Identification of DJ-1/PARK-7 as a determinant of stroma-dependent and TNF-alpha-induced apoptosis in MDS using mass spectrometry and phosphopeptide analysis.

In patients with myelodysplastic syndromes (MDS), apoptosis in hematopoietic cells is up-regulated in low-grade disease, whereas advanced disease is characterized by apoptosis resistance. We have shown that marrow stroma-derived signals convey sensitivity to tumor-necrosis-factor alpha (TNF-alpha)-mediated apoptosis in otherwise-resistant KG1a myeloid cells and CD34(+) cells from MDS marrow. Here, we used a PhosphoScan proteomic liquid chromatography-mass spectrometry method to identify signals relevant for this effect. The transcription factor DJ-1/PARK-7 (DJ-1) was highly phosphorylated in KG1a cells cultured without stroma but dephosphorylated after stroma coculture, whereas expression of p53 increased significantly, suggesting a stroma contact-dependent effect of DJ-1 on p53. In CD34(+) marrow cells from advanced MDS, expression of DJ-1 was up-regulated, whereas p53 levels were low, resulting in significantly greater DJ-1/p53 ratios than in patients with low-grade MDS (P = .01). DJ-1 levels were correlated with increasing International Prognostic Scoring System scores (P = .006). Increasing DJ-1/p53 ratios were associated with an increased risk of mortality, although the correlation did not reach statistical significance (P = .18). These data suggest that DJ-1/p53 interactions contribute to apoptosis resistance in clonal myeloid cells and may serve as a prognostic marker in patients with MDS.