A bipartite butyrate‐responsive element in the human calretinin (CALB2) promoter acts as a repressor in colon carcinoma cells but not in mesothelioma cells

Abstract

The short-chain fatty acid butyrate plays an essential role in colonic mucosa homeostasis through the capacity to block the cell cycle, regulate differentiation and to induce apoptosis. The beneficial effect of dietary fibers on preventing colon cancer is essentially mediated through butyrate, derived from luminal fermentation of fibers by intestinal bacteria. In epithelial cells of the colon, both in normal and colon cancer cells, the expression of several genes is positively or negatively regulated by butyrate likely through modulation of histone acetylation and thereby affecting the transcriptional activity of genes. Calretinin (CALB2) is a member of the EF-hand family of Ca 2þ -binding proteins and is expressed in a majority of poorly differentiated colon carcinoma and additionally in mesothelioma of the epithelioid and mixed type. Since CALB2 is one of the genes negatively regulated by butyrate in colon cancer cells and butyrate decreases calretinin protein expression levels in those cells, we investigated whether expression is regulated via putative butyrate-responsive elements (BRE) in the human CALB2 promoter. We identified two elements that act as butyrate-sensitive repressors in all colon cancer cell lines tested (CaCo-2, HT-29, Co-115/3). In contrast, in cells of mesothelial origin, MeT-5A and ZL34, the same two elements do not operate as butyrate-sensitive repressors and calretinin expression levels are insensitive to butyrate indicative of cell type-specific regulation of the CALB2 promoter. Calretinin expression in colon cancer cells is negatively regulated by butyrate via a bipartite BRE flanking the TATA box and this may be linked to butyrate's chemopreventive activity.

Identification ofcis-andtrans-acting elements regulating calretinin expression in mesothelioma cells

“…A 1.5 kb stretch of the mouse Calb2 promoter (−1485/ + 60bp) was demonstrated to drive reporter expression in cultured neuronal cell derived from primary embryonic mouse brain tissue [12]. Additionally, a bipartite butyrate-responsive element in the human CALB2 promoter was found to act as a repressor element upon butyrate treatment in colon carcinoma but not in mesothelioma cells [16]. However, specific cis -regulatory elements positively regulating calretinin expression had not yet been identified.…”

“…In human colon cancer cells, calretinin expression is downregulated by butyrate, a substance that induces cell differentiation [15]. Butyrate–induced calretinin downregulation is mediated through butyrate dependent repressive elements which are not operational in mesothelioma cells [16]. …”

De novo expression of parvalbumin in ependymal cells in response to brain injury promotes ependymal remodeling and wound repair

“…In nerve cells, the calretinin‐promoter contains a specific AP2‐like element that assures a neuron‐specific pattern of gene‐expression (Billing‐Marczak et al, ). In colon cancer cells, butyrate down‐regulates the expression of calretinin (Haner et al, ), whereas in mesothelioma cells, none of these mechanisms influence its expression (Haner et al, ).…”

Calretinin: from a “simple” Ca2+ buffer to a multifunctional protein implicated in many biological processes

“…Butyrate, a known modulator of histone acetylation, inhibits the cell cycle and leads to enterocyte differentiation. Of the several putative butyrate-responsive elements (BREs) present in the human CALB2 promoter, two elements embracing the TATA box act as butyrate-sensitive repressor elements in colon cancer cells, but not in cells of mesothelial origin (Figure 1; Haner et al, 2010). This supports the notion of cell type-specific CALB2 regulation.…”

“…In the region −90/−80 of the mouse Calb2 gene, an “AP2-like” element (white box) is responsible for neuron-specific expression of the transcript (Billing-Marczak et al, 2002). A bipartite butyrate-responsive element (BRE; checkered boxes) surrounds the TATA box and the TSS (Haner et al, 2010). The non-coding part of exon 1 is shown as a white box and the coding region including the ATG start codon as a striped box.…”