Cellular interactions with the extracellular matrix and with neighboring cells profoundly influence a variety of signaling events including those involved in mitogenesis, survival, and differentiation. Recent advances have provided insights into mechanisms underlying the ability of integrins, cadherins, selectins, and other cell adhesion molecules to regulate signal transduction cascades. These mechanisms often involve the ability of cell adhesion molecules to initiate the formation of organized structures or scaffolds that permit the efficient flow of information in signaling pathways.

Cell to matrix adhesion regulates cellular homeostasis in multiple ways. Integrin attachment to the extracellular matrix mediates this regulation through direct and indirect connections to the actin cytoskeleton, growth factor receptors, and intracellular signal transduction cascades. Disruption of this connection to the extracellular matrix has deleterious effects on cell survival. It leads to a specific type of apoptosis known as anoikis in most non-transformed cell types. Anchorage independent growth is a critical step in the tumorigenic transformation of cells. Thus, breaching the anoikis barrier disrupts the cell's defenses against transformation. This review examines recent investigations into the molecular mechanisms of anoikis to illustrate current understanding of this important process.

The potential use of antisense and siRNA oligonucleotides as therapeutic agents has elicited a great deal of interest. However, a major issue for oligonucleotide-based therapeutics involves effective intracellular delivery of the active molecules. In this Survey and Summary, we review recent reports on delivery strategies, including conjugates of oligonucleotides with various ligands, as well as use of nanocarrier approaches. These are discussed in the context of intracellular trafficking pathways and issues regarding in vivo biodistribution of molecules and nanoparticles. Molecular-sized chemical conjugates and supramolecular nanocarriers each display advantages and disadvantages in terms of effective and nontoxic delivery. Thus, choice of an optimal delivery modality will likely depend on the therapeutic context.

Integrin-mediated adhesion to the extracellular matrix permits efficient growth factor-mediated activation of extracellular signal–regulated kinases (ERKs). Points of regulation have been localized to the level of receptor phosphorylation or to activation of the downstream components, Raf and MEK (mitogen-activated protein kinase/ERK kinase). However, it is also well established that ERK translocation from the cytoplasm to the nucleus is required for G1 phase cell cycle progression. Here we show that phosphorylation of the nuclear ERK substrate, Elk-1 at serine 383, is anchorage dependent in response to growth factor treatment of NIH 3T3 fibroblasts. Furthermore, when we activated ERK in nonadherent cells by expression of active components of the ERK cascade, subsequent phosphorylation of Elk-1 at serine 383 and Elk-1–mediated transactivation were still impaired compared with adherent cells. Elk-1 phosphorylation was dependent on an intact actin cytoskeleton, as discerned by treatment with cytochalasin D (CCD). Finally, expression of active MEK failed to predominantly localize ERK to the nucleus in suspended cells or adherent cells treated with CCD. These data show that integrin-mediated organization of the actin cytoskeleton regulates localization of activated ERK, and in turn the ability of ERK to efficiently phosphorylate nuclear substrates.

Integrins have been implicated in key cellular functions, including cytoskeletal organization, motility, growth, survival, and control of gene expression. The plethora of integrin α and β subunits suggests that individual integrins have unique biological roles, implying specific molecular connections between integrins and intracellular signaling or regulatory pathways. Here, we have used a yeast two-hybrid screen to identify a novel protein, termed Nischarin, that binds preferentially to the cytoplasmic domain of the integrin α5 subunit, inhibits cell motility, and alters actin filament organization. Nischarin is primarily a cytosolic protein, but clearly associates with α5β1, as demonstrated by coimmunoprecipitation. Overexpression of Nischarin markedly reduces α5β1-dependent cell migration in several cell types. Rat embryo fibroblasts transfected with Nischarin constructs have “basket-like” networks of peripheral actin filaments, rather than typical stress fibers. These observations suggest that Nischarin might affect signaling to the cytoskeleton regulated by Rho-family GTPases. In support of this, Nischarin expression reverses the effect of Rac on lamellipodia formation and selectively inhibits Rac-mediated activation of the c-fos promoter. Thus, Nischarin may play a negative role in cell migration by antagonizing the actions of Rac on cytoskeletal organization and cell movement.

Cells selected for overexpression of the integrin a5131 show decreased proliferation and loss of the transformed phenotype. We provide evidence that de novo expression of the integrin ca5,31 in HT29 colon carcinoma cells results in the growth arrest of these cells as characterized by reduced DNA synthesis and cellular proliferation in vitro. In fact, expression of integrin a5f31 on these cells induces the transcription of growth arrest specific gene 1 (gas-i), a gene product known to induce cellular quiescence, but blocks transcription of the immediate early genes c-fos, c-jun, and jun B. In vivo, the a5/31 transfectants display dramatically reduced tumorigenicity as well as a highly differentiated phenotype when compared with their pSVneo-transfected counterparts. Surprisingly, ligation of a5f31 on these cells by cell attachment to a fibronectin substrate not only reverses the growth inhibition and gas-i gene induction but activates immediate early gene transcription. These findings demonstrate that integrin a5131 expression in the absence of attachment to fibronectin activates a signaling pathway leading to decreased cellular proliferation and that ligation of this receptor with fibronectin reverses this signal, thereby contributing to the proliferation of transformed cells.

The toxicology of liposome-encapsulated amphotericin B in mice and its efficacy in the treatment and prophylaxis of systemic candidiasis in these animals were studied. The toxicology studies indicated that the maximal tolerated dose of free amphotericin B was 0.8 mg/kg of body weight and the 50% lethal dose (LD50) was reached at 1.2 mg/kg, while neither the maximal tolerated dose nor the LD50 for the liposomal amphotericin B was reached at a dose of 12 mg/kg. No abnormalities in blood chemistry or histology were observed in the animals injected with encapsulated amphotericin B, while the administration of free amphotericin B was associated with nephrocalcinosis and renal parenchymal edema. The encapsulated drug was as effective as the free drug when used in similar concentrations, while the animals treated with higher concentrations of liposomal amphotericin B (4 mg/kg) had a longer survival time. Thus, an improved therapeutic index resulted by encapsulating amphotericin B in liposomes.

Activation of cytoplasmic tyrosine kinases is an important aspect of signal transduction mediated by integrins. In the human monocytic cell line THP-1, either integrin-dependent cell adhesion to fibronectin or ligation of beta 1 integrins with antibodies causes a rapid and intense tyrosine phosphorylation of two sets of proteins of about 65-75 and 120-125 kDa. In addition, integrin ligation leads to nuclear translocation of the p50 and p65 subunits of the NF-kappa B transcription factor, to activation of a reporter gene driven by a promoter containing NF-kappa B sites, and to increased levels of mRNAs for immediate-early genes, including the cytokine interleukin (IL)-1 beta. The tyrosine kinase inhibitors genistein and herbimycin A block both integrin-mediated tyrosine phosphorylation and increases in IL-1 beta message levels, indicating a causal relationship between the two events. The components tyrosine phosphorylated subsequent to cell adhesion include paxillin, pp125FAK, and the SH2 domain containing tyrosine kinase Syk. In contrast, integrin ligation with antibodies induces tyrosine phosphorylation of Syk but not of FAK or paxillin. In adhering cells, pre-treatment with cytochalasin D suppresses tyrosine phosphorylation of FAK and paxillin but not of Syk, while IL-1 beta message induction is unaffected. These observations indicate that the Syk tyrosine kinase may be an important component of an integrin signaling pathway in monocytic cells, leading to activation of NF-kappa B and to increased levels of cytokine messages.