Differential regulation of intestinal alkaline phosphatase gene expression by Cdx1 and Cdx2

Abstract

-We have examined the role that the caudal-related homeobox transcription factors Cdx1 and Cdx2 play in activating the enterocyte differentiation marker gene intestinal alkaline phosphatase (IAP). Human colon cancer Caco-2 cells were transiently transfected with Cdx1 and/or Cdx2, and semiquantitative RT-PCR was used to study the effects on IAP mRNA expression. Transfections with a variety of IAP-luciferase reporter constructs were used to identify a Cdx response element located within the human IAP gene promoter. Protein-DNA interactions were examined by EMSA. Results showed that Cdx1 markedly induced IAP mRNA expression, whereas Cdx2 did not, and, in fact, inhibited the Cdx1 effects. Functional analysis revealed that Cdx1 transactivates (fourfold, P Ͻ 0.05) the IAP promoter through a novel Cdx response element (GTTTAGA) located between Ϫ2369 and Ϫ2375 upstream of the translational start site. EMSA showed that both Cdx1 and Cdx2 could bind to the cis element, but in cotransfection experiments, Cdx2 inhibited the Cdx1 effects by ϳ50%. Thus we have identified a previously unrecognized interaction between two important gut transcription factors, Cdx1 and Cdx2, in the context of IAP gene regulation. Cdx1 activates the IAP gene via a novel cis element, whereas Cdx2 inhibits the Cdx1 effects. cell cycle; enterocyte differentiation; gene regulation; gut development; homeostasis; intestinal alkaline phosphatase; tumorigenesis INTESTINAL ALKALINE PHOSPHATASE (IAP) is one of four alkaline phosphatase (AP) isoenzymes. In humans, three of the four AP isozyme are tissue specific, i.e., the intestinal AP (IAP), placental AP, and germ cell AP, while the fourth AP gene is the tissue-nonspecific AP present in bone, liver, and kidney (9). IAP is exclusively expressed in villus enterocytes and hence serves as an excellent marker of crypt-villus differentiation (11). IAP represents a major component of the surfactant-like particles seen after fat feeding (19), and Narisawa et al. (24) recently described the phenotype of the IAP knockout mice, indicating that IAP functions to limit fat absorption during high-fat feeding.IAP expression is dramatically regulated by a variety of dietary, developmental, and hormonal factors, e.g., it is induced at the time of postnatal weaning, whereas fasting in the adult rat causes a dramatic decrease in IAP levels. These alterations in IAP levels likely have important physiological consequences regarding the absorption of dietary fat, and we have, therefore, been interested in elucidating the molecular mechanisms that govern IAP gene regulation. Among the known transcriptional regulators of IAP expression are the thyroid hormone receptor and the gut-enriched Kruppel-like factor (KLF4) (10, 23).Cdx1 and Cdx2 are members of the caudal-related homeobox family and appear to play critical roles in gut differentiation, proliferation, and neoplasia. The Cdx proteins are involved in the regulation of intestine-specific genes, such as sucrase-isomaltase, intestinal phospholipase A/lysophospholipase, lactase-p...

Cooperation between GATA4 and TGF-β signaling regulates intestinal epithelial gene expression

“…Under in vivo conditions in which endodermal GATA family members are coexpressed in enteric epithelial cells and interact physically and functionally (12,22,23), such preferential occupation of GATA sites by intestinal GATA factors could result in differential regulation of GATA target genes. In support of the second possibility, a multitude of factors such as Sp1, Sp3, KLF4, HNF4, thyroid hormone receptor, Cdx1 and Cdx2, and Kruppel type zinc finger protein, ZBP-89, have been reported to bind to IAP promoter and regulate IAP promoter activity (3,37,41,52,53,65). Several of these factors bind in close proximity to the nine potential GATA sites present in the IAP promoter.…”

Notch signaling pathway and Cdx2 expression in the development of Barrett's esophagus

“…Cdx2 is a transcriptional activator of a number of intestine-specific genes, including MUC2, sucrose-isomaltase, guanylyl cyclase C, and intestinal alkaline phosphatase (IAP). [37][38][39][40][41] Furthermore, ATOH1 also contributes to induction of the inter-regulation network with Cdx2 and indirectly stimulates cellular transdifferentiation into IM.…”

Epithelial: Lamina Propria Lymphocyte Interactions Promote Epithelial Cell Differentiation

“…Moreover, it was recently shown that CDX2 alters the proliferation of intestinal crypt cells and stimulates the expression of distinct intestinal differentiation markers 14,15 . We therefore examined CDX2 mRNA by Real-Time PCR in T84 cells co-cultured with normal, CD or UC LPL for 4 days (Fig 3).…”

“…In contrast to CDX1 which is mainly expressed in the crypt compartment (although not restricted to proliferative cells) 14 , the CDX2 homeoproteins are mainly expressed in differentiating enterocytes 15 , triggering growth retardation and cell differentiation by overexpression in several intestinal lines in vitro 16 . Furthermore, genes regulated by either CDX1 or CDX2 generally define a functional differentiated phenotype, such as sucraseisomaltase 16 , dipeptidyl peptidase IV 14 , or intestinal alkaline phosphatase (IAP) 15 .…”