Calcium pretreatment induces the decrease in epidermal growth factor binding through the activation of...

Area of Science:

• Cell biology
• Biochemistry
• Molecular signaling

Background:

• Epidermal growth factor (EGF) signaling is crucial for cell growth and differentiation.
• Regulation of EGF receptor (EGFR) binding is essential for controlling cellular responses.

Purpose of the Study:

• To investigate the effect of calcium ions (Ca2+) on EGF binding to its receptor in hepatocytes.
• To elucidate the molecular mechanism underlying Ca2+-induced modulation of EGF receptor binding.

Main Methods:

• Hepatocytes and isolated liver membranes were pretreated with Ca2+ and other agents.
• Epidermal growth factor (EGF) binding assays were performed.
• Scatchard plot analysis was used to characterize binding kinetics.
• Transglutaminase (TGase) activity and protein modification were assessed using TGase inhibitors and labeled putrescine.

Main Results:

• Ca2+ pretreatment significantly decreased EGF binding to its receptor in hepatocytes and isolated liver membranes.
• Scatchard analysis revealed the disappearance of high-affinity EGF receptor binding sites after Ca2+ treatment.
• Ca2+ did not affect EGF receptor degradation.
• The effect of Ca2+ was inhibited by transglutaminase (TGase) inhibitors and abolished upon TGase inactivation.
• Ca2+ treatment led to the incorporation of labeled putrescine into membrane proteins, indicating TGase-mediated modification.

Conclusions:

• Calcium-activated transglutaminase (TGase) plays a key role in reducing EGF binding to its receptor.
• TGase modifies membrane proteins, leading to decreased high-affinity EGF receptor binding.
• This study reveals a novel mechanism for regulating EGF signaling through Ca2+-dependent TGase activity.