TRMT13 inhibits the growth of papillary thyroid cancer by targeting ANAPC4

Abstract

The recently discovered gene TRMT13 encodes a type of RNA methylase and is a member of the CCDC family (also called CCDC76). Here, we delineate its role in papillary thyroid cancer (PTC). Bioinformatics analysis shows significant TRMT13 and ANAPC4 downregulation in PTC and reveals that the expression levels of both genes are linearly correlated. Subsequent analyses confirm that both TRMT13 and ANAPC4 expressions are downregulated in PTC tissues and that this change in expression has a significant impact on cancer diagnosis. We conduct assays on PTC cells subjected to TRMT13 and ANAPC4 silencing or overexpression to assess the biological effects of these genes. We also perform rescue experiments to validate the regulatory effects of TRMT13 on ANAPC4. A nude mouse tumor model is used to evaluate the effects of TRMT13 and ANAPC4 on PTC tumorigenesis. TRMT13 expression is decreased in PTC tissues and cell lines and is positively correlated with that of ANAPC4. Cell assays reveal that TRMT13/ANAPC4 attenuates the malignancy of PTC cells by restraining cell proliferation, migration and invasion, while rescue experiments corroborate that ANAPC4 is a downstream target of TRMT13. In the nude mouse xenograft model, both TRMT13 and ANAPC4 inhibit tumor growth, and TRMT13 and ANAPC4 expression levels are significantly associated with survival. Taken together, these findings lead to the conclusion that TRMT13 inhibits PTC growth via ANAPC4, indicating a new role of TRMT13 and providing insights into the tRNA methyltransferase and coiled-coil domain-containing protein families.

1. Introduction

As of 2020, there were 586,202 new cases of papillary thyroid cancer (PTC) worldwide. PTC accounts for 3.0% of all cancers and is the 11th most common cancer [1]. In China, the incidence of PTC is approximately 15 cases per 100,000 person-years [2], and the five-year survival rate is approximately 84.3% [3]. Despite the relatively low malignancy of PTC, it is inoperable in approximately 5% of all locally advanced cases, and its rate of local recurrence is high [4]. For these reasons, the mortality rate of this disease is also elevated [5].

TRMT13, also known as coiled-coil domain containing 76 (CCDC76), was recently discovered. Liu et al. [6] reported that cytoplasmic hTrmt13 catalyzes the 2′-O-methylation of tRNAs, whereas nuclear hTrmt13 directly binds to DNA as a transcriptional coactivator. However, these functions are mutually exclusive. ANAPC4 or APC4 is an E3 ubiquitin ligase that regulates mitosis and the G1 phase [7‒10]. ANAPC4 abnormalities promote proliferation and correlate with tumor diameter in oral squamous cell carcinoma [11]. ANAPC4 inhibition favors docetaxel resistance in breast cancer [12]. ANAPC4 enables esophageal cancer and neural stem cells to proliferate [13,14]. ANAPC4 transcription and expression are regulated by tRNA methylation and affect cell proliferation [15]. To the best of our knowledge, however, the roles of ANAPC4 in PTC and its relationship with TRMT13 have not yet been investigated. Bioinformatics analysis of The Cancer Genome Atlas (TCGA) data revealed that both TRMT13 and ANAPC4 levels are significantly downregulated and that their expression levels are linearly correlated in PTC tissues [16]. Hence, we investigated the functions and interactions of TRMT13 and ANAPC4 in the onset and progression of PTC.

The present study aimed to clarify the biological roles of TRMT13 and ANAPC4 in PTC via cell (in vitro) and nude mouse (in vivo) models and to examine the regulatory effects of TRMT13 on ANAPC4. The discoveries made herein could help improve both the diagnosis and treatment of PTC and provide novel insights into the molecular roles of tRNA methyltransferases and coiled-coil domain-containing proteins.