Aspartate β-hydroxylase disrupts mitochondrial DNA stability and function in hepatocellular carcinoma

Abstract

The mechanism of aberrant mitochondrial genome and function in hepatocellular carcinoma (HCC) remains largely unknown. Our previous study demonstrated an increased expression of aspartate β-hydroxylase (ASPH) in HCC tissues, which was associated with tumor invasiveness and a worse prognosis. Currently, we unexpectedly observed the presence of ASPH in purified mitochondrial protein fraction. In addition, immunostaining of both exogenously and endogenously expressed ASPH showed a colocalization with mitochondrial biomarkers. This study aimed to investigate whether the mitochondrial ASPH is involved in mitochondrial malfunction in HCC. Our results showed that ASPH overexpression in HCC tissues was correlated with decreased copy numbers of displacement loop (D-loop) and NADH dehydrogenase subunit 1 (ND-1) and enhanced D-loop mutation, suggesting the disrupted mitochondrial DNA (mtDNA) stability. The reduced mtDNA copy numbers were associated with aggressive clinicopathological features of HCC. The loss of mtDNA integrity induced by enforced expression of ASPH was accompanied with mitochondrial dysfunction, which was characterized by the aberrant mitochondrial membrane potential, decreased ATP generation and enhanced reactive oxygen species. In contrast, knocking down ASPH by siRNA in HCC cell lines showed the opposite impact on mtDNA integrity and function. Mass spectrometry and co-immunoprecipitation further identified that ASPH interacted with histone H2A member X (H2AX). ASPH overexpression diminished the interaction between H2AX and mitochondrial transcription factor A (mtTFA), an important DNA-binding protein for mtDNA replication, which then reduced the binding of mtTFA to D-loop region. Collectively, our results demonstrate that ASPH overexpression disrupts the mtDNA integrity through H2AX–mtTFA signal, thereby affecting mitochondrial functions in HCC.

Recent advances in research on aspartate β-hydroxylase (ASPH) in pancreatic cancer: A brief update

“…The overall effect of these processes in PC is the promotion of cell proliferation, migration, invasion, tumor growth, and metastasis [34,37]. ASPH promotes mitochondrial DNA D-loop mutations by inhibiting H2A histone family, member X (H2AX)-mitochondrial transcription factor A (mtTFA) signal Somatic mitochondrial DNA (mtDNA) mutations have been detected in various tumor types, including PC [38][39][40][41]. In HCC tissues and cell lines, the overexpression of ASPH was significantly correlated with decreased copy numbers of displacement loop (D-loop) and nicotinamide adenine dinucleotide (NADH) dehydrogenase subunit 1, and increased somatic mutations in the D-loop [38].…”

“…ASPH promotes mitochondrial DNA D-loop mutations by inhibiting H2A histone family, member X (H2AX)-mitochondrial transcription factor A (mtTFA) signal Somatic mitochondrial DNA (mtDNA) mutations have been detected in various tumor types, including PC [38][39][40][41]. In HCC tissues and cell lines, the overexpression of ASPH was significantly correlated with decreased copy numbers of displacement loop (D-loop) and nicotinamide adenine dinucleotide (NADH) dehydrogenase subunit 1, and increased somatic mutations in the D-loop [38]. The D-loop is a noncoding region of mtDNA which contains the origin of replication for heavy (H) mtDNA strand and the promoters for the transcription of H and light (L) strands [41].…”

“…In HCC cell lines, Tang et al [38] demonstrated that the overexpressed ASPH disrupts the mtDNA integrity and affects mitochondrial function through H2AX-mtTFA signal (Figure 3) [38]. mtTFA is a key regulator of mtDNA transcription and is also important in the maintenance and repair of mtDNA.…”

“…However, it appears FIGURE 3. Aspartate β-hydroxylase (ASPH) disrupts the mitochondrial DNA (mtDNA) integrity and affects mitochondrial function through H2A histone family, member X (H2AX)-mitochondrial transcription factor A (mtTFA) signal in hepatocellular carcinoma (HCC) cells [38]. (A) H2AX transfers mtTFA from the cytoplasm to the mitochondria to participate in the replication, transcription, and repair of mtDNA.…”

“…that overexpressed ASPH competes with mtTFA for binding to H2AX, thus blocking the translocation of mtTFA into the mitochondria and resulting in reduced binding of mtTFA to the D-loop [38,44]. This ultimately disrupts the function of mtTFA in mtDNA replication, transcription and repair ( Figure 3B), leading to increased mutations in the D-loop and other mtDNA regions, reduced mtDNA copy number and decreased expression of mitochondrial respiratory chain enzymes.…”