Breast cancer (BC) is a heterogeneous disease that is classically driven by the estrogen receptor (ER), progesterone receptor (PR) and human epithelial growth factor receptor 2 (EGFR2/HER2) signaling pathways. Triple negative breast cancer (TNBC), is a lethal subtype of invasive BC tumors that are ER-, PR- and HER2-. A subtype of TNBC is claudin low (CL). Dysregulation of claudin proteins disrupts tight junctions, consequently inducing the epithelial-to-mesenchymal transition (EMT) in cancers. This leads to enhanced motility and metastasis. Patients with CL TNBC have worse prognosis than patients with other BC subtypes. PVT1 is a long noncoding RNA (lncRNA) transcribed from the 8q24 genomic locus that has been implicated in multiple cancers including BC. Amplification of the 8q24 gene locus is a common event in many malignant diseases and is associated with poor clinical outcomes.
Although previous research has implicated PVT1 as an important player in BC, the underlying molecular mechanisms of PVT1 in CL TNBC was previously unknown. We assessed PVT1 expression in BC, and we observed that PVT1 exons 4A, 4B, and 9 are significantly upregulated in MDA MB 231 cells (claudin low) and significantly downregulated in MDA MB 468 cells (claudin high), in comparison to T47D (ER+). We have confirmed that claudin expression, specifically claudins 1, 3, 4 and 7, are significantly higher in MDA MB 468 cells and significantly lower in MDA MB 231 cells. Knockdown of PVT1 exon 9 expression in the MDA MB 231 cell line, led to a significant reduction in migration when compared to cells transfected with a control scramble siRNA, indicating that PVT1 exon 9 regulates migration in CL TNBC. Interestingly, we observed that claudin 4 expression, and not claudins 1, 3 and 7, was increased in cells where PVT1 exon 9 was knocked down when compared to the control cells. This indicates that PVT1 exon 9 regulates claudin 4 protein stability in CL TNBC. We also assessed the expression of EMT markers (vimentin, fibronectin, and E-cadherin) in MDA MB 231 cells. We observed no changes in EMT markers when PVT1 exon 9 is knocked down; however, our data suggests that EMT markers are more highly expressed in MDA MB 231 cells in comparison to MDA MB 468 cells. Taken together, our data indicate that PVT1 exon 9 regulates claudin expression and migration in CL TNBC, and may have implications for clinical outcomes in TNBC.
Citation Format: Fayola Levine, Olorunseun Ogunwobi. PVT1 exon 9 transcript regulates claudin 4 expression and migration in triple negative breast cancer [abstract]. In: Proceedings of the AACR Virtual Conference: Thirteenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2020 Oct 2-4. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(12 Suppl):Abstract nr PO-126.