1. NF2/Merlin
Michael Anderson

2. Hepatocellular carcinomas
Diseases
Schwannomas are hallmark trait
Rare
NF2 encoded tumor suppressor Merlin
Neurofibromatosis 2
NF2 mutations found in sporadic mesotheliomas associated with asbestos exposure
Mesotheliomas
NF2 mutations discovered more recently
Help reveal additional cell types affected by NF2 loss
Thyroid carcinomas
Hepatocellular carcinomas
Perineurial tumors

3. Neurofibromatosis 2
Hallmark of disease are schwann cell tumors (schwannomas)
Rare Occurrence
1/25,000 individuals
Autosomal dominant genetic disease
Tumors are benign and slow growing, responding poorly to chemotherapy
Schwannomas most often found on vestibular branch of both 8th cranial nerves
Highly Penetrant
>95%

4. Loss of Merlin leads to SC hyperproliferation and tumorigenesis in animal models
Stained section of schwannoma emanating from the trigeminal nerve of a NF2 mutant mouse
Schwann cell hyperplasia in the sciatic nerve of a NF2 mutant mouse
Loss of Merlin leads to SC hyperproliferation and tumorigenesis in animal models. (A) Hematoxylin and eosin (H&E)-stained section of frank schwannoma emanating from the trigeminal nerve of a P0- Cre;Nf2flox2/flox2 mouse (*). (B) H&E-stained section depicting SC hyperplasia in the sciatic nerve of a P0-Cre;Nf2flox2/flox2 mouse. (C) Malignant peripheral nerve sheath tumor in Nf2a-mutant zebrafish. Zebrafish bearing a germline mutation in one allele of the NF2a gene develop spindle cell tumors that have features in common with nerve sheath tumors from other species (image kindly provided by K. Edepli) (Amsterdam et al. 2004).
Malignant peripheral nerve sheath tumor (MPNST) in NF2 mutant zebrafish.
McClatchey A. I., Giovannini M. Genes Dev. 2005;19:

5. NF2 NF2 is located on Chromosome 22 Tumor suppressor
First tumor suppressor gene to encode more of a structure protein than an inhibitor
Encodes Protein Merlin
Genetics Home Reference, 2007.

6. Merlin Amino Acid similar to Ezrin, Radixin, Moesin (ERM) proteins
Blocks cell proliferation
Located near membrane
Regulates linkage between membrane associated proteins and cytoskeleton
Responsible for receiving and interpreting signals from extracellular milieu

7. Merlin
Serine Residue 518 (S518) phosphorylation weakens self-association inactivating the growth suppressing Merlin
Activation of the small GTPase Rac1 is most common method of phosphorylation of S518
In folded conformation it is the N-terminal and C-terminal that associate
Fagan T., Conjuring with Merlin, 2001

8. Merlin-organized complexes prevent mitogenic signaling and contact-dependent inhibition of proliferation
Merlin-organized complexes prevent mitogenic signaling and contact- dependent inhibition of proliferation. (Left) At low cell density in cell culture, Merlin is predominantly hyperphosphorylated and inactive and mitogenic signaling proceeds. Similarly, upon cell reattachment to certain ECM substrates, a pool of Merlin is rapidly phosphorylated. (Right) At high cell density in cell culture, Merlin is hypophosphorylated, self-associated, and active in mediating contact- dependent inhibition of proliferation. Merlin is recruited to nascent cell:cell boundaries where it appears to stabilize AJs between cells, perhaps by inhibiting Rac/Pak signaling and/or stabilizing the actin cytoskeleton. Under these conditions, Merlin may inhibit signaling from AJ-associated growth-factor receptors. Hypophosphorylated Merlin can also interact with cell:ECM receptors such as CD44, which binds to hyaluronic acid (HA); increased CD44:HA interaction with increased cell density leads to high levels of active Merlin, which may inhibit associated growth-factor receptors. Notably, complete cell detachment also leads to hypophosphorylation and activation of Merlin. Perhaps inhibited mitogenic signaling from multiple complexes accumulates, reaching a threshold that halts proliferation. The study and manipulation of cell:cell contact in two dimensions in cell culture is nonphysiological; in vivo cells in a tissue are contacting other cells and can override contact-dependent inhibition of proliferation under certain normal conditions or in the context of a tumor. Merlin may coordinate the receipt of physical information from the extracellular milieu with the receipt and processing of mitogenic stimuli.
McClatchey A. I., Giovannini M. Genes Dev. 2005;19:

9. Curto M., et al., Contact Dependent Inhibition, 2007.

10. Mutations of NF2
Rare
Often
Deletions
Nonsense
Missense

11. Type of Mutation
Number of people
Number of Families
Nonsense
293
232
Frameshift deletion
159
128
Frameshift insertion 47 41
Indel 10
Splice donor site
174 88
Splice acceptor site
150 86
Missense 35
In-frame deletion 18
In-frame insertion 13 4
Large deletion
141 80
Large insertion 3
Chromosomal translocation 15
Total
1,112
738
Baser M. E., NF2 Mutation Databases, 2004.

12. Oncogenic Properties Blocks cell proliferation Contact Inhibition
Inactivated merlin leads to hyperproliferation
Contact Inhibition
Merlin regulates contact-dependent inhibition of proliferation
Phosphorylation regulated by cellular density
Interaction with Epidermal Growth Factor Receptor
Merlin can inhibit EGFR upon cell to cell contact

13. Summary NF2 encodes protein Merlin
Merlin acts as a tumor suppressor by regulating proliferation
First tumor suppressor to act as more of a structural protein
Merlin located near cell membrane and regulates contact-dependent inhibition of proliferation
Absence of Merlin causes over proliferation and most often Neurofibromatosis
Neurofibromatosis is autosomal dominant most often resulting in schwannomas