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Induction of human myeloblastic ML-1 cell G1 arrest by suppression of K+ channel activity
B Xu1, B A Wilson, L Lu
1Department of Physiology, Wright State University, School of Medicine, Dayton, Ohio 45435, USA.
Abstract:
Our previous studies have shown that a voltage-gated K+ channel is highly expressed in proliferating human myeloblastic ML-1 cells and is suppressed in the early stages of 12-O-tetradecanoylphorbol-13-acetate-induced ML-1 cell differentiation. In the present study, we report that inhibition of the K+ channel activity by 4-aminopyridine (4-AP) suppressed ML-1 cell proliferation, as measured by DNA synthesis. Cell cycle mapping indicated that ML-1 cells were arrested in G1 phase after 24-h treatment with 4-AP. Blockade of ML-1 cells at the G1/S boundary of the cell cycle with aphidicolin revealed that ML-1 cells past the G1 checkpoint were capable of entering S phase and synthesizing DNA independently of the channel blockade. ML-1 cell differentiation, measured by CD14 marker protein expression, revealed that the effect of 4-AP was to cause growth arrest and that it did not cause differentiation. Dephosphorylation of retinoblastoma protein accompanied inhibition of ML-1 cell proliferation and suggested that suppression of K+ channel activity by 4-AP is associated with retinoblastoma protein-mediated G1 arrest in ML-1 cells. Moreover, we found that ML-1 cell volume increased 35 +/- 7% after 4-AP treatment, which could be an early event triggering inhibition of ML-1 cell proliferation. These findings suggest that a 4-AP-sensitive K+ channel may play an important role in the transduction of mitogenic signals in ML-1 cells.
Insights
Inhibition of a specific potassium channel using 4-aminopyridine (4-AP) halts proliferation in human myeloblastic ML-1 cells by causing G1 phase arrest. This channel may be crucial for transmitting growth signals in these cells.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Voltage-gated K+ channels are highly expressed in proliferating human myeloblastic ML-1 cells.
- These channels are suppressed during the early stages of ML-1 cell differentiation induced by 12-O-tetradecanoylphorbol-13-acetate.
Purpose of the Study:
- To investigate the role of a 4-aminopyridine (4-AP)-sensitive K+ channel in ML-1 cell proliferation and differentiation.
- To determine the cell cycle effects and signaling pathways involved in K+ channel inhibition.
Main Methods:
- ML-1 cells were treated with 4-aminopyridine (4-AP) to inhibit K+ channel activity.
- Cell proliferation was measured by DNA synthesis.
- Cell cycle progression was analyzed using cell cycle mapping and aphidicolin blockade.
- Differentiation was assessed by CD14 marker protein expression.
- Retinoblastoma protein dephosphorylation and cell volume changes were monitored.
Main Results:
- 4-AP treatment suppressed ML-1 cell proliferation and induced G1 phase arrest.
- Cells past the G1 checkpoint could enter S phase independently of channel blockade.
- 4-AP caused growth arrest but not differentiation.
- Inhibition of proliferation was associated with retinoblastoma protein dephosphorylation.
- ML-1 cell volume increased significantly after 4-AP treatment.
Conclusions:
- A 4-AP-sensitive K+ channel plays a significant role in transmitting mitogenic signals in ML-1 cells.
- Suppression of this K+ channel activity leads to retinoblastoma protein-mediated G1 arrest.
- Increased cell volume may be an early event triggering proliferation inhibition.