Effect of Β-Sitosterol, a Plant Sterol, on Growth, Protein Phosphatase 2A, and Phospholipase D in LNCaP Cells

Abstract

Previous work from this laboratory suggests an activation of the sphingomyelin cycle as a mechanism for growth inhibition with the incorporation of beta-sitosterol (SIT) into human prostate cancer LNCaP cells. In the present study we examined two key enzymes that have been shown to play a role in the sphingomyelin cycle. Dietary sterols (SIT and cholesterol) were compared for their effect on LNCaP cell growth, phospholipase D (PLD) activity, and protein phosphatase 2A (PP 2A) activity and expression. PP 2A has been suggested as a direct in vitro target of ceramide action on cell growth and apoptosis. Ceramide also inhibits phorbol myristate acetate-stimulated PLD. SIT (16 microM) increased PP 2A activity by 50% compared with cholesterol treatment in LNCaP prostate cells; however, SIT did not alter protein levels of PP 2A. There was an increase in PLD activity in the presence of phorbol myristate acetate in cells supplemented with 16 microM SIT compared with those supplemented with cholesterol after five days of treatment. The present study suggests that the activation of PP 2A added support to the role of the activation of the sphingomyelin cycle by SIT treatment. However, the increase in PLD activity, which was modest but significant, with SIT supplementation suggests that this pathway may be modulated by other mechanisms. This includes the incorporation of SIT into cell membranes that may alter fluidity and, thus, influence the activation of membrane-bound enzymes such as PLD.

Phytosterol Pygeum africanum regulates prostate cancer in vitro and in vivo

“…This agrees with Von Holtz et al [31] who reported that BSitosterol inhibited the growth of LNCaP cells and induced apoptosis via activation of the sphingomyelin cycle or by regulation of the activity of PKC-alpha [34]. Also Awad et al [27] reported that B-Sitosterol might affect membrane structure and function of tumor and host tissues, signal transduction pathways that regulate tumor growth, and apoptosis However, we found no effect of B-Sitosterol on PC-3 cell growth but we did see an effect similar to Awad et al [32] who showed that B-sitosterol inhibited the growth of LNCaP cells in vitro. However, in contrast to our results Awad et al found an effect of B-Sitosterol on PC-3 cell growth in 5% non-stripped serum [33].…”

“…Many compounds have been identified including fatty acids, sterols (B-Sitosterol and Campesterol) and pentcyclic triterpenoids [11]. B-Sitosterol, as one of the marker compounds for Pygeum africanum, has been tested for its ability to inhibit the growth of both PC-3 and LNCaP cells [32,33]. Few studies on the role of B-Sitosterol in prostate cancer have been described.…”

“…Von Holtz et al [31] reported that B-Sitosterol inhibited the growth of LNCaP cells and induced apoptosis via activation of the sphingomyelin cycle. Also Awad et al [32,33] found B-Sitosterol inhibited the growth and dissemination of PC-3 cells both in vitro and in vivo.…”

Cancer chemopreventive activity of a mixture of Chinese herbs (antitumor B) in mouse lung tumor models

“…For example, epidemiologic and experimental studies suggest that dietary PS may offer protection from the most common cancers (Awad and Fink, 2000). Furthermore, both in vitro and in vivo studies suggest that b-sitosterol and campesterol, which are PSs, offer protection from colon (Raicht et al, 1980), prostate (Awad et al, 2000a), and breast cancers (Awad et al, 2000b). Functional analysis revealed that these compounds can stimulate apoptosis in breast and prostate cancer cells (Rao and Janezic 1992;von Holtz et al, 1998), reduce metastasis in MDA-MB-231 cells implanted in SCID mice (Awad et al, 2000c), and inhibit cell growth.…”

Phytosterols as Anticancer Dietary Components: Evidence and Mechanism of Action

“…Apoptosis or programmed cell death, as influenced by PS, has been investigated in two tumor cell lines, MDA-MB-231 and LNCaP cells (34,35). In both cell lines, 16 mol/L SIT was found to stimulate apoptosis by fourto sixfold above control levels after 3-5 d of treatment (34,35). Apoptosis was assessed by measuring the release of nucleosomes into the cytoplasm.…”