Control of Cyclin Ubiquitination by CDK-Regulated Binding of Hct1 to the Anaphase Promoting Complex

Abstract

Proteolysis of mitotic cyclins depends on a multisubunit ubiquitin-protein ligase, the anaphase promoting complex (APC). Proteolysis commences during anaphase, persisting throughout G1 until it is terminated by cyclin-dependent kinases (CDKs) as cells enter S phase. Proteolysis of mitotic cyclins in yeast was shown to require association of the APC with the substrate-specific activator Hct1 (also called Cdh1). Phosphorylation of Hct1 by CDKs blocked the Hct1-APC interaction. The mutual inhibition between APC and CDKs explains how cells suppress mitotic CDK activity during G1 and then establish a period with elevated kinase activity from S phase until anaphase.

The anaphase-promoting complex: a key factor in the regulation of cell cycle

“…The majority of these subunits are stably associated throughout the cell cycle (Peters et al, 1996;Grossberger et al, 1999) except for the different activators whose binding to APC is cell cycle regulated (Fang et al, 1998b;Zachariae et al, 1998a;Cooper et al, 2000). Little is known about how APC core subunits work together to form a functional E3 ligase.…”

“…The APC is a large protein complex containing at least 11 core subunits (Zachariae et al, 1998b;Gmachl et al, 2000;Yoon et al, 2002) that can further associate with at least three known different activators (Fang et al, 1998a, b;Kallio et al, 1998;Zachariae et al, 1998a;Cooper et al, 2000). The majority of these subunits are stably associated throughout the cell cycle (Peters et al, 1996;Grossberger et al, 1999) except for the different activators whose binding to APC is cell cycle regulated (Fang et al, 1998b;Zachariae et al, 1998a;Cooper et al, 2000).…”

Protein kinases controlling the onset of mitosis

“…These include lamins, the phosphorylation of which leads to nuclear membrane breakdown [61], microtubule-associ- ated proteins and kinesin-related motor proteins, which participate in centrosome separation and assembly of the mitotic spindle [62], and proteins that control chromosome condensation such as condensins [63]. In addition to the supervision of mechanistic aspects of mitosis, Cdk1 fulfills a regulatory function through the control of the anaphase-promoting-complex/cyclosome (APC/C) [64,66], a protein destruction machinery that sets the timing of transition through and exit from mitosis by degrading cyclins, Polo-like kinase 1, Aurora-A and -B, Nek2, securin and Cdc20 among others (reviewed in [67]). …”

Degradation of Ndd1 by APC/CCdh1 generates a feed forward loop that times mitotic protein accumulation

“…We set up a screen to identify novel APC/C Cdh1 substrates in budding yeast. We mated the yeast TAP library 25 with a strain expressing constitutively active Cdh1 m11 from an inducible GAL promoter 26 . The library was plated out into 96-well plates with Cdh1 m11 induced or uninduced in alternating rows.…”

“…After an APC/C substrate has been degraded, its accumulation will depend on the time the APC/C is inactivated, as well as on its synthesis. The APC/C Cdh1 is turned off at the end of G1 by inactivating phosphorylation of multiple Cdh1 phosphosites 26 . The inactivation of the APC/C Cdh1 at the onset of S phase however does not lead to instantaneous accumulation of all of its substrates, many of which are required only in mitosis.…”