PB1419 - Illuminating Thrombin-Mediated Induction of Chemoresistance: A Comprehensive Exploration of pro-survival protein MCL1 Upregulation and Post translational Stabilization

Background: The association between idiopathic venous thrombosis and occult cancer is widely recognized. The coagulation protease thrombin mediates its effects by cleaving protease-activated receptor 1 (PAR1), a receptor abundantly expressed on the surface of triple-negative breast cancer (TNBC) cells. While emerging evidence implicates coagulation proteases in facilitating cancer progression, the precise molecular pathways underlying thrombin-mediated induction of chemoresistance remain poorly defined.

Aims: Here, we aim to investigate whether thrombin-induced PAR1 activation in TNBC cells promotes development of a multidrug-resistant phenotype.

Methods: We employed various cell based assay system such as MTT , colony formation assay to determine the effect of thrombin on breast cancer resistance. Additionally we extensively used chromatin immunoprecipitation assay to identify the involvement of potential transcription factor in thrombin mediated chemoresistance. We also utilized alograft mice model to validate our in-vitro observation using PAR1 knock-out 4T1 cells.

Results: Here, we observed that thrombin-induced PAR1 activation in TNBC cells promotes development of a multidrug-resistant phenotype, mechanistically linked to upregulation of the pro-survival protein MCL1. Genetic ablation of MCL1 sensitizes TNBC cells to cytotoxic drugs despite thrombin exposure, affirming MCL1's functional importance. Chromatin immunoprecipitation analyses reveal thrombin triggers protein kinase A-dependent phosphorylation of CREB serine 133, enhancing CREB's affinity for the co-activators CBP and p300. Furthermore, thrombin treatment induces the nuclear translocation of CRTC2 in a calcium dependent manner, which collectively interacts with CREB/CBP-P300. The coordinated action of these transcriptional co-activators facilitates the transcriptional induction of MCL1. We further report that PAR1 activation augments MCL1 binding to the deubiquitinase USP9X, reducing MCL1 turnover.

Conclusion(s): In conclusion the thrombin-PAR1 axis as a novel driver of chemoresistance by up-regulating pro survival protein MCL1. Utilizing FDA-approved oral anticoagulants for selective blocking of thrombin action may serve as a potential therapeutic adjunct for the treatment of triple negative breast cancer