A New Story of the Three Magi: Scaffolding Proteins and lncRNA Suppressors of Cancer

Scaffolding molecules exert a critical role in orchestrating cellular response through the spatiotemporal assembly of effector proteins as signalosomes. By increasing the efficiency and selectivity of intracellular signaling, these molecules can exert (anti/pro)oncogenic activities. As an archetype of scaffolding proteins with tumor suppressor property, the present review focuses on MAGI1, 2, and 3 (membrane-associated guanylate kinase inverted), a subgroup of the MAGUK protein family, that mediate networks involving receptors, junctional complexes, signaling molecules, and the cytoskeleton. MAGI1, 2, and 3 are comprised of 6 PDZ domains, 2 WW domains, and 1 GUK domain. These 9 protein binding modules allow selective interactions with a wide range of effectors, including the PTEN tumor suppressor, the β-catenin and YAP1 proto-oncogenes, and the regulation of the PI3K/AKT, the Wnt, and the Hippo signaling pathways. The frequent downmodulation of MAGIs in various human malignancies makes these scaffolding molecules and their ligands putative therapeutic targets. Interestingly, MAGI1 and MAGI2 genetic loci generate a series of long non-coding RNAs that act as a tumor promoter or suppressor in a tissue-dependent manner, by selectively sponging some miRNAs or by regulating epigenetic processes. Here, we discuss the different paths followed by the three MAGIs to control carcinogenesis.

Rac1 Signaling: From Intestinal Homeostasis to Colorectal Cancer Metastasis

The small GTPase Rac1 has been implicated in a variety of dynamic cell biological processes, including cell proliferation, cell survival, cell-cell contacts, epithelial mesenchymal transition (EMT), cell motility, and invasiveness. These processes are orchestrated through the fine tuning of Rac1 activity by upstream cell surface receptors and effectors that regulate the cycling Rac1-GDP (off state)/Rac1-GTP (on state), but also through the tuning of Rac1 accumulation, activity, and subcellular localization by post translational modifications or recruitment into molecular scaffolds. Another level of regulation involves Rac1 transcripts stability and splicing. Downstream, Rac1 initiates a series of signaling networks, including regulatory complex of actin cytoskeleton remodeling, activation of protein kinases (PAKs, MAPKs) and transcription factors (NFkB, Wnt/β-catenin/TCF, STAT3, Snail), production of reactive oxygen species (NADPH oxidase holoenzymes, mitochondrial ROS). Thus, this GTPase, its regulators, and effector systems might be involved at different steps of the neoplastic progression from dysplasia to the metastatic cascade. After briefly placing Rac1 and its effector systems in the more general context of intestinal homeostasis and in wound healing after intestinal injury, the present review mainly focuses on the several levels of Rac1 signaling pathway dysregulation in colorectal carcinogenesis, their biological significance, and their clinical impact.

Interest of cytology combined with Xpert® HPV and Anyplex® II HPV28 Detection human papillomavirus (HPV) typing: differential profiles of anal and cervical HPV lesions in HIV-infected patients on antiretroviral therapy

OBJECTIVES

The aim of the study was to assess the interest to combine cytological examination and human papillomavirus (HPV) typing of anal and cervical Papanicolaou (Pap) smears of HIV-infected patients on combination antiretroviral therapy (cART), to evaluate whether differences in prevalence exist between anal and cervical squamous intraepithelial lesions in patients with high-risk oncogenic HPV infection.

METHODS

Anal and/or cervical Pap smears were obtained by anoscopy and/or colposcopy in 238 subjects recruited consecutively in 2015: anal smears were obtained from 48 male and female patients [42 men; 35 men who have sex with men (MSM)] and cervical smears from 190 female patients. Cytological Bethesda classification was coupled with HPV typing. HPV typing was performed, on the same smears, using the Xpert^® HPV Assay, which detects only high-risk HPV (hrHPV), and the Anyplex^® II HPV28 Detection assay, which detects hrHPV and low-risk (lr) HPV.

RESULTS

Our data showed clear-cut differences between the anal and cervical samples. Compared with the cervical samples, the anal samples exhibited (1) more numerous cytological lesions, which were histologically proven; (2) a higher hrHPV infection prevalence; (3) a higher prevalence of multiple hrHPV coinfections whatever HPV typing kit was used; (4) a predominance of HPV16 and HPV18/45 types. Overall, there was an almost perfect agreement between the two HPV typing assays (absolute agreement = 90.3%).

CONCLUSIONS

Co-testing consisting of cytology and HPV typing is a useful screening tool in the HIV-infected population on cART. It allows detection of prevalence differences between anal and cervical HPV-related lesions. As recently recommended, anal examination should be regularly performed especially in HIV-infected MSM but also in HIV-infected women with genital hrHPV lesions.

A Squalene-Based Nanomedicine for Oral Treatment of Colon Cancer

Nanotechnology offers many possibilities to improve drug treatments, including with regard to drug pharmacology. The current study reports a simple approach to improve cisplatin efficacy in the treatment of colon cancer through the creation of orally administered squalenoylated nanoparticles loaded with cisplatin (SQ-CDDP NP). Cytotoxic effects of SQ-CDDP NP were assessed in human colonic cells and in mouse models of intestinal cancer. In cell culture, SQ-CDDP NP exhibited at least 10-fold greater cytotoxic potency compared with uncomplexed cisplatin, reflecting an enhancement in intracellular accumulation and DNA platination. Mechanistic investigations showed that SQ-CDDP NP stimulated ROS production, expression of heavy metal-inducible and stress-inducible genes, stress kinase cascades, and apoptosis. In Apc^Min/+ mice, a model of intestinal tumorigenesis, oral administration of SQ-CDDP NP curtailed spontaneous tumor formation and azoxymethane-induced colon carcinogenesis with no apparent evidence of tissue toxicity. Our results offer preclinical validation of a nanocarrier formulation that can safely improve chemotherapeutic efficacy, address risks of drug resistance, and improve patient compliance by enabling oral administration. Cancer Res; 77(11); 2964-75. ©2017 AACR.

Evidence for different expression profiles for c-Met, EGFR, PTEN and the mTOR pathway in low and high grade endometrial carcinomas in a cohort of consecutive women. Occurrence of PIK3CA and K-Ras mutations and microsatellite instability

Molecular and genetic investigations in endometrial carcinogenesis may have prognostic and therapeutic implications. We studied the expression of EGFR, c-Met, PTEN and the mTOR signalling pathway (phospho-AKT/phospho-mTOR/phospho-RPS6) in 69 consecutive tumours and 16 tissue microarrays. We also analysed PIK3CA, K-Ras mutations and microsatellite instability (MSI). We distinguished two groups: group 1 (grade 1 and 2 endometrioid cancers) and group 2 (grade 3 endometrioid and type II clear and serous cell cancers). We hypothesised that these histological groups might have different features. We found that a) survival was higher in group 1 with less aggressive tumours (P⟨0.03); b) EGFR (P=0.01), PTEN and the AKT/mTOR/RPS6 signalling pathway were increased in group 1 versus group 2 (P=0.05 for phospho-mTOR); c) conversely, c-Met was higher (P⟨0.03) in group 2 than in group 1; d) In group 1, EGFR was correlated with c-Met, phospho-mTOR, phospho-RPS6 and the global activity of the phospho-AKT/phospho-mTOR/phospho-RPS6 pathway. In group 2, EGFR was correlated only with the phospho-AKT/phospho-mTOR/phospho-RPS6 pathway, whereas c-Met was correlated with PTEN; e) survival was higher for tumours with more than 50% PTEN-positive cells; f) K-RAS and PIK3CA mutations occurred in 10-12% of the available tumours and MSI in 40.4%, with a loss of MLH1 and PMS2 expression. Our results for endometrial cancers provide the first evidence for a difference in status between groups 1 and 2. The patients may benefit from different targeted treatments, anti-EGFR agents and rapamycin derivatives (anti-mTOR) for group 1 and an anti c-MET/ligand complex for group 2.

