physiology. 195:168-186 (2003). De Groot et al. “RET as a diagonostic and therapeutic target in sporadic and hereditary endocrine tumors.” Endocrine Reviews. 27(5): 535-560. Ichihara et al. “RET and neuroendocrine tumors.” Cancer Letters. 204:197-211 (2004). Manie et al. “The RET receptor: function in development and dysfunction in congenital malformation.” TRENDS in genetics. 17.10:580-589 (2001). Schuchardt et al. “Defects in the kidney and enteric nervous system of mice lacking the tyrosine kinase receptor Ret.” Nature. 367:380-383 (1994). Weinberg, Robert. The Biology of Cancer. New York: Garland Science, 2007.