| Human breast carcinoma is one of the most frequent cancer in the female malignacies and deeply threatens woman health and life quality. Therefore it becomes a very important region in studying the mechanism of breast cancer evolution, searching the novel effective methods of diagnosis and therapy and clarifying the theory basis of improving prognosis.Within the most frequently mutated region on chromosomel7pl3.3 in human cancers, a novel human plasma membrane-associated gene, named CT120, was isolated from a human kidney cDNA library using electronical cloning and RACE. It indicated that CT120 had two isoforms in human being by homogeneous comparing of its amino acids sequencies. The novel gene CT120A consisted of 2145 base pairs and encoded a protein with 257 amino acids.The fourth exon coding 30 amino acids was deleted,giving a new isoform 225 amino acids. CT120A had seven cross-membrance regions and CT120B had six. CT120A might be one gene of GPCR hyper-family. Subcellular localization analysis showed most CT120A and CT120B located on cell membrane and only little on cell plasma, which indicating that CT120 was a novel membrane-associated protein. CT120A could interact with SLC3A2 (member 2 of solute carrier family) and GGTL3B (isoform of y-glutamyltranspeptidase-like 3) in eukaryotic cells by yeast two-hybrid screen and co-immunoprecipitation assay, which suggested that CT120 might assume very essential physiological functions involved in amino acid transport and glutathione metabolism.Database search revealed that homologs of CT120 existed in different organisms from plant to animal kingdoms, which suggested that CT120 was a highly conserved gene during biological evolution. Different expression patterns of CT120 were observed in breast cancer tissue and in paracancerous tissue, suggesting that CT120 might be involve in breast cancer devolopment.To further study the relationships between CT120 and human breast carcinogenesis, we transducted human breast cancerous cells lines with CT120A and CT120B and observed their influence on cell growth. Cloning formation assay and cell proliferation activity analysis showed that overexpression of CT120A significantly promoted the growth of MCF7 and T47D cells.Tumor formation assay of transfected cell in nude mice also suggested overexpression CT120A stimulated the proliferation of T47D cells in vitro. But overexpression of CT120B played the opposite role. It inhibited the growth of T47D in vitro and in vivo. Those results indicated novel gene CT120 may play an importment role in cell proliferation closely related to human breast carcinogenesis.To explore the roles of CT120 in promoting cell proliferation, we investigated the downstream signaling events regulated by CT120 using Atlas human cDNA expressing arrays. CT120A stimulated the growth of breast cancerous cells through upregulating and activating the signal transduction pathways of IL6 gpl30 Jak (Janus protein tyrosine kinase), inhibiting TNF mediated cell apoptosis singal transduction pathways, downregulating cyclin dependent kinases inhibitor pl6 and pl9 and activating epidermal growth factor receptor family. CT120B can inhibited the growth of cancerous cell through upregulating and activating TNF mediated cell apoptosis signal transduction pathway, downregulating the signal transduction pathway of MAPK, downregulating cyclin H> E.In conclusion, the newly identified gene CT120 from chromosome 17pl3.3 was a key gene of cell proliferation closely related to human breast carcinogenesis. CT120A could promote cell proliferation and CT120B could depress cell proliferation. Through exploring the downstream signaling events regulated by CT120, we could anticipate the implication of the signal transduction pathways regulated by CT120 in cell proliferation. At the same time ,we also proceeded the RNA interfered assay. These findings will faciliate the development of new strategies for diagnosis and therapy of human breast malignancies.
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