Zur Rolle der aberranten DNA-Hypermethylierung des Tumorsuppressorgens Inter-alpha-Trypsin-Inhibitor heavy chain 5 (ITIH5) bei akuter myeloischer Leukämie

摘要

Acute myeloid leukemia (AML) is a clonal disorder resulting from uncontrolled proliferation of hematopoietic stem cells. Important genetic findings in AML comprise chromosomal translocations involving different transcription factors and activating point mutations in multiple signal transduction pathways. Hypermethylation of CpG islands within gene promoter regions in collaboration with deacetylation and other histone modifications is associated with transcriptional inactivation and represents, in addition to genetic aberrations, an important mechanism of gene silencing in human cancers. Inter-α-trypsin inhibitors are serum proteases consisting of one light chain, bikunin, and two homologous heavy chains (ITIHs), which stabilize the extracellular matrix (ECM). The putative tumor suppressor gene ITIH5 is the most recent member of the ITIH family and has been reported to be downregulated by DNA hypermethylation in breast cancer. In this study, we determined the methylation status of the promoter-associated CpG island of ITIH5 in both AML cell lines and primary AML patient samples. Methylation specific polymerase chain reaction analysis revealed that the ITIH5 promoter region was hypermethylated in the AML cell lines HL60 and KG-1a. Treatment of cell lines that carry a hypermethylated ITIH5 gene with the demethylating agent 5-aza-2’-deoxycytidine resulted in partial promoter demethylation. We then analyzed the ITIH5 methylation status in primary mononuclear cells obtained from 104 patients with newly diagnosed AML. The frequency of aberrant methylation among the primary patient samples was 14.4% (15 of 104). Among clinical prognostic parameters, we found no significant correlation between hypermethylation of ITIH5 and cytogenetics, elevated serum levels of lactate dehydrogenase, French–American–British subtype, gender, age, peripheral blood cell counts, and overall survival (p=0.08). Since there was a trend toward an association between increased WBC and ITIH5 promoter hypermethylation (p=0.24), we hypothesize that epigenetic dysregulation of ITIH5 may result in an impaired interaction between the leukemic clone and its’ surrounding ECM in the bone marrow. Additionally, the OS curve implies a slight, but not statistically significant advantage for patients who carry a hypermethylated ITIH5 promoter. Concluding, ITIH5 promoter hypermethylation is a novel epigenetic event in AML that may contribute to leukemogenesis by interfering with the interaction between the ECM and the leukemic clone. Though ITIH5 promoter hypermethylation does not appear to be an independent prognostic factor in AML, as it was recently demonstrated in breast cancer.