Stromal matrix metalloproteinase 2 regulates collagen expression and promotes the outgrowth of experimental metastases

Abstract

Breast cancer survival rates decrease from 99% for patients with local disease to 25% for those with distant metastases. Matrix metalloproteinases (MMPs), including MMP2, are associated with metastatic progression. We found that loss of host MMP2 reduces the proliferation of experimental metastases in the lungs and identified fibroblasts in tumour-bearing lungs as the major source of MMP2. In vitro, spheroidal mammary tumour growth was increased by co-culture with control fibroblasts isolated from tumour-bearing lungs but not when fibroblasts with stable Mmp2 knockdown were used. This result prompted us to assess whether MMP2 was responsible for a tumour-proliferative, activated fibroblast phenotype. To test this, we evaluated (i) fibroblasts from wild-type tumour-bearing lungs with or without shRNA-mediated MMP2 knockdown and (ii) normal, quiescent fibroblasts isolated from either WT or Mmp2−/− mice. Quantitative PCR revealed that Mmp2 knockdown attenuated expression of two markers of activation (α-smooth muscle actin and vimentin), but there was minimal expression in quiescent WT or Mmp2−/− fibroblasts, as expected. Placing quiescent fibroblasts under activating conditions led to increases in activation-associated transcripts in WT but not Mmp2−/− fibroblasts. Additionally, Mmp2 knockdown fibroblasts showed significantly decreased expression of the matrix transcripts collagen I, collagen IV and fibronectin. Addition of active TGFβ was sufficient to rescue the MMP2-dependent collagen I and IV expression, while MMP2-induced collagen expression was blocked with addition of TGFβ-1 neutralizing antibody. Gene expression data in stromal cells of human breast cancers reveals that MMP2 expression is also positively correlated with activation and matrix transcripts. Thus, we present a model whereby MMP2 production in tumour fibroblasts is important for TGFβ-1 activity and subsequent activation of fibroblasts to a matrix-producing, proliferation-supportive phenotype. Overall, our results reveal a previously undefined role for MMP2 in metastatic outgrowth mediated by fibroblasts, and extend the mechanisms by which MMPs contribute to tumour progression.

Potential options for managing LOX+ ER− breast cancer patients

“…To explore the underlying mechanism, we reanalyzed breast cancer data from The Cancer Genome Atlas, which revealed that LOX expression correlates with expression of matrix metallopeptidase 2 (MMP2) (Figure 3A, R 2 = 0.47), collagen type I alpha1 (COL1A1) (Figure 3B, R 2 = 0.47), and secreted protein acidic and rich in cysteine (SPARC) (Figure 3C, R 2 = 0.51). Given that MMP2, COL1A1 and SPARC are all pro-metastatic genes [8–10], we suggest these genes play crucial roles in LOX+ breast cancer metastasis. In addition, data mining results from The Comparative Toxicogenomics Database indicates that bisphosphonate down-regulates expression of LOX, MMP2, COL1A1 and SPARC, which means bisphosphonate may suppress cancer metastasis by targeting these four genes.…”

CDDO-Me Alters the Tumor Microenvironment in Estrogen Receptor Negative Breast Cancer

“…As demonstrated in microarray results, expression of matrix metalloproteinases (MMPs) 2 and 15 was significantly decreased in TAMs by CDDO-Me treatment. These MMPs are known to be involved in the remodeling of the TME extracellular environment 45,46 and can enhance metastasis in several solid tumors 28,47 . Interestingly, tissue inhibitor of metalloproteinase 2 (TIMP2) was also attenuated by treatment.…”

“…2c). Because MMP2 has been implicated in metastatic breast disease 28 , we assessed in vivo CDDO-Me effects on expression of this metalloproteinase. As demonstrated in Fig.…”

Current mechanistic insights into the roles of matrix metalloproteinases in tumour invasion and metastasis

“…MMP2 expressed by stromal fibroblasts has also been shown to be important in promoting the growth of metastases in breast cancer [47]. Loss of stromal fibroblast MMP2 reduced the proliferation of metastasis and this was associated with reduced MMP2-induced transforming growth factor beta 1 activity, highlighting the interaction between MMPs and the transforming growth factor pathway [47].…”