Molecular Cloning, Genomic Structure, and Expression Analysis of MUC20, a Novel Mucin Protein, Up-regulated in Injured Kidney

Abstract

Immunoglobulin A nephropathy (IgAN) is the most common primary glomerulonephritis in the world. Here, we identify a cDNA encoding a novel mucin protein, shown previously to be up-regulated in IgAN patients, from a human kidney cDNA library. This protein contains a mucin tandem repeat of 19 amino acids consisting of many threonine, serine, and proline residues and likely to be extensively O-glycosylated; thus, this gene was classified in the mucin family and named MUC20. The human MUC20 gene contains at least four exons and is localized close to MUC4 on chromosome 3q29. We found variations in repeat numbers in the mucin tandem domain, suggesting polymorphism of this region. Northern blot and reverse transcription-PCR analyses revealed that human MUC20 mRNA was expressed most highly in kidney and moderately in placenta, colon, lung, prostate, and liver. Immunohistochemical analysis of human kidney revealed that MUC20 protein was localized in the proximal tubules. Immunoblotting analysis of MUC20 proteins produced in Madin-Darby canine kidney and HEK293 cells indicated the localization of MUC20 protein in a membrane fraction and extensive posttranslational modification. Immunoelectron microscopy of MUC20-producing Madin-Darby canine kidney cells demonstrated that MUC20 protein was localized on the plasma membrane. Expression of MUC20 mRNA in a human kidney cell line was up-regulated by tumor necrosis factor-␣, phorbol 12-myristate 13-acetate, or lipopolysaccharide. Two species of MUC20 mRNA (hMUC20-L and hMUC20-S), resulting from alternative transcription, were identified in human tissue, whereas only one variant was observed in mouse tissues. Mouse MUC20 mRNA was expressed in the epithelial cells of proximal tubules, and the expression increased dramatically with the progression of lupus nephritis in the kidney of MRL/MpJ-lpr/lpr mice.Moreover, the expression of mouse MUC20 was augmented in renal tissues acutely injured by cisplatin or unilateral ureteral obstruction. These characteristics suggest that the production of MUC20 is correlated with development and progression of IgAN and other renal injuries.

Gastric Mucus Alterations Associated With MurineHelicobacterInfection

“…Mucus acts as both a lubricant and as a protective barrier between the contents of the stomach and the mucosal epithelial surface (Shirazi et al 2000). In humans, 21 mucins have been identified in tissues such as lung, nose, salivary glands, and gastrointestinal tract (Chen et al 2004;Higuchi et al 2004). Seven mucins have been identified in mice (muc1, 2, 3, 4, 5ac, 5b, and 6) (Spicer et al 1991;Shekels et al 1995;van Klinken et al 1999;Machado et al 2000;Chen et al 2001;Desseyn et al 2002;Shekels and Ho 2003).…”

Assay of mucins in human tear fluid

“…Mucins are defined as glycoproteins, hydrophilic in nature, that have at least 50-80% of their mass as carbohydrate, O-linked to serine and threonine residues present within tandem repeats of amino acids in their protein backbone (Gendler and Spicer, 1995;Moniaux et al, 2001;Hollingsworth and Swanson, 2004). To date, at least 20 distinct human mucin genes have been cloned (Gendler and Spicer, 1995;Lapensee et al, 1997;Williams et al, 1999;Williams et al, 2001;Yin and Lloyd, 2001;Gum et al, 2002;Pallesen et al, 2002;Chen et al, 2004;Higuchi et al, 2004;Hollingsworth and Swanson, 2004). Of these, MUCs 1, 3A, 3B, 4, 12, 13, 15, 16, 17 and 20 have been characterized as membrane associated.…”

Cigarette Smoke Induces MUC5AC Protein Expression through the Activation of Sp1

“…To date, at least 20 primary human mucin genes (MUCs) have been identified, which are structurally classified as membranebound or secreted (11)(12)(13). Two gel-forming secreted mucins, MUC5B and MUC5AC, are the most abundant mucins expressed in the respiratory tract; MUC5B is constitutively expressed in the airway whereas MUC5AC is highly inducible (14).…”