Oleanolic Acid Inhibits High Salt-Induced Exaggeration of Warburg-like Metabolism in Breast Cancer Cells

Abstract

Cancer cells have a proliferative advantage by utilizing intermediates of aerobic glycolysis (Warburg-effect) for their macromolecule synthesis. Although the exact causes of this Warburg-effect are unclear, high osmotic stress in solid tumor microenvironment is considered as one of the important factors. Oleanolic acid (OA) is known to exert anti-inflammatory and anti-cancer effect. In our current studies, using breast cancer cell lines, we determined the protective role of OA in high salt mediated osmotic stress induced cancer growth. Hypertonic (0.16M NaCl) culture conditions enhanced the cancer cell growth (26%, p<0.05) and aerobic glycolysis as marked by increased glucose consumption (34%, p<0.05) and lactate production (25%, p<0.05) over untreated cells. This effect was associated with increased expression and activity of key rate-limiting enzymes of aerobic glycolysis, namely, hexokinase, pyruvate kinase-typeM2 and lactate dehydrogenase-A. Interestingly, this high salt mediated enhanced expression of aerobic glycolytic enzymes was efficiently reversed by OA along with decreased cancer cell proliferation. In cancer cells, enhanced aerobic glycolysis is associated with decreased mitochondrial activity and mitochondrial-associated caspase activity. As expected, high salt further inhibited the mitochondrial related cytochrome oxidase and caspase-3 activity. However, OA efficiently reversed the high salt mediated inhibition of cytochrome oxidase, caspase activity and pro-apoptotic Bax expression, thus suggesting that OA induced mitochondrial activity and enhanced apoptosis. Taken together, our data indicate that OA efficiently reverses the enhanced Warburg-like metabolism induced by high salt mediated osmotic stress along with potential application of OA in anti-cancer therapy.

Critical role of SIK3 in mediating high salt and IL-17 synergy leading to breast cancer cell proliferation

“…Masui et al have recently demonstrated that mTORC2 enhances Warburg-like glucose metabolism and drug resistance in cancer cells [33]. Previous studies from our lab have demonstrated that high salt enhances Warburg-like metabolism in cancer cells [13]. Our current studies along with previous observations potential suggest a mTORC2/ SIK3 cascade plays an important role in Warburg metabolism and enhances cancer proliferations.…”

Oleanolic Acid Alters Multiple Cell Signaling Pathways: Implication in Cancer Prevention and Therapy

“…This study suggested that oleanolic acid can cause apoptosis through mitochondrial-related pathways promoting the release of mitochondrial-associated caspases and pro-apoptotic Bax proteins [91]. In addition, oleanolic acid inhibited aerobic glycolysis by inducing pyruvate kinase muscle (PKM)isoforms switch from PKM2 to PKM1 through suppression of phosphorylated mTOR, consequently disrupting Warburg effects in various cancer cells [92].…”

Potential anticancer effect of prostratin through SIK3 inhibition

“…We have previously demonstrated that high salt (Δ0.05 M NaCl) synergized with subminimal IL-17 (0.1 pg/ml) (16) to induce a 24% enhanced cell proliferation (4,5,8,22), which will be referred to as stimulating conditions in our current communication. Importantly, Na-MRI based human studies have revealed that breast tumors accumulate high salt for yet unknown reasons (6,7).…”

“…For salt and interleukin-17 treatment conditions, cell culture media was supplemented with 0.05 M NaCl (Sigma-Aldrich; Merck KGaA, Darmstadt, Germany) and 0.1 ng/ml IL-17 (Thermo Fisher Scientific, Inc.). We have previously performed a dose-response for salt (0-0.1 M NaCl) and IL-17 (0-1,000 ng/ ml) and found-out that 0.05 M NaCl provided highest cell proliferation (4,5) and 0.1 ng/ml of IL-17 induced sub-effective inflammatory cytokine response (4,16). All chemicals unless mentioned were obtained either from Sigma-Aldrich; Merck KGaA (Darmstadt, Germany) or Thermo Fisher Scientific, Inc. For siRNA knock down of SIK3 we have used the following two siRNA sequences: SIK3-siRNA-1: 5'-GUG CAG AGU GUU GGA GUC C-3'; scramble SIK3-siRNA-1: 5'-UGG AGG CGA GUC AGU UUG C-3' .…”

“…Several agents have been suggested to induce chronic inflammation (3). Recent evidence from our lab have demonstrated that breast cancer cells cultured under high salt conditions (Δ0.05 M NaCl, 50% above basal culture conditions) were able to upregulate reactive nitrogen species (4,5). Importantly, sodium-MRI studies in breast cancer patients have demonstrated an increased sodium content, of up to 63% above the surrounding soft tissue, in the breast tumors (6,7).…”