MAGE-A4 Interacts with the Liver Oncoprotein Gankyrin and Suppresses Its Tumorigenic Activity

Abstract

Hepatocellular carcinoma ranks among the most common malignancies in Southeast Asia and South Africa. Although there are many modalities of treatment, the recurrence and metastasis rates are high, and the prognosis is unsatisfactory. Gankyrin, a recently found oncoprotein, is a promising target for drug therapy because it is overexpressed in all studied hepatocellular carcinomas. Gankyrin contains six ankyrin repeats and interacts with Rb, Cdk4, and the S6 ATPase of the 26 S proteasome. In this study, a yeast two-hybrid screen with gankyrin has identified MAGE-A4 as another interacting protein. The interaction, mediated by the C-terminal half of MAGE-A4, was reproduced in mammalian cells. The interaction was specific to MAGE-A4, because other MAGE family proteins structurally similar to MAGE-A4, i.e. MAGE-A1, MAGE-A2, and MAGE-A12, did not bind to gankyrin. MAGE-A4 partially suppressed both anchorage-independent growth in vitro and tumor formation in athymic mice of gankyrin-overexpressing cells. The ability of mutant MAGE-A4 to interact with gankyrin correlated with the ability to suppress the anchorage-independent growth. These results demonstrate that MAGE-A4 binds to gankyrin and suppresses its oncogenic activity. So far, the major focus of studies on the MAGE proteins has been on their potential for cancer immunotherapy. Our results may also shed light on novel functions for MAGE-A proteins.Gankyrin (gann ankyrin repeat protein, also known as PSMD10 and p28) is an oncoprotein, the expression of which is increased (1, 2) in hepatocellular carcinomas (HCCs). 1Gankyrin consists of six ankyrin repeats and a 38-amino acid N-terminal extension and binds to the retinoblastoma tumor suppressor protein (Rb), the S6 ATPase subunit of the 26 S proteasome (PSMC4, RPT3, TBP7), and cyclin-dependent kinase 4 (Cdk4) (1, 3, 4). Overexpression of gankyrin increases both the phosphorylation and degradation of Rb in vivo and oncogenically transforms NIH/3T3 cells. Gankyrin binds to Cdk4 and counteracts the inhibitory function of the tumor suppressors p16INK4A and p18 INK4C (4). In a rodent model of hepatocarcinogenesis, gankyrin is overexpressed from the earliest stage of tumor development (5). These findings suggest that gankyrin is a major player in cell cycle control and tumorigenesis in HCCs.The MAGE (melanoma antigen) genes were initially identified because they encode tumor antigens that can be recognized by cytolytic T lymphocytes derived from the blood lymphocytes of cancer patients (6). The MAGE gene family is composed of more than 25 genes in humans and are classified as type I MAGE genes (including MAGE-A, MAGE-B, and MAGE-C genes) and type II MAGE genes, which include those that reside outside of the MAGE-A, MAGE-B, and MAGE-C genomic clusters (7, 8). The MAGE-A subfamily comprises 12 genes (MAGE-A1 to MAGE-A12), and is expressed in various types of tumors but not in normal adult tissues, except for testis and placenta. The MAGE-A antigens are of particular interest for antitumor immunotherapy because they are stri...

Gankyrin oncoprotein overexpression as a critical factor for tumor growth in human esophageal squamous cell carcinoma and its clinical significance

“…12,[31][32][33][34] However, so far there have been no reports on the role of gankyrin in either esophageal cancer or in other gastrointestinal cancers. This study is the first report on gankyrin expression in ESCC.…”

Ankyrin Repeat: A Unique Motif Mediating Protein−Protein Interactions

“…As for gankyrin, its physiological partners include CDK4 (56,58), Rb (65), S6 ATPase of the 26S proteasome (61), MAGE-A4 antigen (66), and HDM2 (67) (Figure 5c). Binding of gankyrin to Rb, S6 ATPase of the 26S proteasome, and HDM2 facilitates the ubiquitin-mediated degradation of Rb, HDM2, and other proteins (65,(67)(68)(69), while binding of gankyrin to MAGE-A4 quenches the oncogenic activity of gankyrin through unknown mechanisms (66). Protein fragmentation studies have demonstrated that the first four ARs of gankyrin are involved in interacting with CDK4 and the last two ARs are responsible for binding to Rb (59).…”

MageA2 restrains cellular senescence by targeting the function of PMLIV/p53 axis at the PML-NBs

“…10 Subsequently, other groups also described an opposite correlation between MAGE-A gene expression and p53 activity. 7,11,12 Interestingly, only MageA4 has been shown to be involved in some potentially anti-tumor functions such as gankyrin oncoprotein inhibition 13 and apoptosis induction. 14,15 It has been demonstrated that escape to cellular senescence is one of the first barriers to be bypassed during transformation.…”