Cellular localization of the proto-oncogenic p53 inhibitor AGR2 protein in breast cancer

Background

Proteomic technologies verified AGR-2 as a protein family overexpressed in human cancers, including breast, prostate and oesophagus cancers, with the ability to inhibit the tumour suppressor protein p53 [1]. The AGR-2 gene is a hormone responsive gene with an unexpected induction by the anticancer drug tamoxifen highlighting the proto-oncogenic role of this protein. The hAGR-2 gene was first described in the MCF-7 breast carcinoma cell line, and was found to be coexpressed with the estrogen receptor (ER), in ER-positive cell lines [2, 3]. Moreover, it was recently revealed that AGR-2 is secreted from androgen-inducible cell lines in prostate cancer cell lines [4].

Methods

Localization studies of AGR-2 were performed using fluorescence microscopy in order to determine in which compartment the protein functions. Yeast two-hybrid analysis has identified potential nuclear and cytoplasmic binding proteins for AGR-2, essential for the upstream or downstream regulation of the AGR-2 pathway.

Results

Anterior gradient 2 encodes one protein that gives rise to two forms: the full-length and the mature. Full-length AGR2wt, which bears the leader sequence, localizes to the ER and the Golgi compartment whereas the mature protein requires the C-terminal KTEL sequence for strong nuclear localization. Deletion of the KTEL, putative ER retention, sequence does not alter the localization of the wt full-length form to a large extent but has a strong effect on the localization shift of the mature form. Subcellular fractionation data verified the difference in the localization patterns of the wt forms and their mutants. Moreover, the localization of the protein and each of the mutants differs significantly in various cell lines, suggesting a multipotent role of the protein when it comes to activation pathways and localization patterns within the cell. Furthermore, we present data showing models of how the AGR-2 family might function as a drug-resistance survival factor in cancer as well as a p53 inhibitor.

Conclusion

All of the above suggest a multipotent role of AGR-2 when it comes to trafficking, cellular localization and activation or inhibition pathways in cancer. The localization of the protein can therefore determine the level of p53 inhibition.