Protein kinase C isoforms differentially phosphorylate Ca(v)1.2 alpha(1c)

Area of Science:

• Cardiovascular Physiology
• Molecular Biology
• Biochemistry

Background:

• Regulation of calcium (Ca2+) influx via L-type Ca2+ channels (Ca(v)1.2) is crucial for cardiac excitation-contraction coupling.
• Ca(v)1.2 channels are implicated in signaling pathways of the renin-angiotensin and sympathetic nervous systems.
• Limited biochemical data exists on the specific protein phosphorylation events regulating Ca(v)1.2.

Purpose of the Study:

• To identify and characterize protein kinase C (PKC) phosphorylation sites on the alpha(1c) subunit of Ca(v)1.2.
• To investigate the differential phosphorylation of Ca(v)1.2 by various PKC isoforms.
• To elucidate the molecular mechanisms underlying PKC-mediated modulation of cardiac contractility.

Main Methods:

• Identification of seven novel PKC phosphorylation sites within the alpha(1c) subunit.
• Utilized phospho-epitope specific antibodies to detect phosphorylation at Ser(1674) and Ser(1928) in HEK cells and rat hearts.
• Employed PMA to induce phosphorylation and bisindolylmaleimide as a PKC inhibitor.

Main Results:

• Both Ser(1674) and Ser(1928) in the Ca(v)1.2 C-terminus are phosphorylated in response to PMA in HEK cells and rat hearts.
• Phosphorylation at Ser(1674) is dependent on specific PKC isoforms (PKCα, βI, βII, γ, δ, θ), while Ser(1928) is targeted by a broader range.
• Demonstrated that PKC isoform specificity in phosphorylation contributes to differential effects on Ca(v)1.2 channel activity.

Conclusions:

• Identified multiple PKC phosphorylation sites on the Ca(v)1.2 alpha(1c) subunit, expanding our understanding of its regulation.
• Established that distinct PKC isoforms phosphorylate specific residues (Ser1674 vs. Ser1928), providing a mechanism for isoform-specific modulation of cardiac function.
• These findings offer molecular insights into how PKC signaling pathways differentially impact cardiac contractility and relaxation.