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Expression of excess receptors and negative feedback control of signal pathways are required for rapid activation and prompt cessation of signal transduction.

Kobayashi H, Azuma R, Yasunaga T - Cell Commun. Signal (2009)

Bottom Line: Intracellular signal proteins are activated at a high level soon after ligand binding, and the activation level decreases in a negative feedback manner without ligand clearance.An initial increase in active cytosolic signal proteins to a high level is required for rapid activation of cellular signal pathways, and a low level of active signal proteins is essential for the rapid shutdown of signal pathways after ligand clearance.The present kinetic analysis revealed that excess receptors and negative feedback regulation promote activation and cessation of signal transduction with a low amount of extracellular ligand.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry, Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1, Inohana, Chuo-ku, Chiba 260-8675, Japan. hiroshi@p.chiba-u.ac.jp.

ABSTRACT

Background: Cellular signal transduction is initiated by the binding of extracellular ligands to membrane receptors. Receptors are often expressed in excess, and cells are activated when a small number of receptors bind ligands. Intracellular signal proteins are activated at a high level soon after ligand binding, and the activation level decreases in a negative feedback manner without ligand clearance. Why are excess receptors required? What is the physiological significance of the negative feedback regulation?

Results: To answer these questions, we developed a Monte Carlo simulation program to kinetically analyze signal pathways using the model in which ligands are bound to receptors and then membrane complexes with other membrane proteins are formed. Our simulation results showed that excess receptors are not required for cell activation when the dissociation constant (Kd) of the ligand-receptor complex is 10-10 M or less. However, such low Kd values cause delayed signal shutdown after ligand clearance from the extracellular space. In contrast, when the Kd was 10-8 M and the ligand level was less than 1 muM, excess receptors were required for prompt signal propagation and rapid signal cessation after ligand clearance. An initial increase in active cytosolic signal proteins to a high level is required for rapid activation of cellular signal pathways, and a low level of active signal proteins is essential for the rapid shutdown of signal pathways after ligand clearance.

Conclusion: The present kinetic analysis revealed that excess receptors and negative feedback regulation promote activation and cessation of signal transduction with a low amount of extracellular ligand.

No MeSH data available.


Related in: MedlinePlus

Negative feedback regulation of the signal pathways. I. The protein amounts and reaction probabilities were set as described in Additional file 1 and 2, respectively. L was added immediately before the 1.2 × 106th step (down arrow, 24 seconds) and removed after the 1.2 × 107th step (upper allow, 240 seconds), as described in the legend of Figure 2. Three simulation results are represented. II. Models for negative feedback regulation used in this study.
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Figure 3: Negative feedback regulation of the signal pathways. I. The protein amounts and reaction probabilities were set as described in Additional file 1 and 2, respectively. L was added immediately before the 1.2 × 106th step (down arrow, 24 seconds) and removed after the 1.2 × 107th step (upper allow, 240 seconds), as described in the legend of Figure 2. Three simulation results are represented. II. Models for negative feedback regulation used in this study.

Mentions: In the simulation of cytosolic signal transduction, the signal pathway was assumed to be as described in the Methods section. When Kd1 and Kd2 were set at 10-5 M and 10-4 M, respectively, ligands were bound to 40% of receptors in the presence of 200 nM L, and rapid formation and dissociation of LRA were demonstrated (Figure 2H). Therefore, we used these conditions for the signal transduction simulation. The concentrations of proteins and kinetic parameters were set as described in Additional file 1 and 2. All signal proteins (B to F) were activated rapidly after the ligand addition under conditions in which all signal proteins were activated at a high level (Figure 3-I, model 2A). However, inactivation of F was shown to be very slow under these conditions, even if the dissociation of the LRA complex was rapid (Figure 3-I, model 2A). As shown in Figure 3-I, when the levels of active B to D were low (Figure 3-I, model 2B), the activation rate of F (1.62 × 10-9 ± 0.08 M s-1, n = 3) was slower than the rate in model 2A (1.89 × 10-9 ± 0.03 M s-1, n = 3), but the inactivation of F was fast in model 2B.


