Hepatomas with activating Ctnnb1 mutations in 'Ctnnb1-deficient' livers: a tricky aspect of a conditional knockout mouse model

Conditional knockout mice, based on the Cre-loxP system, are a widely used model for examining organ-specific gene functions. To date, efficient hepatocyte-specific knockout has been reported in many different models, but little attention has been paid to the long-term stability of the recombination efficiency. In the present study, we characterized Alb-Cre;Ctnnb1flox/flox 'hepatocyte-specific Ctnnb1 knockout' mice of different ages to test whether efficient recombination is maintained over time. At 2 months of age, the knockout mouse livers achieved efficient deletions of β-catenin in hepatocytes. However, as the mice aged, the reappearance and expansion of β-catenin-expressing hepatocytes were observed. In 1-year-old mice, a significant proportion of the pericentral hepatocytes in the knockout mouse livers were replaced with β-catenin-positive hepatocytes, whereas the periportal hepatocytes mostly remained β-catenin-negative. Furthermore, most of the 1-year-old mice spontaneously developed hepatocellular adenomas and carcinomas that were positive for β-catenin and overexpressed glutamine synthetase and Slc1a2, both of which are hallmarks of active β-catenin signaling. Sequencing analysis revealed that the Ctnnb1 alleles were not inactivated but had activating mutations in these tumors. The present study suggests that recombination efficiency should be carefully examined when hepatocyte-specific knockout mice of different ages are analyzed. In addition, illegitimate deletion mutations should be recognized as potential adverse effects of the Cre-loxP system.

Cloning and expression of cDNA for salmon growth hormone in Escherichia coli

cDNA clones encoding chum salmon (Oncorhynchus keta) growth hormone (sGH) have been isolated from a cDNA library prepared from chum salmon pituitary gland poly(A)(+) RNA. Synthetic oligodeoxynucleotide mixtures based on amino acid residues 23-28 of sGH were used as hybridization probes to select recombinant plasmids carrying the sGH coding sequence. The complete nucleotide sequence of sGH cDNA has been determined. The cDNA sequence codes for a polypeptide of 210 amino acids, including a putative signal sequence of 22 amino acids. The 5' and 3' untranslated regions of the message were 64 and 426 bases long, respectively. Mature sGH was efficiently expressed in Escherichia coli carrying a plasmid in which the sGH cDNA was under control of the E. coli trp promoter; sGH comprised about 15% of the total cellular protein in such bacteria. The partially purified sGH from E. coli stimulated the growth of rainbow trout and the activity was indistinguishable from that of natural sGH.

Intraductal carcinosarcoma with a heterologous mesenchymal component originating in intraductal papillary-mucinous carcinoma (IPMC) of the pancreas with both carcinoma and osteosarcoma cells arising from IPMC cells

Carcinosarcoma of the pancreas is extremely rare and its histogenesis is still unclear. This is a report on a 64-year-old female patient with an intraductal carcinosarcoma arising from intraductal papillary-mucinous carcinoma (IPMC) in the pancreas tail. The carcinosarcoma grew as a polypoid mass within the main pancreatic duct. Histologically, the tumour consisted of adenocarcinoma covering the luminal surface of the lesion with minimal stromal invasion, and osteosarcoma occupying the stroma. Immunohistochemical and gene mutation analyses revealed that both the carcinomatous and sarcomatous tumour cells of the carcinosarcoma, as well as the IPMC cells, expressed TP53 and had identical mutations in KRAS and TP53 genes, indicating that these two neoplastic components of the carcinosarcoma shared a common tumorigenesis and arose from the IPMC. This is the first report of a carcinosarcoma originating in IPMC. These findings imply that carcinosarcoma with a heterologous mesenchymal component is of ductal origin.

