Immunoblotting analysis of schwannomin/merlin in human schwannomas

Hypothesis: Absent or reduced expression of schwannomin/merlin is associated with tumorigenesis of sporadic schwannomas. Background: The neurofibromatosis type 2 (NF2) gene frequently is mutated in sporadic vestibular schwannomas. The protein product of the NF2 gene is called schwannomin or merlin. Little is known about the mutated forms of schwannomin/merlin present in schwannomas. Methods: To investigate further the role of schwannomin/merlin in schwannoma tumorigenesis, immunoblotting experiments were performed. Antischwannomin/merlin-specific antibody that recognizes amino terminus of the protein was used to determine the expression levels of schwannomin/merlin in 16 sporadic vestibular schwannomas, I NF2-related vestibular schwannoma, and 5 spinal schwannomas. Results: The antibody detects a protein of approximately 66 kDa in the Triton X-100-insoluble fraction of tumors. The expression of schwannomin/merlin was severely reduced, <35% of control, in 11 (50%) of 22 sporadic schwannomas and in I NF2-related vestibular schwannoma. The intensity of 66-kDa schwannomin/merlin band was moderately reduced, from 35-60%, in 7 (32%) of 22 schwannomas compared to the expression levels found in the human brain. Truncated forms of schwannomin/merlin were identified in three tumors with moderately reduced schwannomin/merlin. Conclusions: These results provide new evidence that inactivation of schwannomin/merlin is an important factor in tumorigenesis of sporadic schwannomas.