Extracellular ATP Regulates CD73 and ABCC6 Expression in HepG2 Cells

Area of Science:

• Biochemistry
• Cell Biology
• Genetics

Background:

• The ATP-binding cassette sub-family C member 6 transporter (ABCC6) is implicated in Pseudoxanthoma elasticum (PXE), a disorder causing ectopic calcification.
• ABCC6 mutations lead to reduced pyrophosphate (PPi), an inhibitor of mineralization, potentially explaining PXE's hallmark calcification.
• ABCC6 facilitates the efflux of ATP, which is extracellularly converted to PPi and adenosine, suggesting a role in purinergic signaling.

Purpose of the Study:

• To investigate whether ABCC6 contributes to the activation of the purinergic system, beyond its role in pyrophosphate production.
• To determine the effect of ABCC6 transport activity on the expression of ABCC6 and NT5E (an ectonucleosidase).

Main Methods:

• Experiments utilized HepG2 cells with ABCC6 knockdown.
• ABCC6 transport activity was inhibited using Probenecid.
• Gene and protein expression levels of ABCC6 and NT5E were analyzed using real-time PCR and western blotting.

Main Results:

• Inhibition of ABCC6 transport activity with Probenecid led to the downregulation of both ABCC6 and NT5E.
• Conversely, treatment with adenosine or ATP resulted in the upregulation of ABCC6 and NT5E.
• These findings suggest a feedback mechanism where ABCC6 activity influences its own expression and that of NT5E.

Conclusions:

• ABCC6 plays a significant role in the activation of the extracellular purinergic system.
• The transporter's activity influences the expression of key components of this system, including NT5E.
• These findings highlight a dual function of ABCC6 in preventing ectopic calcification and modulating purinergic signaling, with implications for understanding PXE pathogenesis.