Distinct overlapping sequences at the carboxy-terminus of merlin regulate its tumour suppressor and morphogenic activity.
The Neurofibromatosis 2 (NF2) gene product merlin is a tumour suppressor, which in addition to inhibiting cell proliferation regulates cell morphology. The morphogenic properties of merlin may play a role in tumour suppression, as patient-derived tumour cells demonstrate cytoskeletal abnormalities. However, it is still unclear how these functions are linked. The N-terminal FERM-domain of merlin is highly homologous to the oncogenic protein ezrin, while the C-termini are less conserved, suggesting that the opposite effect of the proteins on proliferation could be mediated by their distinct C-terminal regions. In this study we characterize the role of the most C-terminal residues of merlin in the regulation of proliferation, cytoskeletal organization, phosphorylation and intramolecular associations. In addition to the two full-length merlin isoforms and truncating mutations found in patients, we focused on the evolutionally conserved C-terminal residues 545-547, also harbouring disease-causing mutations. We demonstrate that merlin induces cell extensions, which result from impaired retraction of protrusions rather than from increased formation of filopodia. The residues 538-568 were found particularly important for this morphogenic activity. The results further show that both merlin isoforms are able to equally inhibit proliferation, whereas C-terminal mutants affecting residues 545-547 are less effective in growth suppression. This study demonstrates that the C-terminus contains distinct but overlapping functional domains important for regulation of the morphogenic activity, intramolecular associations and cell proliferation.
Biomedicum Helsinki, Department of Pathology, University of Helsinki, Helsinki, Finland. minja.pehrsson@helsinki.fi
Minja
M
Laulajainen
Maria
M
Melikova
Taru
T
Muranen
Olli
O
Carpén
Mikaela
M
Grönholm
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D049109:Cell Proliferation; D002522:Chlorocebus aethiops; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism; D003599:Cytoskeleton / Q000235:genetics / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation; D016147:Genes, Tumor Suppressor; D057809:HEK293 Cells; D006801:Humans; D015151:Immunoblotting; D051379:Mice; D008969:Molecular Sequence Data; D025581:Neurofibromin 2 / Q000235:genetics* / Q000378:metabolism; D010641:Phenotype; D010766:Phosphorylation; D020033:Protein Isoforms; D011554:Pseudopodia / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D000099149:Ezrin
D003598:Cytoskeletal Proteins; D025581:Neurofibromin 2; D020033:Protein Isoforms; D000099149:Ezrin