Cloning And Tissue Distribution Of IRBIT,and Its Expression In Liver And Breast Cancer

IRBIT?IP₃ Receptor Binding protein released with Inositol Triphosphate?is widely expressed in diverse tissues and plays critical biological roles in mammals.IRBIT was originally identified as a regulator of the Ca²⁺channel IP₃ receptor?IP₃R?on the endoplasmic reticulum.Now it is clear that IRBIT can interact with many acid-base transporters,contributing to the regulation of intracellular acid-base balance.In addition,IRBIT is involved in regulating the biosynthesis of DNA,the splicing of RNA,the homeostasis of catecholamine,cell apoptosis.IRBIT is also shown to be associated with ovarian cancer.In the present study,we first studied the expression and distribution of IRBIT in mouse tissues by RT-PCR and western blotting,and analyzed the expression and distribution of IRBIT in mouse brain by immunofluorescence.By reverse-transcription polymerase chain reaction?RT-PCR?,we cloned the cDNAs encoding IRBIT and Long-IRBIT?a paralog of IRBIT?from mouse and human tissues.We examined the effect of co-expression of IRBIT or Long-IRBIT on the activity of the electrogenic Na⁺/HCO₃?co-transporter NBCe1-B in Xenopus oocytes by two-electrode voltage clamp.We found that the presence of IRBIT and Long-IRBIT substantially stimulated the transport activity of NBCe1-B.We examined by western blotting the expression of IRBIT in normal and cancerous breast cell lines.Moreover,we examined the expression of IRBIT in breast cancer tissues by western blotting.Our data showed that,compared to the adjacent normal tissues,the expression levels of IRBIT were significantly increased in breast cancer tissues.Similar results were observed in liver cancer tissues.Consistent with the western blotting results,immunofluoresence with tissue arrays showed the expression of IRBIT in breast cancer tissues was significantly higher than that in the adjacent normal tissues.Statistical analysis showed that,in our studied samples,the expression of IRBIT was not significantly associated with the expression of estrogen receptor?ER?,but was somewhat assocaited with progesterone receptor?PR?,human epidermal growth factor receptor?HER2?,and strongly associated with the grading of breast cancers.Our results suggest that IRBIT likely plays an important role in the development of liver and breast cancer.These results may be helpful for the further research on the biological effects of IRBIT,and have certain scientific value for revealing the mechanism of occurrence and development of tumors.It may also have a certain guiding role in the targeted therapy of tumors.