Inhibition of STAT3 and PARP1 reduces TNBC invasion through cytoskeletal remodeling

Triple Negative Breast Cancer (TNBC) is an aggressive, treatment-resistant subtype that disproportionately affects African American women, leading to high mortality. TNBCs have significantly higher metastasis rates compared to the receptor-positive Luminal subtype. Although research is ongoing, the biological mechanisms underlying metastasis in TNBC, particularly those related to cytoskeletal organization, remain unclear. Understanding how TNBC cells migrate, particularly through actin cytoskeleton remodeling, is crucial. Here, we demonstrate that combined inhibition of PAPR1 and STAT3 reduces cytoskeletal remodeling, particularly actin filament remodeling, a key factor in TNBC invasiveness. We used TNBC cell lines BT-549 (mesenchymal phenotype) and MDA-MB-468 (Basal-like 1/Immunomodulatory) to test Olaparib (a PARP1 inhibitor), Stattic (a STAT3 inhibitor), or both. Co-immunoprecipitation was used to study the interaction between PAPR1 and STAT3. We assessed cytoskeletal remodeling by western blotting, phalloidin staining, and cell motility using wound-healing and Boyden chamber invasion assays. The results show that PARP1 interacts with STAT3 in TNBC and poly-ADP-ribosylates STAT3. We observed reduced migration with inhibitors, especially with combined treatment, and disruption of actin cytoskeletal organization with the inhibition of STAT3 and PARP1. Combined PARP1 and STAT3 inhibition led to decreased peripheral actin and stress fiber formation, driven by Cofilin phosphorylation. Additionally, we noted downregulation of LIMK2 (Cofilin kinase) and PDXP (Cofilin phosphatase) with Stattic and dual-inhibitor treatment. The inhibitor treatment also downregulated CCL2 and other cytokines in both cell lines, potentially impacting cytoskeletal organization, possibly via the MAP kinase pathway. These findings suggest potential implications for combination therapies and the development of targeted treatments to improve outcomes, particularly by reducing metastasis. Our research enhances understanding of TNBC metastasis by identifying PARP1 and STAT3 as key regulators of actin cytoskeletal remodeling.