INTERACTION OF DOC2 WITH TCTEX-1, A LIGHT-CHAIN OF CYTOPLASMIC DYNEIN- IMPLICATION IN DYNEIN-DEPENDENT VESICLE TRANSPORT

Doca has one Munc13-interacting domain at the N-terminal region and tw o CS-like domains interacting with Ca2+ and phospholipid at the C-term inal region. Doc2 consists of two isoforms, Doc2 alpha and -beta. Doc2 alpha is specifically expressed in neuronal cells and implicated in C a2+-dependent neurotransmitter release, whereas Doc2 beta is ubiquitou sly expressed and its function is unknown. We show here that both Doc2 alpha and -beta interact with rat tctex-1, a light chain of cytoplasm ic dynein, in both cell-free and intact cell systems. Overexpression o f the N-terminal fragment of Doc2 containing the tctex-1-interacting d omain induces changes in the intracellular localization of cation-inde pendent mannose 6-phosphate receptor and its ligand, cathepsin D, whic h are transported from trans-Golgi network to late endosomes. Overexpr ession of the C-terminal fragment containing two C2-like domains shows the similar effect, but to a lesser extent, whereas overexpression of full-length Doc2 or the C-terminal fragment of rabphilin3 containing two CS-like domains does not show this effect. Because dynein is a min us-end-directed microtubule-based motor protein, these results suggest that Doc2, especially Doc2 beta, plays a role in dynein-dependent int racellular vesicle transport.