Vj. Obremski et al., MERLIN, THE NEUROFIBROMATOSIS TYPE-2 GENE-PRODUCT, AND BETA-1 INTEGRIN ASSOCIATE IN ISOLATED AND DIFFERENTIATING SCHWANN-CELLS, Journal of neurobiology, 37(4), 1998, pp. 487-501
Neurofibromatosis type 2, a disease characterized by the formation of
multiple nervous system tumors, especially schwannomas, is caused by m
utation in the gene-encoding merlin/schwannomin. The molecular mechani
sm by which merlin functions as a tumor suppressor is unknown, but is
hypothesized to involve plasma membrane and cytoskeleton interaction.
Several merlin antibodies were used to study merlin expression, locali
zation, and protein association in primary cultures of rat sensory neu
rons, Schwann cells (SCs), and SCs grown with neurons (SC/N cultures)
before and during differentiation into myelinating cells. Western blot
analysis revealed that neurons predominantly expressed a 68-kD protei
n, but SCs expressed two additional 88- and 120-kD related proteins. E
xtensive immunological characterization demonstrated that the 88-kD pr
otein shared three domains with the 68-kD merlin protein. Western blot
analysis of soluble and insoluble culture fractions demonstrated that
the majority of merlin and related proteins were soluble in isolated
SCs and undifferentiated SC/N cultures, but became insoluble in myelin
ating SC/N cultures. Double immunofluorescence staining suggested that
merlin translocated from the perinuclear cytoplasm in undifferentiate
d SCs to the subplasmalemma in differentiating SCs and partially coloc
alized with beta 1 integrin. Finally, beta 1 integrin antibody coimmun
oprecipitated 68-kD merlin from isolated SC and undifferentiated SC/N
cultures, but predominantly the 88-kD protein from differentiating SC/
N cultures. Together, these results provide evidence that merlin inter
acts with beta 1 integrin and that merlin localization changes from a
cytosolic to cytoskeletal compartment during SC differentiation. (C) 1
998 John Wiley & Sons, Inc.