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Differentiation of mouse myeloid leukemia cells is inhibited by a factor from non-differentiating leukemia cells
Abstract:
Mouse myeloid leukemia cells (MI) were induced to differentiate by a factor(s) (D-factor) in ascitic fluid. An inhibitory activity (I-activity) for the induction of differentiation was present in conditioned medium and lysate of MI cells resistant to the D-factor. The I-activity was non-dialyzable, heat-labile and protease-sensitive. Most of the activity was recovered in the fraction precipitated with 30-50% saturated ammonium sulfate. The fraction inhibited induction of phagocytic activity, migrating activity and morphological changes in MI cells, which are typical properties of differentiated MI cells. Low levels of I-activity were detected in conditioned medium or lysate of MI cells sensitive to the D-factor. The resistant MI cells were sensitized to the D-factor by treatment with a low concentration (5-10 ng/ml) of actinomycin D. The I-activity in conditioned medium of actinomycin D-treated resistant cells decreased with development of sensitivity to the D-factor. These results suggest that production of the I-activity in the resistant cells is closely associated with resistance of the MI cells to the D-factor.
Insights
Mouse myeloid leukemia (MI) cells resistant to differentiation factors (D-factor) produce an inhibitory activity (I-activity). This I-activity is linked to resistance, and its production decreases when cells are sensitized to D-factor.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Mouse myeloid leukemia (MI) cells can be induced to differentiate by specific factors present in ascitic fluid.
- Resistance to this differentiation induction is observed in some MI cell populations.
Purpose of the Study:
- To investigate the mechanism underlying resistance to differentiation in MI cells.
- To identify and characterize factors involved in inhibiting differentiation induction.
Main Methods:
- Induction of differentiation in MI cells using ascitic fluid.
- Analysis of conditioned medium and cell lysates from resistant and sensitive MI cells.
- Biochemical characterization of inhibitory activity (I-activity) including dialysis, heat, and protease sensitivity.
- Fractionation using ammonium sulfate precipitation.
- Assessment of I-activity's effect on differentiation markers (phagocytosis, migration, morphology).
- Sensitization of resistant cells using actinomycin D and monitoring of I-activity levels.
Main Results:
- Resistant MI cells produce an inhibitory activity (I-activity) in their conditioned medium and lysates.
- I-activity is non-dialyzable, heat-labile, and protease-sensitive, with significant presence in 30-50% ammonium sulfate fractions.
- This I-activity effectively inhibits differentiation markers in MI cells.
- Sensitive MI cells exhibit low levels of I-activity.
- Actinomycin D treatment sensitizes resistant cells to D-factor, correlating with a decrease in I-activity.
Conclusions:
- The production of I-activity by MI cells is closely associated with their resistance to differentiation factors.
- I-activity may play a crucial role in maintaining the undifferentiated state of resistant myeloid leukemia cells.