PAK1 and schwannoma: Since the NF2 tumor suppressor gene is deleted in most schwannomas and its gene product, merlin inhibits Pak1 activation in several cell lines, including a mouse fibroblastic line, NIH 3T3 and a rat schwannoma cell line, RT4-DP6 [45,46], it seems very probable that Pak1 activation is critical in schwannoma formation.