Effects of epidermal growth factor on transferrin receptor phosphorylation and surface expression in malignant epithelial cells

Rapid increase in transferrin receptor recycling promotes adhesion during T cell activation

Background

T cell activation leads to increased expression of the receptor for the iron transporter transferrin (TfR) to provide iron required for the cell differentiation and clonal expansion that takes place during the days after encounter with a cognate antigen. However, T cells mobilise TfR to their surface within minutes after activation, although the reason and mechanism driving this process remain unclear.

Results

Here we show that T cells transiently increase endocytic uptake and recycling of TfR upon activation, thereby boosting their capacity to import iron. We demonstrate that increased TfR recycling is powered by a fast endocytic sorting pathway relying on the membrane proteins flotillins, Rab5- and Rab11a-positive endosomes. Our data further reveal that iron import is required for a non-canonical signalling pathway involving the kinases Zap70 and PAK, which controls adhesion of the integrin LFA-1 and eventually leads to conjugation with antigen-presenting cells.

Conclusions

Altogether, our data suggest that T cells boost their iron importing capacity immediately upon activation to promote adhesion to antigen-presenting cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01386-0.

Transferrin Receptor Expression and Iron Uptake in the Injured and Regenerating Rat Sciatic Nerve

Iron-saturated transferrin is a ubiquitous growth factor that plays a critical role in cellular iron uptake, growth and proliferation. Here we have studied the expression and distribution of transferrin receptors and iron uptake following injury of the rat sciatic nerve. Axotomy led to a massive but transient increase (days 2 - 9, maximum day 4) in [125I]transferrin binding at the site of the injury and in the distal, denervated part of the crushed or resected sciatic nerve, shortly preceding the time course of cellular proliferation (Friede and Johnstone, Acta Neuropathol, 7, 218 - 231, 1967; Jurecka et al., Acta Neuropathol, 32, 299 - 312, 1975). An additional, transient increase in specific binding was observed during reinnervation after reconnection of the resected sciatic nerve. Immunocytochemistry using the Ox-26 monoclonal antibody revealed strong and simultaneous expression of the transferrin receptor protein on two different cell types: on a subpopulation of blood-borne macrophages invading the injured peripheral nerve and on Schwann cells reacting to denervation and reinnervation. In addition, studies using intravenously injected radioactive iron (59Fe3+) showed a massive increase in endoneural iron uptake confined to the lesion site and to the distal part of the axotomised sciatic nerve, parallel to the time course of reactive transferrin receptor expression. Since iron is an essential cofactor of a number of key enzymes needed in energy metabolism and DNA synthesis, these data suggest that the induction of transferrin receptor expression may play an important role in the regulation of cellular growth and proliferation during peripheral nerve regeneration.

The roles of iron in health and disease

Iron is vital for almost all living organisms by participating in a wide variety of metabolic processes, including oxygen transport, DNA synthesis, and electron transport. However, iron concentrations in body tissues must be tightly regulated because excessive iron leads to tissue damage, as a result of formation of free radicals. Disorders of iron metabolism are among the most common diseases of humans and encompass a broad spectrum of diseases with diverse clinical manifestations, ranging from anemia to iron overload and, possibly, to neurodegenerative diseases. The molecular understanding of iron regulation in the body is critical in identifying the underlying causes for each disease and in providing proper diagnosis and treatments. Recent advances in genetics, molecular biology and biochemistry of iron metabolism have assisted in elucidating the molecular mechanisms of iron homeostasis. The coordinate control of iron uptake and storage is tightly regulated by the feedback system of iron responsive element-containing gene products and iron regulatory proteins that modulate the expression levels of the genes involved in iron metabolism. Recent identification and characterization of the hemochromatosis protein HFE, the iron importer Nramp2, the iron exporter ferroportin1, and the second transferrin-binding and -transport protein transferrin receptor 2, have demonstrated their important roles in maintaining body's iron homeostasis. Functional studies of these gene products have expanded our knowledge at the molecular level about the pathways of iron metabolism and have provided valuable insight into the defects of iron metabolism disorders. In addition, a variety of animal models have implemented the identification of many genetic defects that lead to abnormal iron homeostasis and have provided crucial clinical information about the pathophysiology of iron disorders. In this review, we discuss the latest progress in studies of iron metabolism and our current understanding of the molecular mechanisms of iron absorption, transport, utilization, and storage. Finally, we will discuss the clinical presentations of iron metabolism disorders, including secondary iron disorders that are either associated with or the result of abnormal iron accumulation.

