The Kresge Hearing Research Institute-3 (KHRI-3) antibody binds to a guinea pig inner ear supporting cell antigen (IESCA) and causes hearing loss. To gain insight into the mechanism of antibody-induced hearing loss, we used antibody immunoaffinity purification to isolate the IESCA, which was then sequenced by mass spectroscopy, revealing 10 guinea pig peptides identical to sequences in human choline transporter-like protein 2 (CTL2). Full-length CTL2 cDNA sequenced from guinea pig inner ear has 85.9% identity with the human cDNA. Consistent with its expression on the surface of supporting cells in the inner ear, CTL2 contains 10 predicted membrane-spanning regions with multiple N-glycosylation sites. The 68 and 72 kDa molecular forms of inner ear CTL2 are distinguished by sialic acid modification of the carbohydrate. The KHRI-3 antibody binds to an N-linked carbohydrate on CTL2 and presumably damages the organ of Corti by blocking the transporter function of this molecule. CTL2 mRNA and protein are abundantly expressed in human inner ear. Sera from patients with autoimmune hearing loss bind to guinea pig inner ear with the same pattern as CTL2 antibodies. Thus, CTL2 is a possible target of autoimmune hearing loss in humans.

Antibodies to the solute carrier protein, CTL2/SLC44A2, cause hearing loss in animals, are frequently found in autoimmune hearing loss patients, and are implicated in transfusion-related acute lung injury. We cloned a novel CTL2/SLC44A2 isoform (CTL2 P1) from inner ear and identified an alternate upstream promoter and exon 1a encoding a protein of 704 amino acids which differs in the first 10–12 amino acids from the known exon 1b isoform (CTL2 P2; 706 amino acids). The expression of these CTL2/SLC44A2 isoforms, their posttranslational modifications in tissues and their localization in HEK293 cells expressing rHuCTL2/SLC44A2 were assessed. P1 and P2 isoforms with differing glycosylation are variably expressed in cochlea, tongue, heart, colon, lung, kidney, liver and spleen suggesting tissue specific differences that may influence function in each tissue. Because antibodies to CTL2/SLC44A2 have serious pathologic consequences, it is important to understand its distribution and modifications. Heterologous expression in X. laevis oocytes shows that while human CTL2-P1 does not transport choline, human CTL2-P2 exhibits detectable choline transport activity.

Galanin receptor 1 (GALR1) maps to a common region of 18q loss in head and neck squamous cell carcinomas and is frequently inactivated by methylation. To investigate effects of GALR1 and its signaling pathways, we stably expressed hemaglutinin-tagged GALR1 in a human oral carcinoma cell line (UM-SCC-1-GALR1) that expresses no endogenous GALR1. In transfected cells, galanin induced activation of the extracellular-regulated protein kinase-1/2 (ERK1/2) and suppressed proliferation. Galanin stimulation mediated decreased expression of cyclin D1 and increased expression of the cyclin-dependent kinase inhibitors (CKI), p27(Kip1) and p57(Kip2). Pretreatment with the ERK1/2-specific inhibitor U0126 prevented these galanin-induced effects. Phosphatidylinositol 3-kinase (PI3K) pathway activation did not differ in UM-SCC-1-GALR1 and UM-SCC-1-mock cells after galanin treatment. Pertussis toxin and LY294002 inhibition demonstrated that galanin and GALR1 induce ERK1/2 activation via Galphai, not the PI3K pathway-linked to the Gbetagamma subunit. Galanin and GALR1 also inhibit colony formation and tumor growth in vivo. Our results implicate GALR1, a Gi protein-coupled receptor, as a tumor suppressor gene that inhibits cell proliferation via ERK1/2 activation.

Purpose Galanin and its three receptors (GALR1-3) are expressed in many normal tissues, but silenced in some tumors. Contradictory roles for galanin and its receptors in various tumors have been reported. To understand their function, investigations of individual GALRs are necessary. In head and neck squamous carcinoma cells (HNSCC) with silenced GALR1 and GALR2, we showed that re-expressed GALR1 suppresses tumor cell proliferation via Erk1/2-mediated effects on cdk inhibitors and cyclin D1. Others showed that GALR2 could induce apoptosis in neuroblastoma cells with wild-type p53, whereas GALR2 stimulated proliferation in small cell lung cancer. In this study, we investigated the role of GALR2 in HNSCC cells that have mutant p53 and do not express GALR1. Experimental Design and Results UM-SCC1, a human oral carcinoma cell line with a splice site mutation causing a 46-bp p53 off frame deletion, was stably transfected to express GALR2 (UM-SCC-1-GALR2). Galanin treatment of UM-SCC-1-GALR2 caused morphological changes and a marked decrease in cell number that were not observed in UM-SCC-1-mock cells. Galanin and GALR2 resulted in decreased BrdU incorporation, p27Kip1 and p57Kip2 up-regulation, and decreased cyclin D1 expression. These effects were similar to GALR1 signaling in HNSCC, however, GALR2 also induced caspase-3-dependent apoptosis, which was confirmed by annexin-V staining and DNA fragmentation analysis. These were not observed with GALR1. Conclusion This study demonstrates that GALR2 re-expression can inhibit cell proliferation and induce apoptosis in HNSCC cells with mutant p53. GALR2 may be a feasible target for HNSCC therapy.

Murine monoclonal antibodies against guinea pig cochlear epithelium were generated with the goal of identifying cochlea-specific antigens and elucidating their function. To compensate for the limited amount of cochlear tissue, intrasplenic immunization was used. Hybridoma supernatants were screened by ELISA for antibody production and for binding to homogenates from cochlea, liver, lung, kidney and brain. Hybrids producing antibody to cochlea were subcloned and tested immunocytochemically against frozen sections and surface preparations of paraformaldehyde-fixed cochlear tissue. KHRI-1, a low titer IgM antibody stained only Hensen cells. KHRI-2, also an IgM antibody, stained tectorial membrane, cells of the spiral limbus, cells bordering the space of Nuel, Hensen cells and the root cells of the spiral prominence. KHRI-3, an IgG1 antibody, stained the phalangeal processes of outer pillar cells and the apical portion of phalangeal processes of Deiters' cells in a distinctive wine goblet pattern on surface preparations. KHRI-3 antibody also reacted with peripheral nerves and pia mater of brain in unfixed frozen sections but the antigenic site was not stable to fixation in contrast to the epitope detected in the cochlea. In Western blots of detergent extracts from cochlea KHRI-3 stained a broad tissue-specific band of Mr 70-75 kDa; a narrower band of Mr 68-70 kDa was identified by KHRI-3 in extracts of tongue and brain. KHRI-1 and KHRI-2 did not detect any proteins in Western blots. The monoclonal antibodies KHRI-1, -2, and -3 which define epitopes expressed by discrete populations of supporting cells in the inner ear should be useful in characterizing the nature and function of cellular structures in the cochlea.