Differential reactivity of human mammary artery and saphenous vein to prostaglandin E(2) : implication for cardiovascular grafts

BACKGROUND AND PURPOSE

Human internal mammary arteries (IMA) and saphenous veins (SV) are frequently used for coronary artery bypass graft surgery. Intra- and postoperatively, the bypass grafts are exposed to inflammatory conditions, under which there is a striking increase in the synthesis of prostaglandin E(2) (PGE(2) ). In this context, the physiological response of these vascular grafts to PGE(2) is highly relevant. The aim of this study was thus to characterize the PGE(2) receptor subtypes (EP(1) , EP(2) , EP(3) or EP(4) ) involved in modulation of the vascular tone in these two vessels.

EXPERIMENTAL APPROACH

Rings of IMA and SV were prepared from 48 patients. The rings were mounted in organ baths for isometric recording of tension, and a pharmacological study was performed, together with associated reverse transcriptase PCR and immunohistochemistry experiments.

KEY RESULTS

PGE(2) induced contractions of IMA (E(max) = 1.43 ± 0.20 g; pEC(50) = 7.50 ± 0.10); contractions were also observed with the EP(3) receptor agonists, sulprostone, 17-phenyl-PGE(2) , misoprostol or ONO-AE-248. In contrast, PGE(2) induced relaxation of the precontracted SV (E(max) =-0.22 ± 0.02 g; pEC(50) = 7.14 ± 0.09), as did the EP(4) receptor agonist, ONO-AE1-329. These results were confirmed by the use of selective EP receptor antagonists (GW627368X, L-826266, ONO-8713, SC-51322) and by molecular biology and immunostaining.

CONCLUSIONS AND IMPLICATIONS

PGE(2) induced potent and opposite effects on the human vascular segments used for grafting, namely vasoconstriction of the IMA and vasodilatation of the SV via EP(3) and EP(4) receptors respectively. These observations suggest that EP(3) and EP(4) receptors could constitute therapeutic targets to increase vascular graft patency.

Identification of mitogen-activated protein/extracellular signal-responsive kinase kinase 2 as a novel partner of the scaffolding protein human homolog of disc-large

Human disc-large homolog (hDlg), also known as synapse-associated protein 97, is a scaffold protein, a member of the membrane-associated guanylate kinase family, implicated in neuronal synapses and epithelial-epithelial cell junctions whose expression and function remains poorly characterized in most tissues, particularly in the vasculature. In human vascular tissues, hDlg is highly expressed in smooth muscle cells (VSMCs). Using the yeast two-hybrid system to screen a human aorta cDNA library, we identified mitogen-activated protein/extracellular signal-responsive kinase (ERK) kinase (MEK)2, a member of the ERK cascade, as an hDlg binding partner. Site-directed mutagenesis showed a major involvement of the PSD-95, disc-large, ZO-1 domain-2 of hDlg and the C-terminal sequence RTAV of MEK2 in this interaction. Coimmunoprecipitation assays in both human VSMCs and human embryonic kidney 293 cells, demonstrated that endogenous hDlg physically interacts with MEK2 but not with MEK1. Confocal microscopy suggested a colocalization of the two proteins at the inner layer of the plasma membrane of confluent human embryonic kidney 293 cells, and in a perinuclear area in human VSMCs. Additionally, hDlg also associates with the endoplasmic reticulum and microtubules in these latter cells. Taken together, these findings allow us to hypothesize that hDlg acts as a MEK2-specific scaffold protein for the ERK signaling pathway, and may improve our understanding of how scaffold proteins, such as hDlg, differentially tune MEK1/MEK2 signaling and cell responses.

Distinct functional outputs of PTEN signalling are controlled by dynamic association with β-arrestins

The tumour suppressor PTEN (phosphatase and tensin deleted on chromosome 10) regulates major cellular functions via lipid phosphatase-dependent and -independent mechanisms. Despite its fundamental pathophysiological importance, how PTEN's cellular activity is regulated has only been partially elucidated. We report that the scaffolding proteins β-arrestins (β-arrs) are important regulators of PTEN. Downstream of receptor-activated RhoA/ROCK signalling, β-arrs activate the lipid phosphatase activity of PTEN to negatively regulate Akt and cell proliferation. In contrast, following wound-induced RhoA activation, β-arrs inhibit the lipid phosphatase-independent anti-migratory effects of PTEN. β-arrs can thus differentially control distinct functional outputs of PTEN important for cell proliferation and migration.

Resistin-like molecule beta regulates intestinal mucous secretion and curtails TNBS-induced colitis in mice

BACKGROUND

Resistin and resistin-like molecule (RELM)beta comprise a novel class of cysteine-rich proteins secreted into the circulation implicated in hepatic insulin resistance and inflammation. RELMbeta is specifically produced by intestinal goblet cells but regulation of its expression and much of its local function are not elucidated. RELMbeta has been suggested to regulate colonic inflammation susceptibility, which is dependent on the mucosal barrier integrity.

METHODS

In this work we explored the physiopathological role of RELMbeta in the colon. Among agents tested, carbachol and gastrin were strong inhibitors of RELMbeta mRNA accumulation. We examined the effect of recombinant RELMbeta on mucin secretion by human mucus-secreting HT29-Cl.16E cells in culture and by mouse colonic goblet cells in vivo.

RESULTS

RELMbeta upregulated MUC2 and M1/MUC5AC gene expression in HT29-Cl.16E cells. RELMbeta enhanced M1/MUC5AC secretion by human colonic HT29-Cl.16E cells and MUC2 secretion by murine intestinal goblet cells. RELMbeta exerted its action exclusively on the apical side of HT29-Cl.16E cells, in agreement with its luminal mucosecretagogue effect in mice. Its action required calcium, protein kinase C, tyrosine kinases, and extracellular-regulated protein kinase activities and was synergized by carbachol. An intracolonic RELMbeta challenge was performed in the trinitrobenzene sulfonic acid (TNBS)-murine model of colitis and macroscopic and histological scores were monitored. The macroscopic and histopathological severity of TNBS-induced colitis was significantly attenuated by RELMbeta pretreatment.

CONCLUSIONS

A direct participation in maintaining the mucosal defense barrier can be ascribed to RELMbeta in line with a regulatory role in intestinal inflammation.

Vasorelaxation induced by prostaglandin E2 in human pulmonary vein: role of the EP4 receptor subtype

BACKGROUND AND PURPOSE

PGE2 has been shown to induce relaxations in precontracted human pulmonary venous preparations, while in pulmonary arteries this response was not observed. We investigated and characterized the prostanoid receptors which are activated by PGE2 in the human pulmonary veins.

EXPERIMENTAL APPROACH

Human pulmonary arteries and veins were cut as rings and set up in organ baths in presence of a TP antagonist. A pharmacological study was performed using selective EP1-4 ligands. The cellular localization of the EP4 receptors by immunohistochemistry and their corresponding transcripts were also investigated in these vessels.

KEY RESULTS

PGE2 and the EP4 agonists (L-902688, ONO-AE1-329) induced potent vasodilatation of the human pulmonary vein, pEC50 values: <7.22+/-0.20, 8.06+/-0.12 and 7.80+/-0.09, respectively. These relaxations were inhibited by the EP(4) antagonist GW627368X and not modified in presence of the DP antagonist L-877499. Higher concentrations (>or=1 microM) of the EP2 agonist ONO-AE1-259 induced relaxations of the veins. The EP4 agonists had no effect on the precontracted arteries. Finally, the EP(1) antagonists ONO-8713 and SC-51322 potentiated the relaxation of the veins induced by PGE2. EP4 and EP1 receptors were detected by immunohistochemistry in the veins but not in the arteries. EP4 mRNA accumulation was also greater in the veins when compared with the arterial preparations.

CONCLUSIONS AND IMPLICATIONS

Of the 4 EP receptor subtypes, smooth muscle cells in the human pulmonary vein express the EP4 and EP1 receptor subtypes. The relaxations induced by PGE2 in this vessel result from the activation of the EP4 receptor.

