Jianyuan Chai

Serum response factor is a critical requirement for VEGF signaling in endothelial cells and VEGF-induced angiogenesis

Angiogenesis, new capillary blood vessel formation, is essential for embryonic development, wound healing, and cancer growth. Vascular endothelial growth factor (VEGF) induces angiogenesis by activating endothelial cell migration and proliferation. Serum response factor (SRF) is a transcription factor important for embryonic development and activation of immediate early gene expression. The roles of SRF in endothelial cell biology and angiogenesis have not been explored. Here we demonstrate that SRF is a downstream mediator of VEGF signaling in endothelial cells and a critical requirement for VEGF‐induced angiogenesis. Knockdown of SRF protein levels in human and rat endothelial cells abolished VEGF‐induced in vitro angiogenesis, impaired endothelial cell migration and proliferation, and inhibited VEGF‐induced actin polymerization and immediate early gene expression. Injection of SRF antisense expression plasmid into gastric ulcers in rats significantly inhibited in vivo angiogenesis in granulation tissue. Mechanistically, this study also revealed that VEGF promotes SRF expression and nuclear translocation and increases SRF binding activity to DNA in endothelial cells through both Rho‐actin and MEK‐ERK dependent signaling pathways. These findings have potential therapeutic implications, e.g., local anti‐SRF treatment may inhibit angiogenesis crucial for tumor growth.

Esophageal malignancy: A growing concern

Esophageal cancer is mainly found in Asia and east Africa and is one of the deadliest cancers in the world. However, it has not garnered much attention in the Western world due to its low incidence rate. An increasing amount of data indicate that esophageal cancer, particularly esophageal adenocarcinoma, has been rising by 6-fold annually and is now becoming the fastest growing cancer in the United States. This rise has been associated with the increase of the obese population, as abdominal fat puts extra pressure on the stomach and causes gastroesophageal reflux disease (GERD). Long standing GERD can induce esophagitis and metaplasia and, ultimately, leads to adenocarcinoma. Acid suppression has been the main strategy to treat GERD; however, it has not been proven to control esophageal malignancy effectively. In fact, its side effects have triggered multiple warnings from regulatory agencies. The high mortality and fast growth of esophageal cancer demand more vigorous efforts to look into its deeper mechanisms and come up with better therapeutic options.

A critical role of serum response factor in myofibroblast differentiation during experimental oesophageal ulcer healing in rats

Background: Myofibroblast differentiation is a key event during wound healing and is triggered primarily by transforming growth factor β (TGFβ). Serum response factor (SRF) is a TGFβ-inducible transcription factor that is important for wound healing. Injection of SRF expression plasmid into rat gastric ulcers significantly accelerated restoration of epithelium and smooth muscle structures. Aim: To determine the role of SRF in oesophageal ulcer healing, especially in myofibroblast differentiation. Subjects: Rats (in vivo), oesophageal epithelial cells (Het1A) and fibroblasts (Rat1-R12) (in vitro) were used. Methods: Oesophageal ulcers were induced in rats with acetic acid and subsequently treated by local injection of plasmids expressing either SRF or SRF antisense sequence. Rats were killed at 1, 3, 6, 9 and 14 days after treatment and tissues collected. For in vitro studies, both Het1A and Rat1-R12 cells were transfected with the plasmids used in ulcer treatment. Results: Upregulation of SRF increased the myofibroblast population in ulcer granulation tissue; knockdown of SRF suppressed this event. In addition, ulceration induced SRF and TGFβ expression coordinately. In vitro studies showed that overexpression of SRF in either oesophageal epithelial cells or fibroblasts was sufficient to induce myofibroblast phenotype. Furthermore, the TGFβ-induced myofibroblast phenotype required integrin-linked kinase (ILK)-mediated SRF activation, as either knockdown of SRF or inactivation of ILK prevented this action. Conclusions: SRF is indispensable for myofibroblast differentiation during oesophageal ulcer healing and is required for TGFβ-induced myofibroblast transition from either epithelial cells or fibroblasts. ILK is a mediator in TGFβ-induced SRF activation and subsequent myofibroblast differentiation. ILK is associated with SRF, and TGFβ enhances this association.

