Sialidase Attenuates Epidermal Growth Factor Response and Abolishes Antiproliferative Effects of Erlotinib in A549Alveolar Epithelial Cells.

Erlotinib is a widely used, reversible tyrosine kinase inhibitor (TKI), targeting pro-proliferative signaling of epidermal growth factor receptor (EGFR). The drug is approved for the first-line treatment of patients with metastatic non-small cell lung cancer with EGFR mutations. Extracellular glycans can affect EGFR expression, dimerization, phosphorylation, and EGF binding. In this study we investigated the effects of EGF and erlotinib on the cell cycle of naive and sialidase (alpha-neuraminidase)-pretreated human A549 alveolar epithelial cells. A549 cells were labeled with propidium iodide, and fractions of cells in different phases of cycle were quantified by flow cytometry. We found that neither did desialilation nor EGF, as well as erlotinib treatment, increase the number of damaged cells (subG0/G1 cell fraction), while erlotinib did significantly increase the number of G0/G1 cells and decrease S + G2/M cell fractions. In naive cells, EGF increased proliferating cell numbers by more than 40%, and this effect was blocked by erlotinib. In desialylated cells, however, proliferation was significantly decreased by about 29%, and EGF and erlotinib did not exert significant effects. We conclude that changes in alveolar epithelial cell membrane glycosylation may affect function of growth-promoting receptors and erlotinib effectiveness.

Exciting new advances in neuro-oncology: the avenue to a cure for malignant glioma.

Malignant gliomas are the most common and deadly brain tumors. Nevertheless, survival for patients with glioblastoma, the most aggressive glioma, although individually variable, has improved from an average of 10 months to 14 months after diagnosis in the last 5 years due to improvements in the standard of care. Radiotherapy has been of key importance to the treatment of these lesions for decades, and the ability to focus the beam and tailor it to the irregular contours of brain tumors and minimize the dose to nearby critical structures with intensity-modulated or image-guided techniques has improved greatly. Temozolomide, an alkylating agent with simple oral administration and a favorable toxicity profile, is used in conjunction with and after radiotherapy. Newer surgical techniques, such as fluorescence-guided resection and neuroendoscopic approaches, have become important in the management of malignant gliomas. Furthermore, new discoveries are being made in basic and translational research, which are likely to improve this situation further in the next 10 years. These include agents that block 1 or more of the disordered tumor proliferation signaling pathways, and that overcome resistance to already existing treatments. Targeted therapies such as antiangiogenic therapy with antivascular endothelial growth factor antibodies (bevacizumab) are finding their way into clinical practice. Large-scale research efforts are ongoing to provide a comprehensive understanding of all the genetic alterations and gene expression changes underlying glioma formation. These have already refined the classification of glioblastoma into 4 distinct molecular entities that may lead to different treatment regimens. The role of cancer stem-like cells is another area of active investigation. There is definite hope that by 2020, new cocktails of drugs will be available to target the key molecular pathways involved in gliomas and reduce their mortality and morbidity, a positive development for patients, their families, and medical professionals alike.

[Effects of Hedyotis diffusa Extract on Epidermal Growth Factor Induced Proliferation, Apoptosis, and TNF-α Induced Inflammatory Factors of HaCaT Cells].