Dicer is required for proper liver zonation

A number of genes and their protein products are expressed within the liver lobules in a region-specific manner and confer heterogeneous metabolic properties to hepatocytes; this phenomenon is known as 'metabolic zonation'. To elucidate the roles of Dicer, an endoribonuclease III type enzyme required for microRNA biogenesis, in the establishment of liver zonation, we examined the distribution of proteins exhibiting pericentral or periportal localization in hepatocyte-specific Dicer1 knockout mouse livers. Immunohistochemistry showed that the localization of pericentral proteins was mostly preserved in Dicer1-deficient livers. However, glutamine synthetase, whose expression is normally confined to a few layers of hepatocytes surrounding the central veins, was expressed in broader pericentral areas. Even more striking was the observation that all the periportal proteins that were examined, including phosphoenolpyruvate carboxykinase, E-cadherin, arginase 1, and carbamoyl phosphate synthetase-I, lost their localized expression patterns and were diffusely expressed throughout the entire lobule. Thus, with regard to periportal protein expression, the consequences of Dicer loss were similar to those caused by the disruption of beta-catenin. An analysis of livers deficient in beta-catenin did not identify the down-regulation of Dicer1 or any microRNAs, indicating that they are not directly activated by beta-catenin. Thus, the present study illustrates that Dicer plays a pivotal role in the establishment of liver zonation. Dicer is essential for the suppression of periportal proteins by Wnt/beta-catenin/TCF signalling, albeit it likely acts in an indirect manner.

Beta-catenin blocks Kras-dependent reprogramming of acini into pancreatic cancer precursor lesions in mice

Cellular plasticity in adult organs is involved in both regeneration and carcinogenesis. WT mouse acinar cells rapidly regenerate following injury that mimics acute pancreatitis, a process characterized by transient reactivation of pathways involved in embryonic pancreatic development. In contrast, such injury promotes the development of pancreatic ductal adenocarcinoma (PDA) precursor lesions in mice expressing a constitutively active form of the GTPase, Kras, in the exocrine pancreas. The molecular environment that mediates acinar regeneration versus the development of PDA precursor lesions is poorly understood. Here, we used genetically engineered mice to demonstrate that mutant Kras promotes acinar-to-ductal metaplasia (ADM) and pancreatic cancer precursor lesion formation by blocking acinar regeneration following acute pancreatitis. Our results indicate that beta-catenin is required for efficient acinar regeneration. In addition, canonical beta-catenin signaling, a pathway known to regulate embryonic acinar development, is activated following acute pancreatitis. This regeneration-associated activation of beta-catenin signaling was not observed during the initiation of Kras-induced acinar-to-ductal reprogramming. Furthermore, stabilized beta-catenin signaling antagonized the ability of Kras to reprogram acini into PDA preneoplastic precursors. Therefore, these results suggest that beta-catenin signaling is a critical determinant of acinar plasticity and that it is inhibited during Kras-induced fate decisions that specify PDA precursors, highlighting the importance of temporal regulation of embryonic signaling pathways in the development of neoplastic cell fates.

Association of ALDH2 genotypes with periodontitis progression

The progression of periodontitis may be affected by ALDH2 genotypes with respect to the oxidation of acetaldehyde to acetate, which leads to the accumulation of acetaldehyde in plasma and potential toxic effects. We examined the prospective association of ALDH2 genotypes in terms of alcohol sensitivity between alcohol consumption and periodontal disease progression. In 2003, 224 of 256 (87.5%) individuals examined at baseline (1999) completed probing pocket depth measurements for the evaluation of periodontitis progression. Missing data on self-reported questionnaires and blood samples were excluded; therefore, 183 samples were analyzed. Individuals who consumed > or = 33.0 g/day of alcohol exhibited high periodontal disease progression risk (OR = 3.54). ALDH2 *1/*2 individuals who consumed > or = 33 g/day of alcohol displayed a significant odds ratio (OR = 4.28) of periodontitis progression risk, in contrast to ALDH2 *1/*1 individuals. These results suggested that alcohol consumption as well as alcohol sensitivity may be a risk factor for periodontitis progression.

Disruption of Dicer1 induces dysregulated fetal gene expression and promotes hepatocarcinogenesis

BACKGROUND & AIMS

Growing evidence suggests that microRNAs coordinate various biological processes in the liver. We describe experiments to address the physiologic roles of these new regulators of gene expression in the liver that are as of yet largely undefined.