A new mRNA splice variant coding for the human EP3-I receptor isoform

The cellular localization of prostaglandin E2 receptors (EP) and their corresponding transcripts were investigated in human gastric and vascular tissues. A strong staining of the EP3 receptor on the gastric glands, mucous cells, media of the mammary and pulmonary arteries was observed by immunohistochemistry. We identified a new mRNA splice variant of the EP3 gene in human gastric fundic mucosa, mammary artery and pulmonary vessels. This EP3-Ic transcript contains exons 1, 2, 3, 5 and 6 of the EP3 gene and should be translated in the EP3-I isoform. In addition, the EP3-Ib, EP3-II, EP3-III, EP3-IV and EP3-e mRNAs were detected in these tissues.

Protein kinase WNK2 inhibits cell proliferation by negatively modulating the activation of MEK1/ERK1/2

The recently identified subfamily of WNK protein kinases is characterized by a unique sequence variation in the catalytic domain and four related human WNK genes were identified. Here, we describe the cloning and functional analysis of the human family member WNK2. We show that the depletion of endogenous WNK2 expression by RNA interference in human cervical HeLa cancer cells led to the activation of the extracellular signal-regulated kinase (ERK)1/2 mitogen-activated protein kinases but, in contrast to the depletion of WNK1, had no effect on ERK5. Furthermore, expression of a kinase-dead WNK2-K207M mutant also activated ERK1/2 suggesting that WNK2 catalytic activity is required. Depletion of WNK2 expression increased G1/S progression and potentiated the cellular response to low epidermal growth factor concentrations. The molecular mechanism of ERK1/2 activation in WNK2-depleted cells lies downstream of the Raf kinases and involves MEK1 phosphorylation at serine 298 in both HeLa and HT29 colon cancer cells. This modification is linked to the upregulation of MEK1 activity toward ERK1/2. Together, these results provide evidence that WNK2 is involved in the modulation of growth factor-induced cancer cell proliferation through the MEK1/ERK1/2 pathway. The data identify WNK2 as a candidate tumor suppressor gene and suggest a coordinated activity of WNK kinases in the regulation of cell proliferation.

Dihydroxyphenylethanol induces apoptosis by activating serine/threonine protein phosphatase PP2A and promotes the endoplasmic reticulum stress response in human colon carcinoma cells

The search for effective chemopreventive compounds is a major challenge facing research into preventing the progression of cancer cells. The naturally occurring polyphenol antioxidants look very promising, but their mechanism of action still remains poorly understood. Here, we show that 2-(3,4-dihydroxyphenyl)ethanol (DPE), a phenol antioxidant derived from olive oil, induces growth arrest and apoptosis in human colon carcinoma HT-29 cells. The mechanisms involve prolonged stress of the endoplasmic reticulum (ER) leading to the activation of the two main branches of the unfolded protein response (UPR), including the Ire1/XBP-1/GRP78/Bip and PERK/eIF2alpha arms. DPE treatment led to overexpression of the pro-apoptotic factor CHOP/GADD153 and persistent activation of the Jun-NH2-terminal kinase/activator protein-1 signaling pathway. DPE concomitantly modulated the extracellular signal-regulated kinase 1/2 and Akt/PKB pro-survival factors by altering their phosphorylation status as well as inhibiting tumor necrosis factor-alpha-induced nuclear factor-kappaB activation by inactivating the phosphorylation of nuclear factor inhibitor-kappaB kinase. These findings prompted us to investigate the possible involvement of phosphatases in DPE-mediated action. Using phosphatase inhibitors and RNA interference to silence the Ser/Thr phosphatase 2A (PP2A) prevented DPE-induced cell death. These findings demonstrate that DPE specifically activates PP2A, which plays a key initiating role in various pathways that lead to apoptosis in colon cancer cells.

Leptin stimulates the proliferation of human colon cancer cells in vitro but does not promote the growth of colon cancer xenografts in nude mice or intestinal tumorigenesis in Apc(Min/+) mice

BACKGROUND AND AIMS

Leptin, the product of the ob gene, has been suggested to increase the risk of colon cancer. However, we have shown that although leptin stimulates epithelial cell proliferation it reduces the development of carcinogen induced preneoplastic lesions in the rat colon. Here, we explored the effect of leptin in vitro on proliferation of human colon cancer cells, and in vivo on the growth of HT-29 xenografts in nude mice and the development of intestinal tumours in Apc(Min/+) mice.

METHODS

Proliferation of HT-29, LoVo, Caco2, and SW 480 cells was assessed in the absence or presence of leptin (20-500 ng/ml) by 3H-thymidine incorporation and cell count. Leptin (800 microg/kg/day) or its vehicle was delivered for four weeks to nude mice, inoculated with HT-29 cells on day 0, and for six weeks to Apc(Min/+) mice.

RESULTS

Leptin dose dependently stimulated cell DNA synthesis and growth in all cell lines. In nude mice, leptin caused a 4.3-fold increase in plasma leptin levels compared with pair fed controls. This hyperleptinaemia, despite leptin receptor expression in tumours, did not induce significant variation in tumour volume or weight. Tumour Ki-67 index was even inhibited. In leptin treated Apc(Min/+) mice, a 2.4-fold increase in plasma leptin levels did not modify the number, size, or distribution of intestinal adenomas compared with pair fed controls.

CONCLUSIONS

Leptin acts as a growth factor on colon cancer cells in vitro but does not promote tumour growth in vivo in the two models tested. These findings do not support a pivotal role for hyperleptinaemia in intestinal carcinogenesis.

Cholinesterase activity in human pulmonary arteries and veins: correlation with mRNA levels

Isolated intact human pulmonary arteries and veins were used to determine the acetylcholinesterase (AChE) or butyrylcholinesterase (BChE) activities in the absence or presence of two selective cholinesterase (ChE) inhibitors, iso-OMPA or BW284c51, respectively. These results were compared with the mRNA levels for each enzyme in human pulmonary vessels. Total ChE activities measured in presence of acetylthiocholine (ACTI, 1 mM) in intact vascular preparations were 45+/-04 and 114+/-07 mU/g tissue in human pulmonary arteries (n=14) and veins (n=14), respectively. These activities were completely abolished in presence of 10 microM neostigmine. In both types of vessels AChE and BChE activities were observed. These activities were at least 2-fold higher in human pulmonary veins when compared with arteries and were correlated with the accumulation of the corresponding transcripts (n=8). In each type of vessel, similar total ChE activities were detected in homogenized and intact preparations, while in human bronchial preparations this activity was 5-fold higher in homogenates than in intact preparations. Together these results provide evidence that the ChE activities in human pulmonary vessels may be extracellular and that the higher activity measured in veins as compared to arteries was associated with the differential accumulation of the corresponding transcripts.

Implication of the MAGI‐1b/PTEN signalosome in stabilization of adherens junctions and suppression of invasiveness

We recently established the critical role of the lipid phosphatase activity of the PTEN tumor suppressor in stabilizing cell-cell contacts and suppressing invasiveness. To delineate the effector systems involved, we investigated the interaction of PTEN with E-cadherin junctional complexes in kidney and colonic epithelial cell lines. PTEN and the p85 regulatory subunit of phosphatidylinositol 3-OH kinase (PI3K) co-immunoprecipitated with E-cadherin and catenins. By using a yeast two-hybrid assay, we demonstrated that PTEN interacted indirectly with beta-catenin by binding the scaffolding protein MAGI-1b. This model was corroborated in various ways in mammalian cells. Ectopic expression of MAGI-1b potentiated the interaction of PTEN with junctional complexes, promoted E-cadherin-dependent cell-cell aggregation, and reverted the Src-induced invasiveness of kidney MDCKts-src cells. In this model, MAGI-1b slightly decreased the activity of AKT, a downstream effector of PI3K. By using dominant-negative and constitutively active AKT expression vectors, we demonstrated that this kinase was included in the pathways involved in Src-induced destabilization of junctional complexes and was necessary and sufficient to trigger invasiveness. We propose that the recruitment of PTEN at adherens junctions by MAGI-1b and the local down-regulation of phosphatidylinositol-3,4,5-trisphosphate pools and downstream effector systems at the site of cell-cell contacts are focal points for restraining both disruption of junctional complexes and induction of tumor cell invasion.

