Mdm2 SNP309 Different Genotypes Distribution in Israeli Population and in Patients with Hematological Malignancies.

P53 is a pivotal tumor suppressor gene that is mutated in half of all human cancers. The Mdm2 protein is a major negative regulator of p53. At residue 309 of the Mdm2 gene, there is a single nucleotide polymorphism (SNP) with a T-to-G substitution. Residue 309 is located in the first intron which is the locus of a P53-responsive promoter. The frequencies of the Mdm2 SNP309 variant genotypes have been reported to be 12% G/G, 40% G/T and 48% to T/T (Bond et.al. Cell 2004, Cancer Research 2005). Recent studies in cell lines (Ibid) showed that the G/G genotype confers an increased affinity to the transcriptional activator Sp1, resulting in higher levels of Mdm2 RNA and protein. A subsequent attenuation of the p53 pathway and reduced apoptosis occurs. It was also shown that Li-Fraumeni pts acquire more cancers at an earlier age when harboring the G/G or G/T genotype at SNP309. Similarly, soft-tissue sarcomas pts acquire cancer at an earlier age when harboring the G/G or G/T genotype at this locus. We analyzed the DNA of 353 healthy individuals of various origins, and determined the distribution of the SNP309 genotypes in the Israeli population. We next studied the genotypes in 219 pts with hematological malignancies: NHL (n=102), CLL (n=47) and MM (n=70). We also analyzed the genotype of 90 pts with colon cancer.

METHODS: The fragment of the first intron of the Mdm2 gene containing SNP309 was amplified by PCR. Dot Blot analysis with P32 γ-d-CTP labeled oligo-probes corresponding to each SNP variant was performed. The method was validated by direct sequencing.

RESULTS:

The distribution of the SNP309 different genotypes in Israeli healthy population is significantly different from the distribution published (p<0.0001): T/T 31% and G/T 49% in the Israeli population versus the reported 48% and 40% respectively. These differences may reflect the different ethnic origin of the cohorts tested. It is worth mentioning that we found different trends among the subpopulations. For example, Israeli Arabs seem to harbor less G/G genotype than other Israeli subpopulations.

No significant differences were found between any of the various tumors studied (Colon ca, NHL, MM, CLL) and the healthy population. Moreover, comparing genotypes between the young age group (≤ 50y) and the old age group (> 50y) within the hematological malignancies did not show any significant differences. In addition, there were no significant differences between the median or average age of the G/G and T/T groups in any of the cancer populations. In conclusion, although it requires further studies, it seems that Mdm2 SNP309 does not play a significant role in the etiology of hematological malignancies compared with the reported role in Li-Fraumeni and soft-tissue sarcomas. These findings may be the consequence of the less prominent role of the p53 pathway in hematological malignancies.