Antimitogenic actions of lectins in cultured human fibroblasts

Abstract

It was previously reported that the lectins wheat germ agglutinin (WGA) and concanavalin A (Con A) inhibit the mitogenic actions of multiple peptide growth factors in human fibroblasts without having a significant effect on mitogen binding. The current studies were designed to further examine the mechanisms of this antimitogenic action of lectins. Addition of WGA at progressively later times after stimulation of fibroblasts with peptide mitogens revealed significant inhibition of DNA synthesis even when the lectin was added 16-20 h after growth factors. This suggests an inhibitory effect on a pathway occurring late in G1, or close to the G1/S boundary. WGA also inhibited stimulation of DNA synthesis by non-peptide agents such as colchicine and vanadate ion, indicating that the lectin inhibits a common distal step in the mitogenic response, rather than acting primarily on events occurring at the level of the growth factor-receptor interaction. WGA had a rapid (within 30 min) inhibitory effect on insulin-stimulated amino acid uptake, but Con A, which like WGA blocked mitogen-stimulated 3H-dT incorporation, had little effect on stimulation of amino acid uptake. Thus the inhibition of DNA synthesis and amino acid uptake by lectins appear to be mediated by distinct mechanisms. WGA binding to fibroblasts persisted even when the lectin was removed from the incubation medium, but unlike 125I-EGF, which was rapidly internalized at 24 degrees C, little 125I-WGA was internalized. Incubation of fibroblasts for 20 h with WGA or Con A was not toxic to cells, since reversal of lectin binding by the appropriate saccharide allowed normal subsequent stimulation of DNA synthesis by EGF and insulin. However, the observation that cells exposed to antimitogenic lectins undergo a marked decrease in cell spreading suggests that changes in cell shape may be relevant to the mechanism by which lectin-treated fibroblasts become unresponsive to mitogenic stimulation.

G Protein-coupled Receptors Desensitize and Down-regulate Epidermal Growth Factor Receptors in Renal Mesangial Cells

“…The proteolytic effect of ConA on EGFR does not universally attenuate EGFR functions, however. In NIH3T3 cells, ConA does not affect EGFR functions such as EGF binding or proximal signals like the activation of phospholipase C-␥ or sodium-proton exchange activity (80,81).…”

Inhibition of AT1 Receptor Internalization by Concanavalin A Blocks Angiotensin II-induced ERK Activation in Vascular Smooth Muscle Cells

“…ConA polyclonally activates T cells (47). On the other hand, ConA inhibits internalization of EGF receptor and the receptor-mediated mitogenic effects without affecting EGF binding and EGF-stimulated changes in pH, calcium, and levels of inositol phosphates in NIH 3T3 cells (48,49 (36 -39). These sites bind a variety of downstream signaling proteins that contain Src homology 2 domains, including Shc (40) and phospholipase C␥ (41), thus leading to ERK activation.…”

“…Subcultured VSMC from passages 3 through 15 were used in the experiments. Subconfluent VSMC were serum-starved in plain medium for 48 (21). Determination of receptor affinity and density and measurement of the surface receptor binding capacity were performed as described previously (19).…”

Effects of plant lectins on in vitro fibroblast proliferation

“…Other lectins tested did not cause lysosome accumulation (Poretz et al, 1980). Carpenter and Stanley (1977), Kaplowitz (1985) and Kaplowitz and Haar (1988) tested the ability of lectins to provoke a cell response that has normally been generated by the interaction of epidermal growth factor (EGF) with human fibroblasts. WGA and concanavalin A (Con A) had little effect on 3H-dT incorporation in cultures of quiescent and confluent fibroblast.…”