Hidden Protein Shield Helps Lung Tumors Survive Osimertinib Treatment

Osimertinib, the third-generation tyrosine kinase inhibitor that transformed the treatment of EGFR-mutant lung adenocarcinoma, almost always loses its grip over time. A new study published in Frontiers in Oncology on 22 October 2026 points to an unexpected culprit in that escape: a stress-responsive protein called ANKRD1, whose stability inside tumor cells is controlled by a tug-of-war between two chemical tags, SUMO and ubiquitin. The research, led by teams at the Third Affiliated Hospital of Kunming Medical University and Yunnan Cancer Hospital, traces a complete regulatory chain from a nuclear zinc finger protein through ANKRD1 protein stability to a receptor tyrosine kinase survival pathway that keeps tumor cells alive under drug pressure.

The investigation began not with a single candidate gene but with a broad computational sweep. The researchers mined five public transcriptomic datasets from the Gene Expression Omnibus, including GSE116959, GSE176348, GSE63459, GSE5281 and GSE5282, looking for genes tied both to lung adenocarcinoma progression and to acquired osimertinib resistance. Differential expression analysis with the limma package, using thresholds of absolute log2 fold change greater than 1 and adjusted p-values below 0.05, produced a list of differentially expressed genes. That list was then filtered through a machine learning pipeline combining random forest, LASSO regression and support vector machine-recursive feature elimination. Three core genes survived the gauntlet, and ANKRD1 emerged as the most consistently upregulated factor in resistant contexts.

Laboratory models reinforced the computational signal. The team generated osimertinib-resistant versions of two human lung adenocarcinoma cell lines, HCC827 and PC9, by escalating drug doses stepwise over four to six months until the cells proliferated stably in 100 nanomolar osimertinib. These resistant lines showed markedly increased IC50 values and elevated ANKRD1 protein levels compared with their drug-sensitive parents. In an exploratory immunohistochemical analysis, three paired tumor specimens from patients with EGFR-mutant lung adenocarcinoma, collected before osimertinib treatment and after acquired resistance developed, showed consistently higher ANKRD1 expression in the resistant samples. The authors are careful to note that this clinical evidence is preliminary: three pairs of specimens cannot support powered conclusions about treatment response or survival.

Functionally, ANKRD1 behaved less like a classical oncogene and more like a stress-adaptive survival factor. Overexpressing ANKRD1 in parental cells reduced their sensitivity to osimertinib, while depleting it from resistant cells restored drug responsiveness. When ANKRD1 was knocked down, cells treated with osimertinib underwent significantly more apoptosis, measured by Annexin V-FITC/PI flow cytometry, and showed reduced proliferation in EdU incorporation assays. In xenograft models, deleting ANKRD1 alone had only a modest effect on tumor growth, but it synergistically enhanced the antitumor efficacy of osimertinib. That context-dependent pattern suggests ANKRD1 matters most when cells are under therapeutic pressure, precisely the situation in which resistant tumors must keep survival signaling running.

To find out how ANKRD1 exerts that protective effect, the researchers turned to RNA sequencing. Overexpressing ANKRD1 produced a distinct set of differentially expressed genes, and intersecting those with resistance-associated signatures narrowed the field to candidate effectors. Among them, MERTK, a member of the TAM receptor tyrosine kinase family with established roles in tumor cell survival and therapeutic tolerance, stood out. ANKRD1 expression positively correlated with MERTK expression, and manipulating ANKRD1 levels changed MERTK output in qRT-PCR and dual-luciferase reporter assays, supporting ANKRD1 as a transcriptional activator of the MERTK gene. Pathway enrichment analysis further revealed enhanced PI3K/AKT signaling in ANKRD1-high cells.

Rescue experiments then confirmed the chain of command. Depleting ANKRD1 reduced MERTK expression and AKT phosphorylation, but re-expressing MERTK partially restored AKT activation and blunted the increased apoptosis and impaired proliferation caused by ANKRD1 loss. The word partially is important: MERTK did not fully account for ANKRD1’s biological effects, indicating that the MERTK-AKT axis is a major but not exclusive downstream route. Additional MERTK-independent transcriptional or signaling programs likely contribute to the resistant phenotype and remain to be mapped.

