Human MUC4 Mucin cDNA and Its Variants in Pancreatic Carcinoma

Abstract

The human MUC4 gene is not expressed in normal pancreas; however, its dysregulation results in high levels of expression in pancreatic tumors. To investigate the tumor-associated expression, MUC4 cDNA was cloned from a human pancreatic tumor cell line cDNA expression library using a polyclonal antibody raised against human deglycosylated mucin and RT-PCR. Pancreatic MUC4 cDNA shows differences in 12 amino acid residues in the non-tandem repeat coding region with no structural rearrangement as compared with tracheal MUC4. The full-length MUC4 cDNA includes a leader sequence, a serine and threonine rich non-tandem repeat region, a central large tandem repeat domain containing 48 bp repetitive units, regions rich in potential N-glycosylation sites, two cysteine-rich domains, EGF-like domains, and a transmembrane domain. We also report the presence of a new EGF-like domain in MUC4 cDNA, located in the cysteine-rich region upstream from the first EGF-like domain. Four distinct splice events were identified in the region downstream of the central tandem repeat domain that generate three new MUC4 cDNA sequences (sv4, sv9, and sv10). The deduced amino acid sequences of two of these variants lack the transmembrane domain. Furthermore, two unique forms of MUC4 (MUC4/Y and MUC4/X) generated as a result of alternative splicing lack the salient feature of mucins, the tandem repeat domain. A high degree of polymorphism in the central tandem repeat region of MUC4 was observed in various pancreatic adenocarcinoma cell lines, with allele sizes ranging from 23.5 to 10.0 kb. MUC4 mRNA expression was higher in differentiated cell lines, with no detectable expression in poorly differentiated pancreatic tumor cell lines.

MUC4 mucin expression in human pancreatic tumours is affected by organ environment: the possible role of TGFβ2

“…As reported in our previous study (Choudhury et al, 2000b), the MUC4 cDNA probe hybridised to a large-sized transcript (B26.5 kb) in CD18/HPAF cells, and showed a smear ranging from 10 to 29 kb in the OT tumours on Northern blot (Figure 1). The conceptual expected transcript size of the MUC4 in HPAF cells will be B26.5 kb (Choudhury et al, 2000a). OT tumours showed an MUC4 transcript similar or little higher than the parental cell line CD18/HPAF (Figure 1).…”

“…Based on the structure, mucins are categorised into three distinct forms: membrane spanning (MUC1, MUC3, MUC4, MUC12 and MUC17), gel forming (MUC2, MUC5AC, MUC5B and MUC6), and soluble (MUC7) . MUC4 has been cloned from the human trachea and human pancreatic tumours, and the full-length cDNA sequence is known (Nollet et al, 1998;Moniaux et al, 1999;Choudhury et al, 2000a). The NH 2 -terminus of MUC4 is composed of a 27-residue signal peptide and a large domain varying in length from 3285 -7285 amino-acid residues as a result of variable number of 16 amino-acid tandem repeat units (VNTR).…”

Multiple roles of mucins in pancreatic cancer, a lethal and challenging malignancy

“…As compared to the secreted mucins, they present a wider and more complex expression pattern. Indeed, they can be expressed in four distinct forms: membrane-anchored, soluble (proteolytic cleavage of the membrane-bound form), secreted (alternatively spliced variants), and lacking the tandem repeat array (alternatively spliced variants) (Wreschner et al, 1990;Choudhury et al, 2000;Moniaux et al, 2000). The ratio of one form to another appears to be tissue-specific and associated to the physiologic conditions (normal or tumoral).…”

“…The overexpression of MUC1 is observed during the early stages of the development of PC, which is further increased in invasive carcinoma (Levi et al, 2004). On the other hand, MUC4 is minimally or not expressed in the normal pancreas or chronic pancreatitis but is highly expressed in human pancreatic tumours and pancreatic tumour cell lines (Balague et al, 1994;Choudhury et al, 2000;Andrianifahanana et al, 2001).…”

Human MUC4 mucin induces ultra-structural changes and tumorigenicity in pancreatic cancer cells

“…MUC4 is highly expressed in human pancreatic tumours and pancreatic tumour cell lines; however, its expression is undetectable in the normal pancreas or chronic pancreatitis (Balague et al, 1994;Hollingsworth et al, 1994;Choudhury et al, 2000a;Andrianifahanana et al, 2001). MUC4 is expressed by metaplastic ducts and its expression increases with increasing grade in pancreatic intraepithelial neoplasias (Swart et al, 2002;Park et al, 2003).…”