Abstract 2387: Targeting PVT1 exon 9 transcript is not pro-apoptotic but induces claudin 4 expression and inhibits migration in triple negative breast cancer cells

Triple negative breast cancer (TNBC) is a lethal molecular subtype of invasive breast cancer (BC) that is ER-, PR- and HER2-. Claudin low (CL) TNBC, a distinct molecular subtype of TNBC, has the worst prognosis compared to other BC subtypes. Aberrant expression of claudin proteins disrupts the function of tight junctions. Consequently, inducing epithelial-to-mesenchymal transition (EMT) in cancers, an important factor for enhanced motility and metastasis. Therefore, understanding the molecular mechanisms that modulate claudin expression in TNBC is crucial. The 8q24 genomic locus is an important cancer susceptibility locus that is associated with poor clinical outcomes in cancer due to common amplification events that occur in many malignant diseases. This locus contains the PVT1 gene, which encodes a long noncoding RNA (lncRNA) that has been implicated in multiple cancers including BC. PVT1 consists of 12 exons that are alternatively spliced to generate lncRNAs. Although previous research has implicated PVT1 as an important player in BC, the underlying molecular mechanisms of PVT1 in CL TNBC is unknown. To examine the role of PVT1 in CL TNBC, we assessed PVT1 expression in T47D (ER+), MDA MB 231 (CL) and MDA MB 468 (claudin high (CH)) BC cells. We observed that PVT1 exons 4A, 4B, and 9 are significantly overexpressed in CL MDA MB 231 and significantly underexpressed in CH MDA MB 468 in comparison to T47D cells, suggesting a protumorigenic role of PVT1 in CL TNBC. We analyzed the functional consequences of siRNA targeting of PVT1 exon 9 expression in CL TNBC cells. siRNA targeting of PVT1 exon 9 expression in the MDA MB 231 CL TNBC cells led to a significant reduction in migration and the re-expression of claudin 4. To determine the role of PVT1 on EMT, we assessed the expression of EMT markers (vimentin, fibronectin, and E-cadherin) in MDA MB 231 cells. We observed no changes in the expression of EMT markers when PVT1 exon 9 is knocked down. However, our data show that mesenchymal markers are more highly expressed in MDA MB 231 cells in comparison to MDA MB 468 cells. Further, knockdown of PVT1 exon 9 did not induce apoptosis in MDA MB 231 cells as assessed by caspase 3 and caspase 9 expression. 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 A. Levine, Olorunseun O. Ogunwobi. Targeting PVT1 exon 9 transcript is not pro-apoptotic but induces claudin 4 expression and inhibits migration in triple negative breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2387.