Abstract
The anticancer effect of (1S,2S,3E,7E,11E)-3,7,11,15-cembratetraen-17,2-olide (LS-1) from Lobophytum sp. has been already reported in HT-29 human colorectal cancer cells. In this study, we examined the effect of LS-1 on the apoptosis induction of SNU-C5/5-FU, fluorouracil-resistant human colon cancer cells. Furthermore, we investigated whether the apoptosis-induction effect of LS-1 could arise from the activation of the TGF-β pathway. In SNU-C5/5-FU treated with LS-1 of 7.1 μM (IC50), we could observe the various apoptotic characteristics, such as the increase of apoptotic bodies, the increase of the sub-G1 hypodiploid cell population, the decrease of the Bcl-2 level, the increase of procaspase-9 cleavage, the increase of procaspase-3 cleavage and the increase of poly(ADP-ribose) polymerase cleavage. Interestingly, the apoptosis-induction effect of LS-1 was also accompanied by the increase of Smad-3 phosphorylation and the downregulation of c-Myc in SNU-C5/5-FU. LS-1 also increased the nuclear localization of phospho-Smad-3 and Smad-4. We examined whether LS-1 could downregulate the expression of carcinoembryonic antigen (CEA), a direct inhibitor of TGF-β signaling. LS-1 decreased the CEA level, as well as the direct interaction between CEA and TGF-βR1 in the apoptosis-induction condition of SNU-C5/5-FU. To examine whether LS-1 can induce apoptosis via the activation of TGF-β signaling, the SNU-C5/5-FU cells were treated with LS-1 in the presence or absence of SB525334, a TGF-βRI kinase inhibitor. SB525334 inhibited the effect of LS-1 on the apoptosis induction. These findings provide evidence demonstrating that the apoptosis-induction effect of LS-1 results from the activation of the TGF-β pathway via the downregulation of CEA in SNU-C5/5-FU.
Highlights
Colon cancer is one of the most prevalent cancers in the United States, and incidence rates of colon cancer have been increasing steadily worldwide [1]
We examined the effect of LS-1 on the apoptosis induction of SNU-C5/5-FU, 5-FU-resistant human colon cancer cells
These results indicate that SNU-C5/5-FU is potentially resistant to 5-FU
Summary
Colon cancer is one of the most prevalent cancers in the United States, and incidence rates of colon cancer have been increasing steadily worldwide [1]. Recent studies indicated that the drug-resistant colon cancer cells could induce a high carcinoembryonic antigen (CEA) level [5]. Recent studies reported that CEA could contribute to the inhibition of anoikis, a form of apoptosis induced by cell detaching, via interfering with TRAIL-R2 signaling [8] or inactivation of the intrinsic apoptosis pathway [9]. Recent studies reported that overexpression of CEA could inhibit the tumor suppresser effect of the TGF-β signaling pathway via CEA direct interaction with TGF-β receptor I [10]. We examined the effect of LS-1 on the apoptosis induction of SNU-C5/5-FU, 5-FU-resistant human colon cancer cells. We investigated whether the apoptosis-induction effect of LS-1 could arise from the activation of the TGF-β pathway via the downregulation of CEA
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