Activated kRas protects colon cancer cells from cucurbitacin-induced apoptosis: The role of p53 and p21

Abstract

Cucurbitacins have been shown to inhibit proliferation in a variety of cancer cell lines. The aim of this study was to determine their biological activity in colon cancer cell lines that do not harbor activated STAT3, the key target of cucurbitacin. In order to establish the role of activated kRas in the responsiveness of cells to cucurbitacins, we performed experiments in isogenic colon cancer cell lines, HCT116 and Hke-3, which differ only by the presence of an activated kRas allele. We compared the activity of 23, 24-dihydrocucurbitacin B (DHCB) and cucurbitacin R (CCR), two cucurbitacins that we recently isolated, with cucurbitacin I (CCI), a cucurbitacin with established antitumorigenic activity. We showed that cucurbitacins induced dramatic changes in the cytoskeleton (collapse of actin and bundling of tubulin microfilaments), inhibited proliferation and finally induced apoptosis of both HCT116 and Hke3 cells. However, the presence of oncogenic k-Ras significantly decreased the sensitivity of cells to the three cucurbitacins tested, CCR, DHCB and CCI. We confirmed that mutational activation of kRas protects cells from cucurbitacin-induced apoptosis using nontransfromed intestinal epithelial cells with inducible expression of k-RasV12. Cucurbitacins induced the expression of p53 and p21 predominantly in HCT116 cells that harbor mutant Ras. Using HCT116 cells with targeted deletion of p53 or p21 we confirmed that p53 and p21 protect cells from apoptosis induced by cucurbitacins. These results demonstrated that sensitivity of human colon cancer cell lines to cucurbitacins depends on the kRas and p53/p21 status, and established that cucurbitacins can exert antitumorigenic activity in the absence of activated STAT3.

Cucurbitacin B induces G2 arrest and apoptosis via a reactive oxygen species‐dependent mechanism in human colon adenocarcinoma SW480 cells

“…5G and 3E). Our results are also consistent with the report that cucB exerted antitumor activity in several human colon cancer cell lines in a STAT3-independent manner [10]. Taken together, these results suggest that inactivation of STAT3 is not essential for cucB to induce apoptosis at least in a part of colon cancer cell lines.…”

“…However, cucB can also exert anti-tumor activity in the absence of activated STAT3 [10]. Therefore, the dependency on the STAT3 pathway of the anti-tumor activity of cucB has been controversial.…”

Cucurbitacin D exhibits its anti-cancer effect in human breast cancer cells by inhibiting Stat3 and Akt signaling

“…Cucurbitacin B induces apoptosis in colon cancer cells expressing p53 42 and enhances the regulatory effect of p53-specific CTL in 16HBE/BPDE tumor cells by inhibiting JAK2/Stat3 activation. 43 Cucurbitacin E decreases the viability of pancreatic cancer cells by suppressing Stat3 phosphorylation and upregulating tumor suppressor p53.…”

Cytotoxic Activity of Kenaf Seed Oils from Supercritical Carbon Dioxide Fluid Extraction towards Human Colorectal Cancer (HT29) Cell Lines

“…Cancer chemoprevention was described as the use of natural synthetic chemicals allowing suppression, retardation, or inversion of carcinogenesis [10]. Apoptosis induction is one of a potent defensive strategies against cancer progression [11–14]. Numerous diet-derived agents are among promising agents and agent combinations that are being evaluated clinically as chemopreventive agents for major cancer targets including colon, breast, prostate, and lung cancers [15].…”