Abstract P1-01-19: The role of S100A7 in microbiota mediated inflammation and breast cancer progression
Authors: Wilkie T , Zhao H , Nasser M , Ahirwar D , Mishra S , Satoskar A , Pancholi V , Ganju R 
Published: February 2018

Introduction

While it is accepted that inflammation is a key component of cancer development, the intricate mechanism linking the two are not fully defined. Unparalleled progress has been underway to provide better understanding of this mechanism. We investigate the role of bacterial microbiota in promoting an inflammatory environment through the induction of the pro-inflammatory molecule, S100A7, and its activation of STAT-3 signaling pathways to promote tumor growth and metastasis in breast cancer (BC).

Methods

Immune-competent mouse models of orthotopic breast cancer was used to identify and characterize populations of bacterial microbiota in the cancerous breast tissue at tumor onset. Isolated tissues were homogenized and cultured, then processed for DNA extraction. Bacterial species were identified by aligning the sequences on NCBI BLAST.

Mouse mammary tissue and tumors were analyzed for S100a7 after intraperitoneal exposure to LPS after cancer cell injections. Isolated tissues were analyzed by IHC, Western Blot analysis and real time RT-PCR.

mRNA and Protein expression using real time PCR, western blot and flow cytometry, and binding assays analyzed expression and affinity of LPS/S100A7/TLR4 in BC cell lines in vitro under varying conditions.

Protein expression and In vitro functional assays including matrigel invasion and wound closure assays determined the effect of LPS/S100A7 on TLR4 and STAT-3 expression and signaling pathways in promoting tumor invasiveness.

Results

We observed microbiota in cancerous breast tissue, which is predominantly composed of Gram-negative bacteria at tumor onset. The population of mainly gram negative bacteria at tumor initiation is unique from those populations from feces and skin. This suggests that breast tissue microbiota may be a potential source of LPS in breast tumors.

Stimulation with LPS induces secretion/expression of S100A7 in mouse mammary tissue and tumors, as well as BC cell lines. Furthermore, inhibition of LPS by polymixin B decreases S100A7 to basal levels in BC cell lines.

LPS/S100A7 combinational treatment has an additive effect on the invasive potential induced by LPS in BC cell lines as shown by invasion assays and wound closure assays. S100A7 over expression increases TLR4 expression as observed by TLR4 mRNA by real time PCR and protein by flow cytometry. Furthermore, secreted S100A7 protein promotes interaction between S100A7 protein and TLR4 receptor in cell lines with endogenous TLR4 expression.

In addition, both S100A7 and LPS stimulation of TLR4 can activate STAT3 signaling pathway, and inhibition of either S100A7 and or TLR4 impairs the invasiveness of BC cell lines.

Conclusion

A unique population of gram negative bacteria characterizes breast cancer tissues. LPS of bacterial cells walls, representative of gram negative bacteria induces S100A7, which interacts with TLR4 to activate the STAT-3 pathway in tumors. This LPS-S100A7-TLR4-STAT3 axis in turn increases the invasiveness of tumor cells to promote tumor metastasis. This suggests that microbiota plays an important role in the initiation and progression of breast cancer through regulation of the pro-inflammatory molecule S100A7.

Citation Format: Wilkie T, Zhao H, Nasser M, Ahirwar D, Mishra S, Satoskar A, Pancholi V, Ganju R. The role of S100A7 in microbiota mediated inflammation and breast cancer progression [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-01-19.