Regulation of phospholipase D activity in a human oligodendroglioma cell line (HOG)

Abstract

Oligodendroglial cells express many specific proteins, such as myelin basic protein (MBP), which are physiologically phosphorylated by protein kinase C (PKC). Diacylglycerols are physiological activators of PKC and can be liberated from phospholipids by the direct receptor-mediated activation of phospholipase C (PL-C) or indirectly via the activation of phospholipase D (PL-D). In a well-characterized human oligodendroglioma (HOG) cell line, PL-C (measured by release of [³H]inositol phosphates) and PL-D (formation of [³H]myristoylated or palmitoylated phosphatidylethanol) were activated by both carbachol (blocked by pirenzepine, suggesting an M1 receptor) and histamine (H1 receptor) but not glutamate, bradykinin, or phenylephrine. PL-C stimulation by carbachol or histamine was completely inhibited by short-term treatment (50 = 5–10 μM) was about the same. We conclude that in this oligodendroglioma, and by inference in oligodendroglial cells, the receptor-coupled PL-D pathway, is at least as important as the PL-C pathway as a source of DAG and that its relationship to PKC is complex.