Objective To observe the effects of Hedyotis diffusa extract (HDE) on the prolifera- tion, apoptosis, and inflammatory factors of HaCaT cells, and to explore its possible molecular mecha- nisms. Methods HaCaT cells were divided into 3 groups, the vehicle group, the control group, and 3 dose HDE groups. No epidermal growth factor (EGF) or HDE was added in the vehicle group. EGF was added with no HDE treatment in the control group. HDE (25, 50, 100 mg/mL) and EGF were added in the 3 HDE groups to co-culture HaCaT cells. The effects of HDE on EGF-induced proliferation of HaCaT cells were de- tected using CCK-8 assay. The effects of HDE on the growth cycle and apoptosis rate of HaCaT cells were measured using flow cytometry. Moreover, protein expression levels of Ki67, Bcl-xL, clAP1 , procaspase- 3, and cleaved caspase-3 were determined using Western blot. In addition, levels of IL-6, IL-8, and IL-10 in the supernatant were detected using ELISA. The level of phosphoration of NF-κB p65 (p-p65) was meas- ured using Western blot. Results Compared with the vehicle group, the absorbance of HaCaT cells and the expression level of Ki67 increased (P <0. 05, P <0. 01) ; levels of p-p65, IL-6, and IL-8 were elevated (P <0. 05, P <0. 01); IL-10 level was lowered (P <0.01) in the control group. Compared with the control group, the absorbance of HaCaT cells and the expression level of Ki67 decreased (P <0.05, P <0.01) ; levels of p-p65, IL-6, and IL-8 were reduced (P <0. 05, P <0. 01); IL-10 level was elevated (P <0. 05, P < 0.01) in the 3 dose HDE groups. Meanwhile, the apoptosis rate of HaCaT cells increased more in the 3 dose HDE groups than in the control group (P <0. 05, P <0. 01). The percentage of HaCaT cells at G1 phase was 58. 51 %, 73.12%, and 79. 95% in 25, 50, and 100 mg/mL HDE groups, respectively, showing statisti- cal difference when compared with that in the control group (52. 85%; P <0. 05, P <0. 01). The percentage and apoptosis rate of HaCaT cells at G1 phase were elevated more in 50 and 100 mg/mL HDE groups than in 25 mg/mL HDE group (P <0. 01). Besides, the percentage and apoptosis rate of HaCaT cells at G1 phase were elevated more in 100 mg/mL HDE group than in 50 mg/mL HDE group (P <0. 05). Compared with the control group, protein expression levels of Bcl-xL and cIAP1 were reduced in 100 mg/mL HDE group (P < 0. 01). There was no statistical difference in caspase-3 total amount (P >0. 05), but cleaved caspase-3 ex- pression increased with statistical difference (P <0. 01). Conclusion HDE inhibited the proliferation of HaCaT cells possibly by arresting HaCaT cell growth at G1 phase, promoted the apoptosis of HaCaT cells by stressing protein expressions of Bcl-xL and cIAPI , and elevating protein expressions of cleaved caspase-3, and suppressed inflammatory response of HaCaT cells via regulating NF-κB expression.

Tl(I) and Tl(III) alter the expression of EGF-dependent signals and cyclins required for pheochromocytoma (PC12) cell-cycle resumption and progression.

The effects of thallium [Tl(I) and Tl(III)] on the PC12 cell cycle were evaluated without (EGF(-)) or with (EGF(+)) media supplementation with epidermal growth factor (EGF). The following markers of cell-cycle phases were analyzed: cyclin D1 (G1 ); E2F-1, cyclin E and cytosolic p21 (G1 →S transition); nuclear PCNA and cyclin A (S); and cyclin B1 (G2). The amount of cells in each phase and the activation of the signaling cascade triggered by EGF were also analyzed. Tl(I) and Tl(III) (5-100 µM) caused dissimilar effects on PC12 cell proliferation. In EGF(-) cells, Tl(I) increased the expression of G1 →S transition markers and nuclear PCNA, without affecting cyclin A or cyclin B1. In addition to those, cyclin B1 was also increased in EGF(+) cells. In EGF(-) cells, Tl(III) increased the expression of cyclin D1, all the G1→S and S phase markers and cyclin B1. In EGF(+) cells, Tl(III) increased cyclin D1 expression and decreased all the markers of G1 →S transition and the S phase. Even when these cations did not induce the activation of EGF receptor (EGFR) in EGF(-) cells, they promoted the phosphorylation of ERK1/2 and Akt. In the presence of EGF, the cations anticipated EGFR phosphorylation without affecting the kinetics of EGF-dependent ERK1/2 and Akt phosphorylation. Altogether, results indicate that Tl(I) promoted cell proliferation in both EGF(-) and EGF(+) cells. In contrast, Tl(III) promoted the proliferation of EGF(-) cells but delayed it in EGF(+) cells, which may be related to the toxic effects of this cation in PC12 cells.

