p53 Expression in four human medulloblastoma-derived cell lines

p53 is a tumor suppressor gene found on the short arm of chromosome 17. Loss of onep53 allele and alteration of the other is found in a variety of tumors, including highgrade glial tumors. Point mutations in the remaining allele occur in a highly conserved region of the gene encompassing exons 5–8. Although 40–50% of medulloblastomas lose sequences on the short arm of chromosome 17, alteration ofp53 in these tumors is infrequent. To further characterize genetic alteration ofp53 in medulloblastoma, we performed a mutational analysis of four medulloblastoma-derived cell lines established by our laboratory. Using two variable-number tandem repeat markers which map distally top53, we found evidence indicating loss of sequences on the distal end of chromosome 17 p in all four lines. However, no gross alterations of thep53 gene were detected. Northern analysis revealed expression of equivalent amounts of full-lengthp53 messenger RNA in each cell line. Using the polymerase chain reaction to amplify exons 5–8 of thep53 gene, we directly sequenced the amplified fragments and detected no mutations in any of the cell lines. Our results demonstrate that loss ofp53 function through gene deletion and/or recesive mutation is not required for growth in our cell lines.