Epidermal growth factor induces terminal differentiation in human epidermoid carcinoma cells

Engineered Fusion Proteins for Efficient Protein Secretion and Purification of a Human Growth Factor from the Green Microalga Chlamydomonas reinhardtii

Light-driven recombinant protein (RP) production in eukaryotic microalgae offers a sustainable alternative to other established cell-culture systems. RP production via secretion into the culture medium enables simple product separation from the cells adding a layer of process value in addition to the algal biomass, which can be separately harvested. For the model microalga Chlamydomonas reinhardtii, a broad range of molecular tools have been established to enable heterologous gene expression; however, low RP production levels and unreliable purification from secretion concepts have been reported. Domesticated C. reinhardtii strains used for genetic engineering are often cell-wall deficient. These strains nevertheless secrete cell-wall components such as insoluble (hydroxy)proline-rich glycoproteins into the culture media, which hinder downstream purification processes. Here, we attempted to overcome limitations in secretion titers and improve protein purification by combining fusion partners that enhance RP secretion and enable alternative aqueous two-phase (ATPS) RP extraction from the culture medium. Protein fusions were strategically designed to contain a stably folded peptide, which enhanced secretion capacities and gave insights into (some) regulatory mechanisms responsible for this process in the algal host. The elevated protein titers mediated by this fusion were then successfully applied in combination with a fungal hydrophobin tag, which enabled protein purification from the complex microalgal extracellular environment by ATPS, to yield functional recombinant human epidermal growth factor (hEGF) from the algal host.

Hypoxia activated EGFR signaling induces epithelial to mesenchymal transition (EMT)

Metastasis is a multi-step process which requires the conversion of polarized epithelial cells to mesenchymal cells, Epithelial–Mesenchymal Transition (EMT). EMT is essential during embryonic morphogenesis and has been implicated in the progression of primary tumors towards metastasis. Hypoxia is known to induce EMT; however the molecular mechanism is still poorly understood. Using the A431 epithelial cancer cell line, we show that cells grown under hypoxic conditions migrated faster than cells grown under normal oxygen environment. Cells grown under hypoxia showed reduced adhesion to the extracellular matrix (ECM) probably due to reduced number of Vinculin patches. Growth under hypoxic conditions also led to down regulation of E-cadherin and up regulation of vimentin expression. The increased motility of cells grown under hypoxia could be due to redistribution of Rac1 to the plasma membrane as opposed to increased expression of Rac1. EGF (Epidermal Growth Factor) is a known inducer of EMT and growth of A431 cells in the absence of oxygen led to increased expression of EGFR (EGF Receptor). Treatment of A431 cells with EGF led to reduced cell adhesion to ECM, increased cell motility and other EMT characteristics. Furthermore, this transition was blocked by the monoclonal antibody Cetuximab. Cetuximab also blocked the hypoxia-induced EMT suggesting that cell growth under hypoxic conditions led to activation of EGFR signaling and induction of EMT phenotype.

A switch role of Src in the biphasic EGF signaling of ER-negative breast cancer cells

It is well established that epidermal growth factor (EGF) is a potent mitogen in cells expressing EGF receptor (EGFR). However, a body of evidence indicated that the effects of mitogenic EGF signaling exhibit a non-monotonic, or biphasic dose response curve; EGF at low concentrations elicits a mitogenic signaling pathway to stimulate cell proliferation while at high concentrations, EGF inhibits cell growth. However, the molecular mechanism underlying this paradoxical effect of EGF on cell proliferation remains largely unknown. Here, we investigated the molecular mechanisms underlying the biphasic EGF signaling in ER-negative breast cancer MDA-MB-231 and MDA-MB-436 cells, both of which express endogenous EGFR. We found that EGF at low concentrations induced the phosphorylation of the Src-Y416 residue, an event to activate Src, while at high concentrations allowed Src-Y527 phosphorylation that inactivates Src. EGF at 10 ng/ml also induced phosphorylation of the MAPK/ERK and activated cyclin D1 promoter activity through the Src/EGFR/STAT5 pathways but not at a higher concentration (500 ng/ml). Our results thus demonstrated that Src functions as a switch of EGF signaling depending on concentrations of EGF.

Phosphoproteomic studies of receptor tyrosine kinases: future perspectives

In the last decade, large-scale mass spectrometry-based phosphoproteomic studies of receptor tyrosine kinases (RTKs) have generated a compendium of signalling networks that are activated downstream of these receptors. In this article, a brief summary of previous phosphoproteomic studies on epidermal growth factor receptor (EGFR) signalling will be presented together with a perspective on the importance for the field to keep pace with new advances in RTK biology. Using examples drawn primarily from studies on the EGFR, c-Met and Flt3 receptors, areas in RTK biology which will greatly benefit from the power of phosphoproteomics will be discussed, including (a) validating oncogenic RTK mutants identified in cancer genome sequencing efforts, (b) spatial RTK signalling networks and (c) understanding crosstalk and co-activation between members of the RTK superfamily.

