Straight S W, Herman B, McCance D J
Department of Microbiology and Immunology, University of Rochester School of Medicine and Dentistry, New York 14642, USA.
J Virol. 1995 May;69(5):3185-92. doi: 10.1128/JVI.69.5.3185-3192.1995.
The human papillomavirus type 16 E5 oncoprotein possesses mitogenic activity that acts synergistically with epidermal growth factor (EGF) in human keratinocytes and inhibits the degradation of the EGF receptor in endosomal compartments after ligand-stimulated endocytosis. One potential explanation for these observations is that E5 inhibits the acidification of endosomes. This may be mediated through the 16-kDa component of the vacuolar proton-ATPase, since animal and human papillomavirus E5 proteins bind this subunit protein. Using a ratio-imaging technique to determine endosomal pH, we found that the acidification of endosomes in E5-expressing keratinocytes was delayed at least fourfold compared with normal human keratinocytes and endosomes in some cells never completely acidified. Furthermore, E5 expression increased the resistance of keratinocytes to protein synthesis inhibition by diphtheria toxin, a process dependent on efficient endosomal acidification. Finally, artificially inhibiting endosomal acidification with chloroquine during the endocytosis of EGF receptors in keratinocytes demonstrated many of the same effects as the expression of human papillomavirus type 16 E5, including prolonged retention of undegraded EGF receptors in intracellular vesicles.
人乳头瘤病毒16型E5癌蛋白具有促有丝分裂活性，可在人角质形成细胞中与表皮生长因子（EGF）协同作用，并在配体刺激的内吞作用后抑制内体区室中EGF受体的降解。对这些观察结果的一种可能解释是，E5抑制内体的酸化。这可能是通过液泡质子ATP酶的16 kDa组分介导的，因为动物和人乳头瘤病毒E5蛋白可结合该亚基蛋白。使用比率成像技术测定内体pH值，我们发现，与正常人角质形成细胞相比，表达E5的角质形成细胞内体的酸化延迟了至少四倍，并且一些细胞中的内体从未完全酸化。此外，E5表达增加了角质形成细胞对白喉毒素抑制蛋白质合成的抗性，这一过程依赖于有效的内体酸化。最后，在角质形成细胞中EGF受体内吞过程中用氯喹人工抑制内体酸化，表现出了许多与16型人乳头瘤病毒E5表达相同的效应，包括未降解的EGF受体在细胞内囊泡中的长时间保留。