METHODS

We disrupted Dicer, an enzyme essential for the processing of microRNAs, in hepatocytes using a conditional knockout mouse model to elucidate the consequences of loss of microRNAs.

RESULTS

The conditional knockout mouse livers showed the efficient disruption of Dicer1 at 3 weeks after birth. This resulted in prominent steatosis and the depletion of glycogen storage. Dicer1-deficient liver exhibited increased growth-promoting gene expression and the robust expression of fetal stage-specific genes. The consequence of Dicer elimination included both increased hepatocyte proliferation and overwhelming apoptosis. Over time, Dicer1-expressing wild-type hepatocytes that had escaped Cre-mediated recombination progressively repopulated the entire liver. Unexpectedly, however, two thirds of the mutant mice spontaneously developed hepatocellular carcinomas derived from residual Dicer1-deficient hepatocytes at 1 year of age.

CONCLUSIONS

Dicer and microRNAs have critical roles in hepatocyte survival, metabolism, developmental gene regulation, and tumor suppression in the liver. Loss of Dicer primarily impairs hepatocyte survival but can promote hepatocarcinogenesis in cooperation with additional oncogenic stimuli.

A low number of tumor infiltrating FOXP3-positive cells after primary systemic chemotherapy is correlated with favorable relapse-free survival in breast cancer patients

Abstract #5043

Background: Cancer cells induce proliferation and local accumulation of immunosuppressive cells such as FOXP3-positive cells which known as regulatory T cells (Tregs). Tregs prevent the maturation of dendritic cells and their capacity to present tumor antigens to cytotoxic T lymphocytes (CTLs) and leads to tumor-induced tolerance. Although cancer chemotherapy was usually considered as immunosuppressive, some chemotherapeutic agents have recently been shown to activate an anticancer immune response, which is involved in the curative effect of these treatments. Therefore, we hypothesized that number of tumor infiltrating FOXP3-positive cells during primary systemic chemotherapy is correlated with therapeutic results in breast cancer patients.
 Methods: To test the hypothesis, between September 2000 and January 2005, breast cancer patients treated with primary systemic chemotherapy (PSC) (n=93) were included in the study. Three cases were excluded because main tumors were resected before PSC and three cases of pathological complete reaction were excluded because they were hard to define “tumor infiltrating” Tregs. To compare the number of FOXP3 positive cells in the tumors before and after PST, both core-needle biopsy (CNB) and surgical resected specimens were stained with FOXP3 monoclonal antibody. Numbers of tumor infiltrating FOXP3-positive cells were counted in 3 and 5 randomly chosen high power fields (CNB and surgical specimens, respectively). A median cutoff of >16.3 and > 6.6 defined patients with high numbers of Tregs (CNB and surgical specimens, respectively). We also divided the patients into four groups (high numbers of FOXP3 positive cells in both CNB and surgical specimens; HH, low numbers in the both specimens; LL, high numbers in CNB and low in the surgical specimens; HL, and low in CNB and high in surgical specimens; LH). All patients were treated with anthracyclin containing therapy and 79.3 %( n=69) of them were added taxanes sequentially.
 Results: In the tumors after PST, numbers of Tregs were significantly higher in lymphvessel invasion positive tumors (P=0.01) and ER negative tumors (P=0.02) but there was no correlation between lymph node involvement and numbers of Tregs (P=0.8). As for the comparison of four groups, LL group shows the longest relapse-free (P=0.04) and overall survival (P=0.09) and HH group shows the shortest relapse-free and overall survival among four groups. Interestingly, HL group shows better outcome than HH group and LH group shows worse one than LL.
 Conclusions: These findings suggest that the control of Tregs in the tumor is important for the control of the disease and Tregs might be an important therapeutic target for breast cancer. Furthermore, it is suggested that some chemotherapeutic agents could be a potential inhibitor of the Tregs in tumor and show antitumor effects addition to their direct cytotoxicity against cancer cells.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 5043.

