STRUCTURAL AND FUNCTIONAL-ANALYSIS OF CYCLIN-DEPENDENT KINASE INHIBITOR GENES (CDKN2A, CDKN2B, AND CDKN2C) IN NEUROBLASTOMA

The status of the CDKN2A gene family, including CDKN2A, CDKN2B, and CD KN2C, was investigated in 24 cases of neuroblastoma. These genes were selected on the basis of 1) high incidence of their inactivation in se veral human cancers and 2) their localization on chromosomal regions ( 9p and 1p) frequently rearranged in neuroblastomas. Detailed molecular analyses indicated the absence of homozygous deletions and point muta tions involving these genes in all investigated tumor samples. However , when loss of heterozygostity for chromosome 9p21 (the region where C DKN2A and CDKN2B are localized) was investigated, 16% of cases showed abnormalities in an area telomeric to the CDKN2A locus. To study trans criptional silencing of the CDKN2A gene, the methylation status of exo n 1 was examined. In about 35% of cases, a partial methylation was evi denced. Analysis of the CDKN2A mRNA expression, however, did not show any relationship between methylation status and gene transcription. Fi nally, expression of the CDKN2B gene was demonstrated in all stage IV neuroblastomas, whereas none of stage I tumors expressed this gene. Th is finding suggests the occurrence of a correlation between CDKN2B tra nscription and tumor phenotype.