No abstract

MUC4 is a heterodimeric membrane mucin, composed of a mucin subunit ASGP-1 (MUC4alpha) and a transmembrane subunit ASGP-2 (MUC4beta), which has been implicated in the protection of epithelial cell surfaces. Surprisingly, development and characterization of a new monoclonal antibody (mAb), called 1G8, against ASGP-2 demonstrated by immunohistochemistry the presence of MUC4 at the luminal surfaces of blood vessels of both normal tissues and tumors. Muc4 was detected with 1G8 and other Muc4 antibodies in blood vessels from humans, rats and mice. This expression of MUC4 in endothelial cells was confirmed by immunoblotting with 1G8 in human umbilical vein endothelial cells (HUVECs), human iliac artery endothelial cells (HIAECs), and human microvascular endothelial cells (HMVECs). MUC4 could be observed on HUVECs grown on either plastic or Matrigel. Finally, MUC4 expression in the three types of endothelial cell lines was confirmed by reverse transcription-polymerase chain reaction (RT-PCR). These results provide, to our knowledge, the first demonstration of a member of the MUC gene family and membrane mucin in blood vessels. As a luminal surface component, the MUC4 is situated to contribute to the non-adhesive luminal surface and to act as an intrinsic protection and survival factor.

Background: Crimean-Congo haemorrhagic fever virus (CCHFV) is considered an emerging or even a probable re-emerging pathogen in southern Europe. Presence of this virus had been reported previously in Spain in 2010. Aim: We aimed to evaluate the potential circulation of CCHFV in western Spain with a serosurvey in asymptomatic adults (blood donors). Methods: During 2017 and 2018, we conducted a CCHFV serosurvey in randomly selected asymptomatic blood donors from western Spain. Three assays using specific IgG antibodies against CCHFV were performed: the VectoCrimea ELISA test, an in-house ELISA and indirect immunofluorescence (EuroImmun) test with glycoprotein and nucleoprotein. Results: A total of 516 blood donors participated in this cross-sectional study. The majority of the study participants were male (68.4%), and the mean age was 46.3 years. Most of the participants came from rural areas (86.8%) and 68.6% had contact with animals and 20.9% had animal husbandry practices. One in five participants (109/516, 21.1%) were engaged in at-risk professional activities such as agriculture and shepherding, slaughtering, hunting, veterinary and healthcare work (mainly nursing staff and laboratory technicians). A total of 15.3% of the participants were bitten by ticks in the days or months before the date of sampling. We detected anti-CCHFV IgG antibodies with two diagnostic assays in three of the 516 individuals and with one diagnostic assay in six of the 516 individuals. Conclusion: Seroprevalence of CCHFV was between 0.58% and 1.16% in Castile-León, Spain. This is the first study in western Spain that showed circulation of CCHFV in healthy people.

Cleavage of Muc4/SMC precursor into two subunits is an essential processing step for maturation and occurs within a GD-PH sequence. Recent evidence indicates that cleavage of the precursor of gel-forming mucin MUC2 within the same tetrapeptide sequence occurs by a non-enzymatic, autocatalytic cleavage at low pH, and in cells in the late secretory pathway. Here we provide evidence that the cleavage step of Muc4/SMC processing occurs by a proteolytic mechanism. First, processing of Muc4/SMC precursor to ASGP-2 was inhibited in the presence of the mechanism-based serine protease inhibitor, Pefabloc SC, under conditions that did not block synthesis of other proteins. This inhibition led to an increased level of the precursor. Second, neutralization of the acidic environment of the late secretory pathway with NH4Cl did not inhibit cleavage of Muc4/SMC precursor. These results indicate that the two mucins can be processed by cleavage at the same peptide site by different mechanisms.