Pristimerin induces apoptosis by targeting the proteasome in prostate cancer cells

Abstract

Pristimerin is a natural product derived from the Celastraceae and Hippocrateaceae families that were used as folk medicines for anti inflammation in ancient times. Although it has been shown that pristimerin induces apoptosis in breast cancer cells, the involved mechanism of action is unknown. The purpose of the current study is to investigate the primary target of pristimerin in human cancer cells, using prostate cancer cells as a working model. Nucleophilic susceptibility and in silico docking studies show that C6 of pristimerin is highly susceptible towards a nucleophilic attack by the hydroxyl group of N-terminal threonine of the proteasomal chymotrypsin subunit. Consistently, pristimerin potently inhibits the chymotrypsin-like activity of a purified rabbit 20S proteasome (IC50 2.2 micromol/L) and human prostate cancer 26S proteasome (IC50 3.0 micromol/L). The accumulation of ubiquitinated proteins and three proteasome target proteins, Bax, p27 and I kappa B-alpha, in androgen receptor (AR)-negative PC-3 prostate cancer cells supports the conclusion that proteasome inhibition by pristimerin is physiologically functional. This observed proteasome inhibition subsequently led to the induction of apoptotic cell death in a dose- and kinetic-dependent manner. Furthermore, in AR-positive, androgen-dependent LNCaP and AR-positive, androgen-independent C4-2B prostate cancer cells, proteasome inhibition by pristimerin results in suppression of AR protein prior to apoptosis. Our data demonstrate, for the first time, that the proteasome is a primary target of pristimerin in prostate cancer cells and inhibition of the proteasomal chymotrypsin-like activity by pristimerin is responsible for its cancer cell death-inducing property.

Pristimerin Inhibits Breast Cancer Cell Migration by Up-regulating Regulator of G Protein Signaling 4 Expression

“…Furthermore, we found that treatment with pristimerin inhibited the migration and invasion of MDA-MB-231 cells in vitro in a dose-dependent manner and the growth and invasion of implanted breast tumors in vivo. These novel data extend previous findings (Wu et al, 2005;Yang et al, 2008;Tiedemann et al, 2009) and suggest that pristimerin may have broad antitumor activity.…”

“…The redundant metastatic signals by different activated GPCRs simultaneously drive the migration of breast cancer cells, which makes the inhibition of breast cancer metastasis by a GPCR-specific inhibitor unfeasible. Ideally, simultaneous 1 can inhibit tumor cell proliferation by inhibiting the NF-κB pathway and cell cycling (Boire et al, 2005;Costa et al, 2008;Yang et al, 2008;Byun et al, 2009;Tiedemann et al, 2009). In addition, prestimerin has been reported to induce caspase-dependent apoptosis of breast cancer cells (Wu et al, 2005) and prostate cancer cells in vitro (Yang et al, 2008).…”

“…Ideally, simultaneous 1 can inhibit tumor cell proliferation by inhibiting the NF-κB pathway and cell cycling (Boire et al, 2005;Costa et al, 2008;Yang et al, 2008;Byun et al, 2009;Tiedemann et al, 2009). In addition, prestimerin has been reported to induce caspase-dependent apoptosis of breast cancer cells (Wu et al, 2005) and prostate cancer cells in vitro (Yang et al, 2008). Recently, pristimerin is reported to be a potent natural triterpenoid inhibitor of 20s proteasome chymotrypsin-like activity in prostate cancer cells (Tiedemann et al, 2009).…”

Highlights of Natural Products in Prostate Cancer Drug Discovery

“…The IC 50 value for the inhibition of purified rabbit 20S proteasome with pristimerin was 2.2 μM. Similarly, pristimerin also potently inhibited 26S proteasome chymotrypsin-like activity in a extract prepared from exponentially grown PC-3 cells, with an IC 50 of 3.0 μM (Yang, Landis-Piwowar et al, 2008). About 40% inhibition of cellular proteasome activity occurred in C4-2B cells with 5 μM of pristimerin and was accompanied by AR suppression with consequent apoptosis induction.…”

“…Pristimerin targets the proteasome to induce apoptosis in human PC-3 and AR-positive C4-2B cells (Yang, LandisPiwowar et al, 2008). Proliferation of PC-3 cells was inhibited by pristimerin (Chang et al, 2003) with induction of apoptosis that correlated with inhibition proteasome activity (Yang, Landis-Piwowar et al, 2008). The IC 50 value for the inhibition of purified rabbit 20S proteasome with pristimerin was 2.2 μM.…”