Protein kinase C β and δ isoenzymes mediate cholesterol accumulation in PMA-activated macrophages

Previously, we showed that PMA activation of human monocyte-derived macrophages stimulates macropinocytosis (i.e., fluid-phase endocytosis) of LDL and transforms these macrophages into foam cells. The current study aimed to learn which PKC isoenzymes mediate cholesterol accumulation in PMA-activated human macrophages incubated with LDL. Cholesterol accumulation by PMA-activated macrophages incubated with LDL was nearly completely inhibited (>85%) by the pan PKC inhibitors Go6850, Go6983, and RO 32-0432, but only was inhibited about 50% by the classical group PKC inhibitor, Go6976. This indicated that cholesterol accumulation was mediated by both a classical group and some other PKC isoenzyme. PKC β was determined to be the classical group isoenzyme that mediated PMA-stimulated cholesterol accumulation. A pseudosubstrate myristoylated peptide inhibitor of PKC α and β showed partial inhibition (≅50%) of cholesterol accumulation. However, a small molecule inhibitor of PKC α, HBDDE, show minimal inhibition of cholesterol accumulation while a small molecule inhibitor of PKC β, LY333513, could completely account for the inhibition of cholesterol accumulation by the classical group PKC isoenzyme. Thus, our findings show that β and some other PKC isoenzyme, most likely δ, mediate cholesterol accumulation when macropinocytosis of LDL is stimulated in PMA-activated human monocyte-derived macrophages.