Regulation of mammalian target of rapamycin complex 1 by Bcl-2 and Bcl-XL proteins

Regulation of PRKN-independent mitophagy

Mitochondria are dynamic, multifunctional cellular organelles that play a fundamental role in maintaining cellular homeostasis. Keeping the quality of mitochondria in check is of essential importance for functioning and survival of the cells. Selective autophagic clearance of flawed mitochondria, a process termed mitophagy, is one of the most prominent mechanisms through which cells maintain a healthy mitochondrial pool. The best-studied pathway through which mitophagy is exerted is the PINK1-PRKN pathway. However, an increasing number of studies have shown an existence of alternative pathways, where different proteins and lipids are able to recruit autophagic machinery independently of PINK1 and PRKN. The significance of PRKN-independent mitophagy pathways is reflected in various physiological and pathophysiological processes, but many questions regarding the regulation and the interplay between these pathways remain open. Here we review the current knowledge and recent progress made in the field of PRKN-independent mitophagy. Particularly we focus on the regulation of various receptors that participate in targeting impaired mitochondria to autophagosomes independently of PRKN.AbbreviationsAMPK: AMP-activated protein kinase; ATP: adenosine triphosphate; BCL2: BCL2 apoptosis regulator; BH: BCL2 homology; CCCP: Carbonyl cyanide m-chlorophenylhydrazone; CL: cardiolipin; ER: endoplasmic reticulum; FCCP: carbonyl cyanide p-trifluoromethoxyphenylhydrazone; IMM: inner mitochondrial membrane; IMS: mitochondrial intermembrane space; LIR: LC3-interacting region; MDVs: mitochondrial-derived vesicles; MTORC1: mechanistic target of rapamycin kinase complex 1; OMM: outer mitochondrial membrane; OXPHOS: oxidative phosphorylation; PD: Parkinson disease; PtdIns3K: phosphatidylinositol 3-kinase; RGC: retinal ganglion cell; RING: really interesting new gene; ROS: reactive oxygen species; SUMO: small ubiquitin like modifier; TBI: traumatic brain injury; TM: transmembrane.

BCL-W is dispensable for the sustained survival of select Burkitt lymphoma and diffuse large B-cell lymphoma cell lines

Dysregulated expression of BCL-2 family proteins allows cancer cells to escape apoptosis. To counter this, BH3-mimetic drugs that target and inhibit select BCL-2 prosurvival proteins to induce apoptosis have been developed for cancer therapy. Venetoclax, which targets BCL-2, has been effective as therapy for patients with chronic lymphocytic leukemia, and MCL-1-targeting BH3-mimetic drugs have been extensively evaluated in preclinical studies for a range of blood cancers. Recently, BCL-W, a relatively understudied prosurvival member of the BCL-2 protein family, has been reported to be abnormally upregulated in Burkitt lymphoma (BL), diffuse large B-cell lymphoma (DLBCL), and Hodgkin lymphoma patient samples. Therefore, to determine if BCL-W would be a promising therapeutic target for B-cell lymphomas, we have examined the role of BCL-W in the sustained growth of human BL- and DLBCL-derived cell lines. We found that CRISPR/CAS9-mediated loss or short hairpin RNA-mediated knockdown of BCL-W expression in selected BL and DLBCL cell lines did not lead to spontaneous apoptosis and had no effect on their sensitivity to a range of BH3-mimetic drugs targeting other BCL-2 prosurvival proteins. Our results suggest that BCL-W is not universally required for the sustained growth and survival of human BL and DLBCL cell lines. Thus, targeting BCL-W in this subset of B-cell lymphomas may not be of broad therapeutic benefit.

The Role of Vitamin D and Sunlight Incidence in Cancer

BACKGROUND

Vitamin D (VD) deficiency affects individuals of different ages in many countries. VD deficiency may be related to several diseases, including cancer.

OBJECTIVE

This study aimed to review the relationship between VD deficiency and cancer.

