Sanchez P, De Carcer G, Sandoval I V, Moscat J, Diaz-Meco M T
Centro de Biología Molecular Severo Ochoa (Consejo Superior de Investigaciones Cientificas-Universidad Autónoma de Madrid), Universidad Autónoma, Canto Blanco, Spain.
Mol Cell Biol. 1998 May;18(5):3069-80. doi: 10.1128/MCB.18.5.3069.
An increasing number of independent studies indicate that the atypical protein kinase C (PKC) isoforms (aPKCs) are critically involved in the control of cell proliferation and survival. The aPKCs are targets of important lipid mediators such as ceramide and the products of the PI 3-kinase. In addition, the aPKCs have been shown to interact with Ras and with two novel proteins, LIP (lambda-interacting protein; a selective activator of lambda/iotaPKC) and the product of par-4 (a gene induced during apoptosis), which is an inhibitor of both lambda/iotaPKC and zetaPKC. LIP and Par-4 interact with the zinc finger domain of the aPKCs where the lipid mediators have been shown to bind. Here we report the identification of p62, a previously described phosphotyrosine-independent p56(lck) SH2-interacting protein, as a molecule that interacts potently with the V1 domain of lambda/iotaPKC and, albeit with lower affinity, with zetaPKC. We also show in this study that ectopically expressed p62 colocalizes perfectly with both lambda/iotaPKC and zetaPKC. Interestingly, the endogenous p62, like the ectopically expressed protein, displays a punctate vesicular pattern and clearly colocalizes with endogenous lambda/iotaPKC and endogenous zetaPKC. P62 colocalizes with Rab7 and partially with lamp-1 and limp-II as well as with the epidermal growth factor (EGF) receptor in activated cells, but not with Rab5 or the transferrin receptor. Of functional relevance, expression of dominant negative lambda/iotaPKC, but not of the wild-type enzyme, severely impairs the endocytic membrane transport of the EGF receptor with no effect on the transferrin receptor. These findings strongly suggest that the aPKCs are anchored by p62 in the lysosome-targeted endosomal compartment, which seems critical for the control of the growth factor receptor trafficking. This is particularly relevant in light of the role played by the aPKCs in mitogenic cell signaling events.
越来越多的独立研究表明，非典型蛋白激酶C（PKC）亚型（aPKCs）在细胞增殖和存活的控制中起着关键作用。aPKCs是重要脂质介质（如神经酰胺和PI 3激酶产物）的作用靶点。此外，aPKCs已被证明与Ras以及两种新蛋白相互作用，即LIP（λ相互作用蛋白；λ/ιPKC的选择性激活剂）和par-4产物（一种在细胞凋亡过程中诱导产生的基因），par-4是λ/ιPKC和ζPKC的抑制剂。LIP和Par-4与aPKCs的锌指结构域相互作用，脂质介质已被证明可结合于此结构域。在此，我们报告了p62的鉴定，p62是一种先前描述的与磷酸酪氨酸无关的p56(lck) SH2相互作用蛋白，它是一种能与λ/ιPKC的V1结构域强烈相互作用、与ζPKC相互作用亲和力较低的分子。我们在本研究中还表明，异位表达的p62与λ/ιPKC和ζPKC完美共定位。有趣的是，内源性p62与异位表达的蛋白一样，呈现点状囊泡模式，并与内源性λ/ιPKC和内源性ζPKC明显共定位。在活化细胞中，p62与Rab7共定位，部分与lamp-1和limp-II以及表皮生长因子（EGF）受体共定位，但不与Rab5或转铁蛋白受体共定位。在功能相关性方面，显性负性λ/ιPKC的表达而非野生型酶的表达，严重损害了EGF受体的内吞膜转运，而对转铁蛋白受体无影响。这些发现强烈表明，aPKCs通过p62锚定在靶向溶酶体的内体区室中，这似乎对生长因子受体运输的控制至关重要。鉴于aPKCs在有丝分裂细胞信号事件中所起的作用，这一点尤为重要。
