HUMAN PANCREATIC ISLETS EXPRESS MRNA SPECIES ENCODING

一个85 kDa的VI族磷脂酶A2酶，命名为iPLA2， 不需要钙离子进行催化的基因最近从 三种啮齿动物。克隆了一个88 kDa的同源酶 来自含有54个氨基酸插入注释的人B淋巴细胞系 存在于啮齿类动物的酶中，但人类细胞以前没有 被观察到表达具有催化活性的iPLA2亚型 而不是88 kDa的蛋白质。我们已经克隆了编码两种基因的cDNA物种 人胰岛RNA和人胰腺组织中iPLA2亚型的差异 胰岛素瘤基因文库。一个亚型是一个85 kDa的蛋白质(SH-iPLA2) 另一个是88 kDa的蛋白(Lh-iPLA2)。这两种编码的记录 在人类原单核细胞U937细胞中也观察到了异构体。 重组SH-iPLA2和LH-iPLA2均具有催化活性 钙离子缺乏和溴酚内酯(BEL)自杀的抑制作用 而SH-iPLA2则不能被激活。 人类iPLA2基因已被发现位于22号染色体上。 Q13.1区域，包含16个外显子，在Lh-iPLA2中表示 文字记录。外显子8在SH-iPLA2转录本中不存在， 这表明它是由Alternative的外显子跳过机制引起的 拼接。人类外显子8编码的氨基酸序列 IPLA2基因富含脯氨酸，具有一个共同的基序： Px5Px8HHPx12Nx4Q与富含Pro的中间连接器域 Smad蛋白DAF-3和Smad4。编码不同物种的mRNA的表达 两种活性明显的iPLA2亚型 这里展示的两种不同类型的人类细胞可能有 关于产品的作用的监管或功能影响 IPLA2基因在细胞生物学过程中的作用

An 85 kDa Group VI phospholipase A2 enzyme, designated iPLA2, that does not require Ca2+ for catalysis has recently been cloned from three rodent species. An homologous 88 kDa enzyme has been cloned from human B-lymphocyte lines that contains a 54 amino acid insert not present in the rodent enzymes, but human cells have not previously been observed to express catalytically active iPLA2 isoforms other than the 88 kDa protein. We have cloned cDNA species that encode two distinct iPLA2 isoforms from human pancreatic islet RNA and a human insulinoma cDNA library. One isoform is an 85 kDa protein (SH-iPLA2) and the other an 88 kDa protein (LH-iPLA2). Transcripts encoding both isoforms are also observed in human promonocytic U937 cells. Recombinant SH-iPLA2 and LH-iPLA2 are both catalytically active in the absence of Ca2+ and inhibited by a bromoenol lactone (BEL) suicide substrate, but LH-iPLA2 is activated by ATP, while SH-iPLA2 is not. The human iPLA2 gene has been fou nd to resi de on chromosome 22 in region q13.1 and to contain sixteen exons represented in the LH-iPLA2 transcript. Exon 8 is not represented in the SH-iPLA2 transcript, indicating that it arises by an exon-skipping mechanism of alternative splicing. The amino acid sequence encoded by exon 8 of the human iPLA2 gene is proline-rich and shares a consensus motif of Px5Px8HHPx12Nx4Q with the proline-rich middle linker domains of the Smad proteins DAF-3 and Smad4. Expression of mRNA species encoding two active iPLA2 isoforms with distinguishable catalytic properties in two different types of human cells demonstrated here may have regulatory or functional implications about the roles of products of the iPLA2 gene in cell biologic processes.