METHODS

We describe the proteins involved in cancer pathogenesis and how those proteins can be influenced by VD deficiency. We also investigated a relationship between cancer death rate and solar radiation.

RESULTS

We found an increased bladder cancer, breast cancer, colon-rectum cancer, lung cancer, oesophagus cancer, oral cancer, ovary cancer, pancreas cancer, skin cancer and stomach cancer death rate in countries with low sunlight. It was also observed that amyloid precursor protein, ryanodine receptor, mammalian target of rapamycin complex 1, and receptor for advanced glycation end products are associated with a worse prognosis in cancer. While the Klotho protein and VD receptor are associated with a better prognosis in the disease. Nfr2 is associated with both worse and better prognosis in cancer.

CONCLUSION

The literature suggests that VD deficiency might be involved in cancer progression. According to sunlight data, we can conclude that countries with low average sunlight have high cancers death rate. New studies involving transcriptional and genomic data in combination with VD measurement in long-term experiments are required to establish new relationships between VD and cancer.

Upregulation of DAPK2 ameliorates oxidative damage and apoptosis of placental cells in hypertensive disorder complicating pregnancy by suppressing human placental microvascular endothelial cell autophagy through the mTOR signaling pathway

Death-associated protein kinase 2 (DAPK2) has indicated functional roles in cellular processes, including survival, apoptosis, and autophagy. This study is aimed to identify the effect of DAPK2 on oxidative damage and apoptosis of placental cells in hypertensive disorder complicating pregnancy (HDCP) through mTOR pathway. Microarray-based gene expression analysis was performed to predict the differentially expressed genes related to HDCP. To investigate the specific mechanism of DAPK2 in HDCP cells, placental microvascular endothelial cells were treated with mimic or siRNA of DAPK2 and mTOR to detect the expression of related genes, cell autophagy and apoptosis and oxidative damage. Finally, rats were modeled with HDCP to verify the cell experiment results. DAPK2 was downregulated in HDCP, and could activate mTOR. Besides, DAPK2 overexpression led to decreases in autophagy in HPVECs as well as apoptosis and oxidative damage in placental cells indicated by a substantial decrease in Beclin-1, LC3 II/LC3 I and Bax along with an increase in Bcl-2, 4EBP1 and p70S6K. It also ameliorates blood pressure elevation in HDCP rats. The study defined remission effect of DAPK2 on placental cell oxidative damage and apoptosis in HDCP via mTOR activation. Together, DAPK2 regulating mTOR pathway presents a promising therapy for HDCP treatment.

Activation of Autophagy Ameliorates Cardiomyopathy in Mybpc3-Targeted Knockin Mice

BACKGROUND

Alterations in autophagy have been reported in hypertrophic cardiomyopathy (HCM) caused by Danon disease, Vici syndrome, or LEOPARD syndrome, but not in HCM caused by mutations in genes encoding sarcomeric proteins, which account for most of HCM cases. MYBPC3, encoding cMyBP-C (cardiac myosin-binding protein C), is the most frequently mutated HCM gene.

METHODS AND RESULTS

We evaluated autophagy in patients with HCM carrying MYBPC3 mutations and in a Mybpc3-targeted knockin HCM mouse model, as well as the effect of autophagy modulators on the development of cardiomyopathy in knockin mice. Microtubule-associated protein 1 light chain 3 (LC3)-II protein levels were higher in HCM septal myectomies than in nonfailing control hearts and in 60-week-old knockin than in wild-type mouse hearts. In contrast to wild-type, autophagic flux was blunted and associated with accumulation of residual bodies and glycogen in hearts of 60-week-old knockin mice. We found that Akt-mTORC1 (mammalian target of rapamycin complex 1) signaling was increased, and treatment with 2.24 mg/kg·d rapamycin or 40% caloric restriction for 9 weeks partially rescued cardiomyopathy or heart failure and restored autophagic flux in knockin mice.

