Abstract
Background: PolyADP ribosylation (PARylation) by PARP1 is a significant post-translational modification affecting protein function in various cancers. However, PARP1 mediated cellular processes in the context of breast cancer are not fully understood. Method: To identify potential targets of PARP1, we carried out whole transcriptome sequencing with shRNA mediated PARP1 knockdown in triple-negative breast cancer (TNBC) cell line and inhibited PARP1 with a known PARP1 inhibitor, PJ34. Results: Analysis of the transcriptomics data revealed that PARP1 is involved in regulating multiple chemokines under basal conditions, including the chemokine ligand 2 (CCL2). PARP1 knockdown and PJ34 mediated inhibition showed reduced CCL2 transcript levels in breast cancer cells, corroborating the findings from the sequencing data. We further showed that PARP1 interacts with the NFκB P65 subunit to regulate transcription of CCL2. Using chromatin immunoprecipitation, we confirm that both PARP1 and P65 localize to the promoter of CCL2, suggesting direct regulation of CCL2 promoter activity. CCL2, in turn, can positively affect the PARP1 pathway, as global PARylation levels increased upon CCL2 treatment. Conclusion: Our results indicate crosstalk between PARP1 and CCL2, which is critical for maintaining CCL2 levels in breast cancer cells and subsequently drives cellular invasiveness.
Highlights
Multiple studies have shown the involvement of the small secreted proteins like cytokines and associated receptors to be involved in cell proliferation and metastasis, causing poor prognosis [1].In breast cancer, along with their direct effects on cell growth and metastasis, chemokines are essential mediators in the tumor microenvironment, maintaining crosstalk in the tumor niche [2].Aggressive types of breast cancer, like triple-negative breast cancer (TNBC), have been shown to have “secretome” comprised of higher concentrations of chemokines such as CXCL1 and CCL2 [3,4]
We examined the total levels of PolyADP Ribose (PAR) and Poly ADP ribose Polymerase 1 (PARP1) in cell lysates from different subtypes of breast cancer cells
PAR levels were higher in triple-negative breast cancer cells, as shown on the western blot (Figure 1A)
Summary
Aggressive types of breast cancer, like TNBCs, have been shown to have “secretome” comprised of higher concentrations of chemokines such as CXCL1 and CCL2 [3,4]. Understanding how these chemokines are maintained and upregulated in breast cancer cells can generate some strategies for therapies. PARP1 knockdown and PJ34 mediated inhibition showed reduced CCL2 transcript levels in breast cancer cells, corroborating the findings from the sequencing data. Conclusion: Our results indicate crosstalk between PARP1 and CCL2, which is critical for maintaining CCL2 levels in breast cancer cells and subsequently drives cellular invasiveness
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