The lipid phosphatase activity of PTEN is critical for stabilizing intercellular junctions and reverting invasiveness

To analyze the implication of PTEN in the control of tumor cell invasiveness, the canine kidney epithelial cell lines MDCKras-f and MDCKts-src, expressing activated Ras and a temperature-sensitive v-Src tyrosine kinase, respectively, were transfected with PTEN expression vectors. Likewise, the human PTEN-defective glioblastoma cell lines U87MG and U373MG, the melanoma cell line FM-45, and the prostate carcinoma cell line PC-3 were transfected. We demonstrate that ectopic expression of wild-type PTEN in MDCKts-src cells, but not expression of PTEN mutants deficient in either the lipid or both the lipid and protein phosphatase activities, reverted the morphological transformation, induced cell-cell aggregation, and suppressed the invasive phenotype in an E-cadherin-dependent manner. In contrast, overexpression of wild-type PTEN did not counteract Ras-induced invasiveness of MDCKras-f cells expressing low levels of E-cadherin. PTEN effects were not associated with marked changes in accumulation or phosphorylation levels of E-cadherin and associated catenins. Wild-type, but not mutant, PTEN also reverted the invasive phenotype of U87MG, U373MG, PC-3, and FM-45 cells. Interestingly, PTEN effects were mimicked by N-cadherin-neutralizing antibody in the glioblastoma cell lines. Our data confirm the differential activities of E- and N-cadherin on invasiveness and suggest that the lipid phosphatase activity of PTEN exerts a critical role in stabilizing junctional complexes and restraining invasiveness.

Phenotypic and functional characterization of human thymic stromal cell lines

To establish new tools for studying human thymic stromal cells, we transfected adherent cells from a human postnatal thymus using a plasmid encoding SV40 large T antigen. Among the cell lines obtained, we characterized four epithelial cell lines (LT-TEC1 to LT-TEC4) and one thymic myoid cell line (MITC). Several morphological, functional and phenotypic differences were observed between these 2 cell types. Epithelial cells were heterogeneous and larger than myoid cells. Untreated LT-TEC lines expressed MHC class I, ICAM-1 and LFA-3 antigens and not MHC class II antigens, similarly to primary thymic epithelial cells (PTEC), while MITC line expressed only class I and LFA-3 antigens. After IFN-gamma treatment, MHC class II and ICAM-1 antigens were markedly upregulated in LT-TEC lines but not in MITC, indicating the absence or a dysfunction of regulatory factors in MITC line. Myoid cells expressed mRNA for all the subunits of the acetylcholine receptor (AChR) while epithelial cells expressed only the alpha, beta and epsilon subunits. Strikingly, LT-TEC produced much more C-C chemokines and IL-6 than MITC cells, while these latter produced higher levels of IL-8 and TNF-alpha. Altogether, these results reveal phenotypic and functional differences between these two stromal cell types, suggesting a potential involvement of myoid cells in the thymic function.

Leptin promotes invasiveness of kidney and colonic epithelial cells via phosphoinositide 3-kinase-, rho-, and rac-dependent signaling pathways

Leptin plays a key role regulating food intake, body weight and fat mass. These critical parameters are associated with an increased risk for digestive and mammary gland cancer in the Western population. Here we determined whether leptin contributes to the invasive phenotype of colonic and kidney epithelial cells at various stages of the neoplastic progression. First, leptin potently (EC50 = 10-30 ng/ml) induces invasion of collagen gels by premalignant familial adenomatous colonic cells PC/AA/C1 and nontumorigenic MDCK kidney epithelial cells, their src-transformed counterparts, and the human adenocarcinoma colonic cells LoVo and HCT-8/S11. Leptin and its Ob-Rb receptors were consistently identified by RT-PCR and immunoblotting in these cell lines, as well as in human colonic epithelial crypts, polyps, colonic tumor resections, and adjacent mucosa. Leptin-induced invasion was effectively blocked by pharmacological inhibitors of several downstream signaling pathways involved in cell transformation, namely, JAK2 tyrosine kinase (AG490), phosphoinositide PI3'-kinase (wortmannin and LY294002), mTOR kinase (rapamycin), and protein kinases C (GF109203X, Gö6976). Accordingly, leptin induces transient elevation of the PI3'-kinase lipid products in JAK2 immunoprecipitates prepared from parental MDCK cells. The leptin effect on invasion was potentiated by the activated form of the small GTPase RhoA and was abrogated by dominant negative mutants of RhoA, Rac1, and the p110alpha of PI3'-K. Our data indicate that leptin may exert a local and beneficial effect on migration of normal colonic epithelial cells and reparation of the inflamed or wounded digestive mucosa. We also emphasize a new role for leptin, linking the nutritional and body fat status to digestive cancer susceptibility by stimulating the invasive capacity of colonic epithelial cells at early stages of neoplasia. This finding has potential clinical implications for colon cancer progression and management of obesity.

B-ind1, a novel mediator of Rac1 signaling cloned from sodium butyrate-treated fibroblasts

Sodium butyrate is a multifunctional agent known to inhibit cell proliferation and to induce differentiation by modulating transcription. We have performed differential display analysis to identify transcriptional targets of sodium butyrate in Balb/c BP-A31 mouse fibroblasts. A novel butyrate-induced transcript B-ind1 has been cloned by this approach. The human homologue of this transcript contains an open reading frame that codes for a protein of 370 amino acids without known functional motifs. In transfected cells, the B-ind1 protein has been found to potentiate different effects of the small GTPase Rac1, such as c-Jun N-terminal kinase activation and transcriptional activity of nuclear factor kappaB (NF-kappaB). In addition, we have demonstrated that B-ind1 forms complexes with the constitutively activated Rac1 protein. To investigate the role of B-ind1 in Rac1 signaling, we have constructed several deletion mutants of B-ind1 and tested their ability to affect the activation of NF-kappaB by Rac1. Interestingly, the fragment encoding the median region of human B-ind1 acted as a dominant-negative variant to block Rac1-mediated NF-kappaB activity. These data define B-ind1 as a novel component of Rac1-signaling pathways leading to the modulation of gene expression.

Deregulated expression of homeobox-containing genes, HOXB6, B8, C8, C9, and Cdx-1, in human colon cancer cell lines

Previously we have demonstrated a reciprocal deregulation of various homeobox genes (HOXB6, B8, C8 and C9 vs Cdx-1) in human colorectal cancer (CRC). In the present study, using RT-PCR, we have investigated the expression pattern of these homeobox genes in various human colon cell lines, representing various stages of colon cancer progression and differentiation. Thus, we have tested polyposis coli Pc/AA adenoma cells, Caco-2, HT-29 and LS174T adenocarcinoma cell lines. All cell lines, except LS174T, demonstrated a pattern of deregulated homeobox gene expression which resembled that of CRC. In contrast, the pattern of expression of these genes in the highly oncogenic LS174T cells, as well as in Caco-2 cells transfected with activated Ha-ras or Polyoma middle T oncogene, resembled that of the normal mucosa. The reciprocal deregulation of HOX and Cdx-1 genes in CRC and in CRC-derived cell lines suggests a possible role in human CRC development.

