A BTB/POZ protein, NAC-1, is related to tumor recurrence and is essential for tumor growth and survival

NAC-1, a potential stem cell pluripotency factor, contributes to paclitaxel resistance in ovarian cancer through inactivating Gadd45 pathway

Nucleus accumbens-1 (Nac1 or NAC-1) belongs to the BTB/POZ (Pox virus and Zinc finger/Bric-a-brac Tramtrack Broad complex) transcription factor family and is a novel protein that potentially participates in self-renewal and pluripotency in embryonic stem cells. In human cancer, NAC-1 is upregulated in several types of neoplasms, but particularly in recurrent chemoresistant ovarian carcinomas, suggesting a biological role for NAC-1 in the development of drug resistance in ovarian cancer. We have assessed this possibility and shown a correlation between NAC-1 expression and ex vivo paclitaxel resistance in ovarian serous carcinoma tissues and cell lines. We found that expression of Gadd45-gamma-interacting protein 1 (Gadd45gip1), a downstream target negatively regulated by NAC-1, was reduced in paclitaxel-resistant cells. Ectopic expression of NAC-1 or knockdown of Gadd45gip1 conferred paclitaxel resistance, whereas NAC-1 knockdown or ectopic expression of Gadd45gip1 increased paclitaxel sensitivity. Furthermore, silencing NAC-1 expression or disrupting NAC-1 homodimerization by a dominant negative NAC-1 protein that contained only the BTB/POZ domain induced the expression of Gadd45gamma, which interacted with Gadd45gip1. Reducing Gadd45gamma expression by small hairpin RNAs partially enhanced paclitaxel resistance. Thus, this study provides new evidence that NAC-1 upregulation and homodimerization contribute to tumor recurrence by equipping ovarian cancer cells with the paclitaxel-resistant phenotype through negative regulation of the Gadd45 pathway.

Structure of the human Nac1 POZ domain

Nac1 is a POZ-domain transcription factor that is involved in the self-renewal of embryonic stem cells. It is overexpressed in ovarian serous carcinoma and targeting the interactions of its POZ domain is a potential therapeutic strategy. Nac1 lacks a zinc-finger DNA-binding domain and thereby differs from most other POZ-domain transcription factors. Here, the crystal structure of the Nac1 POZ domain at 2.1 A resolution is reported. The Nac1 POZ domain crystallized as a dimer in which the interaction interfaces between subunits resemble those found in the POZ-zinc finger transcription factors. The organization of the Nac1 POZ-domain core resembles reported POZ-domain structures, whereas the C-terminus differs markedly. The C-terminal alpha-helix of the Nac1 POZ domain is shorter than that observed in most other POZ-domain transcription factors; variation in the organization of this region may be a general feature of POZ-domain structures.

National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines for Use of Tumor Markers in Testicular, Prostate, Colorectal, Breast, and Ovarian Cancers

Background: Updated National Academy of Clinical Biochemistry (NACB) Laboratory Medicine Practice Guidelines for the use of tumor markers in the clinic have been developed.

Methods: Published reports relevant to use of tumor markers for 5 cancer sites—testicular, prostate, colorectal, breast, and ovarian—were critically reviewed.

Results: For testicular cancer, α-fetoprotein, human chorionic gonadotropin, and lactate dehydrogenase are recommended for diagnosis/case finding, staging, prognosis determination, recurrence detection, and therapy monitoring. α-Fetoprotein is also recommended for differential diagnosis of nonseminomatous and seminomatous germ cell tumors. Prostate-specific antigen (PSA) is not recommended for prostate cancer screening, but may be used for detecting disease recurrence and monitoring therapy. Free PSA measurement data are useful for distinguishing malignant from benign prostatic disease when total PSA is <10 μg/L. In colorectal cancer, carcinoembryonic antigen is recommended (with some caveats) for prognosis determination, postoperative surveillance, and therapy monitoring in advanced disease. Fecal occult blood testing may be used for screening asymptomatic adults 50 years or older. For breast cancer, estrogen and progesterone receptors are mandatory for predicting response to hormone therapy, human epidermal growth factor receptor-2 measurement is mandatory for predicting response to trastuzumab, and urokinase plasminogen activator/plasminogen activator inhibitor 1 may be used for determining prognosis in lymph node–negative patients. CA15-3/BR27–29 or carcinoembryonic antigen may be used for therapy monitoring in advanced disease. CA125 is recommended (with transvaginal ultrasound) for early detection of ovarian cancer in women at high risk for this disease. CA125 is also recommended for differential diagnosis of suspicious pelvic masses in postmenopausal women, as well as for detection of recurrence, monitoring of therapy, and determination of prognosis in women with ovarian cancer.

Conclusions: Implementation of these recommendations should encourage optimal use of tumor markers.

