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Mutation of the p53 gene in human acute myelogenous leukemia
J M Slingerland1, M D Minden, S Benchimol
1Ontario Cancer Institute, Toronto, Canada.
Abstract:
Heterogeneity of p53 protein expression is seen in blast cells of patients with acute myelogenous leukemia (AML). p53 protein is detected in the blasts of certain AML patients but not in others. We have identified p53 protein variants with abnormal mobility on gel electrophoresis and/or prolonged half-life (t 1/2). We have sequenced the p53 coding sequence from primary blast cells of five AML patients and from the AML cell line (OCIM2). In OCIM2, a point mutation in codon 274 was identified that changes a valine residue to aspartic acid. A wild type p53 allele was not detected in these cells. Two point mutations (codon 135, cysteine to serine; codon 246, methionine to valine) were identified in cDNA from blasts of one AML patient. Both mutations were present in blast colonies grown from single blast progenitor cells, indicating that individual leukemia cells had sustained mutation of both p53 alleles. The cDNAs sequenced from blast samples of four other patients, including one with prolonged p53 protein t 1/2 and one with no detectable p53 protein, were fully wild type. Thus, the heterogeneity of p53 expression cannot be explained in all cases by genetic change in the p53 coding sequence. The prolonged t 1/2 of p53 protein seen in some AML blasts may therefore reflect changes not inherent to p53. A model is proposed in which mutational inactivation of p53, although not required for the evolution of neoplasia, would confer a selective advantage, favoring clonal outgrowth during disease progression.
Insights
p53 protein expression varies in acute myelogenous leukemia (AML) blasts. Genetic mutations in p53 do not fully explain this heterogeneity, suggesting other factors influence p53 levels in AML progression.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- p53 protein expression is heterogeneous in acute myelogenous leukemia (AML) blast cells.
- This variability includes detectable p53 in some patients and absence in others.
- p53 protein variants with altered electrophoretic mobility or prolonged half-life have been observed.
Purpose of the Study:
- To investigate the genetic basis for heterogeneous p53 protein expression in AML.
- To identify mutations within the p53 coding sequence in AML patient samples and cell lines.
- To determine if p53 gene mutations account for the observed differences in p53 protein levels and stability.
Main Methods:
- Sequencing of the p53 coding sequence from primary AML blast cells and the OCIM2 AML cell line.
- Analysis of blast colonies derived from single progenitor cells to assess mutation clonality.
- Comparison of p53 sequences from patients with wild-type, mutated, and undetectable p53 protein.
Main Results:
- A point mutation (Valine to Aspartic acid at codon 274) was found in the OCIM2 cell line, with no wild-type p53 allele detected.
- Two point mutations (Cysteine to Serine at codon 135 and Methionine to Valine at codon 246) were identified in one AML patient's cDNA, affecting both p53 alleles.
- p53 coding sequences were wild-type in samples from four other patients, including those with prolonged p53 protein half-life or undetectable p53.
Conclusions:
- Heterogeneity of p53 protein expression in AML is not solely explained by mutations in the p53 coding sequence.
- Prolonged p53 protein half-life in some AML blasts may result from alterations independent of p53 gene mutations.
- Mutational inactivation of p53 may provide a selective advantage for clonal outgrowth during AML progression, even if not essential for initial neoplasia.