Substrate-dependent effect of epidermal growth factor on intercellular adhesion and synthesis of triton-insoluble proteins in human carcinoma A431 cells

Chemoattractant-induced lamellipod extension

The mammary adenocarcinoma cell line MTLn3 is chemotactic towards epidermal growth factor (EGF), and this induced motility is thought to promote breast cancer invasion and metastasis. Stimulation of MTLn3 cells with EGF results in the extension of a flat, thin structure filled with filamentous actin and termed a lamellipod. Lamellipod extension is dependent on actin polymerization and is localized to the border of adherent cells. The structure of EGF-stimulated lamellipods in MTLn3 cells is well suited to analysis of chemoattractant-stimulated protrusion. Actin polymerization occurs within 200 nm of the extending edge of the lamellipod. Although extension of the lamellipod is not dependent upon interaction with the substratum, stabilization of the extended lamellipod is dependent on an adhesive substratum. Dorsal ruffling is suppressed during lamellipod extension. Tyrosine phosphorylation is reduced in preexisting focal contacts compared to new contacts induced by EGF stimulation. The coordination of turnover of focal contacts with lamellipod extension is proposed to result in polarized cell motility in response to gradients of chemoattractants.

Effects of 1,25-dihydroxyvitamin D3 on transformed C3H/10T1/2 fibroblasts grown as multicellular spheroids

We have previously shown that 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) is able to modulate proliferation of C3H/10T1/2 fibroblasts grown in monolayer cell culture. The aim of this study was to investigate the effects of the hormone in a 3-dimensional culture system, which is considered to better reflect the cellular environment that is found in vivo. Two transformed cell lines of C3H/10T1/2 fibroblasts (C116 and TPA 482) were grown as multicellular spheroids, whereas the nontumorigenic C3H/10T1/2 C18 cells failed to form spheroids. The hormone had no effect on spheroids made of TPA 482 cells but had a biphasic effect on C116 spheroid growth with stimulation at low and inhibition at higher concentrations. In C116 spheroids, 10(-8) M 1,25-(OH)2D3 induced complete arrest of spheroid growth. Light and electron microscopic studies and immunocytochemistry showed that 10(-8) M 1,25-(OH)2D3 induced morphological changes in C116 spheroids, with a marked reduction in expression of fibronectin, laminin and the gap junction protein connexin 43. These effects were followed by a loosening of the spheroid structure, detachment of viable cells, and finally disaggregation of the spheroids. The results of this study, together with the data previously obtained in monolayer cell cultures, indicate that the effects of 1,25-(OH)2D3 may be conditioned by the cellular environment. Therefore, the spheroid model is an interesting tool for investigation of the antineoplastic effect of the hormone.

EGF receptor in neoplasia and metastasis

EGFR is a member of the tyrosine kinase family of cell surface receptors with a wide range of expression throughout development and in a variety of different cell types. The receptor can transmit signals to cells: i) upon interaction with ligands such as EGF, TGF alpha, amphiregulin or heparin binding EGF, ii) upon truncation or mutation of extracellular and/or intracellular domains, iii) upon amplification of a basal receptor activity (in the absence of ligand) through cooperation with other cellular signaling pathways or nuclear events (e.g. expression of v-erbA). The activated EGFR can exert pleiotropic functions on cells, depending on their tissue origin and state of differentiation. Under certain conditions it can also contribute to neoplasia and development of metastases. Such conditions can exist upon aberrant receptor/ligand expression and activation (e.g. in the wrong cell; at the wrong time; in the wrong amounts). Aberrant signalling can also occur through constitutive EGFR activation. Oncogenic potential of EGFR has been demonstrated in a wide range of experimental animals. EGFR is also implicated in human cancer, where it may contribute both to the initiation (glioblastoma) and progression (epithelial tumors) of the disease. EGFR may influence key steps in the processes of tumor invasion and dissemination. Involvement of EGFR in tumor spread may indicate a potential use of this receptor as a target for antimetastatic therapy.

Modulation of KB and A431 cell adhesion by epidermal growth inhibitory pentapeptide

A pentapaptide, pyroGlu-Glu-Asp-Ser-GlyOH (EPP), isolated from mouse epidermis, inhibits mitoses and enhances differentiation in primary cultures and in transformed mouse epidermal cells in vitro (Elgjo et al. 1986 b). The present work demonstrates that EPP also modulates the adhesiveness of two human tumour cell lines (KB and A431) of epidermal origin to uncoated plastic and to plastic coated with fibrinogen or collagen type 1. The adhesion modulatory effect of EPP was observed over a broad range of concentrations (10(-12)-10(-6) M), and depended on the substrate the cells were growing on. Thus, when cells were seeded on plastic or collagen, the attachment to the substrate was suppressed at the highest concentrations of EPP, and stimulated at the lowest ones. The opposite concentration-response pattern was observed when fibrinogen was used as substrate.

Cell and environment interactions in tumor microregions: the multicell spheroid model

Abnormal vascularization of malignant tumors is associated with the development of microregions of heterogeneous cells and environments. Experimental models such as multicell spheroids and a variety of new techniques are being used to determine the characteristics of these microregions and to study the interactions of the cells and microenvironments. The special cellular microecology of tumors influences responsiveness to therapeutic agents and has implications for future directions in cancer research.

120 and 80 kd detergent-insoluble glycoproteins as markers of differentiation and adhesion in B16 melanoma

Surface glycoproteins correlating with cell adhesion and differentiation have now been studied in pigmented and amelanotic B16 melanoma cell monolayers and aggregates, labelled with 3H-glucosamine. Solubilization with the non-ionic detergent octyl glucoside revealed mostly adhesion-related changes, which involved a decrease in 140 and 110 kd glycoproteins in both pigmented and amelanotic cell aggregates. Nevertheless, differentiation-regulated changes were preferentially evident in the remaining detergent-insoluble glycoproteins. Pigmented cell monolayers showed a preferential increase in glycoprotein species of about 120 kd and 80 kd, which were not detected in amelanotic monolayers or in pigmented or amelanotic cell aggregates. Our findings suggest the relevance of these cytoskeleton associated glycoproteins as markers of differentiation and adhesion in melanoma cells.