Abstract 188: Phosphorylation of StarD10 advances alcohol induced breast cancer progression

Abstract Introduction: Breast cancer is the second most common cancer among women, and excessive alcohol consumption is a well-established risk factor for various cancers, including breast cancer. Even moderate alcohol consumption (one drink per day) increases breast cancer risk by 10% compared to non-drinking women. The STAR-related lipid transfer domain-containing protein 10 (StarD10), a phosphoprotein, is overexpressed in 35-40% of primary human breast cancers and interacts with the ErbB2 signalling pathway. Our recent studies demonstrated that ethanol administration promotes StarD10 dephosphorylation and increases its activity, as well as enhances ErbB2 expression, which is strongly correlated with increased cell malignancy and aggressiveness. However, the precise role of StarD10 as a subcellular lipid transporter in the regulation of ErbB2 signalling remains unclear. This study aimed to elucidate ethanol-induced changes in StarD10 activity, with the inhibition of its phosphorylation being a potential target for mitigating alcohol-induced breast cancer progression. Materials and Methods: To identify specific phosphorylation sites, phospho-peptide mapping of StarD10 from MCF-7 and SKBR-3 cells was performed. The identified phosphorylation site in StarD10 was further validated by western blot and co-immunoprecipitation studies. A lipid overlay assay was performed to assess StarD10 binding to phospholipids. Results: Phospho-peptide mapping identified threonine 288 (T288) as a specific phosphorylation site, regulated by casein kinase 1α (CK1α). Silencing CK1α blocked StarD10 phosphorylation, mimicking the dephosphorylation effects induced by ethanol. Lipid overlay assay demonstrated that StarD10 binds to a range of phospholipids. We found the interaction of StarD10 with PI(3)P, PI(4)P, PI(5)P, PI(3, 4)P2, PI(3, 5)P2, PI(4, 5)P2, PI(3, 4, 5)P2 in both MCF-7 and SKBR-3 cells. PP2A and PP1, serine/threonine phosphatases regulate protein function by dephosphorylation impacting in several critical cellular pathways. We found that treatment with okadaic acid (a PP2A inhibitor) and calyculin A (a PP1/PP2A inhibitor) blocked ethanol-induced StarD10 dephosphorylation in both MCF-7 and SKBR-3 cells. Also, this treatment inhibited the membrane fluidity as compared to ethanol. It suggests a regulatory role of PP1/PP2A in the StarD10 function. Conclusions: The role of phosphorylated StarD10 in alcohol-induced breast cancer progression is mediated by the phosphorylation of T288 by CK1α. PP1/PP2A acts as a positive regulator of StarD10 activity, further implicating these phosphatases in the progression of ethanol-induced breast cancer. Acknowledgments: R01 AA030576 (NIAAA), Role of StAR-related lipid transfer protein 10 in alcohol-induced breast cancer progression. Citation Format: Manisha Dagar, Andrea Floris, Youngyi Lim, Swati Chandla, Monica Justo, Nirmala Mavila, Komal Ramani, Maria Lauda Tomasi. Phosphorylation of StarD10 advances alcohol induced breast cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 188.