The Role Of GB_1e In Breast Cancer Cells

Gamma-aminobutyric acid?GABA? is a main inhibitory neurotransmitter in central nervous system?CNS?. The metabotropic receptor of GABA?GABA_B receptor? is consisted of GABA_B1 and GABA?B2? subunits, which are distributed in CNS and most of the peripheral tissues. GABA_B1 subunit has multiple alternatively spliced isoforms including GABA_B1a-n. Compared to the full length GABA_B1 a, the truncated isoform GABA_B1 e only contains the extracellular ligand binding domain and 9 amino acids of the transmembrane domain, and GB_1e was only detected at m RNA level in peripheral tissues.Breast cancer is the most frequently diagnosed cancer and the leading cause of cancer death among females worldwide. Between 1980 and the late 1990 s, breast cancer incidence rates rose approximately 30% in Western countries. Though it is a little lower in our country, the average age of patients become younger and there is an increasing incidence rates from countryside.It has been reportetd that GABA_B receptor was involved in tumor development, but the results were controversial probably due to the existence of different GABA_B1 isoforms in different cell lines or tissues. To investigate the function of GB_1e in tumor progression, the expression of GB_1e at mRNA and protein levels were analyzed in human breast, colon and liver cancer cell lines. The results revealed that GB_1e expression level was correlated with the malignancy of cancer cells. Surprisingly, GB_1e was also detected in glioma cell line although its expression was not detected in CNS. And GB_1e has a higher mRNA expression level in 3 of 5 prostate cancer tissure compared to the normal tisser.To figure out the role of GB_1e in breast cancer progression, GB_1e was overexpressed in breast cancer line MCF-7. The results showed that GB_1e not only could be secreted into the medium but also could be absorbed by the cells. GB_1e enhanced proliferation, ERK phosphorylation and epithelial-mesenchymal transition?EMT? of MCF-7 cells. Of interest, medium conditioned by cells overexpressing GB_1e also promoted the clonogenicity of parental MCF-7 cells. In addition, GB_1e protected MCF-7 cells from apoptosis induced by Tm and Tg, which may result in a strong ER stress. Moreover, GB_1e remarkably increased clonogenicity, spheroid formation as well as the mRNA level of stem cell maker CD44 in MCF-7 cells. LC-MS/MS results indicated that GB_1e may interact with SEL1 L, OS9, PTPN12, UGGT1, DAAM, MMS19, and APP. IP results demonstrated that SEL1 L,PTPN12 and DAAM1 have an interaction with GB_1e. Besides, PTPN12 as a tumor suppressor is down regulated in GB_1e overexpressed cells. These observations suggested that GB_1e may potentiate MCF-7 cells to acquire stem cell characteristics through MAPK pathway. The mechanism is under investigation.This is the first time to investigate the function of GABA_BR1 isoform in tumors.It is also the first time to establish contact between GABA_B receptor and tumor niche or cancer stem cells.The data show that GB_1e may play a vital role in breast cancer development.So, it provides a new thought and primary knowledge for the research of GABA_B receptor in tumor, and GB_1e may become a new target in beast cancer therapy.