Calmodulin antagonists decrease the binding of epidermal growth factor to transformed, but not to normal, human fibroblasts

Calmodulin-mediated regulation of the epidermal growth factor receptor

In this review, we first describe the mechanisms by which the epidermal growth factor receptor generates a Ca(2+) signal and, subsequently, we compile the available experimental evidence regarding the role that the Ca(2+)/calmodulin complex, formed after the rise in cytosolic free Ca(2+) concentration, exerts on the receptor. We focus not only on the indirect action that Ca(2+)/calmodulin exerts on the epidermal growth factor receptor, as a result of the activation of distinct calmodulin-dependent kinases, but also, and more extensively, on the direct interaction of Ca(2+)/calmodulin with the receptor. We also describe several mechanistic models that could account for the Ca(2+)/calmodulin-mediated regulation of epidermal growth factor receptor activity. The control exerted by calmodulin on distinct epidermal growth factor receptor-mediated cellular functions is also discussed. Finally, the phosphorylation of this Ca(2+) sensor by the epidermal growth factor receptor is highlighted.

Tritiated thymidine and bromodeoxyuridine double-labelling studies on growth factors and oral epithelial proliferation in the mouse

Mouse tongue epithelium is characterized by a circadian variation in the number of cells undergoing DNA synthesis. Groups of male BDF1 mice were followed over 48 h and a double-labelling method with tritiated thymidine and bromodeoxyuridine used to determine S-phase labelling indices, together with cell influx to and cell efflux from S, at 4-hourly time points. Control animals exhibited diurnal peaks in labelling index at 03:00 with trough activity 12 h later at 15:00. Cell influx peaked at 23:00 with troughs occurring between 11:00 to 15:00. Peak cell efflux occurred at 07:00 with trough activity at 19:00. Animals injected with epidermal growth factor at 05:00 demonstrated a significant fall in both influx and efflux throughout the 48-h period (P < 0.001), but with preservation of labelling indices, suggesting a slower transit of cells through S-phase, whereas epidermal growth factor injected at 15:00 only produced a significant rise in cell-efflux values. Adrenergic stimulation by intravenous phenylephrine/isoprenaline injection at both 05:00 and 15:00 resulted in a significant rise in cell efflux (P < 0.001), although there was also a rise in labelling index in the 15:00 group (P < 0.001). Animals injected with calmodulin at 05:00 demonstrated a significant reduction in labelling index throughout the 48-h period (P < 0.001), but maintained control values for cell influx and efflux, suggesting faster transit of cells through S. Calmodulin injection at 15:00 produced only a significant reduction in cell influx (P < 0.001). Administration of exogenous growth factors significantly alters the normal rhythmical proliferation of oral epithelial cells in a mouse model. These effects appear to be both growth factor- and time-dependent, and may have both physiological and pathological implications.

Mitogenic role for extracellular calmodulin-like activity in normal human umbilical vein endothelial cells

Normal human umbilical vein endothelial cells cultured on gelatin-coated plastic dishes were found to produce a protein in their media which had calmodulin-like immunoreactivity and biological activity. Further identification of the protein was achieved by examining the incorporation of 14C leucine into protein found in the conditioned medium. Cells produced 14C labelled protein in their medium which specifically bound to an affinity column for calmodulin. This latter material stimulated calmodulin dependent phosphodiesterase activity in vitro and this stimulation was inhibited by the addition of the calmodulin antagonist W7. The presence of calmodulin-like activity and immunoreactivity in the media varied as the cells grew from low to high density, a peak of extracellular calmodulin-like activity preceding an increase in cell number. Extracellular calmodulin-like activity did not correlate with the presence of lactate dehydrogenase in the medium. The addition of pure pig brain calmodulin affected the rate of cell proliferation; significant proliferation to pure calmodulin was only seen in cells at low density, at higher density calmodulin either had no effect or inhibited proliferation. Inhibition of extracellular calmodulin activity by a calmodulin antagonist immobilized on agarose beads, or by an antibody to calmodulin significantly decreased proliferation in all dividing cultures. Taken together this data suggests that, in vitro, calmodulin, or a very closely related protein, influences endothelial cell proliferation through an autocrine mechanism.

Inhibition of human ovarian cancer cell proliferation by calmodulin inhibitors and the possible mechanism

Direct inhibitory effects of calmodulin inhibitors on human ovarian cancer cell proliferation in vitro were examined. All calmodulin inhibitors used in this study inhibited proliferation of HR cells derived from human serous cystadenocarcinoma of the ovary in a dose-dependent manner. The degree of inhibition by melittin and W-5 was most marked and was followed by that of W-7, R24571, and bepridil. HR cell proliferation was dose-dependently stimulated by epidermal growth factor (EGF). The stimulatory effects seemed to be a result of the binding of EGF to HR cells. Binding of EGF was significantly inhibited by W-5, R24571, and melittin. These results suggest that inhibition by calmodulin inhibitors of cancer cell proliferation may result in part from the interference in the binding of EGF to the cells.

An extracellular role for calmodulin-like activity in cell proliferation

1. Addition of extracellular pure pig brain calmodulin was found to modulate DNA synthesis and cell proliferation in K562 human leukaemic lymphocytes. At lower cell densities calmodulin significantly stimulated [3H]thymidine uptake; at higher densities it decreased it. 2. A protein biochemically indistinguishable from calmodulin was detected in the cell-conditioned media of rapidly dividing K562 cells. The concentration of calmodulin-like activity found in the conditioned media of these and a range of other normal and neoplastic cells (250-1636 ng/ml) was of the same order as would stimulate DNA synthesis in subconfluent cells. 3. Amounts of extracellular calmodulin-like activity and immunoreactivity varied during cell growth from low to high density, a peak of extracellular calmodulin preceding DNA synthesis in synchronized K562 cells. Extracellular calmodulin concentrations did not correlate with the presence of lactate dehydrogenase in the medium. 4. Inhibition of extracellular calmodulin activity by calmodulin antagonist immobilized on agarose beads, or by antibody to calmodulin, significantly decreased DNA synthesis. 5. These data strongly suggest that calmodulin or a very closely related protein can influence mitosis through an extracellular mechanism.

