Lumican effects in the control of tumour progression and their links with metalloproteinases and integrins.

Lumican is a member of the small leucine-rich proteoglycan family. It is present in numerous extracellular matrices of different tissues, such as muscle, cartilage, and cornea. In skin, lumican is present as a glycoprotein. It plays a critical role in collagen fibrillogenesis, as shown by knocking out of its gene in mice. A direct link between lumican expression and melanoma progression and metastasis has been demonstrated. Lumican was shown to impede tumour cell migration and invasion by directly interacting with the α2β1 integrin. In addition, an active sequence of the lumican core protein, called lumcorin, was identified as being responsible for inhibition of melanoma cell migration. Lumican was also shown to exert angiostatic properties by downregulating the proteolytic activity associated with endothelial cell membranes, particularly matrix metalloproteinase (MMP)-14 and MMP-9. Globally, lumican appears to be a potent agent for inhibiting tumour progression rather than tumorigenesis. However, progressive changes in proteoglycans occur in the tumour environment. The complexity and diversity of proteoglycan structure might be responsible for a variety of functions that regulate cell behaviour. Through their core protein and their glycosaminoglycan chains, proteoglycans can interact with growth factors and chemokines. These interactions affect cell signalling, motility, adhesion, growth, and apoptosis. This review summarizes recent data concerning lumican control of tumour progression in different cancers, with a particular focus on its interactions with MMPs and integrins. Its potential therapeutic implications are discussed.