A team of researchers in China has mapped a previously hidden molecular circuit that helps one of the deadliest liver cancers grow, and their findings point to a new set of targets for intervention. The study, published in Molecular Biology Reports, reveals how an RNA-modifying enzyme called ALKBH5 drives the malignant behavior of intrahepatic cholangiocarcinoma, an aggressive cancer of the bile ducts inside the liver, through a chain of interacting RNA molecules that ends in a calcium channel protein known as ORAI2. The work was led by Yi Tang, Qiuhuan Zhang, and Xuanchao Wen, with correspondence from Zhenyong Tang and Yuntian Tang at The People’s Hospital of Guangxi Zhuang Autonomous Region and Guangxi Academy of Medical Sciences in Nanning.
Intrahepatic cholangiocarcinoma, often abbreviated ICC, arises from the epithelial cells lining the small bile ducts within the liver. It is notoriously difficult to detect early, and most patients are diagnosed at an advanced stage when surgical resection is no longer possible. Even with modern imaging and multidisciplinary treatment, prognosis remains poor. Clinicians have increasingly turned to molecular testing to identify actionable pathways, but the landscape of RNA-based regulators in this cancer is still incompletely understood. The new study adds a critical piece to that puzzle by connecting an epitranscriptomic modifier to a circular RNA and tracing the consequences all the way to tumor growth in living animals.
ALKBH5 is an m6A demethylase, meaning it removes N6-methyladenosine marks from RNA molecules. These marks are among the most common chemical modifications found on messenger RNAs and noncoding RNAs in mammalian cells, and they influence RNA stability, translation, and export from the nucleus. By stripping these marks, ALKBH5 can alter the fate of specific transcripts. Prior research had already implicated ALKBH5 in ICC, showing that it sustains the expression of BUB1B and supports cell proliferation, and that it regulates PD-L1 expression and shapes the tumor immune environment. The current investigation extends that story by asking which circular RNAs ALKBH5 controls in this cancer.
Circular RNAs, or circRNAs, are covalently closed RNA molecules formed when a downstream splice donor joins an upstream splice acceptor, producing a ring instead of a linear chain. Because they lack free ends, circRNAs are resistant to exonuclease degradation and can persist in cells far longer than their linear counterparts. Many circRNAs act as competing endogenous RNAs, or ceRNAs, meaning they soak up microRNAs that would otherwise repress target messenger RNAs. This sponging mechanism creates a regulatory layer in which a noncoding RNA can indirectly increase the expression of a protein-coding gene by titrating away its repressive microRNA.
To identify the key circRNA downstream of ALKBH5, the researchers collected sixteen clinical samples of ICC tumor tissue and matched paracancerous tissue. They confirmed that ALKBH5 was significantly overexpressed in the tumors compared with the adjacent noncancerous tissue. They then performed circRNA sequencing to profile the circular transcriptome and used bioinformatic prediction tools to identify candidate microRNAs and downstream messenger RNAs connected to the top hit. That hit was circ_0032649, a circular RNA whose abundance tracked with ALKBH5 expression in the clinical samples.
The team then depleted ALKBH5 in ICC cell lines using in vitro transfection and measured the consequences with a battery of functional assays. Cell counting kit-8 assays revealed a significant drop in cell viability. Colony formation assays showed reduced clonogenic capacity. Flow cytometry demonstrated that ALKBH5 depletion induced G1-phase cell cycle arrest, meaning cells accumulated before DNA synthesis rather than progressing into the S phase. The depletion also weakened apoptosis resistance, meaning the cancer cells became more willing to undergo programmed cell death, and it suppressed epithelial-mesenchymal transition, the process by which epithelial cancer cells acquire invasive, motile characteristics. Together, these results established ALKBH5 as a central supporter of ICC cell fitness.
