Bartoe Joseph L, McKenna William L, Quan Tiffani K, Stafford Benjamin K, Moore Jenna A, Xia Jun, Takamiya Kogo, Huganir Richard L, Hinck Lindsay
Department of Molecular, Cell, and Developmental Biology, University of California, Santa Cruz, California 95064, USA.
J Neurosci. 2006 Mar 22;26(12):3192-205. doi: 10.1523/JNEUROSCI.3469-05.2006.
In vertebrates, the receptor families deleted in colorectal cancer (DCC) and UNC5 mediate responses to the bifunctional guidance cue netrin-1. DCC mediates attraction, whereas a complex of DCC and UNC5 mediates repulsion. Thus, a primary determinant of the responsiveness of an axon to netrin-1 is the presence or absence of UNC5 family members on the cell surface. Currently, little is known about the role of receptor trafficking in regulating neuronal responses to netrin-1. We show that protein interacting with C-kinase 1 (PICK1) recruits activated protein kinase Calpha (PKCalpha) to MycUNC5A at the plasma membrane, stimulating its endocytosis. We identify two PKCalpha phosphorylation sites at serines 408 and 587, as well as dileucine internalization motifs, which are required for this endocytosis. We find that PKCalpha-stimulated internalization of UNC5A alters the functional response of developing hippocampal axons to netrin-1, preventing UNC5A-mediated growth cone collapse and converting netrin-1-stimulated chemorepulsion to attraction. To address whether this conversion in axonal response occurs in neurons expressing endogenous levels of UNC5, we show that mouse cerebellar granule axons exhibit chemorepulsion in a netrin-1 gradient and that this chemorepulsion is converted to chemoattraction after PKCalpha activation. We demonstrate that this repulsion depends on UNC5A because Unc5a-/- axons are not repelled and show this conversion depends on PICK1 because PICK1-/- axons are not converted to chemoattraction after PKCalpha activation. Together, these data provide a potential mechanism to explain how developing neurons alter their responsiveness to netrin-1 at intermediate choice points as they navigate to their targets.
在脊椎动物中,结直肠癌缺失的受体家族(DCC)和UNC5介导对双功能导向信号分子netrin-1的反应。DCC介导吸引作用,而DCC和UNC5的复合物介导排斥作用。因此,轴突对netrin-1反应性的一个主要决定因素是细胞表面UNC5家族成员的有无。目前,关于受体运输在调节神经元对netrin-1反应中的作用知之甚少。我们发现,与C激酶1相互作用的蛋白(PICK1)将活化的蛋白激酶Cα(PKCα)募集到质膜上的MycUNC5A处,刺激其内化。我们确定了丝氨酸408和587处的两个PKCα磷酸化位点,以及双亮氨酸内化基序,这些是这种内化所必需的。我们发现PKCα刺激的UNC5A内化改变了发育中的海马轴突对netrin-1的功能反应,防止了UNC5A介导的生长锥塌陷,并将netrin-1刺激的化学排斥转变为吸引。为了研究这种轴突反应的转变是否发生在内源性表达UNC5的神经元中,我们表明小鼠小脑颗粒轴突在netrin-1梯度中表现出化学排斥,并且在PKCα激活后这种化学排斥转变为化学吸引。我们证明这种排斥依赖于UNC5A,因为Unc5a-/-轴突不会被排斥,并且表明这种转变依赖于PICK1,因为PICK1-/-轴突在PKCα激活后不会转变为化学吸引。总之,这些数据提供了一种潜在机制,来解释发育中的神经元在向其靶标导航时,如何在中间选择点改变它们对netrin-1的反应性。