title: Differential expression of serum clusterin isoforms in colorectal cancer.
abstract: Clusterin is an enigmatic protein altered in tumors of colorectal cancer patients. Because there is no information available about serum clusterin regarding this pathology, we applied proteomic techniques to analyze its isoforms in donors and patients. First we separated serum proteins through concanavalin A, obtaining a fraction with non- and O-glycosylated proteins (FI) and a second fraction enriched in N-glycoproteins (FII) wherein clusterin was supposed to elute on the basis of its glycosylation. Surprisingly analysis of the FI fraction revealed the existence of an unexpected and aberrantly N-glycosylated clusterin that was overexpressed in patients and comprised at least five isoforms with different isoelectric points. On the other hand, two-dimensional electrophoretic analysis of the clusterin eluted in FII detected one isoform that was increased and 15 isoforms that were decreased or absent in serum of patients. Finally immunoquantification by slot blot showed that in total serum and in FI the clusterin levels were significantly increased in patients, whereas in FII there was no significant variation. Therefore, serum clusterin and some of its isoforms could have a potential value as colorectal tumor markers and are interesting subjects for biomarker studies.
authors.affiliation: Departamento de Bioquímica, Genética e Inmunología, Facultad de Biología, Universidad de Vigo, Campus Universitario, 36310 Vigo, Spain.
authors.forename: Ana M
authors.initials: AM
authors.lastname: Rodríguez-Piñeiro
authors.forename: María Páez
authors.initials: MP
authors.lastname: de la Cadena
authors.forename: Angel
authors.initials: A
authors.lastname: López-Saco
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Rodríguez-Berrocal
mesh_terms: D014408:Biomarkers, Tumor / Q000097:blood* / Q000302:isolation & purification; D001798:Blood Proteins / Q000032:analysis* / Q000302:isolation & purification; D002846:Chromatography, Affinity; D051152:Clusterin / Q000097:blood*; D015179:Colorectal Neoplasms / Q000097:blood* / Q000175:diagnosis; D003208:Concanavalin A / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D005260:Female; D006031:Glycosylation; D006801:Humans; D008297:Male; D008875:Middle Aged; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase / Q000378:metabolism; D020033:Protein Isoforms; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D014408:Biomarkers, Tumor; D001798:Blood Proteins; C495242:CLU protein, human; D051152:Clusterin; D020033:Protein Isoforms; D003208:Concanavalin A; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase