Mutations of the TP53 Gene Play an Important Role in the Pathogenesis of Acute Myeloid Leukemia with Complex Aberrant Karyotype.

Abstract

Acute myeloid leukemia with complex aberrant karyotype is associated with the most unfavorable prognosis of all AML subtypes. Clinical behavior, complexity of karyotype abnormalities and the exponential increase of incidence with age shows similarities to the most common solid tumors. In the latter ones TP53 gene is the most frequently mutated gene identified so far. Therefore, we addressed the role of TP53 in AML with complex aberrant karyotype. In a first step we analyzed 360 AML cases with complex aberrant karyotype using conventional cytogenetics and 24 color FISH to resolve the chromosomal rearrangements in detail. In combination with data from comparative genomic hybridization for a subset of these patients (n=49) we identified 10 genomic regions frequently lost (5q14q33, 7q32q35, 12p13, 13q14, 16q22q24, 17p13, 18q21q22) or gained (11q23q25, 1p33p36, 8q22q24). In all 350 cases interphase FISH with a TP53 probe was performed. In 210 patients (60%) a loss of one TP53 allele was observed. 34 cases (22 with and 12 without TP53 loss) were further evaluated for p53 mutations using the Affymetrix p53 GeneChip assay. All mutations detected were verified by direct sequencing. TP53 mutations were detected in 21 of the 22 cases showing a loss of one TP53 allele (95%), while 9 of 12 cases (75%) without a TP53 loss showed a TP53 mutation on the microarray. Two mutations occurred in introns 4 and 7, while all others were located in exons (e4: n=2, e5: n=10, e6: n=3, e7: n=5, e8: n=8, e9: n=1). 22 mutations were missense mutations resulting in the substitution of a single amino-acid, while 4 were nonsense mutations. One small deletion and one insertion were detected. Four cases without mutations detected by microarray screening and 15 additional cases (9 with and 11 without TP53 loss detected with FISH) were further analyzed by DHPLC (WAVE, Transgenomics). In two of the four cases in which no mutation was detectable on the microarray mutations were found with DHPLC, which are most likely larger deletions not detectable with the p53 GeneChip assay. Furthermore, in 11 of the 15 additional cases a mutation was detected by DHPLC. Thus, in total 43 of 49 cases (88%) showed a TP53 mutation (27/30 (90%) with loss of one TP53 allele and 16/19 (84%) without loss of one TP53 allele). Three of the 6 cases in which no TP53 mutation was detected showed loss of one TP53 allele in FISH analysis. Taken together, only in 3 of 49 cases (6%) no alteration of TP53 was detected. In one of these cases an increased MDM2 expression was found using gene expression microarrays (U133A), another mechanism of inactiving TP53 function. In conclusion, the loss of normal TP53 function by loss of one allele and/or point mutation plays an important role in the pathogenesis of AML with complex aberrant karyotype and may be a major reason for chemoresistance in this prognostically most unfavorable AML subtype. TP53 alterations are detectable in more than 90% of cases with complex aberrant karyotype and are very rare in other AML subtypes. Therefore, we suggest to include the TP53 status in the definition of AML with complex aberrant karyotype.