Localization and characterization of γ-glutamyl cyclotransferase in cancer cells

Abstract

Abstract.Using differential display analysis, we have identified a novel rat gene whose expression is increased during tumor progression in rat mammary carcinoma cell lines. This gene is an ortholog of the human chromosome 7 open reading frame 24 gene (C7orf24) and encodes a protein of 188 amino acids with no recognized protein domains. C7orf24 has been identified as Á-glutamyl cyclotransferase (GGCT), an important enzyme functioning in glutathione homeostasis. Our Northern and Western blot analyses revealed that the GGCT gene is expressed in various normal human and tumor tissues, as well as in cancer cell lines. Among the tumor tissues tested, lung tumor tissue expressed GGCT mRNA more strongly than normal lung tissue. The GGCT protein was found to be localized in the cytoplasmic region of cultured cells, where it forms a homodimer. Analysis of various deletion mutants of the GGCT protein revealed that the region containing amino acid residues 61-120 of the protein is required for its cytoplasmic localization. The comparison of the soft agar colony formation of HBL-100 cells stably expressing GGCT with that of control HBL-100 cells revealed that GGCT does not promote colony formation, suggesting that the role it plays in lung cancer cells is not related to tumorigenesis.

Gamma-Glutamylcyclotransferase: A Novel Target Molecule for Cancer Diagnosis and Treatment

“…The intracellular distribution found by immunohistochemistry was in the cytoplasm and nucleus and these findings were almost consistent with a few other reports [ 12 – 14 ]. Cytoplasmic staining by immunohistochemistry is relatively homogeneous.…”

“…However, no significant changes were observed in comparison with controls [ 7 ]. Independently of our work, Azumi et al also reported findings similar to our results by introducing the GGCT gene into HBL-100 cells, a breast cancer cell line with low-level GGCT expression [ 14 ]. Thus, it is assumed that the involvement of GGCT in malignant transformation was negated.…”

“…However, nuclear reactivity is relatively heterogeneous. Azumi et al analyzed the cellular localization of GGCT using full-length protein and its truncated mutants [ 14 ]. They produced the transfectants (NIH3T3) that express a GFP-GGCT fusion protein or mutants.…”

Knockdown of GGCT inhibits cell proliferation and induces late apoptosis in human gastric cancer

“…Based on theanalysis of two independent studies in Oncomine database, we found that GGCT is highly accumulated in gastric cancer cells. Furthermore, it has beenproved thatGGCTfunctioned as a novel biomarker of esophageal squamous malignancies, as its expression levels strongly correlated with lymph node metastasis and differentiation degree [6–11], in consistent with that overexpression and depletion of GGCT resulted in proliferative and antiproliferative activities in bladder cancer cells, respectively [9]. Here, we observed that GGCT depletion could remarkably inhibit cell proliferation and colony formation activities ofhuman gastric cancer cells.…”

Widespread Expression of γ-Glutamyl Cyclotransferase Suggests It Is Not a General Tumor Marker

“…In a previous study of the intracellular distribution of GGCT, a green fluorescent protein-GGCT fusion protein was only detected in the cytoplasm. However, a deletion mutant lacking GGCT residues 61-120 was localized to the nucleus, suggesting that the central region is required to anchor GGCT in the cytoplasm (Azumi et al 2009). In the present study, we noted that GGCT is sometimes detected in the nucleus of human cells, and we also noted a lower molecular weight variant in some tissues.…”