Role of myofibroblasts at the invasion front

Angiogenesis Inhibition by Vascular Endothelial Growth Factor Receptor-2 Blockade Reduces Stromal Matrix Metalloproteinase Expression, Normalizes Stromal Tissue, and Reverts Epithelial Tumor Phenotype in Surface Heterotransplants

Inhibition of vascular endothelial growth factor (VEGF) signaling, a key regulator of tumor angiogenesis, through blockade of VEGF receptor (VEGFR)-2 by the monoclonal antibody DC101 inhibits angiogenesis, tumor growth, and invasion. In a surface xenotransplant assay on nude mice using a high-grade malignant squamous cell carcinoma cell line (A-5RT3), we show that DC101 causes vessel regression and normalization as well as stromal maturation resulting in a reversion to a noninvasive tumor phenotype. Vessel regression is followed by down-regulation of expression of both VEGFR-2 and VEGFR-1 on endothelial cells and increased association of α-smooth muscle actin–positive cells with small vessels indicating their normalization, which was further supported by a regular ultrastructure. The phenotypic regression of an invasive carcinoma to a well-demarcated dysplastic squamous epithelium is accentuated by the establishment of a clearly structured epithelial basement membrane and the accumulation of collagen bundles in the stabilized connective tissue. This normalization of the tumor-stroma border coincided with down-regulated expression of the stromal matrix metalloproteinases 9 and 13, which supposedly resulted in attenuated turnover of extracellular matrix components permitting their structural organization. Thus, in this mouse model of a human squamous cell carcinoma cell line, blockade of VEGF signaling resulted in the reversion of the epithelial tumor phenotype through stromal normalization, further substantiating the crucial role of stromal microenvironment in regulating the tumor phenotype.

Tumour-stroma interaction: cancer-associated fibroblasts as novel targets in anti-cancer therapy?

Stroma cells, together with extracellular matrix components, provide the microenvironment that is pivotal for cancer cell growth, invasion and metastatic progression. Characteristic stroma alterations accompany or even precede the malignant conversion of epithelial cells. Crucial in this process are fibroblasts, also termed myofibroblasts or cancer-associated fibroblasts (CAFs) that are located in the vicinity of the neoplastic epithelial cells. They are able to modify the phenotype of the epithelial cells by direct cell-to-cell contacts, through soluble factors or by modification of extracellular matrix components. Seminal functional studies in various cancer types, including breast, colon, prostate and lung cancer, have confirmed the concept that fibroblasts can determine the fate of the epithelial cell, since they are able to promote malignant conversion as well as to revert tumour cells to a normal phenotype. This review focuses on characteristic changes of fibroblasts in cancer and provides the experimental background elucidating functional properties of CAFs in the carcinogenic process. A possible implication in lung carcinogenesis is emphasised. Finally, a laser-capture- and microarray-based approach is presented, which comprehensively characterises carcinoma-associated fibroblasts in their in vivo environment for the identification of potential targets for anti-cancer therapy.

Type I collagen synthesis parallels the conversion of keratinocytic intraepidermal neoplasia to cutaneous squamous cell carcinoma

Neoplastic progression of solid tumours is often characterized by a simultaneous increase in matrix protein (eg collagen) synthesis and degradation, and results in the formation of a tumour stroma. At the tumour periphery, this process is believed to facilitate angiogenesis and invasive growth of tumour cells. In various types of carcinoma, differentiation of fibroblasts towards myofibroblasts is thought to play an important role in extracellular matrix remodelling as their emergence coincides with architectural changes in the tumour stroma. Here, distinct architectural changes in collagen fibres are reported in cutaneous squamous cell carcinomas (cSCC) with respect to normal skin and precursor lesions, ie keratinocytic intraepidermal neoplasia (KIN). Simultaneously, type I collagen mRNA was observed in fibroblasts in close proximity to cSCC lesions (19/19) but only in 2 of 10 KIN lesions tested. Interestingly, whereas emerging of myofibroblasts correlated with reduced differentiation of cSCCs, it was not a prerequisite for type I collagen synthesis. These data indicate that type I collagen synthesis by fibroblasts parallels the malignant transformation of human KIN to cSCC.

Invasion and MMP expression profile in desmoid tumours

Desmoid tumours are locally invasive soft tissue tumours in which β-catenin mediated TCF-dependent transcription is activated. The role of soluble factors secreted by the myofibroblastic desmoid tumour, which could stimulate tumour invasiveness, was investigated. Using collagen gel invasion assays, the presence of factors stimulating invasion in desmoid conditioned media (CM) could be established. Since matrix metalloproteinases (MMPs) have been implicated in the process of tumoral invasion, the expression levels of the MMP family members were evaluated. Quantitative reverse transcription–PCR was used to determine the expression levels of MMP1, MMP2, MMP3, MMP7, MMP11, MMP12, MMP13, MMP14 and the inhibitors TIMP1, TIMP2 and TIMP3. Besides overexpression of MMP7, a known TCF-dependent target gene, a striking upregulation of the expression levels of MMP1, MMP3, MMP11, MMP12 and MMP13 in desmoid tumours, compared to unaffected fibroblasts from the same patients, was found. Treating the CM of desmoids with a synthetic and a physiologic MMP inhibitor reduced the invasion-stimulating capacity of the desmoid CM by approximately 50%. These results suggest the involvement of soluble factors, released by the desmoid cells, in stimulating invasion and implicate the MMPs as facilitators of invasion.

