Identification of an Axotomy-Induced Glycosylated Protein, AIGP1, Possibly Involved in Cell Death Triggered by Endoplasmic Reticulum–Golgi Stress

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Abstract
We developed a new method, designated N-linked glycosylation signal (NGS) differential display (DD)-PCR, that enables the identification of genes encoding N-linked glycosylated molecules that exhibit varying patterns of expression. Using this innovative technique, we identified an N-linked glycosylated 11-transmembrane domain protein that is upregulated in response to axotomy. Expression levels increased 3 d after axotomy, reached maximal levels at approximately postoperative days 5–7, and then gradually decreased through day 20. The protein was termed axotomy-induced glycosylated/Golgi-complex protein 1 (AIGP1). AIGP1 immunoreactivity is specifically localized in neurons, with subcellular localization within the Golgi, indicating that AIGP1 is a resident Golgi protein. Moreover, AIGP1 gene expression in cultured neurons is specifically induced by the endoplasmic reticulum (ER)–Golgi stressors tunicamycin and brefeldin A. We observed that the frequency of cell death is increased by AIGP1 overexpression and that the corresponding region of the protein implicated in the activity involves the large eighth and ninth transmembrane loops. Our results suggest that AIGP1 gene activation and protein accumulation in the Golgi complex in response to axotomy-induced ER–Golgi stress may contribute to signaling during programmed cell death in damaged neurons.