Increased membrane-associated phorbol-12,13 dibutyrate (PDBu) receptor function in sickle red cells

Area of Science:

• Hematology
• Biochemistry
• Cell Biology

Background:

• Sickle cell disease is characterized by abnormal red blood cell properties.
• Protein kinase C (PKC) plays a role in red blood cell function and signaling.
• Altered calcium homeostasis is observed in sickle red blood cells.

Purpose of the Study:

• To investigate the binding and activity of protein kinase C in sickle red blood cells.
• To explore the relationship between intracellular calcium and PKC activity in sickle cells.

Main Methods:

• Binding assays using 3H-Phorbol-12,13-dibutyrate (3H-PDBu) to measure PKC receptor binding.
• Phosphorylation studies using gamma-32P-ATP to assess protein kinase activity.
• Ionophore A23187 was used to induce calcium loading in red blood cells.
• Polyacrylamide gel electrophoresis and autoradiography to identify phosphorylated proteins.

Main Results:

• A four-fold increase in 3H-PDBu binding to membrane ghosts from sickle red cells compared to normal controls.
• A two to three-fold increase in the radiolabeling of membrane proteins in sickle red cells.
• Calcium loading enhanced phosphorylation in both normal and sickle red cells, with a greater effect in sickle cells.
• Phosphorylation predominantly occurred on protein bands 3, 4.1, and 4.9, known substrates of PKC.

Conclusions:

• Sickle red blood cells exhibit increased membrane association of protein kinase C.
• Elevated intracellular calcium levels in sickle cells may contribute to increased PKC activity.
• These findings suggest a potential mechanism linking altered calcium metabolism to red cell membrane abnormalities in sickle cell disease.