Epiregulin is critical for the acinar cell regeneration of the submandibular gland in a mouse duct ligation model.

Acinar cell regeneration from tubular structures has been reported to occur in duct-deligated salivary glands. However, the detailed process of acinar cell regeneration has not been clarified. We have developed a mouse duct ligation model to clarify the mechanisms underlying acinar cell regeneration, and we analyzed the epidermal growth factor receptor (EGFR) and epidermal growth factor (EGF) ligands using the model. We studied these ligands expressions in the course of acinar cell regeneration using immunohistochemistry and RT-PCR methods. In the duct-ligated portion of the submandibular gland (SMG) that underwent atrophy, newly formed acinar cells were observed arising from the tubular structures after the release of the duct obstruction. The constitutive expression of EGFR was observed by immunohistochemistry in both the duct-ligated and duct-deligated animals as well as in normal controls. The EGFR phosphorylation detected on the tubular structures after duct ligation paralleled the acinar cell regeneration. RT-PCR showed an increase in the epiregulin and heparin-binding EGF levels from day 0 to day 3 after the release of the duct obstruction. The EGF level was increased only after day 7. In vitro, cultured cells isolated from ligated SMGs proliferated and produced EGF ligands following the addition of epiregulin to the culture medium. These findings suggest that the tubular structures localized in an atrophic gland are the source of acinar cell regeneration of the salivary gland. The induction of EGF ligands, in particular epiregulin, may play an important role in acinar cell regeneration in this model.

Protective effects of N-acetylcysteine on acetic acid-induced colitis in a porcine model.

BACKGROUND: Ulcerative colitis is a chronic inflammatory disease and involves multiple etiological factors. Acetic acid (AA)-induced colitis is a reproducible and simple model, sharing many characteristics with human colitis. N-acetylcysteine (NAC) has been widely used as an antioxidant in vivo and in vitro. NAC can affect several signaling pathways involving in apoptosis, angiogenesis, cell growth and arrest, redox-regulated gene expression, and inflammatory response. Therefore, NAC may not only protect against the direct injurious effects of oxidants, but also beneficially alter inflammatory events in colitis. This study was conducted to investigate whether NAC could alleviate the AA-induced colitis in a porcine model. METHODS: Weaned piglets were used to investigate the effects of NAC on AA-induced colitis. Severity of colitis was evaluated by colon histomorphology measurements, histopathology scores, tissue myeloperoxidase activity, as well as concentrations of malondialdehyde and pro-inflammatory mediators in the plasma and colon. The protective role of NAC was assessed by measurements of antioxidant status, growth modulator, cell apoptosis, and tight junction proteins. Abundances of caspase-3 and claudin-1 proteins in colonic mucosae were determined by the Western blot method. Epidermal growth factor receptor, amphiregulin, tumor necrosis factor-alpha (TNF-α), and toll-like receptor 4 (TLR4) mRNA levels in colonic mucosae were quantified using the real-time fluorescent quantitative PCR. RESULTS: Compared with the control group, AA treatment increased (P < 0.05) the histopathology scores, intraepithelial lymphocyte (IEL) numbers and density in the colon, myeloperoxidase activity, the concentrations of malondialdehyde and pro-inflammatory mediators in the plasma and colon, while reducing (P < 0.05) goblet cell numbers and the protein/DNA ratio in the colonic mucosa. These adverse effects of AA were partially ameliorated (P < 0.05) by dietary supplementation with NAC. In addition, NAC prevented the AA-induced increase in caspase-3 protein, while stimulating claudin-1 protein expression in the colonic mucosa. Moreover, NAC enhanced mRNA levels for epidermal growth factor and amphiregulin in the colonic mucosa. CONCLUSION: Dietary supplementation with NAC can alleviate AA-induced colitis in a porcine model through regulating anti-oxidative responses, cell apoptosis, and EGF gene expression.