Histological diversity in basaloid squamous cell carcinoma of the esophagus

Basaloid squamous cell carcinoma of the esophagus (BSCCE) is a distinct variant of esophageal cancer. This study investigated histopathological variations of BSCCE. Thirty-eight surgical and two endoscopically resected specimens of BSCCE were examined. Histological features were classified into five components: solid nest (SN), microcyst and/or trabecular nest (MT), ductal differentiation (DD), cribriform pattern (CP), and an invasive squamous cell carcinoma (SCC) component. The immunohistochemical phenotypes of each component were examined using antibodies against cytokeratin (CK) 7, CK14, and alpha smooth muscle actin (SMA). SN, MT, DD, CP, and SCC were present in 95.0, 97.5, 27.5, 32.5, and 82.5% of the cases, respectively, and combinations of SN & MT, SN & DD, SN, MT & DD, SN, MT & CP, and SN, MT, DD & CP were found in 50.0, 2.5, 10.0, 17.5, and 15.0%, respectively. All the intraepithelial lesions observed in 18 (45.0%) cases were SCC. Immunoreactivity for CK7, CK14, and SMA was seen in 10.5, 86.8, and 18.4% of SN; 30.8, 97.4, and 38.5% of MT; 54.5, 100.0, and 54.5% of DD; 7.7, 76.9, and 23.1% of CP; and 6.1, 97.0, and 0.0% of SCC, respectively. CK14 immunoreactivity was seen in the periphery of most of the SN component. CK7, CK14, and SMA immunoreactivity was seen in the inner layer, all layers, and the outer layer of DD, respectively. MT and CP showed partial peripheral positivity for CK14 and SMA in microcystic, trabecular, and cribriform-like pseudoglandular structures. BSCCE demonstrates various histopathological and immunohistochemical features including a ductal and cribriform growth pattern.

Distribution and significance of the oesophageal and gastric cardiac mucosae: a study of 131 operation specimens

AIMS

To clarify the distribution and significance of the oesophageal and gastric cardiac mucosae at the oesophago-gastric junction (EGJ).

METHODS AND RESULTS

Oesophagectomy specimens from 131 consecutive patients with middle and upper thoracic oesophageal cancer were examined. The surgically resected specimens including the EGJ were cut into 5 mm thick serial sections and examined histopathologically for the length of the oesophageal and gastric cardiac mucosae and the incidence of columnar epithelial islands (CEIs). We also determined the presence of short-segment Barrett's oesophagus (SSBE) and goblet cell metaplasia in SSBE. Oesophageal cardiac mucosa was found in 125 cases (95%) and gastric cardiac mucosa was found in all cases. The mean length of the oesophageal and gastric cardiac mucosa was 4 mm (range 1-26 mm) and 13 mm (range 2-64 mm), respectively. CEIs were found in 75 cases (57%). SSBE was found in 70 cases (53%), among which goblet cell metaplasia was found in 28 cases (21%). No long-segment Barrett's oesophagus was found. The mean length of oesophageal cardiac mucosa (6 mm) and gastric cardiac mucosa (17 mm) in SSBE was significantly greater than that (3 mm and 8 mm, respectively) in non-SSBE cases (P < 0.0001 and P < 0.0001). The incidence (69%) of CEIs in SSBE was significantly higher than that (44%) in non-SSBE cases (P = 0.005).

CONCLUSIONS

Oesophageal and gastric cardiac mucosae were found frequently. Oesophageal cardiac glands and CEIs might play an important role in the development of SSBE.

Two distinct pathways of tumorigenesis of adenocarcinomas of the esophagogastric junction, related or unrelated to intestinal metaplasia

It is still uncertain whether intestinal metaplasia (IM) of the esophagogastric junction (EGJ) plays a role in the development of adenocarcinoma of the esophagogastric junction (AEGJ). The purpose of the present study was to clarify the relationship between AEGJ and IM in Japanese patients. Forty-eight AEGJ, <3 cm and centered within 1 cm of the EGJ, were investigated. The frequency of IM around AEGJ and the correlation between IM and clinicopathological features were examined. IM was present in the surrounding mucosa in 22 of 48 cases (46%), and was seen more frequently in older patients (P = 0.008). Lymph node metastasis was observed only in cases in which the tumors were not associated with IM (P = 0.017). The gastric phenotype was seen almost exclusively in the group without IM, while the intestinal phenotype was predominant in the group with IM (P = 0.003). The present study found a lower incidence of associated IM than Western studies, and there were significant differences in clinicopathological features between AEGJ with and without IM. It is suggested that AEGJ may develop via two distinct pathways in Japanese patients: IM-related and IM-unrelated.

