Loss of p21ras, p53, and Mdm2 Protein Expression Is Indicative of Worse Prognosis in Myelodysplastic Syndromes.

Abstract

Myelodysplastic syndromes (MDS) comprise a group of clonal disorders of the hematopoietic stem cell characterized by ineffective hematopoiesis and refractory cytopenias that can progress to acute leukemia. In order to identify molecular events implicated in the pathogenesis of MDS, we analyzed the bone marrow expression and mutational status of ras, p53 and mdm2 genes in a cohort of 25 patients with MDS. The expression of p21ras, p53, and Mdm2 proteins was studied in marrow cytopins stained by APAAP (alkaline phosphatase anti-alkaline phosphatase procedure) using monoclonal antibodies Y13-219, PAb 1801 and 2A10 to detect p21ras, p53 and mdm2 proteins, respectively. N-, K-, H-ras and p53 gene mutations were assessed by PCR-SSCP (polymerase chain reaction/single strand conformation polymorphism) and DNA sequencing to exclude the presence of gene mutations. The quantitative wild-type expression of p21ras, p53 and mdm2 proteins in patient samples (combination of number of cells and staining intensity) was compared to the values of expression of these proteins in 7 normal bone marrow samples. We found overexpression of p21ras and p53 proteins in 12/22 (55%) and 7/23 (30%) of the patients. Five of 7 patients who overexpressed wt-p53 also co-overexpressed wt-p21ras protein. We observed absence of expression of p21ras, p53 and mdm2 in 4/22, 4/23 and 9/19 cases, respectively. Overall survival of patients with absence of p21ras and p53 expression was considerably worse than that of patients with normal expression of these proteins (p=0.0006 to p21ras and p=0.004 to p53 by Log-Rank test; p=0.02 to p21ras and p=0.01 to p53 by Cox proportional hazards model after age, neutrophil and platelet count, and hemoglobin adjustment). We also observed that the patients who exhibited hypoexpression (p=0.055) and absence of mdm2 expression (p=0.07) demonstrated a tendency to have worse prognosis (Log-Rank). There was no correlation between variables p21ras, p53 and mdm2 versus hemoglobin, platelet and neutrophil counts and no association between FAB SMD subcategories and absence of p53 and mdm2 expression by Fisher test (two-tailed), but there was a strong over-representation between absence of p21ras expression and MDS with excess of blasts (p=0.0006). There was a significant correlation between p53 and mdm2 gene expression (p=0.03, Pearson). Only one patient harbored one transversion mutation in codon 12 of K-ras gene and did not correlate with p53 overexpression, but with worse prognosis. No p53 mutation was found. Overall, these findings suggest that the via of signal transduction p21ras/p53 and the auto-regulatory genes p53/mdm2 may be active and play a pivotal role in the pathogenesis of MDS. Hence, loss of bone marrow expression of p21ras, p53 and/or mdm2 proteins is an indicator of worse prognosis in MDS and may serve as early markers of leukemic transformation.