A BTB/POZ gene, NAC-1, a tumor recurrence-associated gene, as a potential target for Taxol resistance in ovarian cancer

PURPOSE

We previously determined that NAC-1, a transcription factor and member of the BTB/POZ gene family, is associated with recurrent ovarian carcinomas. In the current study, we investigated further the relationship between NAC-1 expression and ovarian cancer.

EXPERIMENTAL DESIGN

NAC-1 expression was assessed by immunohistochemistry, and clinical variables were collected by retrospective chart review. SiRNA system and NAC-1 gene transfection were used to asses NAC-1 function in Taxol resistance in vivo.

RESULTS

Overexpression of NAC-1 correlated with shorter relapse-free survival in patients with advanced stage (stage III/IV) ovarian carcinoma treated with platinum and taxane chemotherapy. Furthermore, overexpression of NAC-1 in primary tumors predicted recurrence within 6 months after primary cytoreductive surgery followed by standard platinum and taxane chemotherapy. NAC-1 expression levels were measured and compared among the human ovarian cancer cell line (KF28), cisplatin-resistant cell line (KFr13) induced from KF28, and paclitaxel-resistant cell lines (KF28TX and KFr13TX) induced by exposing KF28 and KFr13 to dose-escalating paclitaxel. Overexpression of NAC-1 was observed in only the Taxol-resistant KF28TX and KFr13 TX cells but not in KF28 or cisplatin-resistant KFr13 cells. To confirm that NAC-1 expression was related to Taxol resistance, we used two independent but complementary approaches. NAC-1 gene knockdown in both KF28TX and KFr13TX rescued paclitaxel sensitivity. Additionally, engineered expression of NAC-1 in RK3E cells induced paclitaxel resistance.

CONCLUSIONS

These results suggest that NAC-1 regulates Taxol resistance in ovarian cancer and may provide an effective target for chemotherapeutic intervention in Taxol-resistant tumors.

Characterization and expression of a human KCTD1 gene containing the BTB domain, which mediates transcriptional repression and homomeric interactions

We identified potassium channel tetramerization domain-containing 1 (KCTD1) gene in a human brain cDNA library. Here, we report that the KCTD1 gene contains seven exons, encoding 257 amino acid residues with a predicted molecular mass of 29.4 kDa. Sequence alignments showed KCTD1 protein contains an N-terminal broad-complex, tramtrack, and bric-a-brac (BTB) domain. Northern blot analysis revealed that KCTD1 is expressed in the mammary gland, kidney, brain, and ovary compared to other tissues. Further, the subcellular localization results showed that KCTD1 is localized in the nuclei of HeLa and HBL100 cells. Reporter gene assays in HEK293FT and NIH3T3 cells further indicated that KCTD1 acts as a potent transcriptional repressor and inhibits the transcriptional activity via its BTB domain, though KCTD1 transcriptional repression is unaffected by the HDAC inhibitors, trichostatin A, and sodium butyrate. Finally, we found that the BTB domain of KCTD1 mediates homomeric protein-protein interactions by co-immunoprecipitation and GST pull-down assays. These data present the first characterization of human KCTD1 and suggest that KCTD1 is a nuclear protein that functions as a transcriptional repressor and mediates protein-protein interactions through a BTB domain.

The roles of human sucrose nonfermenting protein 2 homologue in the tumor-promoting functions of Rsf-1

Rsf-1 interacts with human sucrose nonfermenting protein 2 homologue (hSNF2H) to form a chromatin remodeling complex that participates in several biological processes. We have previously shown that Rsf-1 gene amplification was associated with the most aggressive type of ovarian cancer and cancer cells with Rsf-1 overexpression depended on Rsf-1 to survive. In this report, we determine if formation of the Rsf-1/hSNF2H complex could be one of the mechanisms contributing to tumor cell survival and growth in ovarian carcinomas. Based on immunohistochemistry, we found that Rsf-1 and hSNF2H were co-upregulated in ovarian cancer tissues. Ectopic expression of Rsf-1 in SKOV3 ovarian cancer cells with undetectable endogenous Rsf-1 expression enhanced hSNF2H protein levels and promoted SKOV3 tumor growth in a mouse xenograft model. Our studies also indicated that induction of Rsf-1 expression affected the molecular partnership of hSNF2H and translocated hSNF2H into nuclei where it colocalized with Rsf-1. Furthermore, analysis of Rsf-1 deletion mutants showed that the Rsf-D4 fragment contained the hSNF2H binding site based on coimmunoprecipitation and in vitro competition assays. As compared with other truncated mutants, expression of Rsf-D4 resulted in remarkable growth inhibition in ovarian cancer cells with Rsf-1 gene amplification and overexpression, but not in those without detectable Rsf-1 expression. The above findings suggest that interaction between Rsf-1 and hSNF2H may define a survival signal in those tumors overexpressing Rsf-1.

Expression of the bric-a-brac tramtrack broad complex protein NAC-1 in cervical carcinomas seems to correlate with poorer prognosis

PURPOSE

Recent studies have suggested a novel oncogenic role of a bric-a-brac tramtrack broad complex (also known as POZ) domain gene, NAC-1, in ovarian carcinomas. The aim of this study was to clarify the functional role of NAC-1 in human cervical carcinomas.