Functional and histologic changes in the lacrimal gland after botulinum toxin injection.

PURPOSE: The purpose of this study was to evaluate changes in tear volume, epidermal growth factor (EGF), and histology of the rabbit lacrimal gland after intraglandular application of botulinum toxin. METHODS: Ten New Zealand rabbits were separated into 3 groups. Eight rabbits received botulinum toxin injection (2.5 U per 0.1 mL) into the right lacrimal gland and saline injection (0.1 mL) into the left lacrimal gland as a sham control. Two rabbits were untreated to serve as normal controls. Tear volume was measured using cotton thread every 2 weeks, and 4 rabbits were killed after 2 and 4 weeks. The lacrimal glands were surgically excised and sectioned or lysed for gene expression analysis. Epidermal growth factor expression and concentration were evaluated by real-time polymerase chain reaction and enzyme-linked immunosorbent assay; morphometric and histologic analyses were performed. RESULTS: The rabbits that were killed 2 weeks after the injection showed decreased tear volume and increased EGF expression and concentration, but differences were not statistically significant. The rabbits that were killed 4 weeks after the injection exhibited similar results. When all 8 rabbits were considered, we detected a significant decrease in tear volume and increased EGF expression and concentration (P = 0.012, P = 0.011, and P = 0.012, respectively). The EGF level was not significantly correlated with the tear volume. There were no prominent histologic changes between the glands, and the lumen versus fibrosis ratio in the interlobular ducts showed no statistically significant difference. CONCLUSIONS: The use of botulinum toxin in patients with epiphora is effective, safe, and repeatable because it reduces tear volume and increases the EGF level to prevent corneal damage while causing no histologic changes.

Effects of tacrolimus on an organotypic raft-culture model mimicking oral mucosa.

BACKGROUND: Tacrolimus ointment has shown efficacy in treating T-cell-mediated inflammatory oral mucosal diseases, including lichen planus. However, the safety of topical tacrolimus has been questioned, based on its possible association with malignant transformation. AIM: To evaluate the safety aspects of tacrolimus in a three-dimensional in vitro model of oral mucosa containing both multilayered epithelium and connective tissue (raft culture). METHODS: Raft cultures mimicking oral mucosa were topically exposed to tacrolimus, and the effects on cell proliferation and adhesion, epidermal growth factor receptors (EGFR, ERBB2, ERBB3, ERBB4), and apoptosis were evaluated with immunohistochemistry and terminal dUTP nick-end labelling, respectively. Results. The epithelium of the cultures was found to be slightly thinner, but no changes in cell proliferation or adhesion, apoptosis, or expression of epidermal growth factor receptors were detected. CONCLUSIONS: Our results suggest that short-term topical tacrolimus exposure of in vitro constructed oral mucosa does not induce changes in a number of factors known to be involved in malignant transformation.

Sildenafil promotes smooth muscle preservation and ameliorates fibrosis through modulation of extracellular matrix and tissue growth factor gene expression after bilateral cavernosal nerve resection in the rat.

