Mash1 expression is induced in neuroendocrine prostate cancer upon the loss of Foxa2

Abstract

Neuroendocrine (NE) prostate tumors and neuroendocrine differentiation (NED) in prostatic adenocarcinomas have been associated with poor prognosis. In this study, we used the TRAMP mouse model that develops NE prostate tumors to identify key factors that can lead to NED. We have previously reported that NE tumors express the forkhead transcription factor, Foxa2, Mash1 (mouse achaete scute homolog-1), as well as Synaptophysin. In TRAMP, the prostatic intraepithelial neoplasia (PIN) first expresses Foxa2 and Synaptophysin, which then progresses to NE cancer. In order to determine if Foxa2 is dispensable for development or maintenance of NE cancer, a conditional knock-out of Foxa2 in TRAMP mice was generated by breeding mice with two floxed alleles of Foxa2 and one copy of Nkx3.1-Cre. Nkx3.1-Cre/Foxa2(loxP/loxP) mice showed loss of Foxa2 expression in embryonic prostatic buds. No expression of Foxa2 was seen in the adult prostate in either conditional null or control mice. Foxa2 is universally expressed in all wild type TRAMP NE tumors, but Mash1 expression is seen only in a few samples in a few cells. With the loss of Foxa2 in the NE tumors of the TRAMP/Nkx3.1-Cre/Foxa2(loxP/loxP) mice, the expression of the pro-neuronal gene Mash1 is upregulated. NE tumors from both the TRAMP control and Foxa2-deficient TRAMP prostate express Synaptophysin and SV40 Large T-antigen, and both show a loss of androgen receptor expression in NE cells. These studies suggest that the TRAMP NE tumors can form in the absence of Foxa2 by an up regulation of Mash1.

Fig. 1

Foxa2 expression is lost at the prostatic tips at E19.5 UGS from Nkx3.1-Cre^+/−/Foxa2^loxP/loxP. Foxa1 is expressed in the urogenital epithelial (UGE) cells in C57Blk6 wild type mice (A), Nkx3.1-Cre^+/− (B), Nkx3.1-Cre^wt/wt/Foxa2^loxP/loxP (C), Nkx3.1-Cre^+/−/Foxa2^loxP/loxP (D).Foxa2 is expressed in the UGE cells of C57Blk6 wild type mice (E),Nkx3.1-Cre^+/− (F),Nkx3.1-Cre^wt/wt/Foxa2^loxP/loxP (G).Foxa2 expression is deleted in epithelial cells from the E19.5 UGS of Nkx3.1-Cre^+/−/Foxa2^loxP/loxP (H).

Fig. 2

Haemotoxylin and Eosin staining of the prostatic lobes does not show any histological defects in prostates of the Foxa2-deficient mice. H and E on anterior (A), dorsal (B), lateral (C), and ventral (D) prostatic lobes of Foxa2^loxP/loxP mice. H and E on the anterior (E), dorsal (F),lateral(G),and ventral (H) prostatic lobes of Nkx3.1-Cre/Foxa2^loxP/loxP.

Fig. 3

Ablation of Foxa2 in the TRAMP tumors results in increase in Mash-1 expression. Foxa2 is expressed in the neuroendocrine prostate tumors from the TRAMP mice (A), TRAMP/Foxa2^floxP/floxP (E). Foxa2 expression is lost in the NE tumors from TRAMP/NKX3.1-Cre^+/−/Foxa2^floxP/floxP (I). Synaptophysin is expressed by the NE prostate tumors from TRAMP mice (B), TRAMP/Foxa2^floxP/floxP (F), and TRAMP/NKX3.1-Cre^+/−/Foxa2^floxP/floxP (J). Androgen receptor expression is lost in the tumors from wild type TRAMP mice (C), TRAMP/Foxa2^floxP/floxP (G), and TRAMP/NKX3.1-Cre^+/−/Foxa2^floxP/floxP (K). Mash-1 is not expressed in the NE tumors of TRAMP (D), TRAMP/Foxa2^floxP/floxP (H). Mash-1 expression is switched on in the NE prostate tumors of the TRAMP/Nkx3.1-Cre^+/−/Foxa2^loxP/loxP(L).

Fig. 4

Ablation of Foxa2 does not result in Mash-1 expression in the E19.5 UGS. AR is expressed in the epithelial and stromal cells from UGS of Foxa2^loxP/loxP (A) and Nkx3.1-Cre^+/−/Foxa2^loxP/loxP (D) mice. Synaptophysin expression is not detected in the UGS of Foxa2^loxP/loxP (B) and Nkx3.1-Cre^+/−/Foxa2^loxP/loxP (E) mice. Mash-1 is not expressed in UGS of either Foxa2^loxP/loxP (C) or Nkx3.1-Cre^+/−/Foxa2^loxP/loxP (F)mice. Foxa2 and Synaptophysin are co-expressed in 3-week-old prostate of control (G^J) and Nkx3.1-Cre^+/−/Foxa2^loxP/loxP (K^N) mice.