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Mitochondrial iron loss from leukemia cells injured by macrophages. A possible mechanism for electron transport chain
M Wharton1, D L Granger, D T Durack
1Department of Medicine, Duke University Medical Center, Durham, NC 27710.
Abstract:
Activated macrophages inhibit replication of murine lymphoblastic leukemia L1210 cells without lysis. This inhibition of replication is associated with abnormalities of mitochondrial electron transport at the level of NADH dehydrogenase (NADH-DH) and succinate dehydrogenase (SDH). The mechanism of inhibition is unknown, although it has been demonstrated that as NADH-DH and SDH activity is lost, iron is released from cells. Because both NADH-DH and SDH contain numerous iron-sulfur clusters, damage to these structures may be one result of injury by activated macrophages. L1210 cells were labeled with 55Fe and co-cultivated with activated murine peritoneal macrophages (injured L1210 cells). At 48 h, injured L1210 cells had released 83 +/- 8% (mean +/- SEM of 55Fe activity into the media, compared with 25 +/- 4% release from control and 37 +/- 7% from nondividing mitomycin C-treated control cells. All cells were greater than 90% viable. These differences were also reflected in the iron content of the cells. Mitochondria were then separated by centrifugation after cell disruption and 55Fe activity was found to be similarly decreased in both mitochondrial and nonmitochondrial fractions of injured L1210 cells. To further characterize the changes in mitochondrial iron content, mitochondrial proteins from injured and control L1210 cells were separated by IEF and 55Fe activity of gel slices was determined. There was selective loss of 55Fe activity in the area of the gel corresponding to SDH and NADH-DH, suggesting that iron loss from iron-sulfur clusters may occur in L1210 cells injured by activated macrophages. Iron uptake into L1210 cells after removal from macrophages showed a rapid large influx of radioactive iron. L1210 cells in contact with macrophages appear to develop an iron-depleted state, which is dependent on the continued presence of macrophages.
Insights
Activated macrophages inhibit leukemia cell growth by depleting cellular iron, affecting mitochondrial enzymes like NADH dehydrogenase and succinate dehydrogenase. This iron loss disrupts cell replication without causing cell death.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Activated macrophages inhibit murine lymphoblastic leukemia L1210 cell replication.
- This inhibition is linked to mitochondrial electron transport abnormalities, specifically involving NADH dehydrogenase (NADH-DH) and succinate dehydrogenase (SDH).
- Iron release from cells correlates with the loss of NADH-DH and SDH activity, suggesting a role for iron-sulfur clusters.
Purpose of the Study:
- To investigate the mechanism by which activated macrophages inhibit L1210 cell replication.
- To determine if iron loss from mitochondrial iron-sulfur clusters is involved in macrophage-mediated inhibition.
- To characterize the iron-depleted state induced in L1210 cells by activated macrophages.
Main Methods:
- L1210 cells were labeled with 55Fe and co-cultivated with activated murine peritoneal macrophages.
- 55Fe release into the media and cellular iron content were measured.
- Mitochondria were isolated, and 55Fe activity in mitochondrial and non-mitochondrial fractions was assessed.
- Isoelectric focusing (IEF) was used to analyze 55Fe activity in mitochondrial proteins, particularly NADH-DH and SDH.
Main Results:
- Injured L1210 cells released significantly more 55Fe activity (83%) compared to controls (25%).
- A selective loss of 55Fe activity was observed in the mitochondrial fractions, specifically associated with NADH-DH and SDH.
- Cells showed a rapid influx of iron upon removal from macrophage contact, indicating a reversible iron-depleted state.
Conclusions:
- Activated macrophages induce an iron-depleted state in L1210 cells, leading to replication inhibition.
- Iron loss from NADH-DH and SDH iron-sulfur clusters is a key mechanism in macrophage-mediated leukemia cell growth inhibition.
- The observed iron depletion is dependent on the continued presence of activated macrophages.