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Caspases, a family of cysteine proteases, cleave substrates and play significant roles in apoptosis, autophagy, and development. Recently, our group identified 72 genes that interact with Death Caspase-1 (DCP-1) proteins in Drosophila by genetic screening of 15,000 EP lines. However, the cellular functions and molecular mechanisms of the screened genes, such as their involvement in apoptosis and autophagy, are poorly understood in mammalian cells. In order to study the functional characterizations of the genes in human cells, we investigated 16 full-length human genes in mammalian expression vectors and tested their effects on apoptosis and autophagy in human cell lines. Our studies revealed that ALFY, BIRC4, and TAK1 induced autophagy, while SEC61A2, N-PAC, BIRC4, WIPI1, and FALZ increased apoptotic cell death. BIRC4 was involved in both autophagy and apoptosis. Western blot analysis and luciferase reporter activity indicated that ALFY, BIRC4, PDGFA, and TAK1 act in a p53-dependent manner, whereas CPSF1, SEC61A2, N-PAC, and WIPI1 appear to be p53-independent. Overexpression of BIRC4 and TAK1 caused upregulation of p53 and accumulation of its target proteins as well as an increase in p53 mRNA levels, suggesting that these genes are involved in p53 transcription and expression of its target genes followed by p53 protein accumulation. In conclusion, apoptosis and/or autophagy mediated by BIRC4 and TAK1 may be regulated by p53 and caspase activity. These novel findings may provide valuable information that will aid in a better understanding of the roles of caspase-related genes in human cell lines and be useful for the process of drug discovery. [ABSTRACT FROM AUTHOR]

The phosphatase of regenerating liver (PRL) family, including PRL-1, PRL-2, and PRL-3, comprises protein tyrosine phosphatases whose deregulation is associated with the tumorigenesis and metastasis of many types of cancer. However, the underlying mechanism is poorly understood. In this study, aiming to increase understanding of the molecular mechanisms underlying the functions of PRL-1 and PRL-3, a yeast two-hybrid system was employed to screen for their interacting proteins. Alignment with the NCBI BLAST database revealed 12 interactive proteins: Synaptic nuclear envelope protein 2, emerin, mannose 6-phosphate receptor-binding protein 1, low-density lipoprotein receptor-related protein 10, Rab acceptor 1, tumor protein D52-like 2, selectin P ligand (SELPLG), guanylate binding protein 1, transmembrane and ubiquitin-like domain-containing 2, NADH:ubiquinone oxidoreductase subunit B8, syndecan 4 and FK506-binding protein 8 (FKBP8). These proteins are associated with cell proliferation, apoptosis, immune response, cell fate specification and metabolic process in biological process categories, and involved in various signaling pathways, including Alzheimer's disease, Parkinson's disease, Huntington's disease, hypertrophic cardiomyopathy and cell adhesion molecules. Interactions of PRL-1 with the prey proteins SELPLG and FKBP8 were confirmed by immunoprecipitation or immunostaining. Furthermore, SELPLG and FKBP8 suppressed PRL-1- or PRL-3-mediated p53 activity. Identification of the proteins interacting with PRL family proteins may provide valuable information to better understand the mechanism of PRL-mediated signal transduction in cancer and other diverse diseases. [ABSTRACT FROM AUTHOR]

XBP1 (X-box-binding protein 1) is activated in cancer and has a pivotal role in tumorigenesis and progression of human cancer. In particular, the XBP1 transcriptional regulatory network is well known to drive cancer development, but little is known about whether the stability of XBP1 is regulated and, if so, what controls the stability of XBP1. In the present study we show that PIN1 prolyl isomerase interacts with the active form of XBP1 (XBP1s) in a phosphorylation-dependent manner and promotes XBP1s-induced cell proliferation and transformation through the regulation of XBP1 stability. By contrast, depletion of Pin1 in cancer cells reduced XBP1s expression, which subsequently inhibits cell proliferation and transformation. Interestingly, XBP1s activates multiple oncogenic pathways including NF-κB (nuclear factor κB),AP1 (activator protein 1) and Myc, and downregulates PIN1 transcription via a negative-feedback mechanism through p53 induction. Ultimately, reciprocal regulation of Pin1 and XBP1s is associated with the activation of oncogenic pathways, and the relationship of PIN1 and XBP1 may be an attractive target for novel therapy in cancers. [ABSTRACT FROM AUTHOR]