Vegf, Vegf-B, Vegf-C and their receptors KDR, FLT-1 and FLT-4 during the neoplastic progression of human colonic mucosa

Because the crucial role of angiogenesis has been demonstrated in tumor growth and metastasis, the present study was undertaken to characterize the relative expression of vascular endothelial growth factors VEGF (vascular endothelial growth factor), VEGF-B, VEGF-C, and their receptors KDR (kinase insert domain-containing receptor), FLT-1 (fms-like tyrosine kinase), and FLT-4 in human colonic cancers, in relation to the Astler-Coller pathological classification, and to prognosis. VEGF and VEGF-B gene expression was quantified by Northern blot in 72 tumor samples matched with control tissues. VEGF gene expression was 1.4 times higher in adenocarcinomas than in control tissues (p = 0.02), but did not increase further between Astler-Coller tumor stages A and D, and did not correlate with disease recurrence for patients at stages B2 or C. In adenomas, VEGF mRNA levels were not significantly different from those in the paired control colonic mucosa. The expression pattern of VEGF isoforms, mainly identified by RT-PCR (reverse-transcriptase-coupled polymerase chain reaction) as VEGF121 and VEGF165 and to a lesser extent VEGF189, was comparable in tumor and control tissues. VEGF-B mRNA levels were unchanged during the neoplastic progression of colonic mucosa. In contrast to KDR and FLT-4, the expression of VEGF-C and FLT-1 genes increased in some pathological tissues. These results provide evidence that the early and sustained increase in VEGF transcripts and the expression of multiple angiogenic factors and receptors contribute to the development of colon cancer, and thus constitute a putative target for anti-angiogenic drug therapy.

Vegf, Vegf-B, Vegf-C and their receptors KDR, FLT-1 and FLT-4 during the neoplastic progression of human colonic mucosa

Because the crucial role of angiogenesis has been demonstrated in tumor growth and metastasis, the present study was undertaken to characterize the relative expression of vascular endothelial growth factors VEGF (vascular endothelial growth factor), VEGF-B, VEGF-C, and their receptors KDR (kinase insert domain-containing receptor), FLT-1 (fms-like tyrosine kinase), and FLT-4 in human colonic cancers, in relation to the Astler-Coller pathological classification, and to prognosis. VEGF and VEGF-B gene expression was quantified by Northern blot in 72 tumor samples matched with control tissues. VEGF gene expression was 1.4 times higher in adenocarcinomas than in control tissues (p = 0.02), but did not increase further between Astler-Coller tumor stages A and D, and did not correlate with disease recurrence for patients at stages B2 or C. In adenomas, VEGF mRNA levels were not significantly different from those in the paired control colonic mucosa. The expression pattern of VEGF isoforms, mainly identified by RT-PCR (reverse-transcriptase-coupled polymerase chain reaction) as VEGF121 and VEGF165 and to a lesser extent VEGF189, was comparable in tumor and control tissues. VEGF-B mRNA levels were unchanged during the neoplastic progression of colonic mucosa. In contrast to KDR and FLT-4, the expression of VEGF-C and FLT-1 genes increased in some pathological tissues. These results provide evidence that the early and sustained increase in VEGF transcripts and the expression of multiple angiogenic factors and receptors contribute to the development of colon cancer, and thus constitute a putative target for anti-angiogenic drug therapy.

Cloning of a novel human Rac1b splice variant with increased expression in colorectal tumors

Rac1 is a member of the Ras superfamily of small GTPases involved in signal transduction pathways that induce the formation of lamellipodia, stimulate cell proliferation and activate the JNK/SAPK protein kinase cascade. Here we describe that amplification by RT-PCR of the entire Rac1 coding sequence from a series of human adult and fetal tissues revealed beside the expected Rac1 cDNA, a variant product which contained additional 57 nucleotides between codons 75 and 76. This variant resulted in an in-frame insertion of 19 new amino acids immediately behind the switch II region, including two potential threonine phosphorylation sites for casein kinase II and protein kinase C. Primers designed within and downstream of the inserted nucleotide sequence allowed isolation of a genomic clone with intronic consensus sequences demonstrating that the insertion corresponds to a novel, yet undescribed exon 3b. This Rac1 splice variant, designated Rac1b, was predominantly identified in skin and epithelial tissues from the intestinal tract. Most notably, the expression of rac1b versus rac1 was found to be elevated in colorectal tumors at various stages of neoplastic progression, as compared to their respective adjacent tissues. We suggest that the 19 amino acid-insertion following the switch II region may create a novel effector binding site in rac1b, and thus participate in signaling pathways related to the normal or neoplastic growth of the intestinal mucosa.

Establishment of a human thymic myoid cell line. Phenotypic and functional characteristics

The subset of myoid cells is a normal component of the thymic stroma. To characterize these cells, we immortalized stromal cells from human thymus by using a plasmid vector encoding the SV40 T oncogene. Among the eight cell lines obtained, one had myoid characteristics including desmin and troponin antigens. This new line was designated MITC (myoid immortalized thymic cells). These cells expressed both the fetal and adult forms of muscle acetylcholine receptor (AChR) at the mRNA level, as well as the myogenic transcription factor MyoD1. alpha-Subunit AChR protein expression was detected by flow cytometry and the AChR was functional in patch-clamp studies. In addition, AChR expression was down-modulated by myasthenia gravis sera or by monoclonal antibody anti-AChR on MITC line similarly to TE671 rhabdomyosarcoma cells, making the MITC line an interesting tool for AChR antigenic modulation experiments. Finally, the MITC line expressed LFA-3, produced several cytokines able to act on T cells, and protected total thymocytes from spontaneous apoptosis in vitro. These results are compatible with a role of thymic myoid cells in some steps of thymocyte development. Therefore MITC line appears to be a useful tool to investigate the physiological role of thymic myoid cells.

Extracellular regulation of cancer invasion: the E-cadherin-catenin and other pathways

The E-cadherin-catenin complex is pivotal for the regulation of cancer invasion. It not only serves cell-cell adhesion but also transduces signals from the micro-environment to other molecular complexes possibly implicated in invasion. Both functions are disturbed when the extracellular part of E-cadherin is cleaved off. Moreover, upon release into the environment, the E-cadherin fragments may interfere with intact complexes, as indicated by experiments with His-Ala-Val (HAV)-containing peptides that are homologous to parts of the first extracellular domain of E-cadherin. Scatter factor/hepatocyte growth factor (SF/HGF), on binding to its c-met tyrosine kinase receptor, can induce invasion through tyrosine phosphorylation of beta-catenin. SF/HGF-induced invasion is also associated with phosphorylation of pp125FAK, and both invasion and phosphorylation are inhibited by platelet-activating factor (PAF). Activation of the membrane-bound non-receptor tyrosine kinase pp60src can also induce invasion. Signal transduction pathways starting from pp60src include E-cadherin-associated beta-catenin as well as the focal adhesion kinase pp125FAK. Whereas all invasion-inducing pathways implicate phosphoinositide 3-kinase, the PAF pathway seems to be E-cadherin-catenin-independent. We conclude that cancer cell invasion is regulated by paracrine and autocrine factors that are released upon cross-talk with the host cells.

Functional Expression of Receptors for Calcitonin Gene-Related Peptide, Calcitonin, and Vasoactive Intestinal Peptide in the Human Thymus and Thymomas from Myasthenia Gravis Patients

The molecular and functional expression of serpentine membrane receptors for vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP), and calcitonin (CT) were characterized in human thymus and thymomas from myasthenia gravis (MG) patients and thymic epithelial cells either in primary culture (PTEC) or transformed by the siman virus 40 large T (SV40LT) oncogene (LT-TEC). Using RT-PCR combined with Southern analysis, we identified the PCR products corresponding to the receptor (-R) transcripts for VIP, CGRP, and CT in thymus from control subjects and MG patients with either hyperplasia or thymoma. Similar expressions of the VIP- and CGRP-R transcripts were observed in PTEC, whereas the CT-R message was not detected. In LT-TEC, the signals for VIP-R, CGRP-R, and CT-R transcripts were seen with a lower intensity than those in control and MG thymus. In agreement with our molecular analysis, 1) VIP was the most potent peptide among VIP-related peptides (VIP &gt; PACAP &gt; PHM &gt; PHV) to stimulate cAMP production through specific type 1 VIP receptors in both PTEC and LT-TEC; 2) cAMP generation was induced by CGRP in PTEC and by CT in LT-TEC; 3) in frozen thymic sections and by flow cytometry, type 1 VIP-R, CGRP-R, and CT-R were localized in epithelial cells; and 4) in parallel, the transcription of the acetylcholine receptor α subunit (the main autoantigen in MG) was induced by CGRP and CT in PTEC and LT-TEC, respectively. Our data suggest that the neuroendocrine peptides VIP, CGRP, and CT may exert functional roles during MG and malignant transformation of the human thymus.