Mesalazine downregulates c‐Myc in human colon cancer cells. A key to its chemopreventive action?

Background  Dysplasia and malignant transformation of colonocytes in ulcerative colitis are associated with overexpression of c‐Myc and genes regulating cell survival. 5‐Aminosalicylates such as mesalazine may reduce the development of colorectal cancer in ulcerative colitis, but the mechanisms of its chemopreventive action are not clear.

CCN1 induces a reversible epithelial–mesenchymal transition in gastric epithelial cells

CCN1 is a matricellular protein that activates many genes related to wound healing and tissue remodeling in fibroblasts, but its effect on epithelial cells remains unclear. This study examined the role of CCN1 in epithelial wound healing using rat gastric epithelial cells and rat stomach ulcer as in vitro and in vivo models, respectively. We found that CCN1 expression is highly upregulated in the epithelial cells adjacent to a wound and remains high until the wound is healed. Upregulation of CCN1 activates a transient epithelial–mesenchymal transition in the epithelial cells at the migrating front and drives wound closure. Once the wound is healed, these epithelial cells and their progeny can resume their original epithelial phenotype. We also found that CCN1-induced E-cadherin loss is not due to transcriptional regulation but rather protein degradation due to the collapse of adherens junctions, which is contributed by β-catenin translocation. CCN1-activated integrin-linked kinase mediates this process. Finally, our in vivo study showed that locally neutralizing CCN1 drastically impairs wound closure, whereas local injection of recombinant CCN1 protein induces expression of vimentin and smooth muscle α-actin in normal gastric mucosal epithelial cells and accelerates re-epithelialization during ulcer healing. In conclusion, our study indicates that CCN1 can induce reversible epithelial–mesenchymal transition, and this feature may have great value for clinical wound healing.

Reduced expression of epidermal growth factor receptor related protein in gastric cancer

Objectives: The recently cloned epidermal growth factor receptor related protein (ERRP) has been proposed to be a negative regulator of the epidermal growth factor receptor (EGFR). Because of the causal involvement of EGFR and its ligands in gastric cancer growth, we investigated expression of ERRP and cell proliferation in human gastric cancer. Methods: We examined ERRP expression and localisation in surgical specimens of gastric cancers from 47 patients versus non-malignant gastric mucosa and determined their relationship to cell proliferation and differentiation. We also examined expression of ERRP by western blotting in three different gastric cancer cell lines. To further determine the functional properties of ERRP, we examined the effect of ERRP on epidermal growth factor (EGF) induced EGFR phosphorylation essential for its activation in MKN-28 gastric cancer cells. Results: ERRP expression was dramatically reduced in gastric cancers (34% of all specimens positive) compared with non-malignant gastric mucosa (66% of specimens positive). Expression of ERRP in cancer cells inversely correlated with cell proliferation and grade of malignancy. Cell lines derived from metastatic gastric cancers had reduced ERRP expression compared with cell lines derived from a non-metastatic cancer. Exogenous ERRP protein markedly inhibited EGF induced EGFR phosphorylation in gastric cancer cells providing a novel molecular mechanism of its action. Conclusions: Our data indicate that downregulation of ERRP could play an important role in gastric cancer differentiation and progression. ERRP is a negative regulator of tumour cell proliferation and may exert its inhibitory effect, in part, by attenuating EGFR activation.

Potential of casein kinase I in digestive cancer screening

Casein kinase I is a group of ubiquitous Serine/Threonine kinases that have been implicated in both normal cellular functions and several pathological conditions including Alzheimers disease and cancer. Recent findings in colon and pancreatic cancer have brought tremendous attention to these molecules as potential therapeutic targets in treatment of digestive cancers. In this review, we summarize up to date what is known about this family of kinases and their involvement in carcinogenesis and other pathological conditions. Our emphasis is on their implications in digestive cancers and their potential for cancer screening and therapy.

S100A4 in esophageal cancer: Is this the one to blame?