CONCLUSIONS

Altogether, we found that (1) autophagy is altered in patients with HCM carrying MYBPC3 mutations, (2) autophagy is impaired in Mybpc3-targeted knockin mice, and (3) activation of autophagy ameliorated the cardiac disease phenotype in this mouse model. We propose that activation of autophagy might be an attractive option alone or in combination with another therapy to rescue HCM caused by MYBPC3 mutations.

Smyd1C Mediates CD8 T Cell Death via Regulation of Bcl2-Mediated Restriction of outer Mitochondrial Membrane Integrity

The SET and Mynd domain 1 (Smyd1) locus encodes three tissue-restricted isoforms. Two previously characterized isoforms, Smyd1A and Smyd1B, are heart and skeletal muscle-restricted histone methyl transferases. Here we report that a third, non-catalytic isoform, Smyd1C, is expressed predominantly in activated CD8 T cells. While Smyd1C- deficient CD8 T cells undergo activation-induced apoptosis, neither of two classical mechanisms activation-induced cell death nor activated cell autonomous death are utilized. Instead, Smyd1C accumulates within both mitochondria and the immunological synapse where it associates with Bcl-2, FK506-Binding Protein 8/38 (FKBP38) and Calcineurin. This complex maintains Bcl-2 phosphorylation, enhanced mitochondrial localization, and restricted apoptosis of activated CD8 T cells. We suggest that CD8 T cell death is governed, in part, by Smyd1C regulation of Bcl2-mediated restriction of outer mitochondrial membrane integrity.

FKBP8 recruits LC3A to mediate Parkin-independent mitophagy

Mitophagy, the selective removal of damaged or excess mitochondria by autophagy, is an important process in cellular homeostasis. The outer mitochondrial membrane (OMM) proteins NIX, BNIP3, FUNDC1, and Bcl2-L13 recruit ATG8 proteins (LC3/GABARAP) to mitochondria during mitophagy. FKBP8 (also known as FKBP38), a unique member of the FK506-binding protein (FKBP) family, is similarly anchored in the OMM and acts as a multifunctional adaptor with anti-apoptotic activity. In a yeast two-hybrid screen, we identified FKBP8 as an ATG8-interacting protein. Here, we map an N-terminal LC3-interacting region (LIR) motif in FKBP8 that binds strongly to LC3A both in vitro and in vivo FKBP8 efficiently recruits lipidated LC3A to damaged mitochondria in a LIR-dependent manner. The mitophagy receptors BNIP3 and NIX in contrast are unable to mediate an efficient recruitment of LC3A even after mitochondrial damage. Co-expression of FKBP8 with LC3A profoundly induces Parkin-independent mitophagy. Strikingly, even when acting as a mitophagy receptor, FKBP8 avoids degradation by escaping from mitochondria. In summary, this study identifies novel roles for FKBP8 and LC3A, which act together to induce mitophagy.

Translationally controlled tumour protein TCTP is induced early in human colorectal tumours and contributes to the resistance of HCT116 colon cancer cells to 5-FU and oxaliplatin

Background

Translationally controlled tumour protein TCTP is an anti-apoptotic protein frequently overexpressed in cancers, where high levels are often associated with poor patient outcome. TCTP may be involved in protecting cancer cells against the cytotoxic action of anti-cancer drugs. Here we study the early increase of TCTP levels in human colorectal cancer (CRC) and the regulation of TCTP expression in HCT116 colon cancer cells, in response to treatment with the anti-cancer drugs 5-FU and oxaliplatin.

Methods

Using immunohistochemistry, we assessed TCTP levels in surgical samples from adenomas and adenocarcinomas of the colon, compared to normal colon tissue. We also studied the regulation of TCTP in HCT116 colon cancer cells in response to 5-FU and oxaliplatin by western blotting. TCTP mRNA levels were assessed by RT-qPCR. We used mTOR kinase inhibitors to demonstrate mTOR-dependent translational regulation of TCTP under these conditions. Employing the Real-Time Cell Analysis (RTCA) System and the MTS assay, we investigated the effect of TCTP-knockdown on the sensitivity of HCT116 cells to the anti-cancer drugs 5-FU and oxaliplatin.