INTRODUCTION: It has been shown that phosphodiesterase type 5 (PDE5) inhibitors preserve smooth muscle (SM) content and ameliorate the fibrotic degeneration normally seen in the corpora cavernosa after bilateral cavernosal nerve resection (BCNR). However, the downstream mechanisms by which these drugs protect the corpora cavernosa remain poorly understood. AIM: To provide insight into the mechanism, we aimed to determine the gene expression profile of angiogenesis-related pathways within the penile tissue after BCNR with or without continuous sildenafil (SIL) treatment. METHODS: Five-month-old Fisher rats were subjected to BCNR or sham operation and treated with or without SIL (20 mg/kg/BW drinking water) for 3 days or 45 days (N = 8 rats per group). Total RNAs isolated from the denuded penile shaft and prostate were subjected to reverse transcription and to angiogenesis real-time-polymerase chain reaction arrays (84 genes). Changes in protein expression of selected genes such as epiregulin (EREG) and connective tissue growth factor (CTGF) were corroborated by Western blot and immunohistochemistry. MAIN OUTCOMES MEASURES: Genes modulated by BCNR and SIL treatment. RESULTS: A decreased expression of genes related to SM growth factors such as EREG, platelet-derived growth factor (PDGF), extracellular matrix regulators such as metalloproteinases 3 and 9, endothelial growth factors, together with an upregulation of pro-fibrotic genes such as CTGF and transforming growth factor beta 2 were found at both time points after BCNR. SIL treatment reversed this process by upregulating endothelial and SM growth factors and downregulating pro-fibrotic factors. SIL did not affect the expression of EREG, VEGF, and PDGF in the ventral prostate of BCNR animals. CONCLUSIONS: SIL treatment after BCNR activates genes related to SM preservation and downregulates genes related to fibrosis in the corpora cavernosa. These results provide a mechanistic justification for the use of SIL and other PDE5 inhibitors as protective therapy against corporal SM loss and fibrosis after radical prostatectomy.

The roles of integrins in mediating the effects of mechanical force and growth factors on blood vessels in hypertension.

Hypertension is characterized by a sustained increase in vasoconstriction and attenuated vasodilation in the face of elevated mechanical stress in the blood vessel wall. To adapt to the increased stress, the vascular smooth muscle cell and its surrounding environment undergo structural and functional changes known as vascular remodeling. Multiple mechanisms underlie the remodeling process, including increased expression of humoral factors and their receptors as well as adhesion molecules and their receptors, all of which appear to collaborate and interact in the response to pressure elevation. In this review, we focus on the interactions between integrin signaling pathways and the activation of growth factor receptors in the response to the increased mechanical stress experienced by blood vessels in hypertension.

Antitumor activity of taspine by modulating the EGFR signaling pathway of Erk1/2 and Akt in vitro and in vivo.

EGFR, as a critical signaling pathway in many human tumors, has become an important target of cancer drug design. Taspine has shown meaningful angiogenesis activity in previous studies. This paper is to investigate the antitumor action of taspine by modulating the EGFR signaling pathway. The study determined the expression of key signaling molecules of EGFR (EGFR, Akt, p-Akt, Erk, and p-Erk) by Western blot and real-time PCR and analyzed their correlations with subsequent reactions. In addition, the cell proliferation, migration, and EGF production were examined by MTT, transwell system, and ELISA. The antitumor activity in vivo was carried out by xenograft in athymic mice. The results showed that taspine could inhibit A431 and Hek293/EGFR cell proliferation and A431 cell migration as well as EGF production. Compared to the negative control, EGFR, Akt, and phosphorylation of Akt were significantly inhibited by taspine treatment in A431 and HEK293/EGFR cells. Consistent with the inhibition of Akt activity, Erk1/2 and its phosphorylation were reduced. Moreover, taspine inhibited A431 xenograft tumor growth. These results suggest that EGFR activated by EGF and its downstream signaling pathways proteins could be downregulated by taspine in a dose-dependent manner. The antitumor mechanism of taspine through the EGFR pathway lies in the ability to inhibit A431 cell proliferation and migration by reducing EGF secretion. This occurs through the repression of EGFR which mediates not only MAPK (Erk1/2) but also Akt signals.

Acanthosis nigricans in the setting of niacin therapy.