A novel method of cell-specific mRNA transfection

In this study, we developed a cell-specific mRNA transfection system using streptavidin-protein A (ST-PA) fusion protein and monoclonal antibodies (mAbs). We previously reported that ST-PA fusion protein and mAb complexes can transfer certain biotinylated proteins into specific cell types. At this time, we combined an in vitro transcribed biotinylated and self-replicating Sindbis virus genomic RNA with ST-PA fusion protein and mAbs. In the presence of cationic liposomes, to prevent RNA degradation, this complex is able to transfect a reporter gene to specific cancer cells in a mAb does-dependent manner. Even in the absence of cationic liposomes, biotinylated mRNA, ST-PA fusion, and mAb complexes can transfer some types of cancer cell suspension cultures. This cell-specific transfection system is a novel method of introducing various mRNAs into cells that results in high levels of transient protein expression.

Pathophysiology of glial growth factor receptors

Activation and proliferation of glial cells are common events in the pathology of the nervous system. Although we are only beginning to understand the molecular signals leading to glial activation in vivo, there is increasing evidence that growth factors and their receptors may play an important part. In this paper we summarize the data on the pathophysiology of glial growth factor receptors and their ligands in the central and peripheral nervous systems.

The influence of transferrin binding to L2C guinea pig leukemic lymphocytes on the endocytosis cycle kinetics of its receptor

The parameters regulating the internalization and recycling of transferrin-specific receptors were determined in guinea pig leukemic B lymphocytes, in the absence or presence of ligand. We show that after the cells were purified, 45-56% of the total receptors were on the cell surface. In the absence of transferrin, unoccupied receptors are quickly internalized (rate constant, 0.12 min-1) whereas their recycling is much slower (rate constant, 0.026 min-1). This difference between endocytosis and recycling rates leads to a balanced receptor distribution with only 22% of the total receptors outside after incubation of the cells for 20-30 min at 37 degrees C. The internalization rate of occupied receptors, measured in the presence of transferrin is faster (rate constant, 0.21 min-1) than that of unoccupied receptors calculated in the absence of transferrin (0.12 min-1; see above). On the other hand, mere binding of transferrin to its receptor, without internalization, arrested by cytoplasm acidification, is sufficient to induce a large increase (by a factor of seven) in the recycling rate of unoccupied internal receptors from 0.026 min-1 to 0.17 min-1. Thus, in these lymphocytes, transferrin mobilizes internal receptors by modifying the kinetic rates of internalization and recycling, leading to a new equilibrium between external and internal receptors.

Vanadate modulates the activity of a subpopulation of asialoglycoprotein receptors on isolated rat hepatocytes: active surface receptors are internalized and replaced by inactive receptors

In the absence of ligand, sodium vanadate causes a time- and dose-dependent loss of up to approximately 50% of the surface galactosyl receptor (GalR) activity in rat hepatocytes at 37 degrees C. The effect on total (surface plus intracellular) GalR activity is also dependent on exposure time and vanadate concentration. At less than 1 mM, vanadate induces a transient decrease and then partial recovery of cell surface GalR activity. At greater than 3 mM vanadate, surface GalR activity decreases rapidly (t1/2 approximately 2 min). Lost surface activity is initially recovered in digitonin-permeabilized cells, indicating that active surface GalRs redistribute to the cell interior. However, an antibody assay for GalR protein showed that although surface activity decreased, there was no decrease in surface receptor protein. The active intracellular GalRs then slowly inactivate over 30-60 min. With 8 mM vanadate, the loss of both surface and total cellular GalR activity is more rapid and coincident; no lag is observed. Maximal activity loss, however, was still only approximately 50%. Again, no net change was seen in the distribution of GalR protein between the cell surface and the interior. These results indicate that vanadate causes active GalRs to move from the surface to the inside and be replaced by inactive receptors moving from the inside to the cell surface. The Gal receptor system is comprised of two functionally different receptor subpopulations that operate via two distinct intracellular pathways. Only the State 2 GalRs, which recycle constitutively, are sensitive to modulation by vanadate. Consistent with this, vanadate inhibits the endocytosis of 125I-asialoorosomucoid (ASOR) only partially. The rate of uptake and the steady state level of ASOR intracellular accumulation were maximally inhibited by 50 and 70%, respectively, at 0.2 mM vanadate. The rate and extent of degradation of 125I-ASOR were also inhibited by 50-70%. Residual ASOR uptake and degradation is accounted for by the minor vanadate-resistant State 1 Gal receptor pathway.

