IRF8-Mutationsanalyse in hämatologischen Neoplasien

Interferon Regulatory Factor 8 (IRF8) is a transcription factor involved in various physiological processes of the hematopoetic and immune systems. Among these are the early maturation of myeloid cells and B lymphocyte progenitors in the bone marrow, but also some later stages of lymphatic differentiation in the secondary lymphoid organs. Closely connected to this regulatory role of IRF8 are indications that a dysfunction of the protein contributes to the pathogenesis of several hematological and immunological diseases, including hematological tumors. For example, loss of IRF8 expression has been shown in chronic myeloid leukemia (CML) cells. Further, IRF8 antagonizes BCR-ABL, the central oncogenic kinase in CML. Interestingly, IRF8 null mice and the ‘BXH-2’ mice strain, which harbors the IRF8 mutation p.R294C, both develop a CML-like myeloproliferative disease. Thus, IRF8 is an established tumor suppressor in CML. Less is documented for IRF8 mutations in acute lymphoblastic leukemia (ALL). Few pediatric ALL cases are shown to harbor IRF8 mutations. In adult ALL, where BCR-ABL oncogene expression is more common, no IRF8 mutations have been reported. Polymorphisms around the IRF8 gene locus are associated with an increased risk of chronic lymphocytic leukemia (CLL). However, so far there has been no systematic sequencing analysis of IRF8 in CLL. The current study represents a search for IRF8 mutations in various hematological neoplasia. The IRF8 transcripts from 136 patient samples, mostly adult-ALL and CLL, and nine human cell-lines were sequenced. Some of the samples with mutated IRF8 were then examined with regard to IRF8 expression. Altogether, 39% of the samples demonstrated variations of the IRF8 wild-type sequence of any kind, mostly in the form of synonymous (‘silent’) polymorphisms. Three missense mutations were found (two in ALL, one in mantle cell lymphoma) and two of these mutations represent known IRF8 polymorphisms. The mutation p.R296H in one pro-B-ALL sample is not a known polymorphism. It also affects the same amino acid which is mutated in the BXH-2 mouse. Furthermore, the p.R296H mutation was associated with an overexpression of IRF8. In one CLL sample, we found the deletion of 19 nucleotide bases c.1158_1176 near the 3’ coding end of IRF8. This sample demonstrated a lower expression of IRF8 compared to IRF8 wild-type samples. In conclusion, in the current study we found previously unreported non-polymorphism IRF8 mutations in one case of adult ALL and one case of CLL. In pro-B ALL, the same IRF8 amino acid as the one affected in the BXH-2 mouse is mutated. The altered expression of the two IRF8 transcripts carrying non-polymorphism missense mutations suggests a functional role of the mutations. Further studies addressing this are warranted.