We report the case of a 63-year-old obese man with a rapid-onset of widespread acanthosis nigricans (AN) in the setting of having recently initiated treatment with niacin for dyslipidemia. Although obesity and insulin-resistance are risk factors for AN, AN associated with endocrine dysfunction tends to have a more gradual onset and limited involvement. Owing to our patient's age, the rapid onset, and extensive distribution of his eruption, we initially were concerned about paraneoplastic AN. However, an evaluation for a malignant condition was negative. The timing of the onset of our patient's eruption within several months of starting niacin therapy is consistent with niacin-induced AN. Niacin is known to cause rapidly progressive, widespread AN that is reversible upon discontinuation of the medication. We discuss the pathogenesis of AN, which is thought to be the final common manifestation of stimulation of different subtypes of tyrosine kinase receptors by various epidermal growth factors.

The Rheb-mTOR pathway is upregulated in reactive astrocytes of the injured spinal cord.

Astrocytes in the CNS respond to tissue damage by becoming reactive. They migrate, undergo hypertrophy, and form a glial scar that inhibits axon regeneration. Therefore, limiting astrocytic responses represents a potential therapeutic strategy to improve functional recovery. It was recently shown that the epidermal growth factor (EGF) receptor is upregulated in astrocytes after injury and promotes their transformation into reactive astrocytes. Furthermore, EGF receptor inhibitors were shown to enhance axon regeneration in the injured optic nerve and promote recovery after spinal cord injury. However, the signaling pathways involved were not elucidated. Here we show that in cultures of adult spinal cord astrocytes EGF activates the mTOR pathway, a key regulator of astrocyte physiology. This occurs through Akt-mediated phosphorylation of the GTPase-activating protein Tuberin, which inhibits Tuberin's ability to inactivate the small GTPase Rheb. Indeed, we found that Rheb is required for EGF-dependent mTOR activation in spinal cord astrocytes, whereas the Ras-MAP kinase pathway does not appear to be involved. Moreover, astrocyte growth and EGF-dependent chemoattraction were inhibited by the mTOR-selective drug rapamycin. We also detected elevated levels of activated EGF receptor and mTOR signaling in reactive astrocytes in vivo in an ischemic model of spinal cord injury. Furthermore, increased Rheb expression likely contributes to mTOR activation in the injured spinal cord. Interestingly, injured rats treated with rapamycin showed reduced signs of reactive gliosis, suggesting that rapamycin could be used to harness astrocytic responses in the damaged nervous system to promote an environment more permissive to axon regeneration.

The biological framework: translational research from bench to clinic.

The understanding of cellular signaling pathways in malignant tumors is an important aspect of cancer research and modern targeted therapy strategies. Growth factors and their receptors in particular are critical to modern cancer therapy research, because these factors control all phases of tumor development and metastasis. Most importantly, growth factors are responsible for cell survival under cytotoxic drugs and radiotherapy. These growth factor signaling pathways are composed of complex networks that have adapted to efficiently respond to certain disturbances, such as a single agent that targets one aspect of the pathway. Meanwhile, multiple insults to the pathway, such as combination therapy regimens, are known to be effective in shutting down these pathways and, consequently, killing the tumor cell. Research is currently under way to find new ways to exploit fragile aspects of oncogenic networks, such as uncommon, multiple perturbations that target essential hubs through immunotherapy, combinations of antibodies, heat shock protein inhibitors, or novel drug combinations. Complex growth factor signaling networks and novel methods to shut down these networks are described within a framework of engineering and mathematical concepts.

Antitumor effect in medulloblastoma cells by gefitinib: Ectopic HER2 overexpression enhances gefitinib effects in vivo.