The unfolded protein response (UPR) regulates endoplasmic reticulum (ER) homeostasis and protects cells from ER stress. IRE1α is a central regulator of the UPR that activates the transcription factor XBP1s through an unconventional splicing mechanism using its endoribonuclease activity. IRE1α also cleaves certain mRNAs containing XBP1-like secondary structures to promote the degradation of these mRNAs, a process known as regulated IRE1α-dependent decay (RIDD). We show here that the mRNA of CReP/Ppp1r15b, a regulatory subunit of eukaryotic translation initiation factor 2α (eIF2α) phosphatase, is a RIDD substrate. eIF2α plays a central role in the integrated stress response by mediating the translational attenuation to decrease the stress level in the cell. CReP expression was markedly suppressed in XBP1-deficient mice livers due to hyperactivated IRE1α. Decreased CReP expression caused the induction of eIF2α phosphorylation and the attenuation of protein synthesis in XBP1- deficient livers. ER stress also suppressed CReP expression in an IRE1α-dependent manner, which increased eIF2α phosphorylation and consequently attenuated protein synthesis. Taken together, the results of our study reveal a novel function of IRE1α in the regulation of eIF2α phosphorylation and the translational control. [ABSTRACT FROM AUTHOR]

Activation of adiponectin receptors (AdipoRs) by its natural ligand, adiponectin has been known to be involved in modulating critical metabolic processes such as glucose metabolism and fatty acid oxidation as demonstrated by a number of in vitro and in vivo studies over last two decades. These findings suggest that AdipoRs' agonists could be developed into a potential therapeutic agent for metabolic diseases, such as diabetes mellitus, especially for type II diabetes, a long-term metabolic disorder characterized by high blood sugar, insulin resistance, and relative lack of insulin. Because of limitations in production of biologically active adiponectin, adiponectin-mimetic AdipoRs' agonists have been suggested as alternative ways to expand the opportunity to develop anti-diabetic agents. Based on crystal structure of AdipoR1, we designed AdipoR1's peptide agonists using protein-peptide docking simulation and screened their receptor binding abilities and biological functions via surface plasmon resonance (SPR) and biological analysis. Three candidate peptides, BHD1028, BHD43, and BHD44 were selected and confirmed to activate AdipoR1-mediated signal pathways. In order to enhance the stability and solubility of peptide agonists, candidate peptides were PEGylated. PEGylated BHD1028 exhibited its biological activity at nano-molar concentration and could be a potential therapeutic agent for the treatment of diabetes. Also, SPR and virtual screening techniques utilized in this study may potentially be applied to other peptide-drug screening processes against membrane receptor proteins.

Thiazolidinedione class of anti-diabetic drugs which are known as peroxisome proliferator-activated receptor γ (PPAR γ) ligands have been used to treat metabolic disorders, but thiazolidinediones can also cause several severe side effects, including congestive heart failure, fluid retention, and weight gain. In this study, we describe a novel synthetic PPAR γ ligand UNIST HYUNDAI Compound 1 (UHC1) that binds tightly to PPAR γ without the classical agonism and which blocks cyclin-dependent kinase 5 (CDK5)-mediated PPAR γ phosphorylation. We modified the non-agonist PPAR γ ligand SR1664 chemically to improve its solubility and then developed a novel PPAR γ ligand, UHC1. According to our docking simulation, UHC1 occupied the ligand-binding site of PPAR γ with a higher docking score than SR1664. In addition, UHC1 more potently blocked CDK5-mediated PPAR γ phosphorylation at Ser-273. Surprisingly, UHC1 treatment effectively ameliorated the inflammatory response both in vitro and in high-fat diet-fed mice. Furthermore, UHC1 treatment dramatically improved insulin sensitivity in high-fat diet-fed mice without causing fluid retention and weight gain. Taken together, compared with SR1664, UHC1 exhibited greater beneficial effects on glucose and lipid metabolism by blocking CD K5-mediated PPAR γ phosphorylation, and these data indicate that UHC1 could be a novel therapeutic agent for use in type 2 diabetes and related metabolic disorders. [ABSTRACT FROM AUTHOR]