Abstract PO4-05-13: Expression of DLC1/STARD12 and variants in clinical breast cancer and implication in skeletal metastasis

Abstract Introduction: Deleted in Liver Cancer 1 Protein, DLC1, also known as StAR Related Lipid Transfer Domain Containing 12 (StarD12), is a known negative regulator of the Rho GTPases and at the cellular level regulates cell migration. DLC1 gene transcription produces multiple isoforms of the DLC1 protein. The present study examined the clinical and prognostic implications of DLC1 isoforms, DLC1/V1/V2/V3, in relationship with Rho GTPases in human breast cancer. Methods: Expression of three DLC1 isoforms was evaluated in a cohort of breast cancer tissues and against the clinical, pathological and clinical outcome of patients. DLC1 expression was also assessed and compared against Rho GTPases, including Rho and Rho GTP Dissociation Inhibitor (Rho GDI), in the same cohort. Results: DLC1/V3 had a significant impact on the overall survival of patients and high levels were linked to shorter survival (Hazard Ratio=3.551 (95%CI 1.332-9.471, p=0.011), a prediction that was independent of other factors in multivariate analysis. RUC analysis demonstrated a significant predictive value for bone metastasis with DLC1/V3 (RUC=0.714, p=0.020), showing a Hazard ratio of 9.0 (1.8-44.5, p=0.007). Similarly, high DLC1/V2 expression was also linked to a shorter overall survival (p=0.035). DLC1/V2 did not show a significant correlation with bone metastasis. In contrast to V3 and V2 variants, DLC1 had a marginal overall survival benefit for the patients, in that patients with high DLC1 had a longer survival (p=0.056). DLC1/V3 had a contrasting correlation with Rho-A (r=-0.203, p=0.015) and Rho-GDI-G (r=0.194, p=0.019) and the combined expression of DLC1/V3 and RhoA/Rho-GDI-G further identified patients with poorer clinical outcome. Conclusions: DLC1 and its variants have differing impacts on breast cancer; whereas DLC1 appears to be a tumour suppressive molecule, its variant isoform-3 was more oncogenic and a significant negative prognostic factor, together with its regulators Rho and Rho GDI. Citation Format: Binbin Cong, Jane Lane, Xiaoshan Cao, Tracey Martin, Robert E Mansel, Eleri Davies, Wen Jiang. Expression of DLC1/STARD12 and variants in clinical breast cancer and implication in skeletal metastasis abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-05-13.