Protein kinase Cα regulates human monocyte O2̇ production and low density lipoprotein lipid oxidation

Qing Li, Venkita Subbulakshmi, Alan P Fields, Nicole R Murray, Martha K. Cathcart

Research output: Contribution to journalArticle

65 Citations (Scopus)

Abstract

Our previous studies have shown that human native low density lipoprotein (LDL) can be oxidized by activated human monocytes. In this process, both activation of protein kinase C (PKC) and induction of superoxide anion (O2̇ production are required. PKC is a family of isoenzyrnes, and the functional roles of individual PKC isoenzymes are believed to differ based on subcellular location and distinct responses to regulatory signals. We have shown that the PKC isoenzyme that is required for both monocyte O2̇ production and oxidation of LDL is a member of the conventional PKC group of PKC isoenzymes (Li, Q., and Cathcart, M. K. (1994) J. Biol. Chem. 269, 17508-17515). The conventional PKC group includes PKCα, PKCβI, PKCβII, and PKCγ. With the exception of PKCγ, each of these isoenzymes was detected in human monocytes. In these studies, we investigated the requirement for select PKC isoenzymes in the process of monocyte-mediated LDL lipid oxidation. Our data indicate that PKC activity was rapidly induced upon monocyte activation with the majority of the activity residing in the membrane/particulate fraction. This enhanced PKC activity was sustained for up to 24 h after activation. PKCα, PKCβI, and PKCβII protein levels were induced upon monocyte activation, and PKCα and PKCβII substantially shifted their location from the cytosol to the particulate/membrane fraction. To distinguish between these isoenzymes for regulating monocyte O2̇ production and LDL oxidation, PKCα or PKCβ isoenzyme-specific antisense oligonucleotides were used to selectively suppress isoenzyme expression. We found that suppression of PKCα expression inhibited both monocyte-mediated O2̇ production and LDL lipid oxidation by activated human monocytes. In contrast, inhibition of PKCβ expression (including both PKCβI and PKCβH) did not affect O2̇ production or LDL lipid oxidation. Further studies demonstrated that the respiratory burst oxidase responsible for O2̇ production remained functionally intact in monocytes with depressed levels of PKCα because O2̇ production could be restored by treating the monocytes with arachidonic acid. Taken together, our data reveal that PKCα, and not PKCβI or PKCβII, is the predominant isoenzyme required for O2̇ production and maximal oxidation of LDL by activated human monocytes.

Original languageEnglish (US)
Pages (from-to)3764-3771
Number of pages8
JournalJournal of Biological Chemistry
Volume274
Issue number6
DOIs
StatePublished - Feb 5 1999
Externally publishedYes

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LDL Lipoproteins
Protein Kinase C
Monocytes
Lipids
Oxidation
Isoenzymes
Chemical activation
Membranes
Antisense Oligonucleotides

ASJC Scopus subject areas

  • Biochemistry

Cite this

Protein kinase Cα regulates human monocyte O2̇ production and low density lipoprotein lipid oxidation. / Li, Qing; Subbulakshmi, Venkita; Fields, Alan P; Murray, Nicole R; Cathcart, Martha K.

In: Journal of Biological Chemistry, Vol. 274, No. 6, 05.02.1999, p. 3764-3771.

Research output: Contribution to journalArticle

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abstract = "Our previous studies have shown that human native low density lipoprotein (LDL) can be oxidized by activated human monocytes. In this process, both activation of protein kinase C (PKC) and induction of superoxide anion (O2̇ production are required. PKC is a family of isoenzyrnes, and the functional roles of individual PKC isoenzymes are believed to differ based on subcellular location and distinct responses to regulatory signals. We have shown that the PKC isoenzyme that is required for both monocyte O2̇ production and oxidation of LDL is a member of the conventional PKC group of PKC isoenzymes (Li, Q., and Cathcart, M. K. (1994) J. Biol. Chem. 269, 17508-17515). The conventional PKC group includes PKCα, PKCβI, PKCβII, and PKCγ. With the exception of PKCγ, each of these isoenzymes was detected in human monocytes. In these studies, we investigated the requirement for select PKC isoenzymes in the process of monocyte-mediated LDL lipid oxidation. Our data indicate that PKC activity was rapidly induced upon monocyte activation with the majority of the activity residing in the membrane/particulate fraction. This enhanced PKC activity was sustained for up to 24 h after activation. PKCα, PKCβI, and PKCβII protein levels were induced upon monocyte activation, and PKCα and PKCβII substantially shifted their location from the cytosol to the particulate/membrane fraction. To distinguish between these isoenzymes for regulating monocyte O2̇ production and LDL oxidation, PKCα or PKCβ isoenzyme-specific antisense oligonucleotides were used to selectively suppress isoenzyme expression. We found that suppression of PKCα expression inhibited both monocyte-mediated O2̇ production and LDL lipid oxidation by activated human monocytes. In contrast, inhibition of PKCβ expression (including both PKCβI and PKCβH) did not affect O2̇ production or LDL lipid oxidation. Further studies demonstrated that the respiratory burst oxidase responsible for O2̇ production remained functionally intact in monocytes with depressed levels of PKCα because O2̇ production could be restored by treating the monocytes with arachidonic acid. Taken together, our data reveal that PKCα, and not PKCβI or PKCβII, is the predominant isoenzyme required for O2̇ production and maximal oxidation of LDL by activated human monocytes.",
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