Meyer-Ficca Mirella L, Meyer Ralph G, Coyle Donna L, Jacobson Elaine L, Jacobson Myron K
Department of Pharmacology and Toxicology, College of Pharmacy, Arizona Cancer Center, University of Arizona, Tucson, AZ 85724, USA.
Exp Cell Res. 2004 Jul 15;297(2):521-32. doi: 10.1016/j.yexcr.2004.03.050.
Poly(ADP-ribose) glycohydrolase (PARG) is the only protein known to catalyze hydrolysis of ADP-ribose (ADPR) polymers to free ADP-ribose. While numerous genes encode different poly(ADP-ribose) polymerases (PARPs) that all synthesize ADP-ribose polymer, only a single gene coding for PARG has been detected in mammalian cells. Here, we describe two splice variants of human PARG mRNA, which lead to expression of PARG isoforms of 102 kDa (hPARG102) and 99 kDa (hPARG99) in addition to the full-length PARG protein (hPARG111). These splice variants differ from hPARG111 by the lack of exon 1 (hPARG102) or exons 1 and 2 (hPARG99). They are generated by the utilization of ambiguous splice donor sites in the PARG gene 5' untranslated region. The hPARG111 isoform localizes to the nucleus, whereas hPARG102 and hPARG99 are cytoplasmic proteins. The nuclear targeting of hPARG111 is due to a nuclear localization signal (NLS) in exon 1 that was mapped to the amino acids (aa) (10)CTKRPRW(16). Immunocytochemistry, immunoblotting, and PARG enzyme activity measurements show that the cytoplasmic isoforms of PARG account for most of the PARG activity in cells in the absence and presence of genotoxic stress. The predominantly cytoplasmic location of cellular PARG is intriguing as most known cellular PARPs have a nuclear localization.
聚（ADP - 核糖）糖水解酶（PARG）是已知唯一能催化ADP - 核糖（ADPR）聚合物水解为游离ADP - 核糖的蛋白质。虽然众多基因编码不同的聚（ADP - 核糖）聚合酶（PARP），它们都能合成ADP - 核糖聚合物，但在哺乳动物细胞中仅检测到一个编码PARG的基因。在此，我们描述了人PARG mRNA的两种剪接变体，除了全长PARG蛋白（hPARG111）外，它们还导致102 kDa（hPARG102）和99 kDa（hPARG99）的PARG异构体表达。这些剪接变体与hPARG111的不同之处在于缺少外显子1（hPARG102）或外显子1和2（hPARG99）。它们是通过利用PARG基因5'非翻译区中不明确的剪接供体位点产生的。hPARG111异构体定位于细胞核，而hPARG102和hPARG99是细胞质蛋白。hPARG111的核靶向是由于外显子1中的一个核定位信号（NLS），该信号被定位到氨基酸（aa）（10）CTKRPRW（16）。免疫细胞化学、免疫印迹和PARG酶活性测量表明，在不存在和存在基因毒性应激的情况下，PARG的细胞质异构体占细胞中PARG活性的大部分。细胞PARG主要位于细胞质这一现象很有趣，因为大多数已知的细胞PARP都具有核定位。