EXPERIMENTAL DESIGN

NAC-1 expression in cervical cancer was assessed by immunohistochemistry, and data on clinical variables were collected by retrospective chart review. NAC-1 gene knockdown using small interfering RNA and a NAC-1 gene transfection system were used to asses NAC-1 function in cervical cancer in vivo.

RESULTS

Immunohistochemical and gene expression analysis revealed that NAC-1 is significantly overexpressed in cervical adenocarcinomas and adenosquamous carcinomas compared with squamous cell carcinomas. Patients with squamous cell carcinomas positive for NAC-1 expression who received radiotherapy had significantly shorter overall survival than peers whose tumors did not express NAC-1, and multivariate analysis showed that NAC-1 expression was an independent prognostic factor for overall survival after radiotherapy. Overexpressions of the NAC-1 gene stimulated cell proliferation in cervical carcinoma cells of the TCS, CaSki, and HeLa P3 lines, which do not have endogenous NAC-1 expression. NAC-1 gene knockdown inhibited cell growth and induced apoptosis in HeLa, HeLa TG, and ME180 cells, all of which overexpressed NAC-1.

CONCLUSIONS

Our findings suggest that NAC-1 may play an important role in cervical carcinomas; moreover, these findings provide a rationale for future development of NAC-1-based therapy for cervical carcinomas that overexpress this candidate oncogene.

NAC-1 controls cell growth and survival by repressing transcription of Gadd45GIP1, a candidate tumor suppressor

Cancer mortality and morbidity are primarily related to recurrent tumors, and characterization of recurrence-associated genes should illuminate fundamental properties of tumor progression and provide new therapeutic targets. We have previously identified NAC-1, a member of the BTB/POZ gene family and a transcription repressor, as a gene associated with recurrent ovarian carcinomas after chemotherapy. We further showed that homodimerization of NAC-1 proteins is essential for tumor growth and survival. In this study, we applied serial analysis of gene expression and identified growth arrest and DNA-damage-inducible 45-gamma interacting protein (Gadd45GIP1) as one of the downstream genes negatively regulated by NAC-1. NAC-1 knockdown in both SKOV3 and HeLa cells that expressed abundant endogenous NAC-1 induced Gadd45GIP1 expression transcriptionally; on the other hand, engineered expression of NAC-1 in NAC-1-negative RK3E and HEK293 cells suppressed endogenous Gadd45GIP1 expression. In NAC-1-expressing tumor cells, induction of dominant negative NAC-1 conferred a growth-inhibitory effect that can be partially reversed by Gadd45GIP1 knockdown. Induced Gadd45GIP1 expression resulted in growth arrest in SKOV3 and HeLa cells both in vitro and in vivo. In summary, NAC-1 contributes to tumor growth and survival by at least inhibiting Gadd45GIP1 expression, which has a tumor suppressor effect in cancer cells.

Expression and clinical role of the bric-a-brac tramtrack broad complex/poxvirus and zinc protein NAC-1 in ovarian carcinoma effusions

We recently identified NAC-1, member of the bric-a-brac tramtrack broad complex/poxvirus and zinc domain family, as an overexpressed gene in ovarian serous carcinoma and found more frequent NAC-1 protein expression in recurrent compared to primary tumors. In the present study, we assessed the clinical significance of NAC-1 expression in ovarian carcinoma effusions. Formalin-fixed, paraffin-embedded sections from 176 effusions (137 peritoneal, 39 pleural) and 197 corresponding solid tumors (69 primary tumors, 128 solid metastases) were analyzed for NAC-1 expression using immunohistochemistry. Staining intensity and extent results were analyzed for possible association with clinicopathologic parameters and survival. Nuclear NAC-1 immunoreactivity was found in carcinoma cells in 98% of (173/176) effusions, 94% (65/69) of primary tumors, and 95% (121/128) of metastases. Staining intensity and extent were significantly higher in effusions compared with matched solid tumors (P = .002 for intensity, P = .003 for extent compared with primary tumors; P < .001 for both intensity and extent compared with metastases). Furthermore, NAC-1 expression intensity was significantly higher in specimens obtained after the administration of chemotherapy (P = .002) and correlated with shorter progression-free survival (PFS) in analysis of 62 patients with post-chemotherapy effusions (P = .039). International Federation of Gynecology and Obstetrics stage (IV versus III) was the only clinical parameter associated with PFS in this group (P = .004). In Cox analysis, only the International Federation of Gynecology and Obstetrics stage was an independent predictor of shorter PFS (P = .009). In conclusion, NAC-1 expression is higher in ovarian carcinoma cells in effusions compared with their solid tumor counterparts. NAC-1 is up-regulated in tumor cells after chemotherapy, suggesting a role for this protein in tumor progression and in the development of chemotherapy resistance in ovarian cancer.