Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755, USA.
Mol Biol Cell. 2011 Dec;22(24):4822-33. doi: 10.1091/mbc.E11-05-0457. Epub 2011 Oct 12.
INF2 is a unique formin that can both polymerize and depolymerize actin filaments. Mutations in INF2 cause the kidney disease focal and segmental glomerulosclerosis. INF2 can be expressed as two C-terminal splice variants: CAAX and non-CAAX. The CAAX isoform contains a C-terminal prenyl group and is tightly bound to endoplasmic reticulum (ER). The localization pattern and cellular function of the non-CAAX isoform have not been studied. Here we find that the two isoforms are expressed in a cell type-dependent manner, with CAAX predominant in 3T3 fibroblasts and non-CAAX predominant in U2OS, HeLa, and Jurkat cells. Although INF2-CAAX is ER localized in an actin-independent manner, INF2-non-CAAX localizes in an actin-dependent meshwork pattern distinct from ER. INF2-non-CAAX is loosely attached to this meshwork, being extracted by brief digitonin treatment. Suppression of INF2-non-CAAX causes fragmentation of the Golgi apparatus. This effect is counteracted by treatment with the actin monomer-sequestering drug latrunculin B. We also find discrete patches of actin filaments in the peri-Golgi region, and these patches are reduced upon INF2 suppression. Our results suggest that the non-CAAX isoform of INF2 serves a distinct cellular function from that of the CAAX isoform.
INF2 是一种独特的formin，既能聚合又能解聚肌动蛋白丝。INF2 突变会导致肾脏疾病局灶性和节段性肾小球硬化症。INF2 可以表达为两种 C 末端剪接变体：CAAX 和非 CAAX。CAAX 异构体包含 C 末端异戊烯基基团，并与内质网 (ER) 紧密结合。非 CAAX 异构体的定位模式和细胞功能尚未得到研究。在这里，我们发现这两种异构体以细胞类型依赖的方式表达，CAAX 在 3T3 成纤维细胞中占优势，而非 CAAX 在 U2OS、HeLa 和 Jurkat 细胞中占优势。尽管 INF2-CAAX 以肌动蛋白非依赖性方式定位于 ER，但 INF2-non-CAAX 以与 ER 不同的肌动蛋白依赖性网格模式定位。INF2-non-CAAX 松散地附着在这个网格上，通过短暂的二氢月桂酰基肉毒碱处理可以提取出来。抑制 INF2-non-CAAX 会导致高尔基体的碎片化。这种效应可以通过用肌动蛋白单体隔离药物 latrunculin B 处理来抵消。我们还发现高尔基体周围区域存在离散的肌动蛋白丝斑，而在 INF2 抑制后这些斑减少。我们的结果表明，INF2 的非 CAAX 异构体具有与 CAAX 异构体不同的细胞功能。
