Rabdosianone I, a Bitter Diterpene from an Oriental Herb, Suppresses Thymidylate Synthase Expression by Directly Binding to ANT2 and PHB2

Abstract

Natural products have numerous bioactivities and are expected to be a resource for potent drugs. However, their direct targets in cells often remain unclear. We found that rabdosianone I, which is a bitter diterpene from an oriental herb for longevity, Isodon japonicus Hara, markedly inhibited the growth of human colorectal cancer cells by downregulating the expression of thymidylate synthase (TS). Next, using rabdosianone I-immobilized nano-magnetic beads, we identified two mitochondrial inner membrane proteins, adenine nucleotide translocase 2 (ANT2) and prohibitin 2 (PHB2), as direct targets of rabdosianone I. Consistent with the action of rabdosianone I, the depletion of ANT2 or PHB2 reduced TS expression in a different manner. The knockdown of ANT2 or PHB2 promoted proteasomal degradation of TS protein, whereas that of not ANT2 but PHB2 reduced TS mRNA levels. Thus, our study reveals the ANT2- and PHB2-mediated pleiotropic regulation of TS expression and demonstrates the possibility of rabdosianone I as a lead compound of TS suppressor.

Preparation and Application of a Chemical Probe for Identifying the Targets of the Marine Cyclic Peptide Kapakahine A

“…Sesaminol, an ingredient of sesame that is cytotoxic towards the MCF7 human mammary carcinoma cell line [ 16 ], is known to bind to ANT2 and reduce the protein expression of cyclin D1, which is important for the G 1 /S phase transition of the cell cycle. Rabdosianone I, from the medicinal herb Isodon japonicus , binds to PHB2 and ANT2, leading to a decrease in the expression level of thymidylate synthase, resulting in growth inhibition of the human colon adenocarcinoma cell line HT-29 [ 17 ].…”

Essential Protein PHB2 and Its Regulatory Mechanisms in Cancer

“…TS is an S-phase enzyme responsible for catalyzing the methylation of dUMP to produce dTMP, a precursor of DNA synthesis. TS functions as an oncogene; its expression was found to be correlated with colorectal cancer prognosis [ 48 ]. Rabdosianone I, a drug extracted from an oriental herb, has been seen to reduce TS expression in colorectal cancer patients and to bind both PHB2 and ANT2 [ 48 ].…”

“…TS functions as an oncogene; its expression was found to be correlated with colorectal cancer prognosis [ 48 ]. Rabdosianone I, a drug extracted from an oriental herb, has been seen to reduce TS expression in colorectal cancer patients and to bind both PHB2 and ANT2 [ 48 ]. ANT2 and PHB2 were shown to stabilize TS at the protein level with PHB2 also possibly promoting TS transcription with increased TS mRNA levels.…”

“…ANT2 and PHB2 were shown to stabilize TS at the protein level with PHB2 also possibly promoting TS transcription with increased TS mRNA levels. Rabdosianone I bound to both ANT2 and PHB2 caused proteasomal degradation of the TS protein with TS transcription being inhibited when bound to PHB2 alone [ 48 ].…”

“…Stabilizes thymidylate synthase (TS), promoting TS transcription. Rabdosianone I binds ANT2 and PHB2, causing TS degradation and inhibition of TS transcription [ 48 ].…”