Tumours are known as wounds that do not heal - this implies that cells that are involved in angiogenesis and the response to injury, such as endothelial cells and fibroblasts, have a prominent role in the progression, growth and spread of cancers. Fibroblasts are associated with cancer cells at all stages of cancer progression, and their structural and functional contributions to this process are beginning to emerge. Their production of growth factors, chemokines and extracellular matrix facilitates the angiogenic recruitment of endothelial cells and pericytes. Fibroblasts are therefore a key determinant in the malignant progression of cancer and represent an important target for cancer therapies.

Fibroblasts in cancer

Cancer is associated with fibroblasts at all stages of disease progression. This Review discusses the pleiotropic actions of cancer-associated fibroblasts (CAFs) on tumour cells and postulates that they are likely to be a heterogeneous and plastic population of cells in the tumour microenvironment. Among all cells, fibroblasts could be considered the cockroaches of the human body. They survive severe stress that is usually lethal to all other cells, and they are the only normal cell type that can be live-cultured from post-mortem and decaying tissue. Their resilient adaptation may reside in their intrinsic survival programmes and cellular plasticity. Cancer is associated with fibroblasts at all stages of disease progression, including metastasis, and they are a considerable component of the general host response to tissue damage caused by cancer cells. Cancer-associated fibroblasts (CAFs) become synthetic machines that produce many different tumour components. CAFs have a role in creating extracellular matrix (ECM) structure and metabolic and immune reprogramming of the tumour microenvironment with an impact on adaptive resistance to chemotherapy. The pleiotropic actions of CAFs on tumour cells are probably reflective of them being a heterogeneous and plastic population with context-dependent influence on cancer.

The biology and function of fibroblasts in cancer

VPF/VEGF is a multifunctional cytokine that contributes to angiogenesis by both direct and indirect mechanisms. On the one hand, VPF/VEGF stimulates the ECs lining nearby microvessels to proliferate, to migrate, and to alter their pattern of gene expression. On the other hand, VPF/VEGF renders these same microvascular ECs hyperpermeable so that they spill plasma proteins into the extravascular space, leading to the clotting of extravasated fibrinogen with deposition of a fibrin gel. Extravascular fibrin serves as a provisional matrix that favors and supports the ingrowth of new blood vessels and other mesenchymal cells that generate mature, vascularized stroma. These same principles apply in tumors, in several examples of non-neoplastic pathology, and in physiological processes that involve angiogenesis and new stroma generation. In all of these examples, microvascular hyperpermeability and the introduction of a provisional, plasma-derived matrix precede and accompany the onset of EC division and new blood vessel formation. It would seem, therefore, that tumors have "borrowed" fundamental mechanisms that developed in multicellular organisms for purposes of tissue defense, renewal, and repair. VPF/VEGF, therefore has taught us something new about angiogenesis; namely, that vascular hyperpermeability and consequent plasma protein extravasation are important, perhaps essential, elements in its generation. However, this finding raises a paradox. While VPF/VEGF induces vascular hyperpermeability, other potent angiogenic factors apparently do not, at least in subtoxic concentrations that are more than sufficient to induce angiogenesis. Nonetheless, wherever angiogenesis has been studied, the newly generated vessels have been found to be hyperpermeable. How, therefore, do angiogenic factors other than VPF/VEGF lead to the formation of new and leaky blood vessels? We do not as yet have a complete answer to this question. One possibility is that at least some angiogenic factors mediate their effect by inducing or stimulating the expression of VPF/VEGF. In fact, there is already one clear example of this. TGF-alpha is a potent angiogenic factor but does not itself increase microvascular permeability. However, TGF-alpha strikingly upregulates VPF/VEGF expression in cultured keratinocytes and is thought to be responsible, at least in part, for the overexpression of VPF/VEGF in psoriasis. Moreover, overexpression of TGF-alpha, along with that of the EGF receptor with which it interacts, is characteristic of many malignant tumors, raising the possibility that TGF-alpha acts to stimulate VPF/VEGF expression in other types of epithelial cells and in this manner induces angiogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Vascular permeability factor/vascular endothelial growth factor, microvascular hyperpermeability, and angiogenesis.