Functional expression of receptors for calcitonin gene-related peptide, calcitonin, and vasoactive intestinal peptide in the human thymus and thymomas from myasthenia gravis patients

The molecular and functional expression of serpentine membrane receptors for vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP), and calcitonin (CT) were characterized in human thymus and thymomas from myasthenia gravis (MG) patients and thymic epithelial cells either in primary culture (PTEC) or transformed by the simian virus 40 large T (SV40LT) oncogene (LT-TEC). Using RT-PCR combined with Southern analysis, we identified the PCR products corresponding to the receptor (-R) transcripts for VIP, CGRP, and CT in thymus from control subjects and MG patients with either hyperplasia or thymoma. Similar expressions of the VIP- and CGRP-R transcripts were observed in PTEC, whereas the CT-R message was not detected. In LT-TEC, the signals for VIP-R, CGRP-R, and CT-R transcripts were seen with a lower intensity than those in control and MG thymus. In agreement with our molecular analysis, 1) VIP was the most potent peptide among VIP-related peptides (VIP > PACAP > PHM > PHV) to stimulate cAMP production through specific type 1 VIP receptors in both PTEC and LT-TEC; 2) cAMP generation was induced by CGRP in PTEC and by CT in LT-TEC; 3) in frozen thymic sections and by flow cytometry, type 1 VIP-R, CGRP-R, and CT-R were localized in epithelial cells; and 4) in parallel, the transcription of the acetylcholine receptor alpha subunit (the main autoantigen in MG) was induced by CGRP and CT in PTEC and LT-TEC, respectively. Our data suggest that the neuroendocrine peptides VIP, CGRP, and CT may exert functional roles during MG and malignant transformation of the human thymus.

[Tumoral angiogenesis: physiopathology, prognostic value and therapeutic perspectives]

INTRODUCTION

Angiogenesis activation plays a crucial role in tumoral growth and metastases dissemination. This review summarizes and analyzes current knowledge on molecular mechanisms related to angiogenesis and the prognostic value of its effectors. It also focuses on the therapeutical relevance of various drugs that might inhibit angiogenesic processes.

CURRENT KNOWLEDGE AND KEY POINTS

Tumor angiogenesis involves complex interactions between tumoral, stromal, endothelial cells, fibroblasts and the extracellular matrix. Normal and malignant angiogenesis depends on the balance of proangiogenic and antiangiogenic factors. Endothelial cells are activated by growth factors, such as Vascular Endothelial Growth Factor (VEGF), and proliferate; they release proteases able to induce degradation of the basement membrane and extracellular matrix, and undergo migration and tubulogenesis. Angiostatin and endostatin are two powerful inhibitors of angiogenesis in experimental models. Assessment of intratumoral microvessel density and quantification of angiogenic factors, including VEGF, are of prognostic value in most cancers, particularly in breast cancer. However, the use of these prognosis markers in clinical practice is still controversial due to the lack of prospective studies and to technical limits inherent to the scoring and standardization of immunohistochemical methods.

FUTURE PROSPECTS AND PROJECTS

Better understanding of the molecular basis of angiogenesis allows the development of new therapeutical strategies. Biochemical targets of antiangiogenic therapy are: the interaction between angiogenic factors and their receptors; the interaction of endothelial cells with the extracellular matrix; and intracellular signaling pathways. Angiogenesis inhibitors may not cause tumor regression, but inhibit cellular growth and produce "disease dormancy". Extensive phase I to III clinical trials involving antiangiogenesis therapy are in progress.

Inhibition by platelet-activating factor of Src- and hepatocyte growth factor-dependent invasiveness of intestinal and kidney epithelial cells. Phosphatidylinositol 3'-kinase is a critical mediator of tumor invasion

This study was designed to characterize platelet-activating factor receptor (PAF-R) expression and function in normal and cancerous human colonic epithelial cells. PAF-R gene transcripts were analyzed by reverse transcription-polymerase chain reaction and Southern blot, using three sets of primers corresponding either to the coding region of the human PAF-R sequence (polymerase chain reaction product: 682 base pairs (bp)) or to the leukocyte- and tissue-type transcripts of 166 and 252 bp, respectively. An elongated splice variant was identified in the 5'-untranslated region of the tissue-type PAF-R transcript (334 bp) in colonic epithelial crypts and tumors. In human colonic PCmsrc cells transformed by c-src oncogene, the hepatocyte growth factor (HGF)-dependent invasiveness of collagen gels was abolished by 0.1 microM PAF and restored by the PAF-R antagonists WEB2086 and SR27417. PAF blocked HGF-induced tyrosine phosphorylation of p125 focal adhesion kinase. The phosphatidylinositol 3'-kinase (PI3'-K) inhibitors wortmannin and LY294002 totally blocked the HGF-induced invasion. Similar effects were observed in ts-srcMDCK kidney epithelial cells transformed by a v-Src temperature-sensitive mutant: (i) PAF and wortmannin exerted additive inhibitory effects on Src-induced invasion and (ii) activated and dominant negative forms of p110alpha PI3'-K, respectively, amplified and abrogated the Src- and HGF-dependent invasiveness of parental and ts-srcMDCK cells. We also provided the first evidence for the contribution of rapamycin-insensitive, pertussis toxin-dependent G-protein pathways to the integration of the signals emerging from activated Met and PAF receptors. These results indicate that PI3'-K is a critical transducer of invasiveness and strongly suggest that PAF exerts a negative control on invasion by inhibiting this signaling pathway. A possible beneficial role of PAF analogs on tumor invasion is therefore proposed.

Overexpression of stromelysin-3, BM-40/SPARC, and MET genes in human esophageal carcinoma: implications for prognosis

Molecular markers can improve staging and predict aggressive clinical behavior in esophageal cancer, thus helping to define appropriate therapeutic protocols and to identify patients who will benefit from surgery. We therefore characterized, by Northern blot and/or immunohistochemistry, the relative expression of three effectors involved in the invasion, angiogenesis, and dissemination of tumor cells in esophageal cancer versus nontumoral mucosae: (a) stromelysin-3 (ST3), a member of the metalloproteinase family; (b) basement membrane 40/secreted protein acidic and rich in cysteine (BM-40/SPARC), an extracellular matrix-associated protein involved in angiogenesis; and (c) the hepatocyte growth factor receptor MET, which triggers the scattering of epithelial cells. Results were analyzed in relation to clinicopathological parameters (cpTNE) including tumor size (T), lymph node status (N), periesophageal tissue invasion (E), disease recurrence, and overall survival. The ST3, BM-40/SPARC, and MET genes were found to be overexpressed in tumor samples compared to control mucosa. BM-40/SPARC and MET mRNA levels were not linked to any one of the cpTNE, indicating that this overexpression occurs at an early stage of neoplastic progression. In contrast, ST3 expression, identified by immunohistochemistry in fibroblastic cells surrounding neoplastic islets, correlated with tumor size and periesophageal tissue invasion. Of the 36 patients studied, those with high ST3 levels had shorter disease-free survival than those with low levels, but there was no relationship between the cpTNE and disease recurrence or survival. Our study demonstrates that ST3, BM-40/SPARC, and MET are involved in different steps of esophageal carcinogenesis and that ST3 overexpression is a marker of aggressive clinical behavior. We conclude that in esophageal cancer, ST3 might help to assess survival and the risk of recurrence after surgical resection.