Results

1. TCTP levels are significantly increased in colon adenomas and adenocarcinomas, compared to normal colon tissue. 2. TCTP protein levels are about 4-fold upregulated in HCT116 colon cancer cells, in response to 5-FU and oxaliplatin treatment, whereas TCTP mRNA levels are down regulated. 3. mTOR kinase inhibitors prevented the up-regulation of TCTP protein, indicating that TCTP is translationally regulated through the mTOR complex 1 signalling pathway under these conditions. 4. Using two cellular assay systems, we demonstrated that TCTP-knockdown sensitises HCT116 cells to the cytotoxicity caused by 5-FU and oxaliplatin.

Conclusions

Our results demonstrate that TCTP levels increase significantly in the early stages of CRC development. In colon cancer cells, expression of this protein is largely upregulated during treatment with the DNA-damaging anti-cancer drugs 5-FU and oxaliplatin, as part of the cellular stress response. TCTP may thus contribute to the development of anti-cancer drug resistance. These findings indicate that TCTP might be suitable as a biomarker and that combinatorial treatment using 5-FU/oxaliplatin, together with mTOR kinase inhibitors, could be a route to preventing the development of resistance to these drugs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-017-0164-3) contains supplementary material, which is available to authorized users.

B Cell Receptor Activation Predominantly Regulates AKT-mTORC1/2 Substrates Functionally Related to RNA Processing

Protein kinase B (AKT) phosphorylates numerous substrates on the consensus motif RXRXXpS/T, a docking site for 14-3-3 interactions. To identify novel AKT-induced phosphorylation events following B cell receptor (BCR) activation, we performed proteomics, biochemical and bioinformatics analyses. Phosphorylated consensus motif-specific antibody enrichment, followed by tandem mass spectrometry, identified 446 proteins, containing 186 novel phosphorylation events. Moreover, we found 85 proteins with up regulated phosphorylation, while in 277 it was down regulated following stimulation. Up regulation was mainly in proteins involved in ribosomal and translational regulation, DNA binding and transcription regulation. Conversely, down regulation was preferentially in RNA binding, mRNA splicing and mRNP export proteins. Immunoblotting of two identified RNA regulatory proteins, RBM25 and MEF-2D, confirmed the proteomics data. Consistent with these findings, the AKT-inhibitor (MK-2206) dramatically reduced, while the mTORC-inhibitor PP242 totally blocked phosphorylation on the RXRXXpS/T motif. This demonstrates that this motif, previously suggested as an AKT target sequence, also is a substrate for mTORC1/2. Proteins with PDZ, PH and/or SH3 domains contained the consensus motif, whereas in those with an HMG-box, H15 domains and/or NF-X1-zinc-fingers, the motif was absent. Proteins carrying the consensus motif were found in all eukaryotic clades indicating that they regulate a phylogenetically conserved set of proteins.

Vitamin D3 potentiates the growth inhibitory effects of metformin in DU145 human prostate cancer cells mediated by AMPK/mTOR signalling pathway

Metformin and vitamin D₃ both exhibit a strong antiproliferative action in numerous cancer cell lines, including in human prostate cancer cells. Here we showed that the combination of the two drugs had a much stronger effect on DU145 human prostate cancer cell growth than either drug alone. In this research, cell proliferation was measured by methylthiazol tetrazolium (MTT) assay. Cell apoptosis was determined with Hoechst 33342 staining. Western blotting and cell cycle analyses were used to elucidate potential mechanisms of interaction between the drugs. It is shown that in cultured DU145 cells, vitamin D₃ combined with metformin exhibits synergistic effects on cell proliferation and apoptosis. The underlying antitumor mechanisms may involve altered cycle distribution with a G1/S cell cycle arrest, activation of phospho-AMPK with subsequent inhibition of downstream mTOR signalling pathway, down-regulate c-Myc expression, and reducing the level of anti-apoptotic protein p-Bcl-2. In conclusion, metformin and vitamin D₃ synergistically inhibit DU145 cell growth, indicating a promising clinical therapeutic strategy for the treatment of androgen-independent prostate cancer.

