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Rapamycin-FKBP12 blocks proliferation, induces differentiation, and inhibits cdc2 kinase activity in a myogenic cell
1Department of Medicine, Mount Sinai School of Medicine, New York, New York 10029.
Abstract:
Rapamycin is a potent immunosuppressant that binds to the cytosolic protein, FKBP12, and blocks T cell activation. Here we report that rapamycin also blocks myogenic proliferation and induces differentiation, associated with a decrease in p34cdc2 activity and cyclin A levels. In yeast and mammals, rapamycin blocks cell cycle progression by causing G1 arrest, arguing for a conserved signaling pathway governing the G1 to S transition. p34cdc2 has been shown to play a role in both the transition from G1 to S and from G2 to M in yeast. In higher eukaryotes the role of p34cdc2 in G1 to S transition is less clear. Rapamycin and the structurally related macrolide antibiotic FK506 both bind to a cytosolic protein, the FK506-binding protein (FKBP12). We show that inhibition of myogenic proliferation is achieved at low doses of rapamycin (< 1 ng/ml) and is competed by a molar excess of FK506, indicating specificity for FKBP12. The distinct FK506-calcineurin pathway did not affect myogenic proliferation, differentiation, or p34cdc2 kinase activity. Thus, the rapamycin-FKBP12 signaling pathway involves a specific and direct effect on p34cdc2 kinase activity at the G1 to S transition and identifies a regulatory step during myogenic differentiation.
Insights
Rapamycin, an immunosuppressant, halts muscle cell (myogenic) proliferation and promotes differentiation by inhibiting p34cdc2 activity. This reveals a conserved cell cycle pathway involving FKBP12, crucial for G1 to S transition.
Area of Science:
- Cell Biology
- Molecular Biology
- Immunology
Background:
- Rapamycin is a known immunosuppressant that inhibits T cell activation.
- It functions by binding to FKBP12, a cytosolic protein.
- The cell cycle regulation, particularly the G1 to S transition, is critical for cell proliferation.
Purpose of the Study:
- To investigate the effect of rapamycin on myogenic proliferation and differentiation.
- To elucidate the role of the rapamycin-FKBP12 pathway in cell cycle regulation.
- To determine the specific kinase targets and cell cycle phases affected by rapamycin.
Main Methods:
- Treatment of myogenic cells with rapamycin and FK506.
- Assessment of myogenic proliferation and differentiation.
- Measurement of p34cdc2 kinase activity and cyclin A levels.
- Analysis of cell cycle progression (G1 arrest).
Main Results:
- Rapamycin significantly inhibited myogenic proliferation and induced differentiation.
- This effect was associated with decreased p34cdc2 activity and cyclin A levels.
- Rapamycin caused G1 arrest, indicating a conserved role in the G1 to S transition.
- The inhibition was specific to FKBP12 and not mediated by the FK506-calcineurin pathway.
Conclusions:
- The rapamycin-FKBP12 signaling pathway directly impacts p34cdc2 kinase activity at the G1 to S transition.
- This pathway plays a specific regulatory role during myogenic differentiation.
- Rapamycin uncovers a conserved mechanism controlling cell cycle progression and differentiation.