Gastric M1 mucin, an early oncofetal marker of colon carcinogenesis, is encoded by the MUC5AC gene

Gastric M1 mucin and the MUC5AC gene show a similar oncofetal expression in the colon. Our aim was to determine whether M1 mucin is the product of the MUC5AC gene. A recombinant baculovirus encoding the C-terminal portion of the MUC5AC gene as a fusion protein was isolated and the immunoreactivity of the recombinant mucin (rM) toward M1 antibodies studied. Chicken antibodies also were raised against purified rM. Besides its reactivity with L56/C, a serum recognizing the bacterially expressed MUC5AC gene product, rM was endowed with M1 immunoreactivity: (i) rM-expressing cells were stained specifically with anti-M1 serum and with the monoclonal antibody (MAb) 21M1, defining the M1-f epitope; (ii) both L56/C and anti-M1 antibodies recognized the same bands in immunoblots of rM-containing cell extracts; (iii) the 21M1 antibody reacted with rM in an immunoradiometric assay. Among the 7 M1 epitopes, M1-f was the only one encoded by the 3' portion of the MUC5AC gene. It was the only epitope detected in a native mucin M1-derived 170 kDa bromelain proteolytic fragment. Furthermore, the staining patterns of human tissues obtained with either anti-rM chicken antibodies or anti-M1 antibodies were identical. We conclude that M1 immunoreactivity is encoded at least in part by the MUC5AC gene.

Gastric M1 mucin, an early oncofetal marker of colon carcinogenesis, is encoded by the MUC5AC gene

Gastric M1 mucin and the MUC5AC gene show a similar oncofetal expression in the colon. Our aim was to determine whether M1 mucin is the product of the MUC5AC gene. A recombinant baculovirus encoding the C-terminal portion of the MUC5AC gene as a fusion protein was isolated and the immunoreactivity of the recombinant mucin (rM) toward M1 antibodies studied. Chicken antibodies also were raised against purified rM. Besides its reactivity with L56/C, a serum recognizing the bacterially expressed MUC5AC gene product, rM was endowed with M1 immunoreactivity: (i) rM-expressing cells were stained specifically with anti-M1 serum and with the monoclonal antibody (MAb) 21M1, defining the M1-f epitope; (ii) both L56/C and anti-M1 antibodies recognized the same bands in immunoblots of rM-containing cell extracts; (iii) the 21M1 antibody reacted with rM in an immunoradiometric assay. Among the 7 M1 epitopes, M1-f was the only one encoded by the 3' portion of the MUC5AC gene. It was the only epitope detected in a native mucin M1-derived 170 kDa bromelain proteolytic fragment. Furthermore, the staining patterns of human tissues obtained with either anti-rM chicken antibodies or anti-M1 antibodies were identical. We conclude that M1 immunoreactivity is encoded at least in part by the MUC5AC gene.

Differential expression of the CCK-A and CCK-B/gastrin receptor genes in human cancers of the esophagus, stomach and colon

The expression of cholecystokinin (CCK) and gastrin (G) receptors in human gastrointestinal cancers remains poorly documented and is still of a controversial nature. We have measured the levels of mRNA for CCK-A and CCK-B/gastrin receptors using quantitative reverse transcription-polymerase chain reaction (RT-PCR) in primary digestive cancers and hepatic metastases. CCK-A-receptor mRNA was detected in 5 out of 8 esophageal cancers (0.1-1 fg/microg), in 5 out of 8 gastric cancers (0.05-4.2 fg/microg) and in 5 out of 12 colon cancers (0.1-1 fg/microg RNA). CCK-B/gastrin mRNA was not detected in esophageal cancers but was detected in 7 out of 8 gastric cancers (0.05-5.2 fg/microg), and in only 2 out of 12 colon adenocarcinomas (0.05-1 fg/microg RNA). The expression of the CCK-A receptor in esophageal, gastric and colon cancers and of the CCK-B/gastrin receptor in the majority of gastric adenocarcinomas screened may be an important indicator of the influence of CCK and gastrin of local or systemic origin on the growth of these cancers.

Differential expression of the CCK-A and CCK-B/gastrin receptor genes in human cancers of the esophagus, stomach and colon

The expression of cholecystokinin (CCK) and gastrin (G) receptors in human gastrointestinal cancers remains poorly documented and is still of a controversial nature. We have measured the levels of mRNA for CCK-A and CCK-B/gastrin receptors using quantitative reverse transcription-polymerase chain reaction (RT-PCR) in primary digestive cancers and hepatic metastases. CCK-A-receptor mRNA was detected in 5 out of 8 esophageal cancers (0.1-1 fg/microg), in 5 out of 8 gastric cancers (0.05-4.2 fg/microg) and in 5 out of 12 colon cancers (0.1-1 fg/microg RNA). CCK-B/gastrin mRNA was not detected in esophageal cancers but was detected in 7 out of 8 gastric cancers (0.05-5.2 fg/microg), and in only 2 out of 12 colon adenocarcinomas (0.05-1 fg/microg RNA). The expression of the CCK-A receptor in esophageal, gastric and colon cancers and of the CCK-B/gastrin receptor in the majority of gastric adenocarcinomas screened may be an important indicator of the influence of CCK and gastrin of local or systemic origin on the growth of these cancers.

Down-regulation of carcinoembryonic antigen family member 2 expression is an early event in colorectal tumorigenesis

Carcinoembryonic antigen gene family member 2 (CGM2), a member of the carcinoembryonic antigen (CEA) family, is expressed in normal colon and rectum but is down-regulated in colorectal adenocarcinomas. In situ hybridization studies demonstrate that CGM2 expression is limited to epithelial cells in the upper third of the crypts. Two other CEA family members, biliary glycoprotein (BGP) and nonspecific cross-reacting antigen (NCA), are similarly expressed, whereas CEA transcripts were found down to the base of the crypts but were less predominant in the upper region. Only low CGM2 and BGP mRNA levels were seen in colorectal tumors. CEA mRNA was expressed at an equivalent level in normal epithelia and in tumor cells, whereas NCA transcript levels were upregulated in tumor cells. Monoclonal antibodies that recognize the CGM2 protein reveal its presence on the apical membranes of epithelial cells in the upper third of the crypts but its absence from colorectal tumors, which do express the CEA and NCA-50/90 proteins. The newly cloned CGM2 3'-untranslated region was used to probe RNAs from adenomas, colorectal tumors at different stages of progression, and liver metastases of colorectal adenocarcinomas. This showed that CGM2 is already down-regulated in adenomas when compared to normal mucosae. The CGM2 expression pattern along with its sequence homology to BGP suggests a similar tumor suppressor function for CGM2.

Enterocyte differentiation is compatible with SV40 large T expression and loss of p53 function in human colonic Caco-2 cells. Status of the pRb1 and pRb2 tumor suppressor gene products

Transfer of the SV40 large-T (LT) oncogene into isolated human and murine intestinal epithelial cells induced alterations of the ultrastructural organization and polarization of the resulting immortalized cell lines. We now demonstrate that the functional expression of the SV40 LT antigen in Caco-2 cells did not alter phenotypic markers of differentiation, including expression of villin, sucrase-isomaltase, brush border and dome formation. As compared to parental cells, the transfected Caco-2 LT9 cells exhibited similar growth curves and no invasive properties in vitro. The major oncogenic function of the SV40 LT antigen in transfected Caco-2 cells is associated with reduced latency times necessary for the manifestation of tumors in athymic nude mice. The Caco-2 cell line contained deleted and mutant p53 alleles (stop codon in position 204) and has no detectable truncated p53 protein by Western blot. Molecular complexes between the SV40 LT antigen and the retinoblastoma-related proteins pRb1 and Rb2 were clearly identified at the different phases of the growth curve. When compared to normal human colonic crypts, Caco-2 cell differentiation is related to partial redistribution of pRb1 into hypophosphorylated, antiproliferative forms. The pRb2 protein is found elevated in a subset of human colorectal tumors and their corresponding liver metastases. We conclude that: (1) Caco-2 cells exert a dominant control against the oncogenic functions of the LT antigen; (2) loss of p53 function is not restrictive for the establishment of polarity and differentiation of the enterocyte lineage; (3) the levels and phosphorylation status of the Rb1 and Rb2 proteins may play important roles in the proliferation and differentiation of normal and neoplastic human colonic mucosa.

