RET

Multiple Endocrine Neoplasia Type 2 (MEN2)

Brooke Martin

3/20/08

History of RET

• Discovered in 1985 by the transfection of NIH3T3 cells with DNA from T cell lymphoma cells

• RET stands for– rearranged during transfection

• Can have either loss of function or gain of function mutations

RET Properties

• Transmembrane protein and RTK• Mainly found in precursors of the urogenital

system and neural crest• Has 3 isoforms

– short (RET9), middle(RET43), and long (RET51)

• Homodimer– Also pairs with GFR (growth factor

receptor)α 1, 2, 3, and 4• Ligands

– GDNF (glial-derived neurotrophic factor), neurturin (NTN), persephin (PSP), and artemin

GDNF Family with Receptors SIGMA-ALDRICH

RET Properties Continued

•Gene found on long arm of chromosome 10 at 11.2•Gene has 21 exons•Cadherin part must bind with Ca2+ in order for RET to work•5 phosphotyrosine residues

–2 more in long isoform

Protein Structures of RET

Unphosphorylated

Phosphorylated

J. Biol. Chem. v281, p.33577-33587

What Does RET Do Normally?

• Helps with kidney development and enteric nervous system

• Also implicated in cell differentiation and apoptosis

Knockout Mice

• Knockouts had no neurons in the gut, superior cervical ganglia, no kidneys at all or malformed and malfunctioning

• RET null mutation die shortly after birth

• No endocrine organs affected in MEN 2

• Heterozygotes have no apparent defects

MEN 2-multiple endocrine neoplasia type 2

• Inherited form of cancer and very rare• First to be discovered in 1993 that MEN 2 was

caused by germline mutations• Three subtypes

– MEN 2A and MEN 2B– Familial medullary thyroid carcinoma (FMTC)

• Autosomal dominant• RET constitutively active • Endocrine glands affected

– Adrenal, parathyroid, and thyroid• Gain of function mutations

MEN 2A

Codons effected 630, 634,(exon 11) or 609, 611, 618, 620 (exon10)

Mutation to 634 worst90% of MEN 2A have this. 50% have change from a cysteine to argenine

How RET is activeLigand-independent dimerization, loss of disulfide bond between dimers

Tumors developed Pheochromocytoma, MTC

Incidence100% get MTC, 50% pheochromocytoma, 15-30% parathyroid hyperplasia

MEN 2B

Codons affected

918, change from methionine to threonine (exon 16)883 in TK domain but rare (5%)

Most aggressive of the three

95% have the M918T mutation

What keeps RET active

Made to look unlike an RTK from mutation, changes autophosphorylation

Tumors developed and incidence

100% MTC, 50% pheochromocytoma, very rare parathyroid hyperplasia

Pattern of phosphorylation

The proteins phosphorylated differs form MEN 2A

FMTC

• Have the same mutations as 2A in extracellular domain but also can be in TK domain at 768, 790, 791,(exon 13); 804, 844,(exon 14); or 891 (exon15)

• Have mild C cell disease• Low transforming activity can

predispose to FMTC rather than MEN 2A

Treatment and Testing

• Thyroidectomy– Before age 6 or 6-12 depending on mutation– If MEN 2B, needed before a year old– Have to take thyroid for the rest of life

• Chemotherapy not effective• Microarray (best)• Direct sequencing or single-strand

conformational polymorphism• Drugs being tested to disrupt RET

kinase activity– Needs a higher concentration though

Questions?