Tumors are complex tissues composed of neoplastic cells, soluble and insoluble matrix components and stromal cells. Here we report that in melanoma, turn-over of type I collagen (Col(I)), the predominant matrix protein in dermal stroma affects melanoma progression. Fibroblasts juxtaposed to melanoma cell nests within the papillary dermis display high levels of Col(I) mRNA expression. These nests are enveloped by collagen fibers. In contrast, melanoma-associated fibroblasts within the reticular dermis express Col(I) mRNA at a level that is comparable to its expression in uninvolved dermis and reduced amount of collagen protein can be observed. To determine the significance of Col(I) expression in melanoma, we pharmacologically inhibited its transcription in a porcine cutaneous melanoma model by oral administration of halofuginone. When administered before melanoma development, it reduced melanoma incidence and diminished the transition from microinvasive toward deeply invasive growth by limiting the development of a tumor vasculature. Whereas invasive melanoma growth has been correlated with increased blood vessel density previously, our data for the first time demonstrate that the proangiogenic effect of Col(I) expression by fibroblasts and vascular cells precedes the development of invasive melanomas in a de novo tumor model. ' 2007 Wiley-Liss, Inc.Key words: cutaneous melanoma; type I collagen; angiogenesis; MeLiM porcine melanoma model; halofuginone Tumor development and invasion into adjacent tissue is often accompanied by increased architectural disorder of the extracellular matrix (ECM) and cellular components especially at the invasive front of the neoplastic mass. 1 Along with increased production of extracellular proteolytic enzymes, 2-4 increased synthesis of type I collagen (Col(I)) and other matrix components by stromal cells has been documented in skin, mammary, colon and prostate carcinomas. [5][6][7][8][9] In squamous cell carcinomas of the skin, increased Col(I) synthesis by stromal fibroblasts 9 is also accompanied by enhanced remodeling due to increased activity of matrix proteinases. 10 In contrast, cutaneous melanoma, but with the exception of desmoplastic variants, is not associated with strong ECM remodeling, but is mainly characterized by pericellular proteolysis of Col(I) and elastin at the invasive front. 11 Expression of Col(I) and its contribution to melanoma development and progression have not been studied extensively.In skin, the fibril forming Col(I) is predominantly synthesized by fibroblasts and accounts for 80-90% of the collagenous proteins present in the dermis. 12 Col(I) fibers are composed of righthanded triple helical molecules of 1 Col(I)a2 and 2 Col(I)a1 chains and can be found in all dermal layers. 13 However, the architectural organization of Col(I) fibers is different in the papillary and reticular dermis. Whereas, Col(I) is found as a finely woven meshwork of fibers in the papillary dermis, a distinctive pattern of thick Col(I) bundles is found in reticular dermis.Th...

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