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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

Simulation of LRA formation. The number of subspaces for L and the number of molecules were set as shown in the upper Table. The dissociation constants of LR (Kd1) and LRA (Kd2) are indicated in the Figure. The probabilities of LR and LRA formations were set to 0.67. L was added immediately before the 1.2 × 106th step (down arrow, 24 seconds). After the 1.5 × 107th step (upper arrow, 300 seconds), L was allowed to pass through the borders of the simulation box for L, except for the cell surface, and L was deleted in the outside area. Three simulation results are represented.
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Figure 2: Simulation of LRA formation. The number of subspaces for L and the number of molecules were set as shown in the upper Table. The dissociation constants of LR (Kd1) and LRA (Kd2) are indicated in the Figure. The probabilities of LR and LRA formations were set to 0.67. L was added immediately before the 1.2 × 106th step (down arrow, 24 seconds). After the 1.5 × 107th step (upper arrow, 300 seconds), L was allowed to pass through the borders of the simulation box for L, except for the cell surface, and L was deleted in the outside area. Three simulation results are represented.

Mentions: In the first simulation (model 1), the extracellular space and the cell surface consisted of 300 × 300 × 100 and 300 × 300 × 1 subspaces, respectively. The numbers of L, R, and A at zero time were set as described in Figure 2. The setting of L to 180 corresponds to 200 nM. The setting of R and A to 86 corresponds to approximately 10,000 molecules per cell, since the surface area of a spherical cell with a diameter of 10 μm is 314 μm2. More than 99% of R and A were clustered within 1.2 × 106 steps, and hence L was added immediately before the 1.2 × 106th step. The concentration of extracellular ligands may not decrease with their binding to membrane receptors in situ because of the continuous supply of ligands from producing cells. To maintain a constant concentration of L, one molecule of L was set at the opposite side when L was bound to R on the cell surface. When LR dissociated, L was deleted from the opposite boundary until extracellular L decreased to its original level. After the 1.5 × 107th step (t = 3 × 102 seconds), L was allowed to pass through the borders of the simulation box, except for the cell surface and was deleted from the borders.


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)

Simulation of LRA formation. The number of subspaces for L and the number of molecules were set as shown in the upper Table. The dissociation constants of LR (Kd1) and LRA (Kd2) are indicated in the Figure. The probabilities of LR and LRA formations were set to 0.67. L was added immediately before the 1.2 × 106th step (down arrow, 24 seconds). After the 1.5 × 107th step (upper arrow, 300 seconds), L was allowed to pass through the borders of the simulation box for L, except for the cell surface, and L was deleted in the outside area. Three simulation results are represented.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Simulation of LRA formation. The number of subspaces for L and the number of molecules were set as shown in the upper Table. The dissociation constants of LR (Kd1) and LRA (Kd2) are indicated in the Figure. The probabilities of LR and LRA formations were set to 0.67. L was added immediately before the 1.2 × 106th step (down arrow, 24 seconds). After the 1.5 × 107th step (upper arrow, 300 seconds), L was allowed to pass through the borders of the simulation box for L, except for the cell surface, and L was deleted in the outside area. Three simulation results are represented.
Mentions: In the first simulation (model 1), the extracellular space and the cell surface consisted of 300 × 300 × 100 and 300 × 300 × 1 subspaces, respectively. The numbers of L, R, and A at zero time were set as described in Figure 2. The setting of L to 180 corresponds to 200 nM. The setting of R and A to 86 corresponds to approximately 10,000 molecules per cell, since the surface area of a spherical cell with a diameter of 10 μm is 314 μm2. More than 99% of R and A were clustered within 1.2 × 106 steps, and hence L was added immediately before the 1.2 × 106th step. The concentration of extracellular ligands may not decrease with their binding to membrane receptors in situ because of the continuous supply of ligands from producing cells. To maintain a constant concentration of L, one molecule of L was set at the opposite side when L was bound to R on the cell surface. When LR dissociated, L was deleted from the opposite boundary until extracellular L decreased to its original level. After the 1.5 × 107th step (t = 3 × 102 seconds), L was allowed to pass through the borders of the simulation box, except for the cell surface and was deleted from the borders.

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