Ciclopirox inhibits cancer cell proliferation by suppression of Cdc25A

Abstract

Ciclopirox olamine (CPX), an off-patent fungicide, has recently been identified as a novel anticancer agent. However, the molecular mechanism underlying its anticancer action remains to be elucidated. Here we show that CPX inhibits cell proliferation in part by downregulating the protein level of Cdc25A in tumor cells. Our studies revealed that CPX did not significantly reduce Cdc25A mRNA level or Cdc25A protein synthesis, but remarkably promoted Cdc25A protein degradation. This resulted in inhibition of G1-cyclin dependent kinases (CDKs), as evidenced by increased inhibitory phosphorylation of G1-CDKs. Since Cdc25A degradation is tightly related to its phosphorylation status, we further examined whether CPX alters Cdc25A phosphorylation. The results showed that CPX treatment increased the phosphorylation of Cdc25A (S76 and S82), but only Cdc25A-S82A mutant was resistant to CPX-induced degradation. Furthermore, ectopic expression of Cdc25A-S82A partially conferred resistance to CPX inhibition of cell proliferation. Therefore, our findings indicate that CPX inhibits cell proliferation at least in part by promoting Cdc25A degradation.

Ciclopirox activates ATR-Chk1 signaling pathway leading to Cdc25A protein degradation

“…For this, MDA-MB-231 cells were treated with CPX (0-20 μM) for 24 h, followed by Western blot analysis. In line with our previous observation [ 32 ], 24-h treatment with CPX downregulated the protein level of Cdc25A in a concentration-dependent manner (Figures 1A and 1B ). Surprisingly, CPX did not obviously increase cellular protein expression of CK1α; in fact, at high concentrations (10-20 μM) slightly but not significantly downregulated the protein level of CK1α (Figures 1A and 1B ).…”

“…To determine whether activation of Chk1 contributes to CPX-induced Cdc25A degradation, MDA-MB-231 cells were pretreated for 2 h with or without TCS2312 (250 nM), a selective inhibitor of Chk1 [ 53 ], and then incubated with CPX (0-10 μM) for 24 h, followed by Western blotting. Consistent with our previous finding [ 32 ], CPX (5-10 μM) alone obviously downregulated the expression of Cdc25A (Figures 4A and 4B ). Interestingly, CPX-induced Cdc25A degradation was remarkably attenuated by TCS2312, suggesting that CPX-induced Cdc25A degradation may be attributed to activation of Chk1.…”

“…Our previous study has shown that CPX induces the phosphorylation of Cdc25A on S82, and Cdc25A-S82A mutant is resistant to CPX-induced degradation [ 32 ], indicating that the phosphorylation on S82 is essential for CPX-induced Cdc25A degradation. Since CK1α has been reported to be responsible for phosphorylating Cdc25A on S82 [ 40 ], and CK1α is a constitutively active kinase, whose activity is primarily determined by the cellular protein level [ 46 ], we reasoned that CPX-induced phosphorylation of Cdc25A (S82) is through upregulating protein expression of CK1α.…”

“…Recent studies have shown that CPX, at high concentrations (> 10 µM), downregulates the cellular protein expression of cyclins (A, B1, D1 and E) and cyclin-dependent kinases (CDK2 and CDK4), and upregulates the expression of the CDK inhibitor p21 Cip1 [ 5 ]. However, CPX, at low concentrations (≤5 µM), drastically reduces the cellular protein level of Cdc25A, which results in increased inhibitory phosphorylation of G 1 -CDKs, leading to the accumulation of cells in G 1 phase of the cell cycle in tumor cells [ 32 ]. Furthermore, CPX neither alters the mRNA level of Cdc25A, nor reduces the protein synthesis of Cdc25A, but promotes the degradation of Cdc25A [ 32 ].…”

“…However, CPX, at low concentrations (≤5 µM), drastically reduces the cellular protein level of Cdc25A, which results in increased inhibitory phosphorylation of G 1 -CDKs, leading to the accumulation of cells in G 1 phase of the cell cycle in tumor cells [ 32 ]. Furthermore, CPX neither alters the mRNA level of Cdc25A, nor reduces the protein synthesis of Cdc25A, but promotes the degradation of Cdc25A [ 32 ]. To better understand the molecular mechanism of anticancer action of CPX, it is of great importance to elucidate how CPX induces Cdc25A protein degradation.…”