An old dog learns new tricks: a novel function for Cdc20-APC in dendrite morphogenesis in neurons

Abstract

The E3 ubiquitin ligases Cdc20-anaphase-promoting complex (Cdc20-APC) and Cdh1-APC play key roles in cell cycle transitions in proliferating cells. Remarkably, these ubiquitin ligases are also expressed in postmitotic neurons, raising interest in non-mitotic functions of the APC. Cdh1-APC has been implicated in diverse functions in the nervous system, from the control of axon growth and patterning to synapse development to neuron survival. However, until recently the question of whether Cdc20-APC harbors functions in neurons remained unanswered. New evidence from Kim et al. (2009) has uncovered a novel role for Cdc20-APCin dendrite growth and elaboration in post-mitotic neurons. Interestingly, the histone deacetylase HDAC6 augments Cdc20-APC activity at the centrosome by promoting Cdc20 polyubiquitination. In turn, Cdc20-APC triggers the degradation of the centrosomally localized protein Id1 and thereby promotes dendrite growth and elaboration. These findings have advanced our understanding of APC biology in neuronal connectivity in the brain.

Figure 1. Centrosomal Cdc20-APC controls dendrite morphogenesis in post-mitotic neurons

(A) Left: Granule neurons transfected with Cdc20 RNAi or control U6 plasmid along with a GFP expression plasmid were analyzed by immunocytochemistry with the GFP antibody four days after transfection. Representative neurons are shown. Arrows indicate dendrites and arrowheads denote axons. Scale bar represents 10 μm. Right: Total dendrite length from granule neurons transfected with Cdc20 RNAi or control U6 plasmid was measured. Cdc20 knockdown significantly reduced total dendrite length in transfected neurons compared to control U6-transfection (ANOVA; p < 0.0001). (B) Granule neurons were transfected with the Cdc20 RNAi or control U6 plasmid along with an expression plasmid encoding NLS-Cdc20-RES, PACT-Cdc20-RES, PACT, PACT-Cdh1, or control vector and a GFP expression plasmid. Granule neurons were analyzed as in (A). Centrosomally localized Cdc20 (PACT-Cdc20-RES), but not nuclearly localized Cdc20 (NLS-Cdc20-RES) significantly increased total dendrite length compared to the control vector in the background of Cdc20 RNAi (ANOVA, p < 0.0001). (C) 293T cells were transfected with the GFP-Cdc20 expression plasmid or control vector along with a His-myc-ubiquitin expression plasmid and the indicated FLAG-HDAC6 expression plasmids. Lysates were sonicated and immunoprecipitated with GFP antibody. Immunoprecipitates and lysates were immunoblotted with the antibodies as indicated. Asterisk indicates IgG heavy chain. (D) Granule neurons were transfected with the HDAC6 RNAi or control U6 plasmid and expression plasmids encoding HA-ubiquitin and GFP to determine transfection efficiency. Lysates were sonicated and immunoprecipitated with the Cdc20 antibody and immunoprecipitates and lysates were immunoblotted with the antibodies as indicated. (E) The centrosomal HDAC6/Cdc20-APC/Id1 ubiquitin signaling pathway controls dendrite morphogenesis in post-mitotic neurons. Reprinted with permission from Cell.