Endocytotic Adaptor Protein HIP1R Is Required For Neuronal Dendritic Development By Controlling Intracellular Trafficking Of Epidermal Growth Factor Receptors

Huntington-interacting protein 1-related(HIP1R),was identified on the basis of structural homology like its homologue HIP1 and Sla2p.Common to the structure of all Sla2 family members is an N-terminal ANTH(AP180 NH2-terminal homology)domain which could interact with inositol lipids,a central coiled-coil domain that interacts with clathrin light chain,and a C-terminal talin-like domain which could bind to F-actin.Based on the domain features,HIP1R is considered as an endocytic related protein.Our previous study showed that at the early developing.stage of cultured hippocampal neurons,knocking down HIP1R protein induced dramatical decrease of dendritic filopodia number.Dendritic branching and complexity were also significantly reduced after HIP1R deletion,as well as the densities of dendritic spines and PSD95 clusters of mature neurons.However,mechanism of these phenotypes remain unknown.It was reported that HEP1R modulated the degradation of EGFR via clathrin-mediated membrane trafficking pathway.In HIP1R and EGFR both overexpressed HEK293T cells,interaction between HIP1R and EGFR could be easily confirmed.In addition,MAPK/ERK and PI3K-Akt-mTOR pathways play a critical role in neurite extension and dendritic growth.Whether HIP1R knockdown induced neuron development deficiency is through EGFR and its downstream signaling pathways is worthy of further studying.In this study,we found that after HIP 1R knockdown,the activated dependent endocytosis of EGFR was damaged and the phosphorylation of ERK and Akt were decreased accordingly.Meanwhile,EGF-induced neurite and dendrite outgrowth were blocked when HIP1R was deleted.We also found the amino acid sequences of HIP1R,aa 633-822(HIP1R633-822),could interact with EGFR.The expression of dominant-negative HIP1R in hippocampal neurons led to a reduction in the number of initiated neurite and primary dendrites,refecting a requirement for the interaction of HIP1R and EGFR.In conclusion,our study indicates HIP1R regulates the neurite and dendrite development of cultured hippocampal neurons by controling the intracellular trafficking of EGFR and its downstream signaling transduction.