Regulation of the Target of Rapamycin and Other Phosphatidylinositol 3-Kinase-Related Kinases by Membrane Targeting

Phosphatidylinositol 3-kinase-related kinases (PIKKs) play vital roles in the regulation of cell growth, proliferation, survival, and consequently metabolism, as well as in the cellular response to stresses such as ionizing radiation or redox changes. In humans six family members are known to date, namely mammalian/mechanistic target of rapamycin (mTOR), ataxia-telangiectasia mutated (ATM), ataxia- and Rad3-related (ATR), DNA-dependent protein kinase catalytic subunit (DNA-PKcs), suppressor of morphogenesis in genitalia-1 (SMG-1), and transformation/transcription domain-associated protein (TRRAP). All fulfill rather diverse functions and most of them have been detected in different cellular compartments including various cellular membranes. It has been suggested that the regulation of the localization of signaling proteins allows for generating a locally specific output. Moreover, spatial partitioning is expected to improve the reliability of biochemical signaling. Since these assumptions may also be true for the regulation of PIKK function, the current knowledge about the regulation of the localization of PIKKs at different cellular (membrane) compartments by a network of interactions is reviewed. Membrane targeting can involve direct lipid-/membrane interactions as well as interactions with membrane-anchored regulatory proteins, such as, for example, small GTPases, or a combination of both.

Role of mTOR1 and mTOR2 complexes in MEG-01 cell physiology

The function of the mammalian target of rapamycin (mTOR) is upregulated in response to cell stimulation with growing and differentiating factors. Active mTOR controls cell proliferation, differentiation and death. Since mTOR associates with different proteins to form two functional macromolecular complexes, we aimed to investigate the role of the mTOR1 and mTOR2 complexes in MEG-01 cell physiology in response to thrombopoietin (TPO). By using mTOR antagonists and overexpressing FKBP38, we have explored the role of both mTOR complexes in proliferation, apoptosis, maturation-like mechanisms, endoplasmic reticulum-stress and the intracellular location of both active mTOR complexes during MEG-01 cell stimulation with TPO. The results demonstrate that mTOR1 and mTOR2 complexes play different roles in the physiology of MEG-01 cells and in the maturation-like mechanisms; hence, these findings might help to understand the mechanism underlying generation of platelets.

Hypercapnia Inhibits Autophagy and Bacterial Killing in Human Macrophages by Increasing Expression of Bcl-2 and Bcl-xL

Hypercapnia, the elevation of CO2 in blood and tissue, commonly develops in patients with advanced lung disease and severe pulmonary infections, and it is associated with high mortality. We previously reported that hypercapnia alters expression of host defense genes, inhibits phagocytosis, and increases the mortality of Pseudomonas pneumonia in mice. However, the effect of hypercapnia on autophagy, a conserved process by which cells sequester and degrade proteins and damaged organelles that also plays a key role in antimicrobial host defense and pathogen clearance, has not previously been examined. In the present study we show that hypercapnia inhibits autophagy induced by starvation, rapamycin, LPS, heat-killed bacteria, and live bacteria in the human macrophage. Inhibition of autophagy by elevated CO2 was not attributable to acidosis. Hypercapnia also reduced macrophage killing of Pseudomonas aeruginosa. Moreover, elevated CO2 induced the expression of Bcl-2 and Bcl-xL, antiapoptotic factors that negatively regulate autophagy by blocking Beclin 1, an essential component of the autophagy initiation complex. Furthermore, small interfering RNA targeting Bcl-2 and Bcl-xL and the small molecule Z36, which blocks Bcl-2 and Bcl-xL binding to Beclin 1, prevented hypercapnic inhibition of autophagy and bacterial killing. These results suggest that targeting the Bcl-2/Bcl-xL-Beclin 1 interaction may hold promise for ameliorating hypercapnia-induced immunosuppression and improving resistance to infection in patients with advanced lung disease and hypercapnia.