The effects of the epidermal growth factor receptor (EGFR) inhibitor gefitinib on cell growth and signaling were evaluated in three medulloblastoma (MB) cell lines (D283, D341, Daoy), one supratentorial primitive neuroectodermal tumor cell line (PFSK), and four MB primary cultures. Cell lines showed diverse expression of EGFR and human epidermal receptor 2 (HER2), with high levels of constitutively activated HER2 in the HER2-overexpressing D341 and D283 cells. Gefitinib sensitivity varied across lines and was not related to expression of HER receptors or receptor baseline activation. Gefitinib induced G(0)/G(1) arrest in all lines, whereas apoptosis was dose-dependently induced only in D283 and D341 cells. The molecular response to gefitinib was investigated in Daoy and D341 lines, which showed a higher (half-maximal inhibitory concentration [IC(50)], 3.8 microM) and lower (IC(50), 6.6 microM) sensitivity to the agent, respectively. Gefitinib inhibited constitutive and EGF-triggered EGFR phosphorylation in both lines but was ineffective in constitutive activation of HER2 in D341 cells. Phosphorylated AKT inhibition paralleled that of phosphorylated EGFR, suggesting the presence of an autocrine gefitinib-sensitive EGFR/AKT pathway. On the whole, EGF-dependent signaling was less responsive to ligand stimulation and gefitinib inhibition in D341 cells, which correlated with the lower sensitivity to gefitinib's antiproliferative effect of this line. In vivo, the growth of D341 and Daoy xenografts treated with gefitinib at 150 mg/kg per day was inhibited by approximately 50%. Ectopically overexpressed HER2 in Daoy cells significantly increased sensitivity to gefitinib's antitumor effects in vivo (tumor volume inhibition = 78%). Our data indicate that gefitinib might be a molecularly targeted agent for the treatment of MB.

Apical enrichment of human EGF precursor in Madin-Darby canine kidney cells involves preferential basolateral ectodomain cleavage sensitive to a metalloprotease inhibitor.

EGF precursor (proEGF) is a member of the family of membrane-anchored EGF-like growth factors that bind with high affinity to the epidermal growth factor receptor (EGFR). In contrast to human transforming growth factor-alpha precursor (proTGFalpha), which is sorted basolaterally in Madin-Darby canine kidney (MDCK) cells (Dempsey, P., and R. Coffey, 1994. J. Biol. Chem. 269:16878-16889), we now demonstrate that human proEGF overexpressed in MDCK cells is found predominantly at the apical membrane domain under steady-state conditions. Nascent proEGF (185 kD) is not sorted but is delivered equally to the apical and basolateral membranes, where it is proteolytically cleaved within its ectodomain to release a soluble 170-kD EGF form into the medium. Unlike the fate of TGFalpha in MDCK cells, the soluble 170-kD EGF species accumulates in the medium, does not interact with the EGFR, and is not processed to the mature 6-kD peptide. We show that the rate of ectodomain cleavage of 185-kD proEGF is fourfold greater at the basolateral surface than at the apical surface and is sensitive to a metalloprotease inhibitor, batimastat. Batimastat dramatically inhibited the release of soluble 170-kD EGF into the apical and basal medium by 7 and 60%, respectively, and caused a concordant increase in the expression of 185-kD proEGF at the apical and basolateral cell surfaces of 150 and 280%, respectively. We propose that preferential ectodomain cleavage at the basolateral surface contributes to apical domain localization of 185-kD proEGF in MDCK cells, and this provides a novel mechanism to achieve a polarized distribution of cell surface membrane proteins under steady-state conditions. In addition, differences in disposition of EGF and TGFalpha in polarized epithelial cells offer a new conceptual framework to consider the actions of these polypeptide growth factors.

c-Jun N-terminal kinase negatively regulates epidermal growth factor-induced cyclooxygenase-2 expression in oral squamous cell carcinoma cell lines.

Epidermal growth factor (EGF)-induced cyclooxygenase-2 (COX-2) expression in squamous cell carcinomas is mediated through the extracellular signal-regulated kinase 1/2 and p38 pathways. Examination of a basaloid and a conventional oral squamous cell carcinoma cell line revealed that inhibition of c-Jun N-terminal kinase (JNK) with SP600125 increased EGF-induced (but not basal) COX-2 transcription 1.5-1.9-fold in extracellular signal-regulated kinase 1/2 and p38 pathway-dependent manners. Although JNK may phosphorylate the cyclosporine A-sensitive transcription factor, nuclear factor of activated T cells c3, it was seemingly not involved because cyclosporine A did not reduce EGF-induced COX-2 expression. Thus, JNK negatively regulated EGF-induced extracellular signal-regulated kinase 1/2 and/or p38-mediated COX-2 transcription, presumably through activating an unidentified phosphatase.

