The mucin MUC4 and its membrane partner ErbB2 regulate biological properties of human CAPAN-2 pancreatic cancer cells via different signalling pathways

The mucin MUC4 and its membrane partner the ErbB2 oncogenic receptor are potential interacting partners in human pancreatic tumour development. However, the way they function is still largely unknown. In this work, we aimed to identify the cellular mechanisms and the intracellular signalling pathways under the control of both ErbB2 and MUC4 in a human pancreatic adenocarcinomatous cell line. Using co-immunoprecipitation and GST pull-down, we show that MUC4 and ErbB2 interact in the human pancreatic adenocarcinomatous cell line CAPAN-2 via the EGF domains of MUC4. Stable cell clones were generated in which either MUC4 or ErbB2 were knocked down (KD) by a shRNA approach. Biological properties of these cells were then studied in vitro and in vivo. Our results show that ErbB2-KD cells are more apoptotic and less proliferative (decreased cyclin D1 and increased p27kip1 expression) while migration and invasive properties were not altered. MUC4-KD clones were less proliferative with decreased cyclin D1 expression, G1 cell cycle arrest and altered ErbB2/ErbB3 expression. Their migration properties were reduced whereas invasive properties were increased. Importantly, inhibition of ErbB2 and MUC4 expression did not impair the same signalling pathways (inhibition of MUC4 expression affected the JNK pathway whereas that of ErbB2 altered the MAPK pathway). Finally, ErbB2-KD and MUC4-KD cells showed impaired tumour growth in vivo. Our results show that ErbB2 and MUC4, which interact physically, activate different intracellular signalling pathways to regulate biological properties of CAPAN-2 pancreatic cancer cells.

Galectin-3 regulates MUC1 and EGFR cellular distribution and EGFR downstream pathways in pancreatic cancer cells

MUC1 is a transmembrane glycoprotein which is typically expressed at the apical membrane of normal epithelial cells. In cancer cells, the over-expression of MUC1 and its aberrant localization around the cell membrane and in the cytoplasm favours its interaction with different protein partners such as epidermal growth factor receptor (EGFR) and can promote tumour proliferation through the activation of oncogenic signalling pathways. Our aims were to study the mechanisms inducing MUC1 cytoplasmic localization in pancreatic cancer cells, and to decipher their impact on EGFR cellular localization and activation. Our results showed that galectin-3, an endogenous lectin, is co-expressed with MUC1 in human pancreatic ductal adenocarcinoma, and that it favours the endocytosis of MUC1 and EGFR. Depletion of galectin-3 by RNA interference increased the interaction between MUC1 and EGFR, EGFR and ERK-1,2 phosphorylation, and translocation of EGFR to the nucleus. On the contrary, silencing of galectin-3 led to a decrease of cyclin-D1 levels and of cell proliferation. The galectin-3-dependent regulation of MUC1/EGFR functions may represent an interesting mechanism modulating the EGFR-stimulated cell growth of pancreatic cancer cells.

Abstract 1056: Galectin-3 induces MUC1 cytoplasmic retention and regulates the EGF-induced EGFR phosphorylation

