Nuclear localization of APLF facilitates breast cancer metastasis

Most breast cancer deaths result from metastases. We previously reported that DNA repair factor and histone chaperone Aprataxin PNK-like Factor (APLF) is involved in EMT-associated metastasis of triple negative breast cancer (TNBC) cells. However, non-metastatic cells also expressed APLF, the implications of which in disease advancement remain uncertain. Here, we demonstrate that the metastatic prognosis of breast cancer cells may be determined by the cellular localization of APLF. Using TNBC patient samples and cell lines, we discovered that APLF was localized in the nucleus and cytoplasm, whereas other subtypes of breast cancer had cytosolic or perinuclear localization. To investigate metastatic properties in vitro and in vivo, we modeled APLF differential localization by stably producing APLF-tagged nuclear localization signal (NLS) in the luminal subtype MCF7 cells in the absence of putative APLF NLS. Nuclear APLF in non-metastatic MCF7 cells demonstrated pronounced migration, invasion and metastatic potential. We obtained the mechanistic insight from molecular studies that PARP1 could facilitate the transport of APLF from the cytosol to the nucleus, assisting in the metastasis of TNBC cells linked with EMT. Inhibition of PARP1 enzymatic activity with olaparib abrogated the nuclear expression of APLF with loss in expression of genes associated with EMT. Thus, our findings reveal that cellular localization of APLF may predict the risk of breast cancer to metastasize and hence could be exploited to determine the disease progression. We anticipate that the inhibition of cytosolic PARP1-APLF interaction may potentially aid in the prevention of breast cancer metastasis in TNBC patients.