*2.5. KLF5 Is also Crucial for AR-Mediated MYC and Cyclin D1 Expression in PCa Cells*

In PCa cells, AR promotes cell proliferation via the upregulation of a subset of genes such as *MYC* and *CCND1*, and KLF5 has also been shown to upregulate the same two genes in epithelial cells [26–28,44–47]. We thus tested whether KLF5 is also required for AR to upregulate *MYC* and *CCND1* in androgen-responsive PCa cells. In LNCaP and C4-2B cells cultured in normal medium, knockdown of KLF5 decreased the expression MYC and cyclin D1 at both protein (Figure 5a,b) and mRNA levels (Figure 5c,d). When AR activity was inhibited by enzalutamide at 10 μM for 24 h, both MYC and cyclin D1 were significantly downregulated, and silencing KLF5 had little or no effect on the expression of MYC and cyclin D1 (Figure 5a–d). ChIP-PCR demonstrated that the amount of AR bound to the promoters of *CCND1* and *MYC* was apparently reduced by the knockdown of KLF5 (Figure 5e), and similarly, the amount of KLF5 bound to the same two promoters was also reduced by inhibiting AR signaling with enzalutamide treatment in C4-2B cells (Figure 5f).
