The golli-myelin basic protein negatively regulates signal transduction in T lymphocytes Ji-Ming Feng * , Augustine O. Fernandes, Celia W. Campagnoni, Yan-Hong Hu, Anthony T. Campagnoni UCLA Medical School, Neuropsychiatric Institute, Room 47-448, 760 Westwood Plaza, Los Angeles, CA 90024-17519, USA Received 4 February 2004; accepted 29 March 2004 Abstract Protein kinase C (PKC) plays a critical role in signal transduction controlling T lymphocyte activation. Both positive and negative regulation of signal transduction is needed for proper control of T lymphocyte activation. We have found that a golli product of the myelin basic protein (MBP) gene can serve as a negative regulator of signaling pathways in the T lymphocyte, particularly the PKC pathway. Increased expression of golli BG21 in Jurkat T cells strongly inhibits anti-CD3q-induced IL-2-luciferase activity, an indicator of T lymphocyte activation. Golli BG21 can be phosphorylated by PKC in vitro and its phosphorylation increases in PMA-activated Jurkat cells. BG21 inhibits the PMA-induced increase in AP-1 or NF-nB activation, consistent with golli acting in a PKC-mediated cellular event. Golli BG21 inhibition of the PKC pathway is not due to a direct action on PKC activation but in the cascade following PKC activation, since BG21 neither reduces PKC enzyme activity nor blocks the membrane association of PKCu brought on by T lymphocyte activation. The inhibitory function of BG21 is independent of its phosphorylation by PKC because a mutant BG21, in which the PKC sites have been mutated, is as effective as the wild type BG21 in inhibiting the PMA-induced AP-1 activation. Structure – function assays indicate that BG21 inhibitory activity resides in the golli domain rather than in MBP domain of the molecule. These results reveal a novel role for MBP gene products in T lymphocytes within the immune system. D 2004 Elsevier B.V. All rights reserved. Keywords: T lymphocytes; Cellular activation; Protein kinase C; Golli-MBP 1. Introduction The myelin basic proteins (MBPs) have long been known as central nervous system (CNS) self-antigens, which can induce experimental autoimmune encephalomyelitis (EAE) in mice, a model for the inflammatory component of diseases such as Multiple Sclerosis (Martin et al., 1992; Voskuhl, 1998; Huseby and Goverman, 2000). However, a second family of proteins encoded by the MBP gene (called the golli proteins) also has been identified (Campagnoni et al., 1993). The golli proteins are structurally related to the classic MBPs, but are more ubiquitously expressed. While the classic MBPs are expressed almost exclusively in myelin-forming cells, the golli proteins are expressed in neurons and oligodendrocytes (OLs) in the nervous system (Campagnoni and Skoff, 2001), and in thymocytes within thymus (Feng et al., 2000). The golli proteins contain classic MBP sequences (and epitopes) of variable length, depend- ing upon the golli isoform, within their C-terminal regions (see Fig. 1). The biological function of the golli proteins is not yet known. In the CNS, golli proteins are not localized in myelin like the classic MBPs, but are found in the nuclei, cell soma and processes of OLs and neurons (Campagnoni and Skoff, 2001), and in some cases golli proteins are translocated from nuclei to cytoplasm (Landry et al., 1996). These findings indicate that the golli proteins have a distinctly different biological role from that of the classic MBPs. Golli expression in the nervous system begins in many neuronal populations at early embryonic stages when neurons are extending neurites and migrating; and at the earliest stages of process elaboration in OLs just prior to myelination. In vitro transfection studies have shown that 0165-5728/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jneuroim.2004.03.021 * Corresponding author. Tel.: +1-310-825-5006; fax: +1-310-206- 5050. E-mail address: jfeng@mednet.ucla.edu (J.-M. Feng). www.elsevier.com/locate/jneuroim Journal of Neuroimmunology 152 (2004) 57 – 66