Alternative splicing of vitamin D-24-hydroxylase - A novel mechanism for the regulation of extrarenal 1,25-dihydroxyvitamin D synthesis
Alternative splicing of vitamin D-24-hydroxylase - A novel mechanism for the regulation of extrarenal 1,25-dihydroxyvitamin D synthesis
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DOI：
10.1074/jbc.m414522200
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发表时间：
2005-05-27
影响因子：
4.8
通讯作者：
Hewison, M
中科院分区：
文献类型：
--
作者：
Ren, SY;Nguyen, L;Hewison, M
肾上皮细胞合成活性形式的维生素D，即1，25-二羟基维生素D（1，25-（OH）（2）D），在正常钙稳态期间受到严格控制。相比之下，巨噬细胞产生的1，25-（OH）2D通常失调，具有潜在的高钙血症并发症。我们推测这是由于反馈控制酶维生素D-24-羟化酶（CYP 24）对1，25-（OH）2D的异常催化作用。使用鸡HD-11和人THP-1骨髓单核细胞系，我们已经表明，巨噬细胞样细胞表达的CYP 24基因（CYP 24-SV），它编码一个截短的蛋白质的剪接变体。与鸡和人细胞中的完整CYP 24基因产物（分别为508和513个氨基酸）相比，截短的CYP 24-SV版本由351和372个氨基酸组成。这些CYP 24-SV蛋白保留完整的底物结合结构域，但缺乏线粒体靶向序列，因此无催化活性。与CYP 24相同，CYP 24变体的表达由1，25（OH）2D诱导，但没有伴随的24-羟化酶活性升高。然而，在HD-11和THP-1细胞中过表达CYP 24-SV减少了1，25-（OH）2D的合成（40-50%），而反义CYP 24-SV表达使1，25-（OH）2D的产量增加了2-7倍。这些数据表明，CYP 24的选择性剪接导致产生一种显性负作用蛋白，这种蛋白具有催化功能障碍。我们推测CYP 24-SV的表达可能有助于1，25（OH）2D在人体健康和疾病中的细胞外积累。
Synthesis of the active form of vitamin D, 1,25-dihydroxyvitamin D ( 1,25-(OH)(2)D), by renal epithelial cells is tightly controlled during normal calcium homeostasis. By contrast, macrophage production of 1,25-( OH) 2D is often dysregulated with potential hypercalcemic complications. We have postulated that this is due to abnormal catabolism of 1,25-(OH) 2D by the feedback control enzyme, vitamin D-24-hydroxylase (CYP24). Using chick HD-11 and human THP-1 myelomonocytic cell lines, we have shown that macrophage-like cells express a splice variant of the CYP24 gene (CYP24-SV), which encodes a truncated protein. Compared with the holo-CYP24 gene product in chick and human cells (508 and 513 amino acids, respectively), the truncated CYP24-SV versions consisted of 351 and 372 amino acids. These CYP24-SV proteins retained intact substrate- binding domains but lacked mitochondrial targeting sequences and were therefore catalytically inactive. In common with CYP24, expression of the CYP24 variants was induced by 1,25( OH) 2D but without a concomitant rise in 24-hydroxylase activity. However, overexpression of CYP24-SV in HD-11 and THP-1 cells reduced synthesis of 1,25-(OH) 2D (40-50%), whereas antisense CYP24-SV expression increased 1,25-(OH) 2D production by 2-7-fold. These data suggest that alternative splicing of CYP24 leads to the generation of a dominant negative-acting protein that is catalytically dysfunctional. We theorize that expression of the CYP24-SV may contribute to the extracellular accumulation of 1,25(OH) 2D in human health and disease.