Huntingtin participates in CCV endocytosis

BORGONOVO J; CAPELLA P; ROTH G; LUCAS JJ; SOSA MA

Universidad de la Punta (San Luis).

Congreso; XXVII reunión científica anual de la Sociedad de Biología de Cuyo (SBC).; 2009

Sociedad de Biología de Cuyo

Clathrin coated vesicle-mediated endocytosis (CCVE) is a common mechanism in eukariotic cells, to internalize receptors and nutrients into the cells. In neurons, CCVs are required for recycling of membrane proteins after neurotransmitter release. Among several coat proteins, AP-2 appears to contribute to the selectivity in the CCVE. Huntingtin (htt) is a cytoplasmic protein that has been also isolated from CCV. Excessive expansion of polyglutamine (poliQ) in the molecule of htt appears to be responsible for neuronal toxicity associated with Huntington´s disease (HD), that involves dysfunction and death of neurons, particularly the medium spiny neurons of the striatum. This study was aimed to assess whether htt has incidence on CCVE. We evaluated whether the expression of a mutant htt alters the distribution of AP-2, dynamin and HIP1 between cytosol and membranes in different areas of the brain of transgenic mice expressing poliQhtt (HD94) or in striatal cell lines from mouse  (StdhQ111). By immunoblot, we observed a decrease in AP-2 associated with membranes in the striatum of HD94 mice and StdhQ111 cells, compared to controls. However, no change was observed in the distribution of the other proteins studied. By immunoprecipitation, we observed that AP-2 interacts directly with htt and that this interaction is disrupted when htt is mutated. In addition, we have shown that excessive polyQ alters endocytosis of transferrin. These results suggest that alterations in the endocytosis of nerve terminals contribute to the pathogenesis of HD.