Dactylone inhibits epidermal growth factor-induced transformation and phenotype expression of human cancer cells and induces G1-S arrest and apoptosis.

The marine natural chamigrane-type sesquiterpenoid, dactylone, is closely related to secondary metabolites of some edible species of red algae. In the present study, the effect of dactylone was tested on the mouse skin epidermal JB6 P+ Cl41 cell line and its stable transfectants as well as on several human tumor cell lines, including lung (H460), colon (HCT-116), and skin melanomas (SK-MEL-5 and SK-MEL-28). This natural product was effective at nontoxic doses as a cancer-preventive agent, which exerted its actions, at least in part, through the inhibition of cyclin D3 and Cdk4 expression and retinoblastoma tumor suppressor protein (Rb) phosphorylation. The inhibition of these cell cycle components was followed by cell cycle arrest at the G1-S transition with subsequent p53-independent apoptosis. Therefore, these data showed that application of dactylone and related compounds may lead to decreased malignant cell transformation and/or decreased tumor cell proliferation.

Dihydrotestosterone interacts with EGFR/MAPK signalling and modulates EGFR levels in androgen receptor-positive LNCaP prostate cancer cells.

Androgen receptor (AR) signalling plays a pivotal role in prostate cancer pathogenesis and progression. However, androgen-mediated AR signalling is yet to be fully understood. EGFR and MAP kinase signalling pathways play predominant roles in AR function. Therefore, we investigated the interaction of EGFR signalling and AR activity in AR-positive LNCaP cells. We found that 5alpha-dihydrotestosterone (DHT) and EGF had a synergistic effect on AR activity as detected by a luciferase reporter system, although EGF alone did not activate AR. Both ERK1/2 and p38 were involved in DHT and DHT/EGF-induced AR activation as detected by specific MEK and p38 inhibitors. Furthermore, 24-h treatment of the cells with DHT resulted in ubiquitination and down-regulation of the EGFR. This effect could be inhibited by the anti-androgen flutamide, suggesting an androgen-dependent mechanism. On the other hand, DHT-treatment strongly increased AR levels in LNCaP cells. These data suggest a complex regulatory loop between activated AR and EGFR. In conclusion, activation of AR by both DHT and EGF/DHT involves the MAP kinase pathway. Long-term activation of AR results in increase of AR levels, which through so far unknown regulatory mechanisms results in ubiquitination and degradation of the EGFR.

Effect of ascorbic acid and epidermal growth factor in a rat tibia defect

Purpose: Bone repair aims to restore the anatomical, biomechanical, and functional integrity of the affected structure. Here we study the effects of ascorbic acid (AA) and epidermal growth factor (EGF) applied in a single dose and in combination on the repair of a noncritical bone defect model. Methods: Twenty-four rats were divided into four groups: an intact G-1 control group, and three groups that underwent a noncritical bone defect in the right tibia: G-2 treated with AA, G-3 treated with EGF, and G-4 treated with AA in combination with EGF. After 21 days of treatment, rats were sacrificed, the tibias were dissected and a destructive biomechanical analysis of three-point flexion test was performed in a universal testing machine; the values of stiffness, resistance, maximum energy, and energy at maximum load were statistically compared. Results: G-3 and G-4 recovered the biomechanical properties of strength and stiffness of an intact tibia 3 weeks after their application. Not so the energy and energy at maximum load. For G-2, only the stiffness of an intact tibia was recovered. Conclusion: EGF and AA-EGF applied to a noncritical bone defect in the rat tibia favors the recovery of bone resistance and stiffness.