Nuclear versus cytoplasmic localization of filamin a in prostate cancer: Immunohistochemical correlation with metastases

Purpose: We previously showed that nuclear localization of the actin-binding protein, filamin A (Fln A), corresponded to hormone-dependence in prostate cancer. Intact Fln A (280 k Da, cytoplasmic) cleaved to a 90 k Da fragment which translocated to the nucleus in hormone-naïve cells, whereas in hormone-refractory cells, Fln A was phosphorylated, preventing its cleavage and nuclear translocation. We have examined whether Fln A localization determines a propensity to metastasis in advanced androgen-independent prostate cancer. Experimental Design: We examined, by immunohistochemistry, Fln A localization in paraffin-embedded human prostate tissue representing different stages of progression. Results were correlated with in vitro studies in a cell model of prostate cancer. Results: Nuclear Fln A was significantly higher in benign prostate (0.6612 ± 0.5888), prostatic intraepithelial neoplasia (PIN; 0.6024 ± 0.4620), and clinically localized cancers (0.69134 ± 0.5686) compared with metastatic prostate cancers (0.3719 ± 0.4992, P = 0.0007). Cytoplasmic Fln A increased from benign prostate (0.0833 ± 0.2677), PIN (0.1409 ± 0.2293), localized cancers (0.3008 ± 0.3762, P = 0.0150), to metastases (0.7632 ± 0.4414, P < 0.00001). Logistic regression of metastatic versus nonmetastatic tissue yielded the area under the receiver operating curve as 0.67 for nuclear-Fln A, 0.79 for cytoplasmic-Fln A, and 0.82 for both, indicating that metastasis correlates with cytoplasmic to nuclear translocation. In vitro studies showed that cytoplasmic localization of Fln A induced cell invasion whereas nuclear translocation of the protein inhibited it. Fln dephosphorylation with the protein kinase A inhibitor H-89 facilitated Fln A nuclear translocation, resulting in decreased invasiveness and AR transcriptional activity, and induced sensitivity to androgen withdrawal in hormone-refractory cells. Conclusions: The data presented in this study indicate that in prostate cancer, metastasis correlates with cytoplasmic localization of Fln A and may be prevented by cleavage and subsequent nuclear translocation of this protein.