Liver-specific loss of beta-catenin results in delayed hepatocyte proliferation after partial hepatectomy

Recent studies have suggested that beta-catenin is involved in the regulation of hepatocyte proliferation in multiple contexts, including organ development and tumorigenesis. We explored the role of beta-catenin during liver regeneration using T cell factor/lymphoid enhancer factor (TCF/LEF)-reporter mice (TOPGal mice) and liver-specific beta-catenin knockout mice. Liver-specific beta-catenin knockout mice showed a delayed onset of DNA synthesis after hepatectomy, whereas recovery of liver mass was not affected. Among putative beta-catenin target genes examined, the induction of Ccnd1 expression was reduced, whereas the expression of Myc and Egfr was unaffected. Furthermore, cyclin D1 protein levels were not induced, and the expression of cyclins A, E, and proliferating cell nuclear antigen was delayed. Intriguingly, the analysis of TOPGal mice showed that hepatocytes with active TCF/LEF transcription are confined to the pericentral zone and are not increased in number during regeneration, indicating an uncoupling between beta-catenin/TCF signaling activity and hepatocyte proliferation.

CONCLUSION

Our results indicate that beta-catenin is critical for the proper regulation of hepatocyte proliferation during liver regeneration; however, the activity of beta-catenin/TCF signaling does not correlate with hepatocyte proliferation, suggesting that this regulation might be indirect/secondary.

Hedgehog/Ras interactions regulate early stages of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDA) constitutes a lethal disease that affects >30,000 people annually in the United States. Deregulation of Hedgehog signaling has been implicated in the pathogenesis of PDA. To gain insights into the role of the pathway during the distinct stages of pancreatic carcinogenesis, we established a mouse model in which Hedgehog signaling is activated specifically in the pancreatic epithelium. Transgenic mice survived to adulthood and developed undifferentiated carcinoma, indicating that epithelium-specific Hedgehog signaling is sufficient to drive pancreatic neoplasia but does not recapitulate human pancreatic carcinogenesis. In contrast, simultaneous activation of Ras and Hedgehog signaling caused extensive formation of pancreatic intraepithelial neoplasias, the earliest stages of human PDA tumorigenesis, and accelerated lethality. These results indicate the cooperation of Hedgehog and Ras signaling during the earliest stages of PDA formation. They also mark Hedgehog pathway components as relevant therapeutic targets for both early and advanced stages of pancreatic ductal neoplasia.

Primary cilia deletion in pancreatic epithelial cells results in cyst formation and pancreatitis

BACKGROUND & AIMS

Defects in cilia formation or function have been implicated in several human genetic diseases, including polycystic kidney disease (PKD), Bardet-Biedl syndrome, and primary ciliary dyskinesia. Pancreatic lesions are found in approximately 10% of PKD patients, suggesting a connection between cilia defects and pancreatic pathologies. Here, we investigate the role of cilia in pancreas formation and function by analyzing mice that lack cilia in pancreatic cells.

METHODS

Using Cre/lox technology, we conditionally inactivated Kif3a, the gene encoding for a subunit of the kinesin-2 complex that is essential for cilia formation, in pancreatic epithelia. Kif3a mice were studied by immunohistochemical and biochemical methods to assess the morphology and differentiation status of pancreatic cells.