Mechanistically, the researchers used RNA immunoprecipitation to show that ALKBH5 physically binds circ_0032649. They then used dual-luciferase reporter assays to demonstrate that circ_0032649 acts as a sponge for miR-4755-3p, a microRNA that would otherwise repress ORAI2 messenger RNA. When circ_0032649 is abundant, it titrates away miR-4755-3p, allowing ORAI2 expression to rise. ORAI2 is a subunit of store-operated calcium entry channels, which are plasma membrane calcium channels that refill intracellular calcium stores after depletion. Prior work in gastric cancer had shown that ORAI2 promotes tumorigenicity and metastasis through PI3K/Akt signaling and MAPK-dependent focal adhesion disassembly, and studies in breast cancer cells have linked ORAI2 to cell cycle progression. The new findings place ORAI2 at the downstream end of an ALKBH5-circ_0032649-miR-4755-3p ceRNA axis in ICC.
To test whether this axis matters in living organisms, the researchers established a xenograft tumor model by implanting ICC cells into immunocompromised mice. They then delivered lentivirus intratumorally to manipulate ALKBH5 and circ_0032649 expression within the growing tumors. The results showed that the ALKBH5/circ_0032649 axis promoted ICC tumor progression in vivo and altered the expression of the ceRNA regulatory axis, confirming that the molecular chain identified in cell culture also operates within a living tumor microenvironment. The animal experiments were approved by an institutional animal care committee and performed in accordance with ARRIVE guidelines.
The study’s significance lies in connecting an epitranscriptomic modifier to a circular RNA sponge and a calcium channel gene in a single regulatory chain. Prior circRNA research in ICC had identified individual circRNAs such as circSLCO1B3, circACTN4, circUGP2, and circ_0057105 as players in tumor progression, and ALKBH5 had been shown to sustain stemness and regulate immune evasion. But the current work is among the first to show that ALKBH5 directly binds a specific circRNA and uses it to upregulate a calcium channel through microRNA sponging. This adds a mechanistic dimension that links RNA modification chemistry to ion channel biology and tumor growth.
From a translational standpoint, the findings suggest several potential intervention points. Blocking ALKBH5 activity, degrading circ_0032649 with antisense oligonucleotides or small interfering RNAs, or delivering synthetic miR-4755-3p mimics could each disrupt the axis at a different level. Inhibiting ORAI2 or the store-operated calcium entry it mediates represents another possible strategy. Because ALKBH5 is already a subject of drug discovery efforts in other cancers, the new data may accelerate the evaluation of ALKBH5 inhibitors in ICC. The researchers note that their data are available from the corresponding author upon reasonable request, and the work was supported by the National Natural Science Foundation of China and the Natural Science Foundation Project of Guangxi. While clinical application remains distant, the study provides a detailed molecular map that other teams can now use to design targeted experiments and, eventually, therapeutic candidates for this challenging cancer.
Subject of Research: ALKBH5-regulated circ_0032649, acting as a sponge for miR-4755-3p to upregulate ORAI2, facilitates intrahepatic cholangiocarcinoma tumorigenicity
Article Title: ALKBH5-regulated circ_0032649, acting as a sponge for miR-4755-3p to upregulate ORAI2, facilitates intrahepatic cholangiocarcinoma tumorigenicity
Article References: Tang, Y., Zhang, Q., Wen, X., Liu, R., Xie, S., Chen, B., Huang, T., Huang, X., Xie, D., Huang, W., Tang, Z., & Tang, Y. (2026). ALKBH5-regulated circ_0032649, acting as a sponge for miR-4755-3p to upregulate ORAI2, facilitates intrahepatic cholangiocarcinoma tumorigenicity. Molecular Biology Reports, 53(1), Article 1749. https://doi.org/10.1007/s11033-026-12934-0
Image Credits: AI Generated
DOI: 10.1007/s11033-026-12934-0
Keywords: ALKBH5-regulated, circ, acting, sponge, miR-4755-3p, upregulate, ORAI2, facilitates, intrahepatic, cholangiocarcinoma, tumorigenicity, scientific research
News Source: Nathaniel Bowman. (October 18, 2026). Circular RNA circuit driven by ALKBH5 fuels bile duct cancer growth. Scienmag.
