Protein Kinase D Regulates Trafficking of Dendritic Membrane Proteins in Developing Neurons

BISBAL M; DONOSO M; BOLLATI F; SESMA J; QUIROGA S; DIAZ AÑEL A; MALHOTRA V; MARZOLO M; CACERES A

Los Cocos

Workshop; International Workshop on Latest Concepts in Developmental Biology.; 2006

Neurons are highly polarized cells typically extending several short, thick tapering dendrites and one functional distinct long thin axon. Consistent with their different functions, many cell membrane proteins are preferentially distributed either to axons or dendrites, with neurons using different and complementary mechanisms to achieve this goal. It is now accepted that each step along the neuronal membrane trafficking pathway -sorting into carrier vesicles, fission and exit from the Golgi, transport along microtubules, fusion with the plasma membrane, and retention at the plasma membrane- is a potential ?decision site? where molecular selectivity mechanisms could act to govern protein targeting. The identification of proteins and/or signaling pathways that mediate and/or control these ?steps? is of key importance for understanding neuronal polarity.
Protein kinase D1 (PKD1), is a member of a novel family of dyacylglycerol (DAG)-stimulated Ser/Thr kinases  that regulates Golgi to cell surface protein transport. In non-neuronal cells, overexpression of PKD kinase-defective (kd) mutants also leads to extensive tubulation of the trans-Golgi network (TGN), with cargo-containing vesicles failing to detach from it, while ectopic expression of PKD1 over activates the fission reaction leading to Golgi fragmentation. Interestingly, in polarized epithelial cells inhibition of PKD1-3 activity inhibits a membrane fission pathway specifically involved in the transport of cargo carrying basolateral sorting signals. The identification of proteins (or motifs and/or sorting signals) and/or signaling pathways that mediate and/or control these steps is therefore of key importance for understanding neuronal polarity. In this regard, the possible involvement of PKD1 could be of particular interest.
We present evidence that reducing PKD1 levels and/or activity dramatically alters the trafficking and membrane delivery of two dendritic membrane proteins, namely the low-density receptor-related protein (LRP) and the transferrin receptor (TfR), but not of the axonal membrane protein L1. After PKD1 suppression or inactivation, both dendritic proteins distributed to axons and dendrites, but are preferentially delivered to the axonal membrane, a pattern similar to that of L1. This phenotype precedes any significant alteration in dendritic morphology. Thus, by specifying dendritic vesicle identity PKD1 has a key role in neuronal polarity.