Study of post-translational modifications of p53 in multiple myeloma.

TP53 gene alterations remain one of the major determinants of poor prognosis in multiple myeloma (MM). However, p53 dysfunction can also arise through non-genetic mechanisms, like post-translational modifications (PTMs). Indeed, phosphorylation and acetylation play essential roles in modulating p53 stability and activity, but their functional relevance in primary MM samples has not been systematically explored. Here, we quantified the expression of four key p53 PTMs, phosphorylation at S15, S20, and T55, and acetylation at K382, using capillary nanoimmunoassay, in 127 newly diagnosed MM patients. We also evaluated the DNA damage marker γ-H2AX, the kinase Chk2, and the phosphatases PP1A and PP2A-C. We found that p53 PTM expression was highly heterogeneous among patients. p-p53 T55 and Ac-p53 K382 were the most frequently expressed, detected in more than 70% of samples. Patients with double-hit TP53 showed significantly lower p-p53 S20 and p-p53 T55 levels compared with those with normal TP53. Low p53 phosphorylation at S20, S15 and T55 was correlated with higher progression risk (HR = 2.39, p = 0.02; HR = 2.14, p = 0.04; and HR = 2.13, p = 0.005, respectively). We also identified deregulated expression of Chk2 and phosphatases, suggesting upstream regulatory imbalances. This is the first study to quantify p53 PTMs in a large set of MM patients, revealing that post-translational dysregulation contributes to p53 impairment independently of TP53 gene alterations. Characterizing p53 PTMs sheds light on the mechanisms underlying its dysfunction, particularly in patients with an intact TP53 gene, but dysfunctional p53 protein regulation.