Analysis of mutations and expression of GAP-related domain of the neurofibromatosis type 1 (NF1) gene in the progression of chronic myelogenous leukemia.

We investigated mutations in the GTPase activating protein-related domain of the neurofibromatosis type 1 gene (NF1-GRD) and its expression in each phase of chronic myelogenous leukemia (CML). Samples from 45 cases in chronic phase (CP), 41 in acute phase, and four CML cell lines were examined for mutations in the NF1-GRD by single-strand conformation polymorphism (SSCP) analysis and allele specific restriction analysis (ASRA). No mutations were detected in the exon where frequent mutations have recently been reported in human tumors, namely the FLR exon. We also examined for point mutations of the N-ras gene but found no mutations either. In 23 samples from CML cases and four CML cell lines, expression of two types of the NF1-GRD transcripts, type I and type II, were examined by NF1-GRD-specific polymerase chain reaction-based densitometric analysis and by the quantitative assay with coamplification of the NF1-GRD and beta-actin transcripts. Consequently, although expression level of type I transcripts varied among the samples, type II expression was increased in CML cell lines and a minor increase in type II expression was observed in the samples in acute phase compared with CP. However, this difference in type II expression between CP and acute phase was so small that changes of NF1-GRD transcripts as well as NF1-GRD or N-ras mutations might not be responsible for the progression of CML.