Expression of excess receptors and negative feedback control of signal pathways are required for rapid activation and prompt cessation of signal transduction.

Kobayashi H, Azuma R, Yasunaga T - Cell Commun. Signal (2009)

Negative feedback regulation of the signal pathways. I. The protein amounts and reaction probabilities were set as described in Additional file 1 and 2, respectively. L was added immediately before the 1.2 × 106th step (down arrow, 24 seconds) and removed after the 1.2 × 107th step (upper allow, 240 seconds), as described in the legend of Figure 2. Three simulation results are represented. II. Models for negative feedback regulation used in this study.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2666736&req=5

Figure 3: Negative feedback regulation of the signal pathways. I. The protein amounts and reaction probabilities were set as described in Additional file 1 and 2, respectively. L was added immediately before the 1.2 × 106th step (down arrow, 24 seconds) and removed after the 1.2 × 107th step (upper allow, 240 seconds), as described in the legend of Figure 2. Three simulation results are represented. II. Models for negative feedback regulation used in this study.
Mentions: In the simulation of cytosolic signal transduction, the signal pathway was assumed to be as described in the Methods section. When Kd1 and Kd2 were set at 10-5 M and 10-4 M, respectively, ligands were bound to 40% of receptors in the presence of 200 nM L, and rapid formation and dissociation of LRA were demonstrated (Figure 2H). Therefore, we used these conditions for the signal transduction simulation. The concentrations of proteins and kinetic parameters were set as described in Additional file 1 and 2. All signal proteins (B to F) were activated rapidly after the ligand addition under conditions in which all signal proteins were activated at a high level (Figure 3-I, model 2A). However, inactivation of F was shown to be very slow under these conditions, even if the dissociation of the LRA complex was rapid (Figure 3-I, model 2A). As shown in Figure 3-I, when the levels of active B to D were low (Figure 3-I, model 2B), the activation rate of F (1.62 × 10-9 ± 0.08 M s-1, n = 3) was slower than the rate in model 2A (1.89 × 10-9 ± 0.03 M s-1, n = 3), but the inactivation of F was fast in model 2B.

Bottom Line: Intracellular signal proteins are activated at a high level soon after ligand binding, and the activation level decreases in a negative feedback manner without ligand clearance.An initial increase in active cytosolic signal proteins to a high level is required for rapid activation of cellular signal pathways, and a low level of active signal proteins is essential for the rapid shutdown of signal pathways after ligand clearance.The present kinetic analysis revealed that excess receptors and negative feedback regulation promote activation and cessation of signal transduction with a low amount of extracellular ligand.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biochemistry, Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1, Inohana, Chuo-ku, Chiba 260-8675, Japan. hiroshi@p.chiba-u.ac.jp.

ABSTRACT

Background: Cellular signal transduction is initiated by the binding of extracellular ligands to membrane receptors. Receptors are often expressed in excess, and cells are activated when a small number of receptors bind ligands. Intracellular signal proteins are activated at a high level soon after ligand binding, and the activation level decreases in a negative feedback manner without ligand clearance. Why are excess receptors required? What is the physiological significance of the negative feedback regulation?

Results: To answer these questions, we developed a Monte Carlo simulation program to kinetically analyze signal pathways using the model in which ligands are bound to receptors and then membrane complexes with other membrane proteins are formed. Our simulation results showed that excess receptors are not required for cell activation when the dissociation constant (Kd) of the ligand-receptor complex is 10-10 M or less. However, such low Kd values cause delayed signal shutdown after ligand clearance from the extracellular space. In contrast, when the Kd was 10-8 M and the ligand level was less than 1 muM, excess receptors were required for prompt signal propagation and rapid signal cessation after ligand clearance. An initial increase in active cytosolic signal proteins to a high level is required for rapid activation of cellular signal pathways, and a low level of active signal proteins is essential for the rapid shutdown of signal pathways after ligand clearance.

Conclusion: The present kinetic analysis revealed that excess receptors and negative feedback regulation promote activation and cessation of signal transduction with a low amount of extracellular ligand.

No MeSH data available.


Related in: MedlinePlus