Proc. Natl. Acad. Sci. USA Vol. 93, pp. 674-678, January 1996 Genetics

A family of transmembrane proteins with homology to the MET- receptor (RON/MSP/X /neural development) E. MAESTRINI*t, L. TAMAGNONEtI, P. LONGATIt§, 0. CREMONAt, M. GULISANO$, S. BIONE*, F. TAMANINI*, B. G. NEEL§, D. TONIOLO*, AND P. M. COMOGLIOtIl *Institute of Genetics Biochemistry and Evolution, Consiglio Nazionale delle Ricerche, 27100, Pavia, Italy; §Molecular Medicine Unit, Beth Israel Hospital, Boston, MA 02215; IDepartment of Biological and Technological Research, San Raffaele Hospital, 20100, Milano, Italy; and tlnstitute for Cancer Research (IRCC), University of Torino Medical School, 10126, Torino, Italy Communicated by Renato Dulbecco, The Salk Institute for Biological Studies, La Jolla, CA, September 15, 1995 (received for review July 10, 1995)

ABSTRACT In hunting for unknown on the human factor (HGF) family growth factor receptors are implicated in X chromosome, we identified a cDNA in Xq28 encoding a a common array of complex biological functions, including transmembrane protein (SEX) of 1871 amino acids. SEX proliferation, motility, and differentiation of epithelial, endo- shares significant homology with the extracellular domain of thelial, and blood-derived cells (17-19). The protooncogene the receptors encoded by the oncogenes MET, RON, and SEA MET is frequently overexpressed in neoplastic cells and, due [hepatocyte growth factor (HGF) receptor family]. Further to its prominent role in the control of motility and invasion, is screenings of cDNA libraries identified three additional se- involved in metastasis formation (20-22). quences closely related to SEX; these were named SEP, OCT, In this paper, we identify a family of genes encoding putative and NOV and were located on human 3p, 1, and receptors with structural similarities to the extracellular do- 3q, respectively. The proteins encoded by these genes contain main of the MET/HGF receptor. The large cytoplasmic large cytoplasmic domains characterized by a distinctive domains of these proteins display no similarity to TKs; instead, highly conserved sequence (SEX domain). Northern blot they share a highly homologous sequence, suggesting signal analysis revealed different expression of the SEX family of transduction by uncharacterized enzymatic or binding prop- genes in fetal tissues, with SEX, OCT, and NOVpredominantly erties. * * expressed in brain, and SEP expressed at highest levels in kidney. In situ hybridization analysis revealed that SEX has a distinctive pattern of expression in the developing nervous MATERIALS AND METHODS system of the mouse, where it is found in postmitotic neurons Cells and Antibodies. IMR-32, Neuro2a, and COS-7 cell from the first stages of neuronal differentiation (9.5 day lines were obtained from the American Type Culture Collec- postcoitus). The SEX protein (220 kDa) is glycosylated and tion. BOSC23 is a subline of 293T human fetal kidney (23). A exposed at the cell surface. Unlike the receptors of the HGJF glutathione S-transferase fusion protein containing the last 38 family, p220SEx, a MET-SEX chimera or a constitutively amino acids of SEX, obtained by PCR amplification and dimerized TPR-SEX does not show tyrosine kinase activity. cloning in pGEX-lkT vector (Pharmacia), was purified and These data define a family (SEX family) involved in the used as immunogen to raise anti-SEX antibodies in rabbits, development of neural and epithelial tissues, which encodes which were then purified by affinity chromatography. putative receptors with unexpected enzymatic or binding cDNA Library Screening and Cloning of Human and Mu- properties. rine Sequences. The SEX cDNAs were isolated from human fetal brain, skeletal muscle, and total human embryo cDNA Proteins spanning the cell