Glycoprotein Quality Control in the Endoplasmic Reticulum MANNOSE TRIMMING BY ENDOPLASMIC RETICULUM MANNOSIDASE I TIMES THE PROTEASOMAL DEGRADATION OF UNASSEMBLED IMMUNOGLOBULIN SUBUNITS

Quality control in the endoplasmic reticulum must discriminate nascent proteins in their folding process from terminally unfolded molecules, selectively degrading the latter. Unassembled Ig-μ and J chains, two glycoproteins with fiveN-linked glycans and one N-linked glycan, respectively, are degraded by cytosolic proteasomes after a lag from synthesis, during which glycan trimming occurs. Inhibitors of mannosidase I (kifunensine), but not of mannosidase II (swainsonine), prevent the degradation of μ chains. Kifunensine also inhibits J chain dislocation and degradation, without inhibiting secretion of IgM polymers. In contrast, glucosidase inhibitors do not significantly affect the kinetics of μ and J degradation. These results suggest that removal of the terminal mannose from the central branch acts as a timer in dictating the degradation of transport-incompetent, glycosylated Ig subunits in a calnexin-independent way. Kifunensine does not inhibit the degradation of an unglycosylated substrate (λ Ig light chains) or of chimeric μ chains extended with the transmembrane region of the α T cell receptor chain, implying the existence of additional pathways for extracting proteins from the endoplasmic reticulum lumen for proteasomal degradation

Reduction of Interchain Disulfide Bonds Precedes the Dislocation of Ig-µ Chains from the Endoplasmic Reticulum to the Cytosol for Proteasomal Degradation

Proteins that fail to fold or assemble in the endoplasmic reticulum (ER) are generally dislocated across the membrane to be degraded by cytosolic proteasomes. To investigate how the quality control machinery handles individual subunits that are part of covalent oligomers, we have analyzed the fate of transport-competent Ig light (L) chains that form disulfide bonds with short-lived mu heavy chains. When expressed alone, L chains are secreted. In cells producing excess mu, most L chains are retained in the ER as covalent mu-L or mu2-L2 complexes. While mu chains present in these complexes are degraded by proteasomes, L chains are stable. Few L chains are secreted; most reassociate with newly synthesized mu chains. Therefore, interchain disulfide bonds are reduced in the ER lumen before the dislocation of mu chains in a site from which freed L chains can be rapidly reinserted in the assembly line. The ER can thus sustain the simultaneous formation and reduction of disulfide bonds

Delay in cutaneous squamous cell carcinoma diagnosis due to interrupted services is associated with worse prognoses and modified surgical approaches

Background: The delayed diagnosis of skin tumors is associated with a worsened prognosis. The impact of the interruption of clinical and surgical health services during the COVID-19 pandemic lockdowns has been documented among many pathologies. The impact of delayed diagnoses on patients with cutaneous squamous cell carcinomas (cSCCs) is poorly defined. Objective: To compare patient and lesion characteristics and the surgical management of excised cSCCs prior to the pandemic shutdown of services (2018–2019) with the phase following the pandemic’s second wave (2021–2022). Methods: An observational, single-center, cross-sectional study of 416 surgically excised cSCCs over the course of two years was performed. Only patients with histologically confirmed cSCC were enrolled. Data collection included patient demographics and lesion characteristics, time to surgery, surgical approach, and histological data. Results: More cSCC lesions were excised prior to the interruption of services (n = 312 vs. n = 186). Lesions were significantly larger (1.7 ± 1.2 vs. 2.1 ± 1.5 cm; p = 0.006) and more invasive (52% vs. 89%; p < 0.001), in the period 2021–2022. Surgical reconstructive techniques were significantly different (p = 0.001). Metastatic involvement was confirmed in three subjects (one in 2018–2019 and two in 2021–2022). There were no significant differences in the time to surgery or patient characteristics. Multivariable regression analysis identified a 4.7-times higher risk of tumor invasion (OR 4.69, 95%CI 2.55–8.16, p < 0.001), a two-times higher chance of dermo-epidermal grafts (OR 2.06, 95%CI 1.09–3.88, p = 0.025), and a 3.2-times higher risk of positive surgical margins (OR 3.21, 95%CI 1.44–7.17, p = 0.004). Conclusions: Diagnostic delays of cutaneous SCCs associated with reduced patient access to clinical and diagnostic services are associated with a 4.7-times increased risk of more severe invasion, a three-times increased risk of positive surgical margins, and a significant impact on surgical management, compared to the pre-pandemic period. Comparable patient cohort characteristics and time to surgery remained unchanged

Bacterial ligands as flexible and sensitive detectors in rapid tests for antibodies to SARS-CoV-2

Lateral flow immunoassay (LFIA) is widely employed as point-of-care tests (POCT) for the diagnosis of infectious diseases. The accuracy of LFIA largely depends on the quality of the immunoreagents used. Typical LFIAs to reveal the immune response to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) employ anti-human immunoglobulin (hIG) antibodies and recombinant viral antigens, which usually are unstable and poorly soluble. Broad selective bacterial proteins, such as Staphylococcal protein A (SpA) and Streptococcal protein G (SpG) can be considered alternatives to anti-hIG to increase versatility and sensitivity of serological LFIAs because of their high binding capacity, interspecies reactivity, and robustness. We developed two colorimetric LFA devices including SpA and SpG linked to gold nanoparticles (GNP) as detectors and explored the use of a specific, stable, and soluble immunodominant fraction of the nucleocapsid protein from SARS-CoV-2 as the capturing agent. The optimal amount of SpA-GNP and SpG-GNP conjugates and the protein-to-GNP ratios were defined through a full factorial experimental design to maximize the diagnostic sensitivity of the LFIAs. The new LFA devices were applied to analyze 105 human serum samples (69 positive and 36 negatives according to reference molecular diagnostic methods). The results showed higher sensitivity (89.9%, 95% CI 82.7-97.0) and selectivity (91.7%, 82.6-100) for the SpA-based compared to the SpG-based LFA. In addition, 18 serum samples from cats and dogs living with COVID-19 patients were analyzed and 14 showed detectable levels of anti-SARS-CoV-2 antibodies, thus illustrating the flexibility of the SpA- and SpG-based LFAs