Abstract Introduction: Breast cancer remains the second most common cancer among women worldwide. Excessive alcohol consumption significantly increases breast cancer risk, with even moderate drinking (one drink per day) raising the risk by about 10% compared to non-drinkers. STAR-related lipid transfer domain-containing protein 10 (StarD10), a phosphoprotein overexpressed in 35-40% of primary human breast cancers, interacts with the ErbB2 signaling pathway to promote tumor growth. Our previous studies showed that ethanol exposure causes StarD10 dephosphorylation and enhances ErbB2 expression, leading to increased malignancy and aggressiveness. However, the mechanistic role of StarD10 as a subcellular lipid transporter in regulating ErbB2-driven signaling is still not well understood. This study investigates how ethanol affects StarD10 activity and the ErbB2 signaling pathway using three-dimensional breast cancer organoid models. brMaterials and Methods: Lipid overlay assays and co-immunostaining were performed to assess StarD10’s lipid-binding specificity in breast cancer cells (MCF-7, SKBR-3, and BT-474) and three-dimensional breast cancer organoid models (PDxO). Additionally, organoids were CRISPR gene-edited to validate the functional outcome of pre-identified StarD10 phospho-sites. Activation of the ErbB2-regulated AKT-mTOR pathway was analyzed by Western blot. Cell viability and migration were analyzed in CRISPR gene-edited breast cancer cells. brResults: A significant decrease in StarD10 phosphorylation was observed in breast cancer cells (MCF-7, SKBR-3, BT-474) and breast cancer organoids (PDxO) in the presence of ethanol. Lipid overlay assay showed that StarD10 interacts with multiple phosphoinositides, including PI(3)P, PI(4)P, PI(5)P, PI(3,4)P2, PI(4,5)P2, and PI(3,4,5)P3. Co-immunostaining further demonstrated an ethanol-induced increase in the interaction between StarD10 and PIP2/PIP3. Inhibition of PP2A activity by CRISPR-mediated gene editing prevented ethanol-induced StarD10 dephosphorylation and the ErbB2-mediated AKT-mTOR pathway, indicating that these phosphatases act as positive regulators of StarD10 function in the organoid model. Moreover, PP2A gene editing significantly reduced cell viability and migration compared to ethanol-treated cells, suggesting a critical role for PP2A-mediated dephosphorylation of StarD10 in promoting ethanol-induced breast cancer cell aggressiveness. brConclusions: Our findings show that ethanol promotes breast cancer progression by causing dephosphorylation of StarD10 at the T288 residue. Using organoid models, we demonstrate that PP2A phosphatase positively regulates StarD10 activity. Targeting the phosphorylation pathway of StarD10 may serve as a potential therapeutic strategy to reduce alcohol-related breast cancer progression. Citation Format: Manisha Dagar, Youngyi Lim, Swati Chandla, Monica Justo, Nirmala Mavela, Komal Ramani, Maria Lauda Tomasi, . Phosphorylation of StarD10 regulates ErbB2-mediated alcohol-induced breast cancer progression abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 3302.
Dagar et al. (Fri,) studied this question.