Effects of phenothiazines on binding and processing of epidermal growth factor in 3T3 cells

Chlorpromazine (CPZ) or the functionally related N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide caused a rapid decrease in binding of 125I-epidermal growth factor (EGF) that was due to a specific decrease in receptor affinity. The decrease in ligand binding was observed when cells were exposed to CPZ at either 4 degrees C or 37 degrees C but a rapid reversal of CPZs effects was observed only during a 37 degrees C incubation. In contrast to the decrease in 125I-EGF binding seen after short (30 min) accumulations at 37 degrees C, the presence of CPZ caused a large increase in the amount of cell-associated radioactivity after longer periods (over 1 h) of accumulation. Although the CPZ-induced effect was similar in extent to that observed after the addition of methylamine, the increased accumulation after CPZ was probably not due to a nonspecific ionic neutralization of the lysosomes. CPZ did not lower EGF binding in cultures chronically treated with a phorbol ester to reduce protein kinase C levels, although the CPZ-induced increases in accumulation were still observed in cells with reduced protein kinase C activity.

Effects of putative calmodulin antagonists on the binding of [3H]opioid ligands to rat brain membranes: possible involvement of the change in the membrane fluidity

The effects of putative calmodulin antagonists on the binding of [3H]opioid ligands to rat brain membranes were examined. Chlorpromazine, trifluoperazine, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) and N2-dansyl-L-arginine-4-t-butylpiperidine amide (TI 233, No. 233) inhibited the binding of [3H] [D-Ala2, Met5]enkephalinamide ([3H]DALAMID) in a dose-dependent manner, and this inhibition was not necessarily specific for Ca2+. The order of the inhibitory potency on the binding of [3H]DALAMID was chlorpromazine. W-7, TI 233 and trifluoperazine. From the Scatchard plots, the effects of these compounds on the binding of [3H]DALAMID were biphasic. Low concentrations of calmodulin antagonists caused a small but significant increase in the maximal binding (Bmax), but upon a further increase of the concentration, a significant decrease in Bmax was observable; the apparent dissociation constant for the ligand-receptor complexes increased with the increase in the concentration of calmodulin antagonists. TI 233 (1-30 X 10(-6) M) inhibited, somewhat in a ligand selective manner, the binding of [3H]opioid ligands that have been thought to be selective for opioid receptor types. Calmodulin antagonists caused to increase in the fluorescence anisotropy obtained from 1,6-diphenyl-1,3,5-hexatriene-labeled membrane fractions from rat brains, indicating that these compounds were effective for the decrease in the membrane fluidity. The present results indicate that putative calmodulin antagonists can affect the binding of the opioid ligands to rat brain membranes, probably through a mechanism other than one involving calmodulin-related processes.

Calmodulin antagonists stimulate LDL receptor synthesis in human skin fibroblasts

The LDL receptor synthesis of human skin fibroblasts in the presence of the specific calmodulin antagonists trifluoperazine, condensation product of N-methyl-p-methoxyphenethylamine with formaldehyde (compound 48/80) and N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide) (W-7) was studied. Labelling of cells with [35S]methionine followed by immunoprecipitation of radioactive LDL receptor protein with monospecific antibodies revealed that calmodulin antagonists caused a 3-fold increase in the radioactivity of the LDL receptor protein as compared with values found in control cells. A corresponding increase of high-affinity binding and internalization of 125I-labelled LDL was observed. The drugs did not influence the overall protein synthesis or the half-life of the LDL receptor. A concomitant suppression of cholesterol synthesis from [14C]mevalonolactone was found to be an independent effect. The calmodulin antagonist-produced stimulation of LDL receptor synthesis could not be simulated by preincubation of cells with cyclic nucleotide analogues, cholera toxin or 3-isobutyl-1-methylxanthine, known as specific effectors of adenylate cyclase and cyclic nucleotide phosphodiesterase, respectively. Modulation of calcium concentration in the incubation medium had no reproducible effect on the rate of LDL receptor synthesis. The results implicate calmodulin as an intracellular suppressor of LDL receptor synthesis in human skin fibroblasts.

Functional and structural characteristics of EGF and its receptor and their relationship to transforming proteins

Epidermal growth factor (EGF) is a peptide which effects the growth and/or differentiated functions of many cell types. Several pieces of evidence indicate that EGF and its receptor may play a role in carcinogenesis. Functional and structural characteristics of EGF and its receptor and their relationship to transforming proteins are discussed. EGF has extensive homology with alpha-transforming growth factor (alpha-TGF), which may actually be an embryonic form of EGF. Nevertheless, both EGF and alpha-TGF elicit transformation-associated phenotypes in target cells under certain conditions. EGF effects are mediated by a receptor present on the plasma membrane. The EGF receptor is a highly complex protein having several functions in addition to binding EGF in a highly specific manner. One of these functions is to phosphorylate tyrosyl residues on certain proteins. This activity is similar to that expressed by the src family of oncogene-encoded proteins. Besides sharing functional homology the EGF receptor also exhibits structural homology to several oncogene-encoded proteins. The v-erb-B-transforming protein has a striking extent of homology (95%) to the cytoplasmic portion of the EGF receptor. These data support the concept that some aspect of EGF-stimulated metabolism is involved in cellular transformation.