The myofibroblast is the predominant plasminogen activator inhibitor-1-expressing cell type in human breast carcinomas

The tumor level of plasminogen activator inhibitor-1 (PAI-1) is an informative biochemical marker of a poor prognosis in several cancer types. However, the tumor biological functions of PAI-1 and the identity of PAI-1-expressing cells are controversial. With the aim of immunohistochemically localizing PAI-1 in formalin-fixed, paraffin-embedded invasive ductal breast carcinoma samples, we raised new polyclonal antibodies against PAI-1 from different expression systems. The antibodies were affinity purified by absorption on immobilized preparations of PAI-1 different from those used for immunization. The specificity of the antibodies was ensured by immunoblotting analysis. In immunohistochemistry, the staining pattern obtained with the antibodies showed a good correlation with the PAI-1 mRNA expression pattern. In all 25 cases analyzed, PAI-1 immunoreactivity was predominantly localized in fibroblast-like cells. Double-immunofluorescence analyses showed co-expression of PAI-1 and alpha-smooth muscle actin in these cells, suggesting that they are myofibroblasts. PAI-1 was also seen in some myoepithelial cells surrounding occasional foci of ductal carcinoma in situ (9 of 25), some endothelial cells (8 of 25), some cancer cells (3 of 25), and some mast cells (6 of 25). In conclusion, we have provided a robust immunohistochemical procedure for detection of PAI-1 and shown that the majority of the PAI-1-expressing cells in invasive ductal breast carcinomas are myofibroblasts.

Role of tissue stroma in cancer cell invasion

Maintenance of epithelial tissues needs the stroma. When the epithelium changes, the stroma inevitably follows. In cancer, changes in the stroma drive invasion and metastasis, the hallmarks of malignancy. Stromal changes at the invasion front include the appearance of myofibroblasts, cells sharing characteristics with fibroblasts and smooth muscle cells. The main precursors of myofibroblasts are fibroblasts. The transdifferentiation of fibroblasts into myofibroblasts is modulated by cancer cell-derived cytokines, such as transforming growth factor-beta (TGF-beta). TGF-beta causes cancer progression through paracrine and autocrine effects. Paracrine effects of TGF-beta implicate stimulation of angiogenesis, escape from immunosurveillance and recruitment of myofibroblasts. Autocrine effects of TGF-beta in cancer cells with a functional TGF-beta receptor complex may be caused by a convergence between TGF-beta signalling and beta-catenin or activating Ras mutations. Experimental and clinical observations indicate that myofibroblasts produce pro-invasive signals. Such signals may also be implicated in cancer pain. N-Cadherin and its soluble form act as invasion-promoters. N-Cadherin is expressed in invasive cancer cells and in host cells such as myofibroblasts, neurons, smooth muscle cells, and endothelial cells. N-Cadherin-dependent heterotypic contacts may promote matrix invasion, perineural invasion, muscular invasion, and transendothelial migration; the extracellular, the juxtamembrane and the beta-catenin binding domain of N-cadherin are implicated in positive invasion signalling pathways. A better understanding of stromal contributions to cancer progression will likely increase our awareness of the importance of the combinatorial signals that support and promote growth, dedifferentiation, invasion, and ectopic survival and eventually result in the identification of new therapeutics targeting the stroma.

Plasmin produces an E-cadherin fragment that stimulates cancer cell invasion

Matrix metalloproteases from the cell surface cleave an 80 kDa E-cadherin fragment (sE-CAD) that induces invasion of cancer cells into collagen type I and inhibits cellular aggregation. Conditioned media from MDCKts.srcCl2 cells at 40 degrees C and 35 degrees C, PCm.src5 and COLO-16 cells at 37 degrees C contained spontaneously released sE-CAD; these 48 h old conditioned media were capable of inhibiting E-cadherin functions in a paracrine way. Here we show direct cleavage of the extracellular domain of E-cadherin by the serine protease plasmin. sE-CAD released by plasmin inhibits E-cadherin functions as evidenced by induction of invasion into collagen type I and inhibition of cellular aggregation. This functional inhibition by sE-CAD was reversed by aprotinin or by immunoadsorption on protein Sepharose 4 fast flow beads with antibodies against the extracellular part of E-cadherin. Our results demonstrate that plasmin produces extracellular E-cadherin fragments which regulate E-cadherin function in cells containing an intact E-cadherin/catenin complex.