PCID2 Facilitates the Nuclear Export, but not the Centrosomal Localization, of BRCA2 in Hs578T Breast Cancer Cells

Abstract

PCI‐domain containing protein 2 (PCID2) assists in the export of proteins from the nucleus to the cytoplasm. PCID2 also localizes to the centrosome, where it is present more frequently in cells exhibiting an abnormally high number of centrosomes, an aberration associated with the development of cancer. Several proteins that negatively regulate the centrosome cycle are typically found in the nucleus, and we have previously discovered that PCID2 is involved in the nuclear export and centrosomal localization of one key centrosome cycle regulator, BRCA1. Therefore, PCID2 may play a role in the regulation of the centrosome cycle by delivering key regulators of duplication. BRCA2 is a nuclear tumor suppressor that travels to the centrosome, where it helps to arrest the centrosome cycle and prevent overduplication. BRCA2 mutations are associated with the development of breast and ovarian cancers, both of which are also associated with centrosomal overduplication. We proposed that PCID2 aids in the transport of BRCA2 from the nucleus to the centrosome. Using siRNA knockdown of PCID2 and subsequent immunofluorescence studies of BRCA2 and γ‐Tubulin, we found that the loss of PCID2 significantly decreased the amount of BRCA2 able to be exported from the nucleus to the cytoplasm, with Hs578T breast cancer cells depleted of PCID2 demonstrating a 37% increase in nuclear BRCA2 retention. However, the loss of PCID2 demonstrated no significant impact on the ability of BRCA2 to localize to centrosomes. Our results indicate that while PCID2 affects the cellular localization of BRCA2 by assisting its nuclear transport, it likely does not directly influence the recruitment of cytoplasmic BRCA2 to the centrosome. Ongoing studies are exploring the relationship of PCID2 to BRCA2 export and centrosomal localization in ovarian cancer cells and are attempting to confirm the presence of a PCID2‐BRCA2 nuclear export complexes in breast and ovarian cancer cells. These findings will shed light on the process by which PCID2 role in nuclear transport and the centrosome cycle, leading to a better understanding of centrosomal amplification and tumorigenesis in a variety of cancer types.