Department of Biochemistry and Pharmacology , University of Massachusetts Medical School , Worcester , Massachusetts 01605 , United States.
Program in Chemical Biology , University of Massachusetts Medical School , 364 Plantation Street , Worcester , Massachusetts 01605 , United States.
Biochemistry. 2019 Jul 9;58(27):3042-3056. doi: 10.1021/acs.biochem.9b00225. Epub 2019 Jun 27.
Protein arginine deiminases (PADs) are calcium-dependent enzymes that mediate the post-translational conversion of arginine into citrulline. Dysregulated PAD activity is associated with numerous autoimmune disorders and cancers. In breast cancer, PAD2 citrullinates histone H3R26 and activates the transcription of estrogen receptor target genes. However, PAD2 lacks a canonical nuclear localization sequence, and it is unclear how this enzyme is transported into the nucleus. Here, we show for the first time that PAD2 translocates into the nucleus in response to calcium signaling. Using BioID2, a proximity-dependent biotinylation method for identifying interacting proteins, we found that PAD2 preferentially associates with ANXA5 in the cytoplasm. Binding of calcium to PAD2 weakens this cytoplasmic interaction, which generates a pool of calcium-bound PAD2 that can interact with Ran. We hypothesize that this latter interaction promotes the translocation of PAD2 into the nucleus. These findings highlight a critical role for ANXA5 in regulating PAD2 and identify an unusual mechanism whereby proteins translocate between the cytosol and nucleus.
蛋白质精氨酸脱亚氨酶（PADs）是一种依赖于钙的酶，可介导精氨酸的翻译后转化为瓜氨酸。PAD 活性失调与许多自身免疫性疾病和癌症有关。在乳腺癌中，PAD2 使组蛋白 H3R26 瓜氨酸化并激活雌激素受体靶基因的转录。然而，PAD2 缺乏经典的核定位序列，目前尚不清楚该酶如何被转运到细胞核内。在这里，我们首次表明 PAD2 会响应钙信号转导而进入细胞核。使用 BioID2，一种用于鉴定相互作用蛋白的邻近依赖性生物素化方法，我们发现 PAD2 在细胞质中优先与 ANXA5 结合。钙与 PAD2 的结合削弱了这种细胞质相互作用，从而产生了可以与 Ran 相互作用的钙结合 PAD2 池。我们假设这种相互作用促进了 PAD2 向核内的转运。这些发现突出了 ANXA5 在调节 PAD2 中的关键作用，并确定了一种蛋白质在细胞质和细胞核之间转运的不寻常机制。
