Department of Integrated OMICS for Biomedical Science, WCU Program of Graduate School, Yonsei University , Seoul 120-749 , Korea.
Biol Open. 2013 May 29;2(7):695-702. doi: 10.1242/bio.20134606. Print 2013 Jul 15.
Keratin 8 and 18 (K8/K18) are major intermediate filament proteins of liver hepatocytes. They provide mechanical and nonmechanical stability, thereby protecting cells from stress. Hence, K8-null mice are highly sensitive to Fas-mediated liver cell apoptosis. However, the role of c-Flip protein in K8-null related susceptibility to liver injury is controversial. Here we analyzed c-Flip protein expression in various K8 or K18 null/mutant transgenic livers and show that they are similar in all analyzed transgenic livers and that previously reported c-Flip protein changes are due to antibody cross-reaction with mouse K18. Furthermore, analysis of various apoptosis- or cell survival-related proteins demonstrated that inhibition of phosphorylation of NF-κB and various stress activated protein kinases (SAPKs), such as p38 MAPK, p44/42 MAPK and JNK1/2, is related to the higher sensitivity of K8-null hepatocytes whose nuclear NF-κB is rapidly depleted through Fas-mediated apoptosis. Notably, we found that NF-κB and the studied protein kinases are associated with the K8/K18 complex and are released upon phosphorylation. Therefore, interaction of keratins with cell survival-related protein kinases and transcription factors is another important factor for hepatocyte survival.
角蛋白 8 和 18（K8/K18）是肝实质细胞的主要中间丝蛋白。它们提供机械和非机械稳定性，从而保护细胞免受应激。因此，K8 缺失的小鼠对 Fas 介导的肝细胞凋亡非常敏感。然而，c-Flip 蛋白在 K8 缺失相关肝损伤易感性中的作用存在争议。在这里，我们分析了各种 K8 或 K18 缺失/突变转基因肝脏中的 c-Flip 蛋白表达，结果表明在所有分析的转基因肝脏中它们是相似的，并且先前报道的 c-Flip 蛋白变化是由于抗体与小鼠 K18 的交叉反应。此外，对各种凋亡或细胞存活相关蛋白的分析表明，抑制 NF-κB 和各种应激激活蛋白激酶（SAPKs），如 p38 MAPK、p44/42 MAPK 和 JNK1/2 的磷酸化，与 K8 缺失肝细胞的高敏感性有关，其核 NF-κB 通过 Fas 介导的凋亡迅速耗尽。值得注意的是，我们发现 NF-κB 和研究的蛋白激酶与 K8/K18 复合物相关，并在磷酸化后释放。因此，角蛋白与细胞存活相关蛋白激酶和转录因子的相互作用是肝细胞存活的另一个重要因素。
