Konference: 2015 57th ASH Annual Meeting - účast ČR
Kategorie: Mnohočetný myelom
Téma: 102. Regulation of Iron Metabolism: Poster III
Číslo abstraktu: 3351
Autoři: RNDr. Leona Rašková-Kafková, Ph.D.; MVDr. Zuzana Somíková; Mgr. Jana Kučerová; Mgr. Lenka Calábková; Mgr. Pavla Lužná; Mgr. Ján Štetka; Mgr. Dana Šimková; MvDr. Dalibor Doležal; Doc.RNDr. Vladimír Divoký, Ph.D.
A group of 10 preleukemia mice and a group of 10 control mice aged 7 month were treated twice daily with DFO doses adjusted to 88,8 mg/kg (i.p. injection) in order to mimic serum concentrations of the drug achieved in patients. After 6 weeks of chelator administration, the treatment lead to the activation of Chk1(S345) in the bone marrow (BM) of control mice, but did not result in accumulation of γH2AX, a marker of DNA damage, in BM of these mice. In contrast, in preleukemia mice, with already activated threshold of ATR-Chk1 signaling (marker of ongoing oncogene-induced replication stress), Chk1(S345) remained unchanged after DFO treatment. However, we observed significant accumulation of γH2AX foci in oncogene-positive BM cells. These data suggested that iron removal may induce Chk1 activation in vivo, and, in addition, may reinforce activation of DDR in preleukemia cells perhaps due to synthetic effect of iron chelation with oncogene activation resulting in increased levels in DDR signaling (assessment of oxidative DNA damage (8-oxoguanine staining) is ongoing).
Next, we analyzed whether iron chelation in both groups of mice influences DNA replication, in which the limiting step is the availability of dNTPs. The RR activity was significantly decreased in the BM of both groups of DFO-treated mice, however, with no impact on the concentration of BM dNTPs; in fact, dNTPs have accumulated in BM of these mice. We revealed that this was a consequence of the activation of S-phase checkpoint in control mice, and of a decrease of actively replicating myeloid cells and activation of G2/M checkpoint in preleukemia mice.
Cellular iron depletion was shown to activate p38MAPK pathway (Yu Y, Richardson DR. J Biol Chem. 2011;286(17):15413-27.). p38MAPK pathway, and its component MK2, establishes intra-S-phase cell cycle checkpoint and activates G2/M checkpoint (as a part of DDR, in parallel to Chk1 activation (Reinhardt HC, et al. Curr Opin Cell Biol. 2009;21:245-55.)). Indeed, our preliminary result revealed phosphorylated MK2 specifically in preleukemia mouse BM treated with DFO. Since we did not detect increased apoptosis in BM of DFO treated mice, and because p38MAPK pathway is involved in the activation of ER stress and autophagy, we tested whether markers of ER stress and autophagy are detectable in the mice upon DFO treatment. MyD116 (marker of recovery from ER stress) and LC3-II (marker of autophagy), were specifically induced in preleukemia cells upon DFO treatment.
Collectively, these data demonstrate that preleukemia cells exposed to DFO activate distinct but functionally overlapping signaling pathways, resulting in reinforced DDR. Whether this mechanism could increase a barrier against leukemia transformation of chelated MDS patients remains to be investigated.
Authorship: LRK and ZS: equal credit as first authors. Acknowledgment: Supported by the Czech Science Foundation (P301/12/1503) and by IGA_LF_2015_015.
Datum přednesení příspěvku: 7. 12. 2015