Department of Molecular Genetics, Kawasaki Medical School, Kurashiki 701-0192, Japan.
Blood Cells Mol Dis. 2012 Jun 15;49(1):60-6. doi: 10.1016/j.bcmd.2012.03.004. Epub 2012 Apr 5.
The feline leukemia virus subgroup C receptor 1 (FLVCR1) is a heme exporter that maintains the intracellular heme concentration. FLVCR1 was previously assumed to be involved in Diamond-Blackfan anemia, and it was recently reported that mutations in the FLVCR1 gene are found in patients with posterior column ataxia and retinitis pigmentosa (PCARP). Four mutations in FLVCR1 (Asn121Asp, Cys192Arg, Ala241Thr, and Gly493Arg) are located within putative transmembrane domains; however, the effects of FLVCR1 mutations on PCARP are unclear. In this study, we analyzed the function of FLVCR1 mutants by using a fluorescent heme analog as a transporter substrate, and found that all 4 FLVCR1 mutants lost their heme export activity. To investigate the mechanism responsible for this loss of activity, we determined the subcellular localization of FLVCR1 mutants. FLVCR1 mutants did not localize to the plasma membrane and were observed in intracellular structures, including lysosomes. We hypothesize that the loss of function of FLVCR1 mutants is caused by their mislocation. We examined the half-life of FLVCR1 in cells, which was >16h for wild-type FLVCR1 compared with 2-4h for the mutants. Based on these results, we propose that FLVCR1 mutants failed to fold properly in the ER, were rapidly degraded in the lysosomes, and therefore, could not export heme out of cells. Thus, accumulation of heme in FLVCR1-mutant cells could cause cellular toxicity.
猫白血病病毒亚群 C 受体 1（FLVCR1）是一种血红素输出蛋白，可维持细胞内血红素浓度。FLVCR1 先前被认为与 Diamond-Blackfan 贫血有关，最近有报道称，FLVCR1 基因突变存在于后柱共济失调和视网膜色素变性（PCARP）患者中。FLVCR1 中的 4 个突变（Asn121Asp、Cys192Arg、Ala241Thr 和 Gly493Arg）位于假定的跨膜结构域内；然而，FLVCR1 突变对 PCARP 的影响尚不清楚。在这项研究中，我们通过使用荧光血红素类似物作为转运体底物来分析 FLVCR1 突变体的功能，发现所有 4 个 FLVCR1 突变体均丧失了血红素输出活性。为了研究导致这种活性丧失的机制，我们确定了 FLVCR1 突变体的亚细胞定位。FLVCR1 突变体不能定位于质膜，而是存在于包括溶酶体在内的细胞内结构中。我们假设 FLVCR1 突变体的功能丧失是由其定位错误引起的。我们检查了 FLVCR1 在细胞中的半衰期，野生型 FLVCR1 的半衰期>16h，而突变体的半衰期为 2-4h。基于这些结果，我们提出 FLVCR1 突变体在 ER 中不能正确折叠，在溶酶体中迅速降解，因此不能将血红素输出细胞。因此，FLVCR1 突变体细胞内血红素的积累可能导致细胞毒性。
