Purvalanol A is a specific CDK inhibitor which triggers apoptosis by causing cell cycle arrest in cancer cells. Although it has strong apoptotic potential, the mechanistic action of Purvalanol A on significant cell signaling targets has not been clarified yet. Polyamines are crucial metabolic regulators affected by CDK inhibition because of their role in cell cycle progress as well. In addition, malignant cells possess impaired polyamine homeostasis with high level of intracellular polyamines. Especially induction of polyamine catabolic enzymes spermidine/spermine N1-acetyltransferase (SSAT), polyamine oxidase (PAO) and spermine oxidase (SMO) induced toxic by-products in correlation with the induction of apoptosis in cancer cells. In this study, we showed that Purvalanol A induced apoptosis in caspase- dependent manner in MCF-7 ER(+) cells, while MDA-MB-231 (ER-) cells were less sensitive against drug. In addition Bcl-2 is a critical target for Purvalanol A, since Bcl-2 overexpressed cells are more resistant to Purvalanol A-mediated apoptosis. Furthermore, exposure of MCF-7 cells to Purvalanol A triggered SSAT and PAO upregulation and the presence of PAO/SMO inhibitor, MDL 72,527 prevented Purvalanol A-induced apoptosis.

Bag-1, Bcl-2 associated athanogene-1, is a multifunctional protein that can regulate a wide variety of cellular processes: proliferation, cell survival, transcription, apoptosis and motility. Bag-1 interacts with various targets in the modulation of these pathways; yet molecular details of Bag-1's involvement in each cellular event are still unclear. We first showed that forced Bag-1 expression promotes cell survival and prevents drug-induced apoptosis in MCF-7 breast cancer cells. Increased mRNA expressions of c-myc protooncogene and ornithine decarboxylase (ODC), biosynthetic enzyme of polyamines, were detected in Bag-1L+ cells, and western blots against the protein product of c-Myc and ODC confirmed these findings. Once ODC, a c-Myc target, gets activated, polyamine biosynthesis increases. We observed enhanced polyamine content in the Bag-1L+ cells. On the contrary, when polyamine catabolic mechanisms were investigated, Bag-1 silencing suppressed biosynthesis of polyamines because of the downregulation of ODC and upregulation of PAO. Exposure of cells to apoptotic inducers enhances the cell death mechanism by producing toxic products such as H2 O2 and aldehydes. Bag-1L+ cells prevented drug-induced PAO activation leading to a decrease in H2 O2 production following cisplatin or paclitaxel treatment. In this line, our results suggested that Bag-1 indirectly affects cell survival through c-Myc activated signalling that causes elevation of ODC levels, leading to an increase of the polyamine content.

Background: Cisplatin, a DNA damaging agent, induces apoptosis through increasing DNA fragmentation. However, identification of intrinsic resistance molecules against Cisplatin is vital to estimate the success of therapy. Bag-1 (Bcl-2-associated anthanogene) is one anti-apoptotic protein involved in drug resistance impacting on therapeutic efficiency. Elevated levels of this protein are related with increase cell proliferation rates, motility and also cancer development. For this reason, we aimed to understand the role of Bag-1 expression in Cisplatininduced apoptosis in HeLa cervix cancer cells. Cisplatin decreased cell viability in time-and dose-dependent manner in wt and Bag-1L+HeLa cells. Although, 10μM Cisplatin treatment induced cell death within 24h by activating caspases in wt cells, Bag-1L stable transfection protected cells against Cisplatin treatment. To assess the potential protective role of Bag-1, we first checked the expression profile of interacting anti-apoptotic partners of Bag-1. We found that forced Bag-1L expression prevented Cisplatin-induced apoptosis through acting on Mcl-1 expression, which was reduced after Cisplatin treatment in wt HeLa cells. This mechanism was also supported by the regulation of heat shock protein (Hsp) family members, Hsp90 and Hsp40, which were involved in the regulation Bag-1 interactome including several anti-apoptotic Bcl-2 family members and c-Raf.

The cell cycle is tightly regulated by the family of cyclin-dependent kinases (CDKs). CDKs act as regulatory factors on serine and threonine residues by phosphorylating their substrates and cyclins. CDK‑targeting drugs have previously demonstrated promising effects as cancer therapeutics both in vitro and in vivo. Roscovitine, a purine‑derivative and specific CDK inhibitor, has been demonstrated to arrest the cell cycle and induce apoptosis in a number of different cancer cell lines, including HeLa cervical cancer cells. In the present study, roscovitine was able to decrease both the cell viability and cell survival as well as induce apoptosis in a dose‑dependent manner in HeLa cells by modulating the mitochondrial membrane potential. The decrease of anti‑apoptotic B-cell lymphoma 2 (Bcl‑2) and Bcl-2 extra large protein expression was accompanied by the increase in pro‑apoptotic Bcl-2-associated X protein and P53-upregulated modulator of apoptosis expression. The marked decrease in Bcl‑2 following exposure to roscovitine (20 µM) for 48 h prompted us to determine the autophagic regulation. The outcome revealed that roscovitine triggered Beclin‑1 downregulation and microtubule-associated light chain 3 cleavage starting from 12 h of incubation. Another biomarker of autophagy, p62, a crucial protein for autophagic vacuole formation, was diminished following 48 h. In addition, monodansyl cadaverin staining of autophagosomes also confirmed the autophagic regulation by roscovitine treatment. The expression levels of different Bcl‑2 family members determined whether apoptosis or autophagy were induced following incubation with roscovitine for different time periods. Downregulation of pro‑apoptotic Bcl‑2 family members indicated induction of apoptosis, while the downregulation of anti‑apoptotic Bcl‑2 family members rapidly induced autophagosome formation in HeLa cells.

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