PDF, English Download (5MB) | Terms of use

Abstract

The tumor microenvironment (TME) is now recognized as an important factor in breast cancer progression and is crucial in determining the response to anti-cancer therapies. Fibroblasts are one component of the TME that are activated in the early stages of oncogenesis and remodel the TME as an early tissue repair response. In the later stages of tumor progression, these activated fibroblasts get transformed into cancer associated fibroblasts (CAFs) that promote tumor progression. The mechanisms underlying this transformation of fibroblasts from normal activated fibroblasts to CAFs remain largely unknown. To address this, bone marrow derived mesenchymal stromal cells (MSCs) that are known to be a significant source of CAFs were treated with conditioned media of a breast cancer cell line, namely, MDA-MB-23, to induce a CAF-like - phenotype. Activation of MSCs was confirmed by assessing their contractility and expression of CAF markers. Gene expression and secretome analysis was performed to identify differentially expressed genes and differentially secreted factors upon activation. Stanniocalcin 1 (STC1), a CAF-secreted protein implicated in metastasis and therapy resistance, was found to be upregulated upon conditioned media treatment. Therefore, the aim of this study was to understand the mechanism of STC1 upregulation and its involvement in the activation of fibroblasts. STC1 knockdown using RNAi both in conditioned media treated MSCs and patient derived activated CAFs showed inhibitory effects on activation status of these cells. Moreover, this down-regulation resulted in a decrease in the expression of several proteins such as NOTCH3, NOTCH4 and β-catenin suggesting possible mechanisms by which STC1 regulates the activation of fibroblasts. Furthermore, the upregulation of STC1 upon conditioned media treatment was found to be dependent on RELA and RELB transcription factors indicating that NF-κB signaling might be involved in its transcriptional regulation. In conclusion, this study demonstrates STC1 as an important factor in the activation of CAFs. Investigating the mechanism of the involvement of STC1 in the unabated activation of CAFs will enable a deeper understanding of the tumor microenvironment and its role in the tumor progression.