In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 109, No. 39 ( 2012-09-25)
Abstract:
Our results demonstrate that patterns of epithelial migration and local dissemination are strongly constrained by the local ECM microenvironment. Furthermore, they suggest that cancer cells might express all the molecules necessary for sustained local dissemination but remain indolent if the basement membrane remains intact. However, once the basement membrane is disrupted, the resulting direct contact between cancer cells and the stromal collagen I matrix could acutely induce protrusive and disseminative cell behaviors. Consistent with this model, correlative studies in human breast tumors showed that even microscopic breaks in the myoepithelium correlated with poor prognosis of patients ( 5 ). Conversely, our data reveal that even metastatic human breast tumors are highly context sensitive, and changes in their molecular environment can suppress their invasive and disseminative cell behaviors. Therefore, therapeutic strategies that target ECM-tumor signaling interactions might control invasion and metastasis in breast cancer patients. Recent efforts to sequence the genomes of human breast tumors have revealed mutations in multiple families of cell-adhesion genes, including those encoding classical cadherins and proto-cadherins ( 4 ). Using our system, we evaluated the effects on cell behavior of genetic alterations in different ECM environments. We asked whether deletion of a gene encoding a cell-adhesion protein could induce sustained dissemination of noncancerous cells. We observed that deletion of the P-cadherin gene ( Cdh3 ) was sufficient for sustained dissemination into collagen I ( Fig. P1 I – L ) but not into Matrigel. Together, these data suggest that the consequences of deletion of a cell-adhesion gene are strongly dependent on the current ECM microenvironment. We next asked whether a protrusive, disseminative response to collagen I was tumor specific. Therefore we compared the disseminative behaviors of tumor organoids from a genetically engineered mouse model of mammary carcinoma with those of mammary organoids from normal mice ( Fig. P1 E – H ). Surprisingly, collagen I also induced protrusive and disseminative behaviors in normal mammary epithelial cells ( Fig. P1 F ). However, normal epithelium disseminated only transiently and eventually restored a normal program of branching morphogenesis. In contrast, dissemination of carcinoma cells persisted throughout culture ( Fig. P1 G ). Taken together, these data demonstrate that collagen I induces a conserved dissemination response in mammary epithelial cells that is self-limiting in normal cells and sustained in malignant cells. To determine the role of the ECM in the dissemination of tumors, we isolated tumor organoids from primary human breast tumors ( n = 7) and allocated them to two ECM conditions ( Fig. P1 A – D ): ( i ) laminin-rich Matrigel to model the normal basement membrane and ( ii ) collagen I to model the stromal ECM surrounding invasive cancers. In all cases, we observed that the ECM regulated the dissemination of tumor organoids ( Fig. P1 B – D ). In gels composed of Matrigel, tumor organoids either were indolent or grew collectively. In contrast, in gels composed of collagen I, organoids from the same tumor invaded with protrusions and disseminated cells. These data demonstrate that the ECM microenvironment dictates the migratory and disseminative behaviors of human breast tumors. In vivo, it is difficult to perturb the ECM microenvironment without also altering other aspects of the normal mammary gland or mammary tumor. Moreover, the restricted penetration of light into mammary tissues limits the direct observation of cell behaviors in vivo. 3D ex vivo models of both normal and malignant mammary epithelial growth were developed to address this challenge ( 3 ). In this system, primary tissue is digested enzymatically into cohesive epithelial groups (termed “organoids”) and is embedded in 3D gels composed of ECM proteins. This feature enabled us to control the local ECM, observe acute changes in cell behavior, and study the stepwise events that occur during local tumor dissemination. The word “disseminate” is derived from the Latin word disseminare and translated literally means “to scatter seeds.” In cancer, tumors disseminate cells to distant sites, providing the seeds for metastatic disease. How tumor cells escape from the primary tumor is incompletely understood. It is known that the genotype of the cancer cells and the composition of the extracellular matrix (ECM) change in parallel during the progression of breast cancer ( 1 , 2 ). Here, we tested the specific importance of the ECM for tumor cell dissemination and demonstrated that the ECM regulates the disseminative potential even of metastatic human tumors.
Type of Medium:
Online Resource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.1212834109
Language:
English
Publisher:
Proceedings of the National Academy of Sciences
Publication Date:
2012
detail.hit.zdb_id:
209104-5
detail.hit.zdb_id:
1461794-8
SSG:
11
SSG:
12
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