Pancreatic ductal adenocarcinoma (PDAC) is thought to derive from the epithelial ductal cells of which the apical pole is facing the lumen of the pancreatic ducts. In physiological state, the transmembrane mucin MUC1 is expressed at the apical pole where it protects the cell, senses the environment and modulates signal transduction notably by interacting with EGFR. In tumor cells, the localization of MUC1 glycoprotein is modified. MUC1 expression at the membrane becomes circumferential and accumulates in the cytoplasm. This sequestration is thought to deliver oncogenic signals to the cell, and is used by pathologists on fine-needle aspirates of pancreatic lesions as an indicator of malignancy. However, the mechanisms explaining the modified topography of MUC1 expression in cancer cells are still unknown. Since it was previously demonstrated that endogenous lectins from the galectin family, especially galectin-3 and −4, control the apical targeting of glycoproteins in epithelial cells, our aim was to study the role of galectin-3 in the control of MUC1 expression topography in PDAC, and in the cell invasiveness in vitro. To this end we stably and selectively knocked-down (KD) galectin-3 expression by shRNA approach in the pancreatic polarized CAPAN-1 cells. Three different shRNA targeting LGALS3 mRNA were designed (sh1, sh2, sh3) together with a scramble control one (sc). Sh1 and sh3 cells were selected on the basis of the efficiency of the KD evaluated both at RNA and protein levels. Galectin-3 down-regulation is associated with a decrease of both MUC1 and EGFR protein levels. However, sh1 and sh3 cells expressed 2-fold higher levels of phosphoEGFR in response to EGF treatment than sc cells. The localization of MUC1 and EGFR was studied by confocal microscopy. In sc cells, MUC1 staining mainly concerns the apical surface and the cytoplasm as expected. In sh1 cells, invalidation of galectin-3 led to a strong decrease of MUC1 cytoplasmic labeling. To check the clinical relevance of our data, we performed MUC1 and galectin-3 immunostaining on 16 human PDAC surgically removed in our hospital. In all PDAC, 100% of the tumor cells exhibited a positive and strong MUC1 immunostaining that concerned the cell cytoplasm. By contrast, in normal ductal cells MUC1 staining was restricted to the apical side. Galectin-3 staining was weaker and more heterogeneous than that of MUC1. In all PDAC, 5-80% of the tumor cells were galectin-3 positive with a variable intensity of the immunostaining. Finally, sh1, sh3 and sc cell invasiveness was assessed in vitro on collagen type I matrix. Preliminary results showed that sh1 and sh3 cells lost their in vitro invasive phenotype. In conclusion, our data showed that galectin-3 is responsible for MUC1 cytoplasmic retention in pancreatic tumor cells. Silencing of galectin-3 promotes MUC1 localization at the cell membrane, and increases EGF-induced EGFR phosphorylation.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1056.

[Indigenous medical assistance in Madagascar (1898-1950)]

The foundations of local health services in Madagascar were laid when the island was taken over by the French in 1896. Medical care was a major priority for the first colonial governor named General Galliéni. Local health services expanded greatly from 1896 to 1950 thanks notably to institutions such as the Tananarive Medical School and Pasteur Institute. These services played a crucial role in the fight against smallpox and bubonic plague. However they were also used for political purposes by both colonial and independent governments. In sum the history of local health services in Madagascar can be described as a battle between political power and scientific knowledge. The overall result is positive for some and controversial for others.

Three-Dimensional Ultrastructural Karyotype Analysis from the Meiotic Parthenogenetic Nematode Heterodera betulae

Meiotic chromosome structure and function are described in the plant-parasitic nematode Heterodera betulae. Twelve synaptonemal complexes (SCs) were reconstructed from pachytene nuclei; therefore, n=12 is predicted for this species. Morphologically distinct sex chromosomes were not observed. Only one end of the SC is attached to the nuclear envelope, and there is no bouquet arrangement at pachytene. The structure of the SC in this meiotic parthenogenetic nematode was different than in other nematodes that reproduce via amphimixis; a striated central element with transverse filaments was not observed. Multiple SCs, or polycomplexes, were present in the nucleus. Recombination nodules were not observed. The centrioles were comprised of nine doublet microtubules connected by a ring, which is a distinct modification from the typical nine triplet microtubules without any interconnecting structure.

Meiotic Structures in the Animal-Parasitic Nematode Ascaris megalocephala: Synaptonemal Complexes, Recombination Nodules, and Centrioles

Two synaptonemal complexes (SCs) were present in the pachytene nuclei of Ascaris megalocephala. The SC was tripartite and comprised of two lateral elements (25 nm) with a striated central element (25 nm) and a central region of 65 nm. Spherical recombination nodules were observed to be associated only with the central element, although they are non-existent in the related A. lumbricoides var. suum (Goldstein, 1977). The SCs were attached to the nuclear envelope at only one end, while the other end was free in the nucleoplasm. This lack of bouquet formation of the chromosomes is consistent with all other nematodes studied. Morphologically distinct sex chromosomes were not observed, which differs from the presence of five Y-chromosomes present in A. lumbricoides var. suum (Goldstein and Moens, 1976). Centrioles (0.2 microm wide) reproduced by budding off the parental centriole. The centrioles consisted of nine singlet microtubules connected by an electron-dense proteinaceous ring. This structure is consistent with centrioles described in other nematodes, yet distinctly different from the centriole structure observed in most organisms in which it consists of nine triplet microtubules without any connecting ring. Multiple synaptonemal complexes, or polycomplexes, are found in A. megalocephala and A. lumbriocoides var. suum. They appear as stacked SC and are present inside the nucleus during zygotene and in the cytoplasm at pachytene.