LIPOPOLYSACCHARIDE STIMULATES DIFFERENTIAL EXPRESSION OF MYRISTOYLATED PROTEIN-KINASE-C SUBSTRATES IN MURINE MICROGLIA

Microglia rapidly respond to Lipopolysaccharide (LPS) by transformatio n from resting to active states and secretion of several neuro- and im mune-regulators including tumour necrosis factor alpha (TNF-alpha), in terleukin 1 beta (IL-1 beta), and interleukin 6 (IL-6). With longer LP S treatment, microglia are converted to reactive or phagocytic states with characteristics similar to macrophages in inflammation and injury processes, We have investigated LPS-mediated changes in two myristoyl ated substrates of protein kinase C (PKC): MARCKS (myristoylated alani ne-rich C kinase substrate) and MRP (MARCKS-related protein). Within 6 hours of addition, LPS induced a twofold increase in [H-3]myristoylat ed and immunoreactive MARCKS protein and a sevenfold increase in MRP, The differential effect of LPS on expression of MRP vs, MARCKS was eve n more dramatic at the level of transcription: S1 nuclease protection assays revealed a 40-fold increase in MRP mRNA levels (maximum at 4-6 hours), whereas a threefold increase was observed for MARCKS, TNF alph a and colony-stimulating factor 1 (CSF-1), two cytokines which are ind uced by LPS, did not reproduce the observed effect of LPS on MARCKS an d MRP gene transcription, CSF-1 also induced differential transcriptio n of MRP, but of lower magnitude (threefold) and more sustained than b y LPS, Accordingly, these two substrates for PKC are differentially up -regulated by LPS, apparently independent of TNF alpha or CSF-1. (C) 1 996 Wiley-Liss, Inc.