Proteoglycans of the extracellular matrix and growth control

Regulated cell growth results from the biological balance between soluble g rowth-regulating factors, their receptors and the elicited signal cascade o n the one hand side and from extracellular macromolecular components and th eir interplay with membrane receptors on the other side. Proteoglycans have recently been recognized not only to play a part in providing shape and bi omechanical strength of organs and tissues, but also to exhibit direct and indirect cell signalling properties. In this review, we discuss the direct growth-regulating role of proteoglycans with special emphasis on the lectic an family and on the family of small proteoglycans with leucine-rich repeat s (SLRPs). Indirect actions of proteoglycans by modulation of growth factor activities and growth factor distribution are exemplified by discussing th e TGF-beta -binding properties of SLRPs and the interactions of core protei ns of matrix proteoglycans with other growth factors. It is emphasized that the modulatory role of proteoglycans on cell proliferation cannot be separ ated from their participation in tissue organization in general, thereby ex plaining the diverse and sometimes contradictory reports on the effects of proteoglycans on cell proliferation and differentiation. (C) 2001 Wiley-Lis s, Inc.