1. RET Receptor
Ashley Bass

2. 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

3. 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

4. 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

5. 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

7. 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

8. 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

9. 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

10. 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)

11. 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

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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

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