Nuclear Import Receptor KPNA2 Bind To Transcription Factor C-Jun And Preliminary Research On Biology Significance

AP-1 family is composed of several types of homo- or hetero-dimmers by Jun, Fos, ATF and JDP, which associate with AP-1 binding sites of target genes to control their expression. Activator proterin-1 (AP-1) transcription factor family participates in lots of intracellular evens including cell proliferation, differentiation, apoptosis, as well as regulation of tumorigenesis, invasiveness and metastasis.AP-1 functions mainly in nucleus. The subunits of AP-1 are transported into nucleus immediately after their translation. There are many transport receptors mediating nuclear translocation of AP-1 subunits, and some important subunits could be regulated by different transport receptors. However, details of the mechanism of AP-1 nuclear translocation are still unclear. Studying on AP-1 nuclear translocation mechanism is useful for our understanding on the whole AP-1 regulation pathway. c-Jun is a main AP-1 subunit and has essential function for AP-1 activity. The nuclear transport of c-Jun is important for regulation of AP-1 pathway.KPNA2 is a nuclear import receptor in importinαfamily, which can recognize and bind to nuclear localization signal (NLS) in target proteins to form a nuclear import complex with other related proteins, mediating the nuclear translocation of target proteins. Recently, lots of studies indicate that KPNA2 is linked to cell proliferation and tumorgenesis and highly expressed in tumor cells in different tissues.This paper tested the unknown interaction between KPNA2 and c-Jun, a protein pair uncovered by a yeast two hybrid screen in human liver cDNA library. We also investigated the function of these proteins primarily. The results are helpful to expand our understanding about the regulation mechanism of AP-1 pathway.We confirmed the physiological interaction between KPNA2 and c-Jun by yeast two hybrid assay , extragenous and semi-endogenous co-immunoprecipitation (co-IP) , GST-pull down and fluorescence co-localization. We also verified interaction domains of these proteins. We found over-expression of KPNA2 had no significant effect on sub-cellular localization of c-Jun and transcription activity of PA-1, indicating nuclear translocation of c-Jun is controlled by many different factors. We further tested the interaction between KPNA2 and c-Jun in AICAR treated cells. We found that AICAR can disturb their association, leading to partial cytoplasm localization of c-Jun and inhibition of AP-1 activity. These results showed that the interaction between KPNA2 and c-Jun could exert important function in nuclear transport of c-Jun and AP-1 pathway regulation in some specific cell conditions.Besides KPNA2, we found there is interaction existed between c-Jun and another importinαfamily member KPNA1, indicating there are variable mechanisms to regulate nuclear translocation of c-Jun.Although over-expression KPNA2 barely influenced AP-1 transcription activity, the results of real-time quantitative PCR showed instead of AP-1 itself, KPNA2 do affect expression level of downstream genes of AP-1 and most of these genes are tumor-related. This suggests KPNA2 effect AP-1 activity in various ways, and the molecular mechanism should be investigated further.