OSP/Claudin-11 Forms a Complex with a Novel Member of the Tetraspanin Super Family and b1 Integrin and Regulates Proliferation and Migration of Oligodendrocytes Seema K. Tiwari-Woodruff,* Alex G. Buznikov,* Trung Q. Vu,* Paul E. Micevych,‡§ Kendall Chen,* Harley I. Kornblum,§i and Jeff M. Bronstein*i *Department of Neurology, ‡Department of Neurobiology, §Department of Molecular and Medical Pharmacology and Pediatrics, and iThe Brain Research Institute, University of California at Los Angeles School of Medicine, Los Angeles, California 90095 Abstract. Oligodendrocyte-speciﬁc protein (OSP)/ claudin-11 is a major component of central nervous system myelin and forms tight junctions (TJs) within myelin sheaths.TJs are essential for forming a paracellular barrier and have been implicated in the regulation of growth and differentiation via signal transduction path- ways. We have identiﬁed an OSP/claudin-11–associated protein (OAP)1, using a yeast two-hybrid screen. OAP-1 is a novel member of the tetraspanin superfamily, and it is widely expressed in several cell types, including oligoden- drocytes. OAP-1, OSP/claudin-11, and b1 integrin form a complex as indicated by coimmunoprecipitation and confocal immunocytochemistry. Overexpression of OSP/ Introduction Myelin is essential for the effective and rapid propagation of action potentials and therefore, the functional integrity of the nervous system. Membrane processes from oligo- dendrocytes in the central nervous system (CNS)1 and Schwann cells in the peripheral nervous system wrap around axons in a tight spiral-like manner, increasing the resistance to current perpendicular to the axons. Oligo- dendrocytes arise from precursor cells located in ventral regions of the neural tube during development of the CNS. These precursor cells must proliferate, migrate throughout the CNS, and differentiate in order to form mature myelin. The molecular mechanisms modulating these events are not completely understood but can be directed in culture by several growth factors, including platelet-derived growth factor and basic FGF (Levine and Dou, 1991). In S.K. Tiwari-Woodruff and A.G. Buznikov contributed equally to this work. Address correspondence to Jeff Bronstein, UCLA School of Medicine, Dept. of Neurology, RNRC 710 Westwood Plaza, Los Angeles, CA 90024. Tel.: (310) 794-2158. Fax: (310) 206-9819. E-mail: jbronste@ucla.edu 1Abbreviations used in this paper: CNS, central nervous system; ECM, extracellular matrix; MBP, myelin basic protein; OAP, OSP-associated protein; ONPG, 5-bromo-4-chloro-3-indolyl-b-D-galactopyranoside; OSP; oligodendrocyte-specific protein; PLP, proteolipid protein; SD, synthetic dropout; TJ, tight junction; TM4SF, transmembrane 4 superfamily. claudin-11 or OAP-1 induced proliferation in an oligo- dendrocyte cell line. Anti–OAP-1, anti–OSP/claudin-11, and anti–b1 integrin antibodies inhibited migration of primary oligodendrocytes, and migration was impaired in OSP/claudin-11–deﬁcient primary oligodendrocytes. These data suggest a role for OSP/claudin-11, OAP-1, and b1 integrin complex in regulating proliferation and migration of oligodendrocytes, a process essential for normal myelination and repair. Key words: tight junctions • myelin • TM4SF • brain • OAP-1 recent years, there has been considerable progress in the identification of glial proteins involved in the elaboration and maintenance of myelin. Myelin basic proteins (MBPs) and proteolipid protein (PLP) make up nearly 80% of the total myelin proteins in the CNS (for reviews see Campagnoni, 1988; Bronstein et al., 1997) with myelin–oligodendrocyte protein (Gardinier et al., 1992), myelin–oligodendrocyte basic protein (Holz et al., 1996), and myelin-associated glycoprotein contributing as minor components (for review see Campagnoni and Macklin, 1988). Oligodendrocyte-specific protein (OSP) is a putative four-transmembrane protein that is primarily expressed in oligodendrocytes of the CNS and Sertoli cells of testes in the adult mouse (Bronstein et al., 1996; Morita et al., 1999). OSP is the third most abundant CNS myelin protein, con- tributing 7% of the total myelin protein (Bronstein et al., 1997), and was found recently to share sequence homology with the claudin family of tight junction (TJ) proteins (Morita et al., 1999). OSP forms TJs in cell culture and to more accurately reflect its function, OSP was renamed OSP/claudin-11 (Morita et al., 1999). Although classical TJs have not been described in myelin, similar structures have been reported (Dermietzel et al., 1980), and OSP/ claudin-11 localizes to these structures (Morita et al., ª The Rockefeller University Press, 0021-9525/2001/04/295/11 $5.00 The Journal of Cell Biology, Volume 153, Number 2, April 16, 2001 295–305 http://www.jcb.org/cgi/content/full/153/2/295 295