Subcellular localization of the ABCG2 transporter in normal and malignant human gallbladder epithelium

Abstract

Epithelium of the gallbladder and biliary tract is exposed to high concentrations of potentially harmful exogenous and endogenous compounds excreted into primary bile. As the ATP-dependent efflux pump ABCG2 can prevent cellular accumulation of anticancer drugs, estrogen sulfate, xenobiotics, porphyrins, and sterols, its expression in the biliary tract might mediate protection by hindering their penetration. We therefore investigated the expression and subcellular distribution of ABCG2 in normal and malignant human gallbladder. After demonstrating ABCG2 expression in gallbladder epithelium by RT-PCR and Western blotting, we analyzed the subcellular localization of ABCG2 by indirect immunofluorescence in gallbladder adenocarcinoma specimens, and compared it to that in cholelithiasis, and normal gallbladder samples (n ¼ 54). In control, cholelithiasis, and well-differentiated tumor samples (grade 1, T1-3), ABCG2 is present at the luminal membrane of epithelial cells, which was proven by colocalization of apical-bound TRITC-labeled lectin (wheat germ agglutinin). In poorly differentiated gallbladder adenocarcinomas, intracellular ABCG2, in addition to luminal ABCG2 immunoreactivity, was found in 13/21 carcinoma samples (grade 2 and 3, T2-4, Po0.01). In 3/11 of grade 3 tumors, ABCG2 was present in the cytoplasmatic compartment only (Po0.01). In proliferating bile ducts of cholangiocarcinomas, ABCG2 showed an analogous staining pattern with presence in cytosolic compartments. However, the apical marker enzyme neutral endopeptidase remained on the membrane in all samples. To study whether phosphatidylinositol 3-kinase (PI3K) signaling might be necessary for ABCG2 membrane insertion, we treated freshly isolated human gallbladder epithelial cells with the PI3K inhibitor wortmannin. As assessed by indirect immunofluorescence, this maneuver redistributes ABCG2 to intracellular compartments. In conclusion, our data suggest a protective role for ABCG2 in well-differentiated gallbladder epithelial cells. Cytoplasmatic accumulation of ABCG2 in poorly differentiated carcinomas might coincide with malfunctioning of PI3K-signaling pathways during tumor progression. Laboratory Investigation (2004) 84, 1024-1036, advance online publication, 7 May 2004; doi:10.1038/labinvest.3700127Keywords: ABCG2; gallbladder epithelium; gallbladder carcinoma; cholelithiasis; phosphatidylinositol 3-kinase; BCRP; neutral endopeptidase Cholelithiasis, and as a complication, acute cholecystitis, are among the most common gastrointestinal diseases in industrialized countries, while carcinomas of the gallbladder are quite rare. Although cholelithiasis is considered an important risk factor for gallbladder carcinoma, only 1-2% of patients who have operations for gallstones are diagnosed with gallbladder cancer at the time of surgery. The epidemiological characteristics of cholelithiasis and gallbladder cancer are closely related. Risk factors associated with the formation of cholesterol gallstones including estrogen exposure, nutritional factors, obesity...

Molecular Pharmacology of ABCG2 and Its Role in Chemoresistance

“…As such, these processes should involve ABCG2 if its main physiologic function is to protect the body from exposure to harmful xenobiotics. Consistent with this, ABCG2 expression is found in the canalicular membrane of hepatocytes (Maliepaard et al, 2001a), in the bile ducts (Vander Borght et al, 2006), in the gallbladder (Aust et al, 2004), and in the apical membrane of proximal kidney tubule epithelial cells (Huls et al, 2008) (Fig. 8).…”

Pancreatic stellate/myofibroblast cells express G-protein-coupled melatonin receptor 1

“…The green MT1 staining in a stromal cell is also seen in Fig. 1B, in which the epithelial cells in the pancreatic ducts are identified by staining for CK19 (red fluorescence) [14]. However, these ductal epithelial cells are negative for MT1.…”

“…Double immunofluorescence staining of MT1 and the respective marker protein (see below) was performed on the paraffin-embedded sections after deparaffinization and antigen retrieval as described [14]. The rabbit polyclonal antibodies against the melatonin receptor MT1 (type 1A, ab13036) and MT2 (type 1B, ab13357) were purchased from Abcam (Cambridge, UK).…”

“…But the expression of MT1 and MT2 in pancreatic beta cells, and pancreatic carcinoma cell lines indicates that these receptors might be important for physiological and pathophysiological processes in this organ [14,15].…”

Ion Transport Across the Gallbladder Epithelium

“…Although gallbladder carcinoma is quite rare, colelithiasis is also considered an important risk factor for this kind of tumour [14].…”