Human colorectal carcinogenesis is associated with deregulation of homeobox gene expression

In the present study, the possible involvement of homeobox-containing genes in colorectal cancer (CRC) development was investigated. Using a stepwise screening approach and RT-PCR, we have demonstrated that the human HOXB6, B8, C8 and C9 are overexpressed at various stages of CRC. In contrast, all CRC cases exhibited a marked decrease in the homeodomain-containing Cdx1 gene expression. Recent data which suggest a regulatory link between HOXB8 and several tumor suppressor genes, such as DCC, APC, and TGF beta, sustain a possible implication of homeobox genes in colon carcinogenesis. Moreover, our data showing a decrease in Cdx1 expression are consistent with the notion that genes functioning in the establishment and maintenance of the intestinal epithelium might, upon deregulation, disturb the normal control of cellular proliferation, differentiation, and death, thus leading to cancer development.

[Oncogenic activation of p21ras or pp60c-src in human colonic Caco-2 cells induces post-translation alterations of syndecan-1]

The protein encoded by ras and src protooncogenes are frequently activated in a constitutive state in human colorectal cancer. In this study, we investigated the effect of oncogenic p21ras and Py-MT/pp60c-src on the synthesis of syndecan-1, a membrane anchored proteoglycan playing a role in cell-matrix interaction and neoplastic growth control. To this end, we used Caco-2 cells transfected with an activated (Val-12) human Ha-ras gene or the polyoma middle T (Py-MT) oncogene, a constitutive activator of pp60c-src tyrosine kinase activity. As compared to control vector-transfected Caco-2 cells, both oncogene-transfected cells exhibited: (1) a decrease in syndecan-1 specific activity; (2) a decrease in size and sulfation of syndecan-1 ectodomain glycosaminoglycan side chains; and (3) an active heparanase specifically degrading the heparan sulfate chains. In conclusion, the tumorigenic progression induced by oncogenic p21ras or Py-MT/pp60c-src is associated with marked alterations of syndecan-1 at the post-translational level.

Evidence for a role of Rho-like GTPases and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) in transforming growth factor beta-mediated signaling

Transforming growth factor beta (TGF-beta) is a multifunctional factor that induces a wide variety of cellular processes which affect growth and differentiation. TGF-beta exerts its effects through a heteromeric complex between two transmembrane serine/threonine kinase receptors, the type I and type II receptors. However, the intracellular signaling pathways through which TGF-beta receptors act to generate cellular responses remain largely undefined. Here, we report that TGF-beta initiates a signaling cascade leading to stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) activation. Expression of dominant-interfering forms of various components of the SAPK/JNK signaling pathways including Rho-like GTPases, mitogen-activated protein kinase (MAPK) kinase kinase 1 (MEKK1), MAPK kinase 4 (MKK4), SAPK/JNK, and c-Jun abolishes TGF-beta-mediated signaling. Therefore, the SAPK/JNK activation contributes to TGF-beta signaling.

Progression of familial adenomatous polyposis (FAP) colonic cells after transfer of the src or polyoma middle T oncogenes: cooperation between src and HGF/Met in invasion

Little is known about the the signalling pathways driving the adenoma-to-carcinoma sequence in human colonic epithelial cells. Accumulation and activation of the src tyrosine kinase in colon cancer suggest a potential role of this oncogene in this early progression. Therefore, we introduced either activated src (m-src), polyoma-MT alone or combined with normal c-src in the adenoma PC/AA/C1 cell line (PC) to define the function and phenotypic transformations induced by these oncogenes in familial adenomatous polyposis (FAP) colonic epithelial cells. Functional expression of these oncoproteins induced the adenoma-to-carcinoma conversion, overexpression of the hepatocyte growth factor (HGF) receptor Met, but failed to confer invasiveness in vivo and in vitro, or to produce alterations in cell proliferation and differentiation. In contrast, PC-msrc cells became susceptible to the HGF-induced invasion of collagen gels and exhibited sustained activation of the pp60src tyrosine kinase and Tyr phosphorylation of the 120-kDa E-cadherin, which was further increased by HGF Transcripts of HGF were clearly identified by reverse transcription-polymerase chain reaction (RT-PCR) and Southern blot in the parental and transformed PC cells, suggesting an autocrine mechanism. Taken together, the data indicate that: (1) experimental activation of src and PyMT pathways directly induces tumorigenicity and Met upregulation in a colon adenoma cell line; (2) HGF-activated Met and src cooperate in inducing invasion; (3) in view of the molecular associations between catenins and cadherin or the tumour-suppressor gene product APC, the cell adhesion molecule E-cadherin may constitute a downstream effector of src and Met.

Human cord blood monocytes undergo terminal osteoclast differentiation in vitro in the presence of culture medium conditioned by giant cell tumor of bone

Osteoclasts (OCs), which form by fusion of hematopoietic precursor cells, are typically present in large numbers in giant cell tumors of bone (GCTBs). These tumors may, therefore, contain cells which secrete factors that stimulate recruitment and differentiation of OC precursors. Multinucleated cells resembling OCs also form in cultures of human cord blood monocytes (CBMs) stimulated by 1.25 dihydroxyvitamin D3, but these cells lack the ability to form bone resorption pits, the defining functional characteristic of mature OCs. CBMs may thus require additional stimulation to form OCs; we therefore investigated whether GCTBs are a source of such a stimulus. CBMs were stimulated in long term (21 day) culture by medium conditioned by explants of GCTBs; media collected within 15 days of explant (early-CM) and after 15 days (late-CM) were employed. We also cocultured CBMs with primary GCTB-derived stromal cells as well as immortalized bone marrow stroma-derived cells. CBMs stimulated by early-CM formed resorption pits on cortical bone slices; however, stimulation by late-CM resulted in virtually no resorption. Both early-CM and late-CM increased CBM proliferation, but not the proportion of vitronectin receptor positive or multinucleated cells. Coculture of CBMs with stromal cells of GCTBs or bone marrow did not result in bone resorption, although these stromal cells (most expressing alkaline phosphatase but progressively losing parathyroid hormone receptor expression) expressed mRNA for cytokines involved in OC differentiation, including macrophage-CSF, granulocyte-macrophage-CSF, IL-11, IL-6, and stem cell factor. Our results indicate that CBMs are capable of terminal OC differentiation in vitro, a process requiring 1,25 dihydroxyvitamin D3 as well as diffusible factor(s) which can be derived from GCTB. Stromal cells of GCTB may produce such factors in vivo, but do not support OC differentiation in vitro, possibly through phenotypic instability in culture.

Loss of sst2 somatostatin receptor gene expression in human pancreatic and colorectal cancer

Five somatostatin receptor subtypes (sst1 to sst5) have been cloned. We demonstrated previously that sst2 and sst5 mediate the antiproliferative effect of the somatostatin analogues octreotide and vapreotide. Using reverse transcription-PCR, we investigated gene expression of the five receptors in 47 human normal and cancerous tissues or cell lines from pancreatic and colorectal origin. mRNAs of somatostatin receptor subtypes were detected in 98% of samples, with more than two mRNA subtypes being expressed in 55% of cases. sst1, sst4, and sst5 were heterogeneously expressed in both normal and cancerous tissues; sst3 was rarely or not expressed. sst2 was present in normal pancreatic tissues but was absent in exocrine pancreatic carcinomas and their metastases. sst2 mRNAs were detected in normal colon, sporadic polyadenomas, and 50% of Dukes' stage B and 20% of Dukes' stage C carcinomas but were undetectable in Dukes' stage D carcinomas, hepatic metastases, and adenomas from familial adenomatous polyposis. The loss of sst2 expression could represent a growth advantage in these tumors and provide an explanation for the lack of therapeutic effect of somatostatin analogues in such adenocarcinomas. A subtyping of somatostatin receptors should be carried out before considering a somatostatin analogue treatment in patients with colorectal or pancreatic cancer.