RESULTS

Tissue-specific loss of Kif3a in pancreatic cells resulted in severe pancreatic abnormalities including acinar-to-ductal metaplasia, fibrosis, and lipomatosis. Ductal metaplasia appears to be due to expansion of ductal cells rather than transdifferentiation of acinar cells. Cyst formation, aberrant ductal morphology, and extensive fibrosis associated with severe adhesion to adjacent organs were commonly observed in aged Kif3a mutant mice. Deletion of Kif3a using different pancreas-specific Cre strains suggests that these pancreatic phenotypes might be caused by the absence of cilia in ductal cells. Activation of transforming growth factor beta and Mitogen-activated protein kinase kinase/extracellular signal-regulated kinase (MEK/ERK) pathways may play a role in these phenotypes.

CONCLUSIONS

These results demonstrate that the absence of cilia in pancreatic cells produces pancreatic lesions that resemble those found in patients with chronic pancreatitis or cystic fibrosis.

Interobserver variability in histologic recognition, interpretation of KIT immunostaining, and determining MIB-1 labeling indices in gastrointestinal stromal tumors and other spindle cell tumors of the gastrointestinal tract

The authors studied the concordance among seven pathologists for the histologic diagnosis, interpretation of KIT immunostaining, and determining MIB-1 labeling indices (LI) in 80 adult patients with primary spindle cell tumors, mainly of the gastrointestinal tract, mesentery, retroperitoneum, and pelvis, based on the review of tissue sections using an immunohistochemical panel of antibodies for KIT/CD117, CD34, desmin, smooth muscle actin (SMA), and S-100 protein. Tumors included 30 gastrointestinal stromal tumors (GISTs), 10 leiomyomas, 10 leiomyosarcomas, 10 schwannomas, 10 solitary fibrous tumors, and 10 desmoid-type fibromatoses. The overall concordance with the original diagnosis of each histologic type was 97.9%, the kappa value ranging from 0.95 to 1.00 (mean 0.97), indicating a perfect agreement. The overall interlaboratory concordance with the original interpretation of KIT immunostaining was 91.3%, the kappa value ranging from 0.77 to 0.90 (mean 0.86). The overall interlaboratory concordance with the original interpretation of KIT immunostaining was 91.9%, the kappa value ranging from 0.72 to 0.93 (mean 0.85). The overall concordance for determining MIB-1 LI was 90% with the original evaluation, and the overall kappa value ranged from 0.62 to 0.86 (mean 0.77). These results indicate that it is possible to reliably diagnose GIST and other spindle cell tumors of the gastrointestinal tract with the use of an immunohistochemical panel of antibodies for KIT, CD34, desmin, SMA, and S-100 protein. Although there is clearly unavoidable inter-observer and interlaboratory variability in the interpretation of KIT immunostained sections and interobserver variability in the determination of MIB-1 LI, the concordance between observes is very acceptable, and in most instances such variability can be eliminated by careful reviewing of the hematoxylin and eosin and immunostained sections.

Liver-specific loss of beta-catenin blocks glutamine synthesis pathway activity and cytochrome p450 expression in mice

There is accumulating evidence that Wnt/beta-catenin signaling is involved in the regulation of liver development and physiology. The presence of genetic alterations resulting in constitutive beta-catenin stabilization in human and murine liver tumors also implicates this pathway in hepatocyte proliferation. In the present study, we generated hepatocyte-specific beta-catenin knockout mice to explore the role of beta-catenin in liver function. Conditional knockout mice were born at the expected Mendelian ratio and developed normally to adulthood, indicating beta-catenin is dispensable for essential liver function under normal breeding conditions. However, the liver mass of knockout mice was 20% less than those of mice in the control groups. Expression analysis revealed loss of genes required for glutamine synthesis in knockout mice. Loss of the liver glutamine synthesis pathway did not affect the blood ammonia level in mice fed a standard diet, yet, knockout mice showed significantly elevated blood ammonia levels with high-protein dietary feeding. Furthermore, the expression of two cytochrome P450 enzymes, CYP1A2 and CYP2E1, was almost completely abolished in livers from hepatocyte-specific beta-catenin knockout mice. Consequently, these mice were resistant to acetaminophen challenge, confirming the requirement of these cytochrome P450 enzymes for metabolism of xenobiotic substances. In conclusion, in addition to regulating hepatocyte proliferation, beta-catenin may also control multiple aspects of normal liver function.