VPF/VEGF is a multifunctional cytokine that contributes to angiogenesis by both direct and indirect mechanisms. On the one hand, VPF/VEGF stimulates the endothelial cells lining nearby microvessels to proliferate, to migrate and to alter their pattern of gene expression. On the other hand, VPF/VEGF renders these same microvascular endothelial cells hyperpermeable so that they spill plasma proteins into the extravascular space, leading to profound alterations in the extracellular matrix that favor angiogenesis. These same principles apply in tumors, in several examples of non-neoplastic pathology, and in physiological processes that involve angiogenesis and new stroma generation. In all of these examples, microvascular hyperpermeability and the introduction of a provisional, plasma-derived matrix precede and accompany the onset of endothelial cell division and new blood vessel formation. It would seem, therefore, that tumors have made use of fundamental pathways that developed in multicellular organisms for purposes of tissue defense, renewal and repair. VPF/VEGF, therefore, has taught us something new about angiogenesis; namely, that vascular hyperpermeability and consequent plasma protein extravasation are important--perhaps essential--elements in its generation. However, this finding raises a paradox. While VPF/VEGF induces vascular hyperpermeability, other potent angiogenic factors apparently do not, at least in sub-toxic concentrations that are more than sufficient to induce angiogenesis (Connolly et al., 1989a). Nonetheless, wherever angiogenesis has been studied, the newly generated vessels have been found to be hyperpermeable. How, therefore, do angiogenic factors other than VPF/VEGF lead to the formation of new and leaky blood vessels? We do not as yet have a complete answer to this question. One possibility is that at least some angiogenic factors mediate their effect by inducing or stimulating VPF/VEGF expression. In fact, there are already clear example of this. A number of putative angiogenic factors including small molecules (e.g. prostaglandins, adenosine) as well as many cytokines (e.g. TGF-alpha, bFGF, TGF-beta, TNF-alpha, KGF, PDGF) have all been shown to upregulate VPF/VEGF expression. Further studies that elucidate the crosstalk among various angiogenic factors are likely to contribute significantly to a better understanding of the mechanisms by which new blood vessels are formed in health and in disease.

Vascular permeability factor/vascular endothelial growth factor:A multifunctional angiogenic cytokine

Fibrosis is a pathological scarring process that leads to destruction of organ architecture and impairment of organ function. Chronic loss of organ function in most organs, including bone marrow, heart, intestine, kidney, liver, lung, and skin, is associated with fibrosis, contributing to an estimated one third of natural deaths worldwide. Effective therapies to prevent or to even reverse existing fibrotic lesions are not yet available in any organ. There is hope that an understanding of common fibrosis pathways will lead to development of antifibrotic therapies that are effective in all of these tissues in the future. Here we review common and organ-specific pathways of tissue fibrosis.

https://www.physiology.org/doi/pdf/10.1152/ajpcell.00328.2012

Cellular Mechanisms of Tissue Fibrosis. 1. Common and organ-specific mechanisms associated with tissue fibrosis

The structural proteins of the scirrhous line 1 and the medullary line 10 bile duct carcinomas, both syngeneic in strain 2 Sewall-Wright inbred guinea pigs, were studied. Tumor structural proteins were compared with those of healing wounds. A provisional stromal matrix of cross-linked fibrin and fibronectin was initially deposited in both tumors and wounds and was subsequently replaced by granulation tissue containing collagen types I and III. The amounts of stromal fibrin-fibronectin and collagen were characteristic of each tumor: Line 1 contained significantly greater amounts than line 10. These differences were augmented when line 1 tumor rejection was prevented with cyclosporine, permitting time for stromal maturation. In tumors and wounds laminin and collagen type IV were found only in basement membranes. The findings suggest that 1) tumor desmoplasia is analogous to wound healing, 2) both processes involve replacement of an antecedent fibrin-fibronectin provisional matrix, 3) the extent of fibrin-fibronectin is characteristic of each tumor, and 4) tumor desmoplasia correlates with the amount of fibrin-fibronectin matrix deposited.

Pathogenesis of Desmoplasia. I. Immunofluorescence Identification and Localization of Some Structural Proteins of Line 1 and Line 10 Guinea Pig Tumors and of Healing Wounds 1,2

For the investigation of the pathogenesis of desmoplasia, the capacities to synthesize collagen in vitro of 2 bile duct carcinomas (lines 1 and 10) of Sewall-Wright inbred strain 2 guinea pigs and of syngeneic dermal fibroblasts were studied. Line 10 cells synthesized collagen type IV as judged by sensitivity to bacterial collagenase, by immunoprecipitation, by migration of pro alpha (IV) chains and pepsin-resistant fragments on sodium dodecyl sulfate-polyacrylamide gels, and by immunofluorescence. Line 1 cells also synthesized small amounts of collagenase-sensitive protein. Neither line 1 nor line 10 cells synthesized detectable collagen type I, III, or V. Only about 1% of [14C]proline incorporated by tumor cells was found in collagenase-sensitive protein. In contrast, dermal fibroblasts synthesized 4 and 128 times as much collagenase-sensitive protein as line 10 and line 1 cells, respectively, amounting to 20% of total protein synthesized. Fibroblasts produced mostly collagen types I and III, in a ratio of 7:1, and smaller amounts of collagen type V. Thus lines 1 and 10 carcinoma cells produce primarily basement membrane collagen, whereas interstitial collagens, abundant in desmoplastic tumor stroma, are fibroblast products.

Pathogenesis of Tumor Desmoplasia. II. Collagens Synthesized By Line 1 And Line 10 Guinea Pig Carcinoma Cells And By Syngeneic Fibroblasts In Vitro

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Pathogenesis of Desmoplasia. I. Immunofluorescence Identification and Localization of Some Structural Proteins of Line 1 and Line 10 Guinea Pig Tumors and of Healing Wounds 1,2

Pathogenesis of Tumor Desmoplasia. II. Collagens Synthesized By Line 1 And Line 10 Guinea Pig Carcinoma Cells And By Syngeneic Fibroblasts In Vitro