Activation of polyamine catabolic enzymes involved in diverse responses against epibrassinolide-induced apoptosis in LNCaP and DU145 prostate cancer cell lines

Abstract

Epibrassinolide (EBR) is a biologically active compound of the brassinosteroids, steroid-derived plant growth regulator family. Generally, brassinosteroids are known for their cell expansion and cell division-promoting roles. Recently, EBR was shown as a potential apoptotic inducer in various cancer cells without affecting the non-tumor cell growth. Androgen signaling controls cell proliferation through the interaction with the androgen receptor (AR) in the prostate gland. Initially, the development of prostate cancer is driven by androgens. However, in later stages, a progress to the androgen-independent stage is observed, resulting in metastatic prostate cancer. The androgen-responsive or -irresponsive cells are responsible for tumor heterogeneity, which is an obstacle to effective anti-cancer therapy. Polyamines are amine-derived organic compounds, known for their role in abnormal cell proliferation as well as during malignant transformation. Polyamine catabolism-targeting agents are being investigated against human cancers. Many chemotherapeutic agents including polyamine analogs have been demonstrated to induce polyamine catabolism that depletes polyamine levels and causes apoptosis in tumor models. In our study, we aimed to investigate the mechanism of apoptotic cell death induced by EBR, related with polyamine biosynthetic and catabolic pathways in LNCaP (AR+), DU145 (AR-) prostate cancer cell lines and PNT1a normal prostate epithelial cell line. Induction of apoptotic cell death was observed in prostate cancer cell lines after EBR treatment. In addition, EBR induced the decrease of intracellular polyamine levels, accompanied by a significant ornithine decarboxylase (ODC) down-regulation in each prostate cancer cell and also modulated ODC antizyme and antizyme inhibitor expression levels only in LNCaP cells. Catabolic enzymes SSAT and PAO expression levels were up-regulated in both cell lines; however, the specific SSAT and PAO siRNA treatments prevented the EBR-induced apoptosis only in LNCaP (AR+) cells. In a similar way, MDL 72,527, the specific PAO and SMO inhibitor, co-treatment with EBR during 24 h, reduced the formation of cleaved fragments of PARP in LNCaP (AR+) cells.

Calreticulin is a fine tuning molecule in epibrassinolide‐induced apoptosis through activating endoplasmic reticulum stress in colon cancer cells

“…Surprisingly, FHC and MEF cells continued to live in media with the same EBR concentration during the exact time points as cancer cells. These data, suggesting that normal cells were poorly affected by EBR treatment, were correlating with our previous findings on EBR not cytotoxic to PNT1a normal prostate epithelial cells …”

“…Although EBR, one of the brassinosteroid family members, has been shown to strongly promote cell expansion and proliferation in plant cells, its apoptotic function by affecting many important cellular mechanisms, such as Bcl‐2 family members, cell survival kinases, polyamine metabolic enzymes, and cell cycle regulatory proteins, was demonstrated . Our latest findings also indicated that CALR, a key chaperone protein playing role in protein folding in the ER lumen, was drastically affected by EBR treatment in prostate cancer cells .…”

“…Epibrassinolide (EBR), a member of brassinosteroids plant growth regulator, is a polyhydroxysteroid with a structural similarity to mammalian steroid hormones. EBR exerts apoptotic effect in various cancer cells in a caspase‐dependent and nuclear steroid hormone receptor (NHR)‐independent manner . Our recent study using SILAC approach (stable isotope labeling by amino acids in cell culture) revealed that not only steroid signaling but also protein folding is mainly affected by EBR treatment in NHR positive prostate cancer cells.…”

Steroid plant hormones: Effects outside plant kingdom

“…Apoptotic effects of brassinolide on human prostate cancer PC-3 cells was shown to be associated with caspases-3 activation [112]. EBl-induced apoptosis of LNCaP and DU-145 cancer cells was accompanied by a decrease of intracellular polyamine levels and a significant down-regulation of ornithine decarboxylase [113].…”

Polyamines and transglutaminases: biological, clinical, and biotechnological perspectives

“…Apoptotic cell death induced by epibrassinolide (EBR), a biologically active compound of the brassinosteroids, related to polyamine biosynthetic and catabolic pathways in LNCaP (AR? ), DU145 (AR-) prostate cancer cell lines and PNT1,a normal prostate epithelial cell line, has been investigated (Obakan et al (2013). Induction of apoptotic cell death was observed in prostate cancer cell lines after EBR treatment.…”