The EP1 subtype of prostaglandin E2 receptor: role in keratinocyte differentiation and expression in non-melanoma skin cancer

We have previously demonstrated that the EP1 subtype of PGE2 receptor is expressed in the differentiated compartment of normal human epidermis and is coupled to intracellular calcium mobilization. We therefore hypothesized that the EP1 receptor is coupled to keratinocyte differentiation. In in vitro studies, radioligand binding, RT-PCR, immunoblot and receptor agonist-induced second messenger studies demonstrate that the EP1 receptor is up-regulated by high cell density in human keratinocytes and this up-regulation precedes corneocyte formation. Moreover, two different EP1 receptor antagonists, SC51322 and AH6809, both inhibited corneocyte formation. SC51322 also inhibited the induction of differentiation-specific proteins, cytokeratin K10 and epidermal transglutaminase. We next examined the immunolocalization of the EP1 receptor in non-melanoma skin cancer in humans. Well-differentiated SCCs exhibited significantly greater membrane staining, while spindle cell carcinomas and BCCs had significantly decreased membrane staining compared with normal epidermis. This data supports a role for the EP1 receptor in regulating keratinocyte differentiation.

ABINs inhibit EGF receptor-mediated NF-kappaB activation and growth of EGF receptor-overexpressing tumour cells

The epidermal growth factor receptor (EGFR) is frequently overexpressed in various tumours of epidermal origin and is held responsible for tumourigenicity and tumour persistence. Increased nuclear factor (NF)-kappaB activity has been suggested to be involved in the malignant behaviour of EGFR-overexpressing cells. However, the mechanisms that regulate EGF-induced NF-kappaB activation are still largely unknown. Here we show that EGF can induce NF-kappaB-dependent gene expression independently from IkappaBalpha degradation or p100 processing in EGFR-overexpressing HEK293T cells. Moreover, EGF-induced NF-kappaB activation could be inhibited by overexpression of ABINs, which were previously identified as intracellular inhibitors of tumour necrosis factor, interleukin-1 and lipopolysaccharide-induced NF-kappaB activation. Knockdown of ABIN-1 by RNA interference boosted the NF-kappaB response upon EGF stimulation. The C-terminal ubiquitin-binding domain containing region of ABINs was crucial and sufficient for NF-kappaB inhibition. Adenoviral gene transfer of ABINs reduced constitutive NF-kappaB activity as well as the proliferation of EGFR-overexpressing A431 and DU145 human carcinoma cells. Altogether, these results demonstrate an important role for an ABIN-sensitive non-classical NF-kappaB signalling pathway in the proliferation of EGFR-overexpressing tumour cells, and indicate a potential use for ABIN gene therapy in the treatment of cancer.

Cancer biology and hormesis: human tumor cell lines commonly display hormetic (biphasic) dose responses

This article assesses the nature of the dose-response relationship of human tumor cell lines with a wide range of agents including antineoplastics, toxic substances (i.e., environmental pollutants), nonneoplastic drugs, endogenous agonists, and phyto-compounds. Hormetic-like biphasic dose responses were commonly reported and demonstrated in 136 tumor cell lines from over 30 tissue types for over 120 different agents. Quantitative features of these hormetic dose responses were similar, regardless of tumor cell line or agent tested. That is, the magnitude of the responses was generally modest, with maximum stimulatory responses typically not greater than twice the control, while the width of the stimulatory concentration range was usually less than 100-fold. Particular attention was directed to possible molecular mechanisms of the biphasic nature of the dose response, as well as clinical implications in which a low concentration of chemotherapeutic agent may stimulate tumor cell proliferation. Finally, these findings further support the conclusion that hormetic dose responses are broadly generalizable, being independent of biological model, endpoint measured, and stressor agent, and represent a basic feature of biological responsiveness to chemical and physical stressors.

An immune reaction may be necessary for cancer development

Background

The hypothesis of immunosurveillance suggests that new neoplasms arise very frequently, but most are destroyed almost at their inception by an immune response. Its correctness has been debated for many years.

In its support, it has been shown that the incidences of many tumor types, though apparently not all, tend to be increased in immunodeficient animals or humans, but this observation does not end the debate.

Alternative model

There is an alternative to the surveillance hypothesis; numerous studies have shown that the effect of an immune reaction on a tumor is biphasic. For each tumor, there is some quantitatively low level of immune reaction that, relative to no reaction, is facilitating, perhaps even necessary for the tumor's growth in vivo. The optimum level of this facilitating reaction may often be less than the level of immunity that the tumor might engender in a normal subject.

