Hypoxia induced by benign intestinal epithelial cells is associated with cyclooxygenase-2 expression in stromal cells through AP-1-dependent pathway

Fibroblast Subsets in Intestinal Homeostasis, Carcinogenesis, Tumor Progression, and Metastasis

Simple Summary

Colorectal cancer often develops via the adenoma–carcinoma sequence, a process which is accompanied by (epi) genetic alterations in epithelial cells and gradual phenotypic changes in fibroblast populations. Recent studies have made it clear that these fibroblast populations which, in the context of invasive cancers are termed cancer-associated fibroblasts (CAFs), play an important role in intestinal tumor progression. This review provides an overview on the emerging role of fibroblasts in various stages of colorectal cancer development, ranging from adenoma initiation to metastatic spread of tumor cells. As fibroblasts show considerable heterogeneity in subsets and phenotypes during cancer development, a better functional understanding of stage-specific (alterations in) fibroblast/CAF populations is key to increase the effectiveness of fibroblast-based prognosticators and therapies.

Abstract

In intestinal homeostasis, continuous renewal of the epithelium is crucial to withstand the plethora of stimuli which can damage the structural integrity of the intestines. Fibroblasts contribute to this renewal by facilitating epithelial cell differentiation as well as providing the structural framework in which epithelial cells can regenerate. Upon dysregulation of intestinal homeostasis, (pre-) malignant neoplasms develop, a process which is accompanied by (epi) genetic alterations in epithelial cells as well as phenotypic changes in fibroblast populations. In the context of invasive carcinomas, these fibroblast populations are termed cancer-associated fibroblasts (CAFs). CAFs are the most abundant cell type in the tumor microenvironment of colorectal cancer (CRC) and consist of various functionally heterogeneous subsets which can promote or restrain cancer progression. Although most previous research has focused on the biology of epithelial cells, accumulating evidence shows that certain fibroblast subsets can also importantly contribute to tumor initiation and progression, thereby possibly providing avenues for improvement of clinical care for CRC patients. In this review, we summarized the current literature on the emerging role of fibroblasts in various stages of CRC development, ranging from adenoma initiation to the metastatic spread of cancer cells. In addition, we highlighted translational and therapeutic perspectives of fibroblasts in the different stages of intestinal tumor progression.

Cyclooxygenase-2/carbonic anhydrase-IX up-regulation promotes invasive potential and hypoxia survival in colorectal cancer cells

Inflammation promotes colorectal carcinogenesis. Tumour growth often generates a hypoxic environment in the inner tumour mass. We here report that, in colon cancer cells, the expression of the pro-inflammatory enzyme cyclooxygenase-2 (COX-2) associates with that of the hypoxia response gene carbonic anhydrase-IX (CA-IX). The COX-2 knockdown, achieved by the stable infection of a COX-2 specific short harpin RNA interference (shCOX-2), down-regulates CA-IX gene expression. In colorectal cancer (CRC) cells, PGE₂, the main COX-2 gene products, promotes CA-IX gene expression by ERK1/2 activation. In normoxic environment, shCOX-2 infected/CA-IX siRNA transfected CRC cells show a reduced level of active metalloproteinase-2 (MMP-2) that associates with a decreased extracellular matrix invasion capacity. In presence of hypoxia, COX-2 gene expression and PGE₂ production increase. The knockdown of COX-2/CA-IX blunts the survival capability of CRC cells in hypoxia. At a high cell density, a culture condition that creates a mild pericellular hypoxic environment, the expression of COX-2/CA-IX genes is increased and triggers the invasive potential of colon cancer cells. In human colon cancer tissues, COX-2/CA-IX protein expression levels, assessed by Western blot and immunohistochemistry, correlate each other and increase with tumour stage. In conclusion, these data indicate that COX-2/CA-IX interplay promotes the aggressive behaviour of CRC cells.

Identification of a novel repressor element in the cyclo-oxygenase-2 promoter and its nuclear binding protein

Cyclo-oxygenase-2 (COX-2) has important functions in many diseases. Although its transcriptional regulation has been investigated in considerable detail, some important elements remain unknown. The aim of the present study was to demonstrate the existence of a novel repressor element in the mouse COX-2 promoter and characterize some of its binding proteins. In order to identify the repressor element, the activity of the mouse COX-2 promoter was investigated in the pancreatic beta-cell line RINm5F using a series of deletion and mutant constructs. The ability of nuclear proteins to bind to this repressor element was then determined by an electrophoretic mobility shift assay and the proteins binding to this repressor element were purified and identified by mass spectrometry. One of the nuclear proteins identified was overexpressed to examine its inhibitory effect on COX-2 promoter activity. We found a novel repressor element located from nucleotides -655 to -632 of the mouse COX-2 promoter region. Some proteins from RINm5F cell nuclear extracts bound to this element, one of which was identified as non-POU-domain-containing, octamer-binding protein (NonO). Overexpression of NonO significantly inhibited wild-type COX-2 promoter activity, but had no effect when the repressor element was mutated. In conclusion, we have demonstrated that a regulatory 'spot' is present in the COX-2 promoter. This provides additional data on COX-2 gene regulation and may provide an insight into the clinical treatment of diseases where COX-2 is highly expressed.

Cyclo-oxygenase-2 over-expression is associated with human esophageal squamous cell carcinoma

Cyclo-oxygenase (COX)-2 is not usually detectable in normal tissues but is induced in inflammation and carcinogenesis. The level of COX-2 is elevated in cancer tissues of the colon, bladder, and skin. In the esophagus, squamous cell carcinoma and adenocarcinoma are known to express COX-2. The purpose of this study was to clarify the association of COX-2 expression with clinicopathological factors of squamous cell carcinoma. The immunohistochemical expression of COX-2 was examined in 48 surgical specimens of esophageal squamous cell carcinoma. Although COX-2 over-expression was more frequently observed in tumors invading the submucosa (T1b, 76.4%), muscularis propria (T2, 57.1%), adventitia, or adjacent organs (T3 approximately 4, 83.3%), even 33.3% of mucosal cancers, such as T1a, showed COX-2 over-expression. COX-2 over-expression was present in 82.3% of lymph node-negative patients but in only 54.8% of lymph node positive patients. There was no difference in COX-2 over-expression between the earlier stages (0 and I, 60%) and more advanced stages (II approximately IV, 69.6%). COX-2 over-expression did not correlate with survival during 3 years of follow-up. These findings suggest that COX-2 is associated with the phenotype of the esophageal squamous cell carcinoma cells, including superficial cancer cells, and may be related to tumor growth in esophageal squamous cell carcinoma.