The most novel part of the study concerns how ANKRD1 itself is kept stable. Co-immunoprecipitation assays showed that ANKRD1 undergoes selective modification by SUMO1, with no detectable modification by SUMO2/3/4. SUMOylation and ubiquitination turned out to be inversely related: resistant cells carried less ubiquitinated ANKRD1, while inhibiting SUMOylation increased its ubiquitination. Because ubiquitin conjugation targets proteins for proteasomal destruction, this antagonism provides a direct mechanism for controlling ANKRD1 abundance. Cycloheximide chase assays, which block new protein synthesis and track degradation of existing protein, confirmed that ANKRD1 turns over faster when the SUMO system is compromised, and that proteasome inhibition could rescue the loss.

Upstream of that balance sits a nuclear protein called ZNF593, identified as an ANKRD1 interactor by mass spectrometry and validated by co-immunoprecipitation, immunofluorescence co-localization and proximity ligation assay. When ZNF593 was depleted, ANKRD1 SUMOylation dropped, ubiquitination rose, and the protein degraded more rapidly, a degradation that proteasome inhibition reversed. ZNF593 knockdown also phenocopied ANKRD1 depletion, increasing apoptosis, reducing proliferation and suppressing MERTK-AKT signaling. The authors caution, however, that their evidence does not establish ZNF593 as a bona fide SUMO E3 ligase; it may instead facilitate recruitment or accessibility of the SUMO conjugation machinery, potentially involving the UBC9 enzyme, and the precise biochemical mechanism remains unresolved.

A single lysine residue, K41, appears to sit at the heart of the entire regulatory network. Of three candidate modification sites identified by structural analysis, K5, K41 and K61, only the K41 mutation disrupted both SUMOylation and ubiquitination simultaneously, and it also weakened the interaction between ANKRD1 and ZNF593. AlphaFold-based structural prediction placed K41 at the interaction interface, suggesting the residue may have a dual role: coordinating competing post-translational modifications while also helping maintain the protein surface that ZNF593 recognizes. Functionally, the K41 mutant failed to activate AKT signaling and, in an orthotopic lung tumor model monitored by bioluminescence imaging, showed markedly attenuated ANKRD1-driven tumor growth and resistance under osimertinib treatment. The authors stop short of calling K41 a definitive molecular switch, describing it instead as a critical regulatory residue within the ANKRD1 proteostatic network, and note that direct assignment of K41 as a SUMO or ubiquitin acceptor site will require additional biochemical or mass-spectrometric evidence.

The study carries clear limitations alongside its promise. Clinical validation rests on only three paired specimens, and the in vivo work was performed in immunodeficient nude mice, which cannot capture the immune microenvironment contributions of MERTK, a receptor with known immunoregulatory functions; future work in immunocompetent or humanized models will be needed. Still, the findings sketch a testable vulnerability: ANKRD1 could be evaluated as a candidate biomarker in larger clinically annotated cohorts, pharmacological MERTK inhibition might be worth testing in ANKRD1-high resistant tumors, and the ANKRD1-ZNF593 interaction or its associated proteostatic machinery could offer a drug target. The authors emphasize that none of these translational possibilities was directly tested in the present study. What the work does establish is a mechanistic link between post-translational protein homeostasis and receptor tyrosine kinase signaling in acquired osimertinib resistance, adding a proteostasis layer to the familiar catalogue of secondary EGFR mutations, bypass pathway activation and lineage plasticity, and framing the ZNF593-ANKRD1-MERTK axis as a rational focus for the next round of preclinical investigation.

Subject of Research: SUMOylation-dependent stabilization of ANKRD1 and its role in acquired osimertinib resistance in EGFR-mutant lung adenocarcinoma

Article Title: SUMOylation counteracts ubiquitination to stabilize ANKRD1 and promote osimertinib resistance in lung adenocarcinoma

Article References: Fan, B., Lei, Q., Wang, H., Xin, C., Li, X., Zhu, X., Kong, J., Xie, S., Shang, J., Li, Z., Deng, C., Lv, D., & Wang, W. (2026). SUMOylation counteracts ubiquitination to stabilize ANKRD1 and promote osimertinib resistance in lung adenocarcinoma. Frontiers in Oncology, 16, Article 1960448. https://doi.org/10.3389/fonc.2026.1960448

Image Credits: AI Generated

DOI: 10.3389/fonc.2026.1960448

Keywords: osimertinib resistance, lung adenocarcinoma, ANKRD1, ZNF593, SUMOylation, ubiquitination, MERTK, AKT signaling, EGFR-mutant, post-translational modification, drug resistance, proteostasis