An immunohistochemical assessment of cellular proliferation markers in head and neck squamous cell cancers

Prognostic information is essential for the evaluation, judgement and optimal treatment of patients with squamous cell cancers (SCCs) of the upper aerodigestive tract. Using immunohistochemical and flow cytometric techniques, we have studied the significance of cellular expression of the Ki-67 antigen, epidermal growth factor receptor (EGFR), the transferrin receptor (TFR) and DNA ploidy status in a prospective analysis of patients with SCCs of the head and neck region. All 42 fresh tumour samples (five well differentiated; 28 moderately differentiated; nine poorly differentiated) expressed both EGFR and TFR to varying degrees. Receptor expression was most marked on the peripheral invading margin of cancer cell islands although staining was also demonstrated in a random fashion within cellular islands and consistently along the basal cell layer of overlying stratified squamous epithelium. The percentage of cancer cells that reacted with the Ki-67 monoclonal antibody was assessed as low (less than 10%) in 15 samples (35.8%), intermediate (10-30%) in 19 samples (45.2%) and high (greater than 30%) in eight samples (19.0%). Eleven of 15 samples (73%) with a low percentage reactivity were DNA diploid, whereas seven of eight samples (87.5%) with a high percentage reactivity were DNA aneuploid. Poorly differentiated SCCs were significantly more often aneuploid than were either moderately or well differentiated tumours. Our results suggest that EGFR and TFR are widely distributed on SCCs, especially on proliferating cells at the invading tumour margin. In addition, there is a close spatial correlation between cells expressing EGFR, TFR and those expressing the Ki-67 antigen. Tumours in which the staining intensity for both EGFR and TFR was intense invariably expressed the Ki-67 antigen in a high proportion of cells. Further patient follow-up will be important in determining whether intense EGFR and TFR staining, combined with a high percentage reactivity with Ki-67 antibody and DNA aneuploidy, will ultimately define a subset of head and neck cancer patients with a poor clinical outcome.

Characterization of the synergistic effect of insulin and transferrin and the regulation of their receptors on a human colon carcinoma cell line

The human colon carcinoma cell line, HCT 116, can be grown in chemically defined media in the absence of exogenous growth factors. The addition of transferrin and insulin will significantly stimulate growth. The interaction of these growth factors with their receptors was studied to determine whether the synergistic action of insulin and transferrin on growth involved alterations in the growth-factor receptors. Redistribution of the transferrin receptor occurred in the presence of transferrin or transferrin plus insulin. The presence of insulin in the growth media resulted in occupation of cell-surface insulin receptors without a reduction in total insulin binding. Addition of transferrin with insulin resulted in a decrease in insulin binding to its receptor, with no alteration in receptor affinity. It appears that transferrin plays a role in regulating the insulin receptor and that this may contribute to the synergistic effect of insulin and transferrin on growth.

Increase of transferrin receptors and iron uptake in regenerating motor neurons

After injury, motor neurons exhibit a number of metabolic and protein changes that are assumed to be part of an inherent neuronal regeneration program, which, when activated, eventually leads to functional restitution. The mechanisms underlying this regeneration are unclear, but it may be expected that factors supporting neuronal growth or survival play an important role in the restoration of neuronal integrity. A number of neuronal growth-associated proteins have been identified, but their functional roles remain unclear. This paper shows that axotomy results in a strong increase in transferrin receptors (TfRs) in regenerating motor neurons and that this phenomenon is functionally associated with an elevated uptake of exogenous iron. The association of TfR expression in regenerating motor neurons with direct uptake of iron into the brain provides evidence that iron uptake into neural tissue may be related to neuronal metabolic activation. We suggest that the enhanced capacity of regenerating motor neurons to bind transferrin and to take up iron plays an important role in neuronal repair.

Induction of c-fos by an anti-epidermal growth factor receptor monoclonal antibody

The effect of epidermal growth factor (EGF) or a monoclonal antibody to the human EGF receptor on c-fos and c-myc gene expression was examined in KB epidermoid carcinoma cells. EGF increased c-fos transcripts within 30 min and c-myc transcripts within 6-24 hours. The antibody transiently increased c-fos expression within 30 minutes, but did not alter expression of c-myc. Cycloheximide potentiated the c-fos induction by both EGF and antibody. C-fos induction by antibody was less consistent, and was of briefer duration and lesser intensity than the induction by EGF. Nuclear transcription of c-fos decreased in cells treated with EGF or antibody, indicating that c-fos induction by EGF or antibody resulted from post-transcriptional mechanisms.