Metastasis is the main reason for cancer-related death. S100A4 is one of the key molecules involved in this event. Several studies have shown that overexpression of S100A4 in non-metastatic cancer cells can make them become metastatic, and knockdown of S100A4 in metastatic cancer cells can curtail their invasive nature. A study by Chen et al([2]) published in the World J Gastroenterol 18(9): 915-922, 2012 is a typical example. This study showed in vitro and in vivo evidence that S100A4 expression level determines the invasiveness of esophageal squamous carcinoma. Considering the fact that more than half of the cancer-related deaths are caused by malignancies derived from the digestive system and esophageal cancer is the 4th top contributor to this fraction, this study warrants more attention.

CCN1 Induces β-Catenin Translocation in Esophageal Squamous Cell Carcinoma through Integrin α11.

Aims. Nuclear translocation of β-catenin is common in many cancers including esophageal squamous cell carcinoma (ESCC). As a mediator of Wnt signaling pathway, nuclear β-catenin can activate many growth-related genes including CCN1, which in turn can induce β-catenin translocation. CCN1, a matricellular protein, signals through various integrin receptors in a cell-dependent manner to regulate cell adhesion, proliferation, and survival. Its elevation has been reported in ESCC as well as other esophageal abnormalities such as Barretts esophagus. The aim of this study is to examine the relationship between CCN1 and β-catenin in ESCC. Methods and Results. The expression and correlation between CCN1 and β-catenin in ESCC tissue were examined through immunohistochemistry and further analyzed in both normal esophageal epithelial cells and ESCC cells through microarray, functional blocking and in situ protein ligation. We found that nuclear translocation of β-catenin in ESCC cells required high level of CCN1 as knockdown of CCN1 in ESCC cells reduced β-catenin expression and translocation. Furthermore, we found that integrin α 11 was highly expressed in ESCC tumor tissue and functional blocking integrin α 11 diminished CCN1-induced β-catenin elevation and translocation. Conclusions. Integrin α 11 mediated the effect of CCN1 on β-catenin in esophageal epithelial cells.

Gastric Ulcer Healing – Role of Serum Response Factor

Histologically, a gastric ulcer is viewed as a necrotic lesion penetrating through the entire mucosal thickness of the stomach. Because of its great similarities with ulcers in other parts of the digestive tract, gastric ulcer is often reviewed with esophageal and duodenal ulcers together as peptic ulcer disease (PUD). Although it is not as common as duodenal ulcers, gastric ulcers are more often to develop malignancy. PUD can be found in any part of the world and is probably the most common chronic infection in human population. It causes considerable loss of life year and creates a great economic burden (Figure 1). It had a tremendous effect on morbidity and mortality until the last few decades of the last century when epidemiological trends started to point to an impressive fall in its incidence, particularly in the Western countries. The reason why the rates of PUD decreased is thought to be the development of new effective medication, and of course, the discovery of the pathogen – Helicobacter pylori. It is now commonly accepted that the main cause of PUD is H. pylori, a helix-shaped Gram-negative bacterium, which infects more than 50% of world population and can be transmitted by contaminated food, groundwater, and even through human saliva (such as from kissing or sharing food utensils). For this reason, higher incidence of PUD is found in the third world countries and low socioeconomic groups. In the developed countries, on the other hand, although H. pylori infection is under controlled, thanks to the easy access to advanced treatment and better living condition, extensive use of non-steroidal anti-inflammatory drugs (NSAIDs) keeps the incidence of complicated gastric ulcer and hospitalization stable (Feinstein et al, 2010). Treatment of PUD usually involves a combination of antibiotics (e.g. metronidazole, clarithromycin, tetracycline, amoxicillin), acid suppressors (e.g. cimetidine, ranitidine, omeprazole, lansoprazole), and mucosa protectors (e.g. bismuth subsalicylate). Unfortunately, patients have to take as many as 20 pills a day and often end up with multiple side effects including nausea, vomiting, diarrhea, dizziness, and headache. Perforated ulcers require surgical repair, while bleeding ulcers have to be taken care by endoscopic cautery, injection or clipping. In any case, healing of an ulcer normally requires multiple molecular and cellular processes to achieve. This chapter will dissect molecular and cellular mechanisms of gastric ulcer healing and focus on an important molecule – Serum Response Factor (SRF) and its role in this event.