23221

RHOBTB2

DBC2;Rho-related BTB domain containing 2;RHOBTB2;Rho-related BTB domain containing 2

deleted in breast cancer 2 gene protein|p83|rho-related BTB domain-containing protein 2

8p21.3

protein-coding

A previously uncharacterized gene, DBC2 (deleted in breast cancer), was cloned from a homozygously deleted region at human chromosome 8p21. DBC2 contains a highly conserved RAS domain and two putative protein interacting domains. Our analyses indicate that DBC2 is the best candidate tumor suppressor gene from this region. It lies within the epicenter of the deletions and is homozygously deleted in 3.5% (7/200) of breast tumors. mutation analysis of DBC2 led to discovery of two instances of somatic missense mutations in breast tumor specimens, whereas no missense mutations were found in other candidates from the region. Unlike other genes in the region, expression of DBC2 is often extinguished in breast cancer cells or tissues. Moreover, our functional analysis revealed that DBC2 expression in breast cancer cells lacking DBC2 transcripts causes growth inhibition. By contrast, expression of a somatic mutant discovered in a breast cancer specimen does not suppress the growth of breast cancer cells.

Deleted in Breast cancer-2, Dbc2, identified as a candidate tumor suppressor gene for breast cancer and other human malignancies, is a member of a novel gene family encoding putative small GTPases designated as Rhobtb. In this report, we describe the spatio-temporal expression of mDbc2/Rhobtb2 mRNA during mammary gland development and embryogenesis in the mouse. We have first determined that mDbc2/Rhobtb2 transcripts are expressed at low, but seemingly constant levels during mammopoiesis. Secondly, we have found that mDbc2/Rhobtb2 is expressed highly and specifically in the central and peripheral nervous systems during mouse embryogenesis. While our results do not reveal any connection between elevated expression of mDbc2/Rhobtb2 and a specific stage of mammary gland development, they strongly support a role for this gene during development of the nervous system.

The expression of tumor suppressor gene DBC2 causes certain breast cancer cells to stop growing [M. Hamaguchi, J.L. Meth, C. Von Klitzing, W. Wei, D. Esposito, L. Rodgers, T. Walsh, P. Welcsh, M.C. King, M.H. Wigler, DBC2, a candidate for a tumor suppressor gene involved in breast cancer, Proc. Natl. Acad. Sci. USA 99 (2002) 13647-13652]. Recently, DBC2 was found to participate in diverse cellular functions such as protein transport, cytoskeleton regulation, apoptosis, and cell cycle control [V. Siripurapu, J.L. Meth, N. Kobayashi, M. Hamaguchi, DBC2 significantly influences cell cycle, apoptosis, cytoskeleton, and membrane trafficking pathways. J. Mol. Biol. 346 (2005) 83-89]. Its tumor suppression mechanism, however, remains unclear. In this paper, we demonstrate that DBC2 suppresses breast cancer proliferation through down-regulation of Cyclin D1 (CCND1). Additionally, the constitutional overexpression of CCND1 prevented the negative impact of DBC2 expression on their growth. Under a CCND1 promoter, the expression of CCNE1 exhibited the same protective effect. Our results indicate that the down-regulation of CCND1 is an essential step for DBC2s growth suppression of cancer cells. We believe that this discovery contributes to a better understanding of DBC2s tumor suppressor function.

RhoBTB2 was isolated recently as a tumor suppressor gene from human chromosome 8p21.3. Although RhoBTB2 was found to be frequently lost in breast cancer lines, expression status of RhoBTB2 in sporadic breast cancer tissues and its clinical and prognostic value, however, remain unclear. Tissue samples from breast cancer patients and normal controls and cell samples from cell lines were collected and reverse transcription (RT)-PCR was used to monitor the presence of RhoBTB2 mRNA. The protein expression of RhoBTB2 was detected by immunohistochemical staining. Cumulative survival time was assessed by the Kaplan-Meier method and Cox regression model. We discovered that RhoBTB2 expression was lacking in a breast ductal epithelial carcinoma cell line T-47D but was expressed in other types of tumor cell lines and normal tissues we tested. The results from tissue samples showed that RhoBTB2 was absent in 60% of breast cancers on both the mRNA and protein level. The results from RT-PCR were completely uniform with those from immunohistochemistry. We demonstrated that loss of RhoBTB2 more frequently occurred in postmenopausal patients of age >or=50 yr old and in patients with infiltrating ductal carcinoma of the breast. The prognostic value of RhoBTB2 in breast cancers also be assessed by a long-term follow-up investigation and we found that patients with RhoBTB2-negative breast cancer were linked to poor clinical prognosis. Therefore, the loss of RhoBTB2 expression is a common occurrence in breast cancers and it is an important factor in the development and prognosis of sporadic breast cancer.

AIMS: To investigate the expression of EMP1 in oral squamous cell carcinoma (OSCC) tissues and its correlation with available clinical parameters of patients with OSCC. METHODS: The mRNA levels of EMP1 were measured in 18 paired OSCC and corresponding adjacent normal tissues using RT-PCR. Another 45 pairs of OSCC samples were selected to detect the mRNA level of EMP1 using quantitative RT-PCR (qRT-PCR). The protein levels of EMP1 were also evaluated in 60 cases of patients with OSCC using immunohistochemical staining. The correlation between EMP1 expression and clinical parameters was analysed with non-parametric analysis. RESULTS: The results of RT-PCR and qRT-PCR showed that, compared with the paired normal tissues, the mRNA levels of EMP1 were significantly decreased in OSCC. The immunohistochemical results indicated that the EMP1 protein was also downregulated in OSCC (p=0.031). Decreased expression of EMP1 was significantly correlated with clinical stage (p=0.002) and lymph node metastasis (p=0.044) of patients with OSCC. Meanwhile, there was a significant difference between OSCCs at early and advanced stages (p=0.003), and between OSCCs with lymph node metastasis and no lymph node metastasis (p=0.045), respectively. CONCLUSIONS: The results suggest that EMP1 may be a tumour suppressor and associated with lymph node metastasis in OSCC.

RhoBTB2 was isolated recently as a tumor suppressor gene from sporadic breast cancer. Although RhoBTB2 was found to be frequently lost in breast cancer and a variety of cancers, its antitumor effect, however, remains unclear. In this study, we constructed a recombinant expression vector pEGFP-N1-RhoBTB2 and transfected it into RhoBTB2-negative breast tumor cell line T-47D. Stable transformanted cells were identified by fluorescence microscope, RT-PCR and Western blot. Cell viability was measured by MTT assay. Colony forming efficiency of breast tumor cells was detected by colony formation assay. Morphological change of apoptotic cells was observed by hematoxylin-eosin staining. Apoptotic ratio was determined by flow cytometry. Cell invasion and migration ability assay were performed using transwell system. Overexpression of RhoBTB2 in breast tumor cells significantly inhibited the proliferation and colony formation of tumor cells. In addition, RhoBTB2 also elevated the apoptotic ratio and caused typical changes of apoptotic morphology in breast tumor cells of RhoBTB2 overexpression. But RhoBTB2 did not influence the invasion and migration ability of breast tumor cells. Therefore, RhoBTB2 is an important tumor suppressor gene related with breast cancer and may play antitumor roles by inhibiting proliferation, preventing colony formation and promoting the apoptosis of tumor cells. However, the precise mechanism behind the antitumor effects of RhoBTB2 needs to be investigated further.