Screening and identification of the proteins interacting with the transcription factor X-box binding protein 1

X-box binding protein1 (XBP1) is an important transcription factor, which participates in many signal transduction procession. To investigate the biological function of XBP1, yeast two-hybrid system to screen proteins interacting with XBP1 in hepatocytes was performed. The XBP1 coding sequence was amplified by polymerase chain reaction (PCR) method, and was cloned in pGEM-T vector. After the target region was sequenced, it was subcloned into the bait plasmid pGBKT7, then was transformed into yeast AH109(a type). After the expression of bait plasmid pGBKT7-XBP1 in AH109 yeast strains were proved by Western blot. The transformed yeast AH109 was mated with yeast Y187(alpha type) containing hepatocyte cDNA library plasmids pACT2 in 2xYPDA medium. Diploid yeast was plated on synthetic dropout nutrient medilium (SD/-Trp-Leu-His-Ade) containing X-alpha-gal for selection and screening. After sequencing and verifying ORF of positive colonies, 7 different kinds of proteins were obtained. In order to further testify the interaction between the screened proteins and XBP1, one of positive colonies MT1E was cloned. The interaction between MT1E and XBP1 in vitro/in vivo were examined successfully with GST pulldown and coimmunoprecipitations. It was shown that MT1E would be a new regulatory protein of XBP1. These screened proteins by yeast two-hybird system were closely correlated with liver fundamental metabolism,protein synthesis and transport, cell proliferation and apoptosis. The results mentioned above contributed to reveal the XBP1 biological function, and brought some new clues for further exploration of the expressing and regulating mechanism of XBP1.