MicroRNAs (miRNAs) are a class of small, non-coding, single-stranded RNAs that negatively regulate gene expression by mainly binding to 3′ untranslated region (UTR) of target mRNAs at the post-transcriptional level. Recent studies have demonstrated that aberrant expressions of miRNAs are closely associated with the development, invasion, metastasis and prognosis of various cancers including prostate cancer (PCa). The proposed molecular mechanisms that underlie the aberrant expression of miRNAs result from gene changes, epigenetic modification and alteration of Dicer abundance. Although up to 50 miRNAs have been reported to be significantly expressed in human PCa, only a small number of them were experimentally shown to make contribution to the pathogenesis of PCa. The aim of this review is to describe the mechanisms of several known miRNAs, summarize recent studies on the relevance of altered expression of oncogenic miRNAs (e.g. miR-221/-222, miR-21, and miR-125b) and tumor suppressor miRNAs (e.g. miR-101, miR-126*, miR-146a, miR-330, miR-34 cluster, and miR-200 family) for PCa. Additionally, their potential clinical applications and prospects in PCa, such as biomarkers and clinical therapies, are also briefly discussed.

Ferroptosis suppressor protein 1 (FSP1, also known as AIMF2, AMID or PRG3) is a recently identified glutathione-independent ferroptosis suppressor^1–3, but its underlying structural mechanism remains unknown. Here we report the crystal structures of Gallus gallus FSP1 in its substrate-free and ubiquinone-bound forms. The structures reveal a FAD-binding domain and a NAD(P)H-binding domain, both of which are shared with AIF and NADH oxidoreductases^4–9, and a characteristic carboxy-terminal domain as well. We demonstrate that the carboxy-terminal domain is crucial for the catalytic activity and ferroptosis inhibition of FSP1 by mediating the functional dimerization of FSP1, and the formation of two active sites located on two sides of FAD, which are responsible for ubiquinone reduction and a unique FAD hydroxylation respectively. We also identify that FSP1 can catalyze the production of H₂O₂ and the conversion of FAD to 6-hydroxy-FAD in the presence of oxygen and NAD(P)H in vitro, and 6-hydroxy-FAD directly inhibits ferroptosis in cells. Together, these findings further our understanding on the catalytic and ferroptosis suppression mechanisms of FSP1 and establish 6-hydroxy-FAD as an active cofactor in FSP1 and a potent radical-trapping antioxidant in ferroptosis inhibition.

Combination therapy is frequently used in cancer treatments. Delivery of combined anticancer agents loaded in a nanocarrier would be a promising option for combination therapy. Here, we designed PEGylated nano-liposomes for co-delivery Docetaxel (Doc) and Resveratrol (Res) to evaluate antitumor efficiency of the combined drugs in prostate cancer. The average diameter of the liposomes was 99.67 nm with a spheral-like shape. Drug release studies showed that both drugs could synchronously leak from the liposomes in a sustained release behavior. Cellular uptake results demonstrated that liposomes could effectively deliver more cargos into cells than other formulations. Moreover, co-loaded liposomes with Doc/Res in a molar ratio of 1:2 exhibited significantly higher cytotoxicity than a mixed solution containing both drugs on cancer cells. In the study of caspase 3, we found that the combination of Doc and Res could significantly increase the activity of caspase 3 enzyme compared with Doc alone. Animal studies revealed that co-encapsulated Doc/Res in liposomes predominantly inhibited tumor growth in PC3 bearing Balb/c nude mice, as evidenced by a change in cell proliferation and apoptosis parameters. Importantly, little toxicities and prolonged survival time were observed in mice treated with liposome-loaded Doc/Res than control group exposed to liposome-free Doc/Res. These results provided evidence that loading of Doc/Res in a nano-liposome is an efficient delivery formulation for synergistic treating prostate cancer.

Anterior gradient 2 (AGR2), a protein belonging to the protein disulfide isomerase (PDI) family, is overexpressed in multiple cancers and promotes angiogenesis to drive cancer progression. The mechanisms controlling AGR2 abundance in cancer remain largely unknown. Here, we observed that AGR2 expression is significantly suppressed by proteasome inhibitor MG132/bortezomib at mRNA and protein levels in lung cancer cells. MG132-mediated repression of AGR2 transcription was independent of ROS generation and ER stress induction, but partially resulted from the downregulated E2F1. Further investigation revealed that MG132 facilitated polyubiquitinated AGR2 degradation through activation of autophagy, as evidenced by predominant restoration of AGR2 level in cells genetic depletion of Atg5 and Atg7, or by autophagy inhibitors. Activation of autophagy by rapamycin noticeably reduced the AGR2 protein in cells and in the mouse tissue samples administrated with bortezomib. We also provided evidence identifying the K48-linked polyubiquitin chains conjugating onto K89 of AGR2 by an E3 ligase UBR5. In addition, an autophagy receptor NBR1 was demonstrated to be important in polyubiquitinated AGR2 clearance in response to MG132 or bortezomib. Importantly, downregulation of AGR2 by proteasome inhibition significantly enhanced antitumor activity of bevacizumab, highlighting the importance of AGR2 as a predictive marker for selection of subgroup patients in chemotherapy.

We previously reported that marchantin M (Mar) is an active agent to induce apoptosis in human prostate cancer (PCa), but the molecular mechanisms of action remain largely unknown. Here, we demonstrate that Mar potently inhibited chymotrypsin-like and peptidyl-glutamyl peptide-hydrolyzing activities of 20S proteasome both in in vitro and intracellular systems and significantly induced the accumulation of polyubiquitinated proteins in PCa cells. The computational modeling analysis suggested that Mar non-covalently bound to active sites of proteasome β5 and β1 subunits, resulting in a non-competitive inhibition. Proteasome inhibition by Mar subsequently resulted in endoplasmic reticulum (ER) stress, as evidenced by elevated glucose-regulated protein 78 and CHOP, increased phospho-eukaryotic translation initiation factor 2α (eIF_2α), splicing of X-box-binding protein-1 and dilation of the ER. However, Mar-mediated cell death was not completely impaired by a pan inhibitor of caspases. Further studies revealed that the Mar-induced cell death was greatly associated with the activation of autophagy, as indicated by the significant induction of microtubule-associated protein-1 light chain-3 beta (LC3B) expression and conversion. Electron microscopic and green fluorescent protein-tagged LC3B analyses further demonstrated the ability of autophagy induction by Mar. Time kinetic studies revealed that Mar induced a rapid and highly sustained processing of LC3B in treated cells and simultaneously decreased the expression of p62/SQSTM1. Pharmacological blockade or knockdown of LC3B and Atg5 attenuated Mar-mediated cell death. The autophagic response triggered by Mar required the activation of RNA-dependent protein kinase-like ER kinase/eIF_2α and suppression of the phosphatidylinositol-3 kinase/Akt/mammalian target of rapamycin axis via preventing activation and expression of Akt. Our results identified a novel mechanism for the cytotoxic effect of Mar, which strengthens it as a potential agent in cancer chemotherapy.