Tumor protein D52 represents a negative regulator of ATM protein levels.

Tumor protein D52 (TPD52) is a coiled-coil motif bearing hydrophilic polypeptide known to be overexpressed in cancers of diverse cellular origins. Increased TPD52 expression is associated with increased proliferation and invasive capacity in different cell types. Recent studies have reported a correlation between TPD52 transcript levels and G 2 chromosomal radiosensitivity in lymphocytes of women at risk of hereditary breast cancer, and that TPD52 knockdown significantly reduced the radiation sensitivity of multiple cancer cell lines. In this study, we investigated possible roles for TPD52 in DNA damage response, and found that increased TPD52 expression in breast cancer and TPD52-expressing BALB/c 3T3 cells compromised ATM-mediated cellular responses to DNA double-strand breaks induced by γ-ray irradiation, which was associated with downregulation of steady-state ATM protein, but not transcript levels, regardless of irradiation status. TPD52-expressing 3T3 cells also showed significantly increased radiation sensitivity compared with vector cells evaluated by clonogenic assays. Furthermore, direct interactions between exogenous and endogenous ATM and TPD52 were detected by GST pull-down and co-immunoprecipitation assays. We also identified the interaction domains involved in this binding as TPD52 residues 111-131, and ATM residues 1-245 and 772-1102. Taken together, our results suggest that TPD52 may represent a novel negative regulator of ATM protein levels.

MAL2 and tumor protein D52 (TPD52) are frequently overexpressed in ovarian carcinoma, but differentially associated with histological subtype and patient outcome.

BACKGROUND: The four-transmembrane MAL2 protein is frequently overexpressed in breast carcinoma, and MAL2 overexpression is associated with gain of the corresponding locus at chromosome 8q24.12. Independent expression microarray studies predict MAL2 overexpression in ovarian carcinoma, but these had remained unconfirmed. MAL2 binds tumor protein D52 (TPD52), which is frequently overexpressed in ovarian carcinoma, but the clinical significance of MAL2 and TPD52 overexpression was unknown. METHODS: Immunohistochemical analyses of MAL2 and TPD52 expression were performed using tissue microarray sections including benign, borderline and malignant epithelial ovarian tumours. Inmmunohistochemical staining intensity and distribution was assessed both visually and digitally. RESULTS: MAL2 and TPD52 were significantly overexpressed in high-grade serous carcinomas compared with serous borderline tumours. MAL2 expression was highest in serous carcinomas relative to other histological subtypes, whereas TPD52 expression was highest in clear cell carcinomas. MAL2 expression was not related to patient survival, however high-level TPD52 staining was significantly associated with improved overall survival in patients with stage III serous ovarian carcinoma (log-rank test, p < 0.001; n = 124) and was an independent predictor of survival in the overall carcinoma cohort (hazard ratio (HR), 0.498; 95% confidence interval (CI), 0.34-0.728; p < 0.001; n = 221), and in serous carcinomas (HR, 0.440; 95% CI, 0.294-0.658; p < 0.001; n = 182). CONCLUSIONS: MAL2 is frequently overexpressed in ovarian carcinoma, and TPD52 overexpression is a favourable independent prognostic marker of potential value in the management of ovarian carcinoma patients.

Stimulation of mesangial cells by angiotensin II and lipopolysaccharide increases expression of interleukin-18, but not IL-18 receptor.

BACKGROUND/AIMS: Mesangial cell (MC) hyperplasia is associated with several kidney diseases. Experimental studies confirm upregulation of IL-18 in glomerular disease and renal allograft rejection. We evaluated whether MCs express IL-18 and IL-18 receptor-α (IL-18Rα) with and without stimulation by LPS, AngII and PDGF. METHODS: Glomeruli were isolated using Dynabeads perfusion. MCs were cultured by glomerular explantation. IL-18 and IL-18Rα expression were detected by RT-PCR, ELISA and flow cytometry. RESULTS: Significantly higher levels of IL-18 expression were detected in isolated glomeruli, compared to cortical tissue devoid of glomeruli, and in MCs, compared to tubular cells (both p < 0.01). Increased IL-18 expression was detected in MCs, but not podocytes, endothelial cells or tubular cells in response to LPS stimulation. IL-18 mRNA and protein expression were significantly upregulated by AngII (p < 0.05) and LPS (p < 0.01), but not PDGF-BB, in primary MCs and a MC line (MES13). IL-18Rα mRNA was almost undetectable in MCs treated with or without LPS, AngII and PDGF-BB. IL-18Rα protein was not detected by flow cytometry. CONCLUSIONS: MCs express IL-18, which was significantly increased after LPS and AngII stimulation, but do not express appreciable levels of IL-18Rα. MC-derived IL-18 is unlikely to be an autocrine mediator in glomerular disease given the lack of IL-18Rα.

TPD52, a candidate gene from genomic studies, is overexpressed in testicular germ cell tumours.

Several genomic regions are recurrently over- or underrepresented in testicular germ cell tumours (TGCTs), but only a fraction of their genes change their expression accordingly. Two publications to date have studied DNA copy numbers and associated gene expression changes on a genome-wide level to identify key players in TGCT tumorigenesis. Here, we compare lists of significant genes in these studies, and show that 17 genes are common to both. These include concomitant gain and over-expression of JUB, NRXN3, and TPD52, and loss and under-expression of C11orf70 and CADM1, in addition to 12 overexpressed genes located on the chromosome arm 12p. We performed immunohistochemical analysis of TPD52 on a tissue microarray, which showed complete absence of TPD52 protein in normal germ cells and most intratubular germ cell neoplasias. TPD52 was expressed in two-thirds of seminomas and embryonal carcinomas, and at intermediate frequencies in the more differentiated non-seminomas.

Tumor protein D52 overexpression and gene amplification in cancers from a mosaic of microarrays.

The tumor protein D52 gene is increasingly recognized to be overexpressed in different cancer types, frequently through gain of the corresponding locus at chromosome 8q21.13. This review summarizes the literature identifying D52 overexpression and/or gene amplification in different cancers, as well as recent publications directly analyzing D52 functions. Since D52 overexpression is increasingly being identified in tumors of different cellular origins, this is likely to perturb fundamental cell properties common to different cell types. Furthermore,since increased D52 expression occurs at different stages of tumorigenesis and progression, this could contribute to these processes through multiple mechanisms. Although functions are beginning to emerge from targeted studies, the pathways through which D52 overexpression contributes to cell transformation and the molecular interactions required remain undefined. In summary, while targeting D52 overexpression could provide therapeutic benefits in many cancer types, this will require an improved understanding of D52's cellular and molecular functions.