Conclusion

The failure of a tumor to grow as well in the normal as it does in the immunosuppressed host is probably not caused by a lack of tumor-cell killing in the suppressed host. Instead, the higher level of immune response in a normal animal, even if it does not rise to tumor-inhibitory levels, probably gives less positive support to tumor growth. This seems more than a semantic distinction.

Tissue transglutaminase was up-regulated by EGF-retinoid interplay in epithelial carcinoma cells

Retinoids have been shown the most powerful inducers of transglutaminase activity, a well known marker of differentiation. In this work, we tested the effects of all-trans retinoic acid and EGF, used alone or in combination, on transglutaminase activity in a squamous, epithelial carcinoma cell line, HEp-2. We demonstrated that nanomolar EGF further enhances transglutaminase activity previously induced by all-trans retinoic acid. Confocal laser scanning microscopy revealed functional changes in transglutaminase activity localisation, at first restricted to the outermost region of cytosol, then diffused both in the membrane region and extracellular space. RT-PCR showed the presence of mRNA transcripts of different transglutaminases (1, 2, 3). Transglutaminase 2 expression was increased by either all-trans retinoic acid or EGF, and further up-regulated by the simultaneous addition of both substances. These effects were confirmed by Western blotting with transglutaminase 2 specific antibody. The results obtained by combined use of retinoic acid and EGF suggest that transglutaminase activity and expression are differently regulated, and that EGF-signalling can be involved in differentiation of epithelial carcinoma cells induced by retinoids.

Fatty acid synthase is required for the proliferation of human oral squamous carcinoma cells

Fatty acid synthase (FAS) is the enzyme responsible for the endogenous synthesis of saturated long-chain fatty acids from the precursors acetyl-CoA and malonyl-CoA. A growing body of evidence indicates that FAS is over expressed in several human cancers, such as prostate, breast, bladder, liver, lung, melanoma and oral squamous cell carcinoma (SCC). In the present study we used human oral SCC cell lines (SCC-4, -9, -15 and -25) as a model to investigate the role of FAS in the pathogenesis of oral cancer. RT-PCR and western blot experiments demonstrated that FAS is differentially expressed by the four oral SCC cell lines, with the highest production in SCC-9 followed by SCC-25. FAS expression in SCC-4 and -15 was similarly lower than the other cell lines. Proliferation curves and immunocytochemistry for PCNA and Ki-67 demonstrated that SCC-25 has the highest proliferative potential. In addition, the specific inhibitor of FAS activity cerulenin was able to significantly reduce the proliferation of oral SCC cells. Expression of androgen receptor was low in SCC-4, -9 and -15 and undetectable in SCC-25, whereas EGFR and c-erb-B2 were expressed in high amounts by the four cell lines. Immunocytochemical reactions showed that SCC-25 expresses higher levels of EGF compared to the other three cell lines. Finally, oral SCC cells exposed to nanomolar concentrations of exogenous EGF presented a reduction in the FAS protein levels concomitant with a decrease in their proliferation rates. Taken together, our results indicate that FAS is expressed in an apparently androgen-independent fashion in oral SCC cells and it is necessary for their proliferation.

Growth regulation of primary human keratinocytes by prostaglandin E receptor EP2 and EP3 subtypes

We examined the contribution of specific EP receptors in regulating cell growth. By RT-PCR and northern hybridization, adult human keratinocytes express mRNA for three PGE2 receptor subtypes associated with cAMP signaling (EP2, EP3, and small amounts of EP4). In actively growing, non-confluent primary keratinocyte cultures, the EP2 and EP4 selective agonists, 11-deoxy PGE1 and 1-OH PGE1, caused complete reversal of indomethacin-induced growth inhibition. The EP3/EP2 agonist (misoprostol), and the EP1/EP2 agonist (17-phenyl trinor PGE2), showed less activity. Similar results were obtained with agonist-induced cAMP formation. The ability of exogenous dibutyryl cAMP to completely reverse indomethacin-induced growth inhibition support the conclusion that growth stimulation occurs via an EP2 and/or EP4 receptor-adenylyl cyclase coupled response. In contrast, activation of EP3 receptors by sulprostone, which is virtually devoid of agonist activity at EP2 or EP4 receptors, inhibited bromodeoxyuridine uptake in indomethacin-treated cells up to 30%. Although human EP3 receptor variants have been shown in other cell types to markedly inhibit cAMP formation via a pertussis toxin sensitive mechanisms, EP3 receptor activation and presumably growth inhibition was independent of adenylyl cyclase, suggesting activation of other signaling pathways.