Alanyl-tRNA synthetase AARS1: A novel lactate sensor and lactyltransferase mediating p53 lactylation and tumorigenesis

Abstract

In a recent study published in Cell, Zong et al. discovered that alanyl-tRNA synthetase 1 (AARS1) senses the accumulated lactate and subsequently facilitates global lysine lactylation in tumor cells.¹ Furthermore, they found that p53 is a crucial target protein of AARS1-mediated lactylation. Due to the structural similarity between lactate and l-alanine, AARS1 has the capability to directly bind to lactate and transfer it to the K120 and K139 residues of p53 under conditions involving ATP consumption. The lactylation of p53 impairs its DNA binding, liquid–liquid phase separation (LLPS), and transcriptional activation ability, ultimately promoting cancer progression. Additionally, the study revealed that β-alanine inhibits the binding of AARS1 to lactate, suggesting potential implications for cancer treatment. This study identified a novel lactate sensor and lactyltransferase, opening new avenues for furture research on lactylation.

In 2019, Zhang et al. reported that lactate, which is a byproduct of glycolysis, can modify histones by lactylation.² The Warburg effect explains how the tumor cells rely on glycolysis as the primary energy source, causing accumulation of high lactate levels. Besides, the acidic intratumoral environment causes protein lactylation, ultimately altering the functions of many proteins, promoting cancer progression. As our understanding of lactylation has increased, numerous “readers” and “erasers” of lactylation have been identified.^{3, 4} However, few “writers” of lactylation have been reported. In an effort to fill this gap in knowledge, Zong et al. discovered AARS1 as a novel lactyltransferase responsible for mediating global lactylation in cancer cells. Their findings highlight how AARS1 links cell metabolism with proteome alteration and plays a role in regulating carcinogenesis. Overall, this study shed light on the intricate relationship between energy metabolism and protein lactylation in cancer cells and provide valuable insights into potential targets for cancer therapeutic intervention.

When evaluating the TCGA breast cancer data set, Zong et al. found that intratumoral lactate may inhibit p53 functions. Furthermore, intratumoral lactate accumulation was closely associated with cancer progression in a mouse model of mammary tumor virus-polyoma middle T antigen transgenic breast cancer. To investigate the role of lactate in vivo, Zong et al. injected mice intraperitoneally with sodium lactate and observed that p53 activity was significantly inhibited in cancer cells. Moreover, knocking out lactate dehydrogenase A in mice resulted in reduced levels of intratumoral lactate and increased p53 activity. To determine whether lactate directly antagonized p53 functions in vitro, Zong et al. used a cell-free system based on luciferase fragment complementation assay to measure p53 activity. They found that tumor cells could sense lactate and induce p53 lactylation, diminishing its activity.

To identify the proteins involved in mediating p53 lactylation, Zong et al. performed a genome-wide CRISPR screen, which revealed AARS1 as the most strongly hit associated with lactylation. Upon depletion of AARS1, tumor proliferation, and colony formation were significantly reduced, whereas expression levels of p53 and its target proteins increased. Subsequently, Zong et al. used proteomics to analyze the global lysine lactylome with AARS1 knockdown or overexpression, thereby identifying AARS1 as a key molecule for cellular lysine lactylation.

To elucidate the mechanisms underlying AARS1-mediated lactylation, Zong et al. initially determined that AARS1 directly catalyzes lactylation using lactate as a substrate through microscale thermophoresis. Subsequently, molecular docking revealed that AARS1 could directly bind to lactate via its conserved residues. This binding was inhibited by β-alanine, which shares structural similarity with lactate. AARS1 catalyzed the formation of lactate-AMP intermediates in an ATP-dependent manner, and then transfered lactate to conjugate covalently on lysine residues of target proteins (Figure 1). This process has been observed not only in mammals but also in Escherichia coli, indicating an ancient function of AARS1 in catalyzing lysine lactylation across species.

To further investigate how AARS1 regulated p53 functions, Zong et al. used mass spectrometry and found that K120 and K139 residues located in the DNA binding domain of p53 could be lactylated by AARS1. Furthermore, lactylation of endogenous p53 at these residues was confirmed by using site-specific antibodies. P53 is a well-known tumor suppressor that exerts antitumor effects through LLPS upon binding to DNA containing p53-responsive elements (Figure 1).⁵ However, it was observed that site-specific lactylated p53 obtained via a genetic code expansion system exhibited significantly decreased binding to DNA, thus disrupting its LLPS and transcriptional activity, ultimately leading to tumorigenesis (Figure 1). In addition, multiple disease-associated K120 and K139 variants of p53 mimic its lactylation, resulting in defects in LLPS and tumor suppression capacity. To inhibit p53 lactylation in tumors effectively, Zong et al. tested β-alanine, a commonly used sports supplement. The results showed that β-alanine could serve as an inhibitor of AARS1-mediated p53 lactylation, thereby preventing p53 inactivation and improving the efficacy of cancer chemotherapy.

In summary, tumor-derived lactate is a natural inhibitor of p53, and AARS1 is an intracellular lactate sensor and lactyltransferase that mediates lysine lactylation targeting p53. Lactylation of K120 and K139 residues in the DNA binding domain of p53 impairs its DNA binding capacity and LLPS, thereby abrogating its tumor suppression functions in vitro and in vivo. The research also provides a therapeutic approach to restore p53 tumor suppressor activity by blocking p53 lactylation with β-alanine, which enhances cancer chemotherapy efficacy by competing with lactate for AARS1 binding. This study extends our knowledge of protein lactylation and reveals a direct interaction between the lactate and tumor progression. In the future, the remaining AARS1 target proteins and the regulatory effects of lactylation on the physiological or pathological functions of these proteins should be explored. Additionally, it is probable that other proteins other than AARS1 are also waiting to be discovered as novel lactyltransferases.

Qiqing Yang and Heyu Li conceived and drafted the manuscript. Qiqing Yang drew the figure. Long Zhang provided valuable discussion and revised the manuscript. All authors have read and approved the article.

Author Long Zhang is an Editorial board member of MedComm – Oncology. Author Long Zhang was not involved in the journal's review of or decisions related to this manuscript. The remaining authors declare no conflict of interest.

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