Serum levels of an isoform of apolipoprotein A-II as a potential marker for prostate cancer.
OBJECTIVE
We recently showed that protein expression profiling of serum using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF MS) has potential as a diagnostic approach for detection of prostate cancer. As a parallel effort, we have been pursuing the identification of the protein(s) comprising the individual discriminatory "peaks" and evaluating their utility as potential biomarkers for prostate disease.


METHODS
We employed liquid chromatography, gel electrophoresis and tandem mass spectroscopy to isolate and identify a protein that correlates with observed SELDI-TOF MS mass/charge (m/z) values. Immunodepletion, immunoassay, and Western analysis were used to verify that the identified protein generated the observed SELDI peak. Subsequent immunohistochemistry was used to examine the expression of the proteins in prostate tumors.


RESULTS
An 8,946 m/z SELDI-TOF MS peak was found to retain discriminatory value in each of two separate data sets with an increased expression in the diseased state. Sequence identification by liquid chromatography-MS/MS and subsequent immunoassays verified that an isoform of apolipoprotein A-II (ApoA-II) is the observed 8,946 m/z SELDI peak. Immunohistochemistry revealed that ApoA-II is overexpressed in prostate tumors. SELDI-based immunoassay revealed that an 8.9-kDa isoform of ApoA-II is specifically overexpressed in serum from individuals with prostate cancer. ApoA-II was also overexpressed in the serum of individuals with prostate cancer who have normal prostate-specific antigen (0-4.0 ng/mL).


CONCLUSIONS
We have identified an isoform of ApoA-II giving rise to an 8.9K m/z SELDI "peak" that is specifically overexpressed in prostate disease. The ability of ApoA-II to detect disease in patients with normal prostate-specific antigen suggests potential utility of the marker in identifying indolent disease.
Malik
Gunjan
G
Department of Microbiology and Molecular Cell Biology, Virginia Prostate Center, Eastern Virginia Medical School, 700 West Olney Road, Norfolk, VA 23501, USA.
Ward
Michael D
MD
Gupta
Saurabh K
SK
Trosset
Michael W
MW
Grizzle
William E
WE
Adam
Bao-Ling
BL
Diaz
Jose I
JI
Semmes
O John
OJ
D016633:Apolipoprotein A-II / Q000032:analysis / Q000097:blood* / Q000302:isolation & purification; D014408:Biomarkers, Tumor / Q000032:analysis / Q000097:blood*; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D011467:Prostate / Q000737:chemistry / Q000473:pathology; D017430:Prostate-Specific Antigen / Q000097:blood; D019048:Prostatic Intraepithelial Neoplasia / Q000097:blood / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000097:blood* / Q000175:diagnosis / Q000378:metabolism; D020033:Protein Isoforms / Q000032:analysis / Q000097:blood / Q000302:isolation & purification; D012680:Sensitivity and Specificity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D016633:Apolipoprotein A-II; D014408:Biomarkers, Tumor; D020033:Protein Isoforms; D017430:Prostate-Specific Antigen