FEBS Letters最新文献

HECT-E3 ligases play an essential role in catalyzing the transfer of ubiquitin to protein substrates. The noncatalytic roles of HECT-E3 ligases in cells are unknown. Here, we report that a HECT-E3 ligase, HACE1, functions as an adaptor independent of its E3 ligase activity. We identified Spindlin-1, a histone reader, as a new HACE1-associated protein. Interestingly, we found that HACE1 promotes Spindlin-1 degradation via the proteasome in an ubiquitination-independent manner. Functionally, we demonstrated that the loss of HACE1 results in weak cell-cell adhesion due to Spindlin-1-mediated accumulation of GDNF, a negative regulator of cell adhesion. Together, our data suggest that HACE1 acts as a molecular adaptor and plays an important noncatalytic role in presenting selected substrates directly to the proteasome for degradation.

Leishmania internalize hemoglobin (Hb) via a specific receptor (HbR) for their survival. To identify the Hb-binding domain of HbR, we cloned and expressed several truncated proteins of HbR and determined their ability to bind Hb. Our findings reveal that 90% of Hb-binding activity is retained in HbR^41-80 in comparison with HbR^1-471 . We synthesized a 40 amino acid peptide (SSEKMKQLTMYMIHEMVEGLEGRPSTVRMLPSFVYTSDPA) corresponding to HbR^41-80 and found that it specifically binds Hb. Subsequently, we found that the HbR^41-80 peptide completely blocks Hb uptake in both promastigote and amastigote forms of Leishmania and, thereby, inhibits the growth of the parasite. These results demonstrate that HbR^41-80 is the Hb-binding domain of HbR, which might be used as a potential therapeutic agent to inhibit the growth of Leishmania.

Mutations in PINK1 (PTEN-induced putative kinase 1) are associated with autosomal recessive early-onset Parkinson's disease. Full-length PINK1 (PINK1-l) has been extensively studied in mitophagy; however, the functions of the short form of PINK1 (PINK1-s) remain poorly understood. Here, we report that PINK1-s is recruited to ribosome fractions after short-term inhibition of proteasomes. The expression of PINK1-s greatly inhibits protein synthesis even without proteasomal stress. Mechanistically, PINK1-s phosphorylates the translation elongation factor eEF1A1 during proteasome inhibition. The expression of the phosphorylation mimic mutation eEF1A1S396E rescues protein synthesis defects and cell viability caused by PINK1 knockout. These findings implicate an important role for PINK1-s in protecting cells against proteasome stress through inhibiting protein synthesis.

Transplantation of in vitro-manipulated cells is widely used in hematology. While transplantation is well recognized to impose severe stress on transplanted cells, the nature of transplant-induced stress remains elusive. Here, we propose that the lack of amino acids in serum is the major cause of transplant-induced stress. Mechanistically, amino acid deficiency decreases protein synthesis and nutrient consummation. However, in cells with overactive AKT and ERK, mTORC1 is not inhibited and protein synthesis remains relatively high. This impaired signaling causes nutrient depletion, cell cycle block, and eventually autophagy and cell death, which can be inhibited by cycloheximide or mTORC1 inhibitors. Thus, mTORC1-mediated amino acid signaling is critical in cell fate determination under transplant-induced stress, and protein synthesis inhibition can improve transplantation efficiency.

Integrin-mediated adhesion regulates cellular responses to changes in the mechanical and biochemical properties of the extracellular matrix. Cell-matrix adhesion regulates caveolar endocytosis, dependent on caveolin 1 (Cav1) Tyr14 phosphorylation (pY14Cav1), to control anchorage-dependent signaling. We find that cell-matrix adhesion regulates pY14Cav1 levels in mouse fibroblasts. Biochemical fractionation reveals endogenous pY14Cav1 to be present in caveolae and focal adhesions (FA). Adhesion does not affect caveolar pY14Cav1, supporting its regulation at FA, in which PF-228-mediated inhibition of focal adhesion kinase (FAK) disrupts. Cell adhesion on 2D polyacrylamide matrices of increasing stiffness stimulates Cav1 phosphorylation, which is comparable to the phosphorylation of FAK. Inhibition of FAK across varying stiffnesses shows it regulates pY14Cav1 more prominently at higher stiffness. Taken together, these studies reveal the presence of FAK-pY14Cav1 crosstalk at FA, which is regulated by cell-matrix adhesion.

The majority of mitochondrial proteins are nuclear encoded and imported into mitochondria as precursor proteins via dedicated translocases. The translocase of the inner membrane 22 (TIM22) is a multisubunit molecular machine specialized for the translocation of hydrophobic, multi-transmembrane-spanning proteins with internal targeting signals into the inner mitochondrial membrane. Here, we undertook a crosslinking-mass spectrometry (XL-MS) approach to determine the molecular arrangement of subunits of the human TIM22 complex. Crosslinking of the isolated TIM22 complex using the BS3 crosslinker resulted in the broad generation of crosslinks across the majority of TIM22 components, including the small TIM chaperone complex. The crosslinking data uncovered several unexpected features, opening new avenues for a deeper investigation into the steps required for TIM22-mediated translocation in humans.

Aims: Treatment of in-stent restenosis of coronary stents is challenging. The use of drug-coated balloons (DCB) is a promising technique to treat in-stent restenosis without adding another metal layer. The aim of the AGENT ISR randomised trial is to evaluate angiographic and clinical outcomes in patients with ISR of a previously treated lesion who were treated with either a DCB with a new coating formulation (Agent) or a standard DCB (SeQuent Please).

Methods and results: AGENT ISR is a multicentre, randomised, open-label, non-inferiority study comparing the Agent and SeQuent Please DCB. A total of 125 patients (mean age ~68 years, 18% female) with in-stent restenosis of a previously treated lesion <28 mm in length were randomised at 11 sites in Europe to Agent (n=65) or SeQuent Please (n=60). The primary endpoint, six-month in-stent late lumen loss, in the Agent group (0.397±0.43 mm [n=51]) was non-inferior to that of the SeQuent Please group (0.393±0.536 mm [n=49]), as the two-sided upper 95% confidence boundary for the difference between groups was less than the pre-specified non-inferiority margin of 0.20 (difference 0.004, 95% CI [-0.189, 0.196]; pnon-inferiority=0.046). At one year, mortality was 3.1% in Agent and 1.7% in SeQuent Please patients (p>0.99), target lesion revascularisation 7.7% versus 10.0% (p=0.89), and stent thrombosis 0% versus 3.3% (p=0.44). Similar improvements in quality of life were seen in the two groups.

Conclusions: In this head-to-head comparison of two DCB, Agent proved to be non-inferior to SeQuent Please for in-stent late lumen loss at six months.

Clinical trials registration: NCT02151812 (http://clinicaltrials.gov/).

Dimerization of the small GTPase Arf is prerequisite for the scission of COPI-coated transport vesicles. Here, we quantify the monomer/dimer equilibrium of Arf within the membrane and show that after membrane scission, Arf dimers are restricted to donor membranes. By hydrogen exchange mass spectrometry, we define the interface of activated dimeric Arf within its switch II region. Single amino acid exchanges in this region reduce the propensity of Arf to dimerize. We suggest a mechanism of membrane scission by which the dimeric form of Arf is segregated to the donor membrane. Our data are consistent with the previously reported absence of dimerized Arf in COPI vesicles and could explain the presence of one single scar-like noncoated region in each COPI vesicle.