**5. Conclusions**

To prevent the development and progression of CRPC, the preservation of AR signaling after ADT is essential. In this study, we demonstrated that loss of fibroblast-dependent AR activation and expression of AR-V7 protein in PCa cells may be involved in the mechanism of acquired resistance to castration. In near future, clear molecular markers are needed to identify the degree of AR dependence in PCa cells interacting with fibroblasts before ADT is started, e.g., expression of AR-V7 proteins is one of the candidates.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2077-0383/8/9/1379/s1, Figure S1: Effects of ADT on histopathological characteristics of xenografts derived from co-inoculation of E9 cells with fibroblasts in vivo; Figure S2: E ffects of ADT on histopathological characteristics of xenografts derived from co-inoculation of F10 cells with fibroblasts in vivo; Figure S3: E ffects of ADT on histopathological characteristics of xenografts derived from co-inoculation of AIDL cells with fibroblasts in vivo; Figure S4: Expression of EGFR protein in human PCa cell lines; Figure S5: Effects of growth factors on PSA secretion from LNCaP sublines in vitro; Table S1: MVD changes in E9 tumors after ADT; Table S2: MVD changes in F10 tumors after ADT; Table S3: MVD changes in AIDL tumors after ADT.

**Author Contributions:** Conceptualization, Ke.I. (Kenichiro Ishii) and Y.S.; investigation, I.M., T.S., Ka.I. (Kazuhiro Iguchi), K.N. and H.K.; writing—original draft preparation, Ke.I. (Kenichiro Ishii); writing—review and editing, H.I., Y.H. and K.A.

**Funding:** This research was funded by Ministry of Education for Science and Culture of Japan, gran<sup>t</sup> numbers 16K11000 to Kenichiro Ishii and 26462408 to Yoshiki Sugimura.

**Acknowledgments:** We would like to thank Yumi Yoshikawa for their technical support.

**Conflicts of Interest:** The authors declare no conflict of interest.
