ANAPC4

ANAPC4 Full Name

anaphase promoting complex subunit 4

ANAPC4 Introduction

ANAPC4 (anaphase promoting complex subunit 4, also known as APC4) is an essential core component of the anaphase-promoting complex/cyclosome (APC/C), a large multi-subunit E3 ubiquitin ligase that controls cell cycle progression by targeting key regulatory proteins for proteasomal degradation. The APC/C is one of the most complex ubiquitin ligases in eukaryotic cells, composed of at least 14 distinct subunits, and is required for the metaphase-to-anaphase transition and for mitotic exit. ANAPC4 serves as a critical scaffold within the APC/C, contributing to the structural integrity of the complex and facilitating substrate recognition and ubiquitination. The protein is ubiquitously expressed in proliferating cells and is essential for embryonic development, as demonstrated by the embryonic lethality of ANAPC4 knockout in animal models. In addition to its canonical role in cell cycle regulation, accumulating evidence has implicated ANAPC4 in various human cancers, where its dysregulation contributes to chromosomal instability, aneuploidy, and tumor progression. The localization of the ANAPC4 gene at chromosome 4p15.31, a region frequently amplified in certain cancer types, further supports its potential oncogenic role.

Figure 1. Schematic structure of ANAPC4.

Biological Functions in Cell Cycle Regulation and APC/C Activity
ANAPC4 functions as an essential scaffold within the APC/C complex, contributing to both the structural integrity of the complex and the catalytic efficiency of substrate ubiquitination. The APC/C targets two major classes of substrates for degradation during mitosis: securin and cyclin B. Securin degradation activates separase, which cleaves the cohesin complex holding sister chromatids together, triggering anaphase onset. Cyclin B degradation inactivates cyclin-dependent kinase 1 (CDK1), promoting mitotic exit, cytokinesis, and the return to interphase. ANAPC4 directly contributes to substrate recognition by stabilizing the interaction between the APC/C core and its activator subunits CDC20 (in early mitosis) and CDH1 (in late mitosis and G1 phase). The WD40 repeats of ANAPC4 form a binding platform for CDC20 and CDH1, and mutations in these repeats impair APC/C activity and cause mitotic arrest. Beyond its role in mitosis, APC/C also functions in the G1 phase to maintain the quiescent state by degrading cell cycle activators, and in post-mitotic neurons where it regulates synaptic function and long-term memory formation through the degradation of specific substrates including the transcription factor ID2. ANAPC4 is also required for the degradation of the DNA damage response protein CLSPN (Claspin) after DNA repair, linking the APC/C to the cellular response to genotoxic stress. In addition, the APC/C-ANAPC4 complex participates in the regulation of centrosome duplication, spindle assembly checkpoint (SAC) silencing, and the maintenance of genomic stability. Loss of ANAPC4 function leads to mitotic arrest, chromosome mis-segregation, aneuploidy, and ultimately cell death, underscoring its essential role in cell division.

Clinical Significance: Cancer and Therapeutic Implications
ANAPC4 has been increasingly implicated in human cancer, where it appears to function primarily as an oncogene. The ANAPC4 gene is located at chromosome 4p15.31, a region that is frequently amplified in several cancer types including breast cancer, ovarian cancer, lung cancer, and hepatocellular carcinoma (HCC). Copy number gain or amplification of ANAPC4 correlates with increased mRNA and protein expression, and high ANAPC4 expression is associated with advanced tumor stage, poor differentiation, lymph node metastasis, and reduced patient survival. In hepatocellular carcinoma, ANAPC4 is significantly overexpressed compared to adjacent non-tumor liver tissue, and high ANAPC4 expression independently predicts poor prognosis. Knockdown of ANAPC4 in HCC cell lines suppresses cell proliferation, induces G2/M phase arrest, promotes apoptosis, and inhibits tumor growth in mouse xenograft models. Mechanistically, ANAPC4 promotes cancer cell proliferation by enhancing the degradation of the CDK inhibitor p21 (CIP1/WAF1), thereby allowing uncontrolled cell cycle progression. ANAPC4 also stabilizes the oncogene MDM2, which in turn targets the tumor suppressor p53 for degradation, further driving tumorigenesis. In breast cancer, ANAPC4 overexpression correlates with aggressive subtypes including triple-negative breast cancer (TNBC) and with resistance to chemotherapy.

Alternate Names for ANAPC4

ANAPC4; anaphase promoting complex subunit 4; APC4; anaphase-promoting complex subunit 4; cyclosome subunit 4;