Integrins: Molecular and biological responses to the extracellular matrix Edited by D. A. Cheresh and R. P. Mecham. San Diego, California: AP Professional-Academic Press. (1994). 278 pp. $89.95

It has been clear since the pioneering experiments of P. Weiss and C. Grobstein in the 1940s and 1950s that the interaction between cells and the "ground substance" in their environment is critical to their proper function and differentiation. During the next three decades, experiments from many labs refined and extended this observation , demonstrating that interactions with the extracellular matrix not only affect cell behavior (adhesion, migration, morphology) but also cause changes in gene expression and cell differentiation. However, the lack of molecular information about how cells interact with components of their surrounding matrix limited progress in understanding the mechanisms by which such interactions influence cell function. The purification of cellular receptors for extracel-lular matrix proteins in the 1980s and the subsequent recognition that these, along with the very late antigen (VLA) proteins of leukocytes and the platelet glycoprotein lib/ Ilia, formed a superfamily of cell adhesion receptors, revolutionized the field of cell-extracellular matrix interactions, and has led to far-ranging advances in our understanding of their importance. The name integrins was introduced in 1986 to describe these receptors, which, as transmem-brane heterodimers that interact both with extracellular ligands and with the internal cytoskeleton, can "integrate" the external and internal environments of the cell. The growth of the integrin field in the past decade has been staggering. To date, 27 different heterodimeric inte-grins have been identified, and some integrin subunits also exist as structural variants, further increasing the diversity of these receptors. Our understanding of the biological importance of integrins, as well as the complexity and subtlety of their function and regulation, has increased dramatically as well. Integrins are now known to function both as structural elements that physically link matrix components to the actin cytoskeleton and as signal transduc-tion molecules that effect changes in gene expression and cell behavior in response to ligand binding or mechanical stimulation. Integrin-mediated signaling is of fundamental importance in many diverse biological processes, such as the regulation of cell proliferation, cell differentiation, and cell death; directed movements during embryogenesis; and tissue remodeling during the inflammatory response and in wound healing. Integrins do not have any intrinsic kinase activity, so the recent demonstrations that the tyro-sine kinase pp125 ~AK binds to integrin 131 and that integrin binding activates components of the Ras/MAP kinase pathways, have generated enormous excitement about their functions as signaling receptors. Up to now, the state of integrin research has been reported …