RESUMO
Molecular catch bonds are ubiquitous in biology and essential for processes like leucocyte extravasion1 and cellular mechanosensing2. Unlike normal (slip) bonds, catch bonds strengthen under tension. The current paradigm is that this feature provides 'strength on demand3', thus enabling cells to increase rigidity under stress1,4-6. However, catch bonds are often weaker than slip bonds because they have cryptic binding sites that are usually buried7,8. Here we show that catch bonds render reconstituted cytoskeletal actin networks stronger than slip bonds, even though the individual bonds are weaker. Simulations show that slip bonds remain trapped in stress-free areas, whereas weak binding allows catch bonds to mitigate crack initiation by moving to high-tension areas. This 'dissociation on demand' explains how cells combine mechanical strength with the adaptability required for shape change, and is relevant to diseases where catch bonding is compromised7,9, including focal segmental glomerulosclerosis10 caused by the α-actinin-4 mutant studied here. We surmise that catch bonds are the key to create life-like materials.
Assuntos
Actinas , Ligação ProteicaRESUMO
The collapse of polypeptides is thought important to protein folding, aggregation, intrinsic disorder, and phase separation. However, whether polypeptide collapse is modulated in cells to control protein states is unclear. Here, using integrated protein manipulation and imaging, we show that the chaperonin GroEL-ES can accelerate the folding of proteins by strengthening their collapse. GroEL induces contractile forces in substrate chains, which draws them into the cavity and triggers a general compaction and discrete folding transitions, even for slow-folding proteins. This collapse enhancement is strongest in the nucleotide-bound states of GroEL and is aided by GroES binding to the cavity rim and by the amphiphilic C-terminal tails at the cavity bottom. Collapse modulation is distinct from other proposed GroEL-ES folding acceleration mechanisms, including steric confinement and misfold unfolding. Given the prevalence of collapse throughout the proteome, we conjecture that collapse modulation is more generally relevant within the protein quality control machinery.
RESUMO
BACKGROUND: 18F-fluorocholine positron emission tomography/computed tomography (F-choline PET/CT) is considered a cornerstone in the staging and restaging of patients with prostate cancer (PCa). The aim of this study was to retrospectively assess unusual uptakes in patients who underwent a F-choline PET/CT for the initial staging or for the restaging of a relapsing PCa. METHODS: Three hundred and sixty-eight PCa patients were staged or restaged using F-choline PET/CT. Unusual uptakes were defined as uptakes occurring outside the usual paths of diffusion of PCa or as uptake in bone with a clear morphological evidence of nonmetastatic lesion. RESULTS: We found unusual uptakes in 47/368 patients (12.8%). Among them, 41/47 presented with benign F-choline uptake, usually within lymph nodes, due to inflammatory processes (22/47). Other benign processes were found in: thyroid (3/47), adrenal gland (3/47), brain (2/47), liver (1/47), bowel (3/47), frontal sinus (1/47), lungs (4/47), parotid gland (1/47) and bone (1/47). The six remaining patients presented with a second cancer, including lymphoma (1/47), non-small cell lung cancer (4/47) and neuroendocrine tumor (1/47). CONCLUSIONS: unusual uptakes on F-choline PET/CT are quite frequent and should be explored since they may correspond to non-PCa.
RESUMO
BACKGROUND: Enterocolitis is a rare, but serious gastrointestinal complication associated with docetaxel-based chemotherapy in patients with cancer. The incidence, clinical presentation and outcome of enterocolitis in patients with cancer treated with docetaxel-based chemotherapy was assessed in this study Patients and Methods: All patients treated with docetaxel for cancer between January 2010 and December 2014 at the University Hospital of Besançon were identified and their medical records reviewed. RESULTS: During this period, 1,227 patients received docetaxel chemotherapy and gastrointestinal events occurred in 381 (31.1%) patients. In multivariate analysis, a higher risk of gastrointestinal events was associated with a higher dose of docetaxel (≥75 mg/m2) (odds ratio(OR)=46.2; 95% confidence interval(CI)=5.4-397.0, p=0.0005) and the first cycle of docetaxel (OR=4.2; 95% CI=1.8-10.1, p=0.001). Among the 381 patients with gastrointestinal events, grade 3/4 neutropenia, diarrhea, febrile neutropenia, mucositis, nausea/vomiting, and rectal bleeding were diagnosed in 65 (17.1%), 51 (13.4%), 37 (9.7%); 12 (3.1%), seven (1.8%) and three (0.8%) patients, respectively; 54 patients (14.2%) were hospitalized. Computed tomographic scan was performed for 39 patients (10.2%). Twenty-seven patients presented radiological signs of enterocolitis. Three deaths (0.8%) related to enterocolitis were recorded. Docetaxel was resumed in 261 patients (68.5%) and the dose was reduced in 89 patients (23.4%). Docetaxel was discontinued in 120 patients (31.5%). CONCLUSION: Gastrointestinal events in patients treated with docetaxel may be a potential sign of fatal enterocolitis and require particular attention. Dose reduction at the first cycle may reduce the risk of such events.
