Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors in the human digestive tract, but their molecular etiology and cellular origin are unknown. Sequencing of c-kit complementary DNA, which encodes a proto-oncogenic receptor tyrosine kinase (KIT), from five GISTs revealed mutations in the region between the transmembrane and tyrosine kinase domains. All of the corresponding mutant KIT proteins were constitutively activated without the KIT ligand, stem cell factor (SCF). Stable transfection of the mutant c-kit complementary DNAs induced malignant transformation of Ba/F3 murine lymphoid cells, suggesting that the mutations contribute to tumor development. GISTs may originate from the interstitial cells of Cajal (ICCs) because the development of ICCs is dependent on the SCF-KIT interaction and because, like GISTs, these cells express both KIT and CD34.

WT1 was first identified as a tumor suppressor involved in the development of Wilms' tumor. Recently, oncogenic properties of WT1 have been demonstrated in various hematological malignancies and solid tumors. Because WT1 has been identified as a molecular target for cancer immunotherapy, immunohistochemical detection of WT1 in tumor cells has become an essential part of routine practice. In the present study, the expression of WT1 was examined in 494 cases of human cancers, including tumors of the gastrointestinal and pancreatobiliary system, urinary tract, male and female genital organs, breast, lung, brain, skin, soft tissues and bone by immunohistochemistry using polyclonal (C-19) and monoclonal (6F-H2) antibodies against WT1 protein. Staining for C-19 and 6F-H2 was found in 35-100 and 5-88% of the cases of each kind of tumor, respectively. WT1-positive tumors included tumor of the stomach, prostate, and biliary and urinary systems, and malignant melanomas. A majority of the positive cases showed diffuse or granular staining in the cytoplasm, whereas ovarian tumors and desmoplastic small round cell tumors frequently showed nuclear staining. Glioblastomas, some of soft tissue sarcomas, osteosarcomas, and malignant melanomas of the skin showed extremely strong cytoplasmic staining as compared with other tumors. Western blot analysis showed that WT1 protein was predominantly expressed in the cytoplasm of the tumor cells in two cases of lung adenocarcinoma, supporting the intracytoplasmic staining for WT1 using immunohistochemistry. Immunohistochemical detection with routinely processed histologic sections could provide meaningful information on the expression of WT1 in cancer cells.

No abstract

The ␣1-6 fucosylated ␣-fetoprotein (AFP) present in serum of patients with hepatocellular carcinoma (HCC) has been employed for the differential clinical diagnosis of HCC from chronic liver diseases. The molecular mechanism by which this alteration occurs, however, remains largely unknown. To address this issue, we purified GDP-L-Fuc:Nacetyl-␤-D-glucosaminide ␣1-6 fucosyltransferase (␣1-6 FucT), an enzyme involved in the ␣1-6 fucosylation of N-glycans from porcine brain, as well as from a human gastric cancer cell line, and cloned their genes. In this study, levels of ␣1-6 FucT mRNA expression and the activity of this enzyme for 12 human HCC tissues were examined and compared with that in surrounding tissues and normal livers. The mean ؎ SD for ␣1-6 FucT activity was 78 ؎ 41 pmol/h/mg in normal control liver, 202 ؎ 127 pmol/h/mg in adjacent uninvolved liver tissues (chronic hepatitis: 181 ؎ 106 pmol/h/mg; liver cirrhosis: 233 ؎ 164 pmol/h/mg), and 195 ؎ 72 pmol/h/mg in HCC tissues. The mRNA expression of ␣1-6 FucT was also enhanced in proportion to enzymatic activity except for a few cases, suggesting that ␣1-6 FucT expression is increased in chronic liver diseases, especially liver cirrhosis. Transfection of ␣1-6 FucT gene into cultured rat hepatocytes markedly increased ␣1-6 FucT activity and led to an increase in lens culinaris agglutinin (LCA) binding proteins in both cell lysates and condition media. When the ␣1-6 FucT gene was transfected into a human HCC cell line, Hep3B, which originally showed low levels of ␣1-6 FucT expression, ␣1-6-fucosylated AFP was dramatically increased in the condition media. Collectively, these results suggest that the enhancement of ␣1-6 FucT expression increased the fucosylation of several proteins, including AFP, and that the level of ␣1-6-fucosylated AFP in patients with HCC was in part caused by up-regulation of the ␣1-6 FucT gene expression. (HEPATOLOGY 1998;28:944-952.)

No abstract