Macrophage-specific
apolipoprotein E (
apoE) secretion plays an important protective role in
atherosclerosis. However, the precise signaling mechanisms regulating
apoE secretion from primary human monocyte-derived macrophages (HMDMs) remain unclear. Here we investigate the role of
protein kinase C (PKC) in regulating basal and stimulated
apoE secretion from HMDMs. Treatment of HMDMs with structurally distinct pan-PKC inhibitors (
calphostin C,
Ro-31-8220,
Go6976) and a PKC inhibitory
peptide all significantly decreased
apoE secretion without significantly affecting
apoE mRNA or
apoE protein levels. The PKC activator
phorbol 12-myristate 13-acetate (PMA) stimulated
apoE secretion, and both PMA-induced and apoAI-induced
apoE secretion were inhibited by PKC inhibitors. PKC regulation of
apoE secretion was found to be independent of the
ATP binding cassette transporter ABCA1. Live cell imaging demonstrated that PKC inhibitors inhibited vesicular transport of
apoE to the plasma membrane. Pharmacological or
peptide inhibitor and knockdown studies indicate that classical
isoforms PKCα/β and not PKCδ, -ε, -θ, or -ι/ζ
isoforms regulate
apoE secretion from HMDMs. The activity of myristoylated
alanine-rich
protein kinase C substrate (MARCKS) correlated with modulation of PKC activity in these cells, and direct
peptide inhibition of MARCKS inhibited
apoE secretion, implicating MARCKS as a downstream effector of PKC in
apoE secretion. Comparison with other secreted
proteins indicated that PKC similarly regulated secretion of
matrix metalloproteinase 9 and chitinase-3-like-1
protein but differentially affected the secretion of other
proteins. In conclusion, PKC regulates the secretion of
apoE from primary human macrophages.