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Merlin, the neurofibromatosis type 2 gene product, and beta1 integrin associate in isolated and differentiating
V J Obremski1, A M Hall, C Fernandez-Valle
1Orlando Regional Healthcare System/Health Research Institute, Florida 32806, USA.
Abstract:
Neurofibromatosis type 2, a disease characterized by the formation of multiple nervous system tumors, especially schwannomas, is caused by mutation in the gene-encoding merlin/schwannomin. The molecular mechanism 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, localization, and protein association in primary cultures of rat sensory neurons, 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 protein, but SCs expressed two additional 88- and 120-kD related proteins. Extensive immunological characterization demonstrated that the 88-kD protein 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 myelinating SC/N cultures. Double immunofluorescence staining suggested that merlin translocated from the perinuclear cytoplasm in undifferentiated SCs to the subplasmalemma in differentiating SCs and partially colocalized with beta1 integrin. Finally, beta1 integrin antibody coimmunoprecipitated 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 interacts with beta1 integrin and that merlin localization changes from a cytosolic to cytoskeletal compartment during SC differentiation.
Insights
Neurofibromatosis type 2 is linked to merlin protein mutations. This study shows merlin interacts with beta1 integrin and moves to the cell membrane during Schwann cell differentiation, suggesting a role in tumor suppression.
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- Neurofibromatosis type 2 (NF2) is characterized by nervous system tumors, particularly schwannomas, stemming from mutations in the merlin/schwannomin gene.
- The tumor suppressor function of merlin is not fully understood but is thought to involve interactions with the plasma membrane and cytoskeleton.
- Investigating merlin's behavior in neural cells is crucial for understanding NF2 pathogenesis.
Purpose of the Study:
- To investigate merlin expression, localization, and protein associations in rat sensory neurons and Schwann cells (SCs) during differentiation.
- To determine how merlin's cellular location changes as SCs differentiate into myelinating cells.
- To explore potential interactions between merlin and other cellular proteins, such as beta1 integrin.
Main Methods:
- Utilized merlin antibodies for Western blot analysis and double immunofluorescence staining.
- Examined merlin expression in isolated SCs and neuron-SC co-cultures (SC/N) before and during differentiation.
- Performed co-immunoprecipitation assays to identify merlin-interacting proteins.
Main Results:
- Identified merlin isoforms (68, 88, and 120 kD) in neurons and SCs, with the 88-kD protein sharing domains with 68-kD merlin.
- Observed a shift in merlin localization from soluble fractions in undifferentiated cells to insoluble fractions in myelinating SCs.
- Demonstrated merlin translocation to the subplasmalemma and partial colocalization with beta1 integrin in differentiating SCs.
- Showed beta1 integrin co-immunoprecipitated merlin, predominantly the 88-kD isoform in differentiating SCs.
Conclusions:
- Merlin interacts with beta1 integrin in Schwann cells.
- Merlin's cellular localization shifts from the cytoplasm to the cytoskeleton during Schwann cell differentiation.
- These findings provide insights into the molecular mechanisms underlying merlin's tumor suppressor function in NF2.