Membranous expression of secreted frizzled-related protein 4 predicts for good prognosis in localized prostate cancer and inhibits PC3 cellular proliferation in vitro.
OBJECTIVE
Activation of the Wnt-signaling pathway is implicated in aberrant cellular proliferation in a variety of cancers. Secreted frizzled-related protein 4 (sFRP4) is a secreted protein with putative inhibitory activity of the Wnt-signaling cascade through binding and sequestering Wnt ligands. Because sFRP4 mRNA is overexpressed in prostate cancers (PCs), the aim of this study was to define the pattern of sFRP4 protein expression in normal and malignant human prostate tissue and to determine whether changes in expression were associated with disease progression and prognosis, as well as to define the phenotype of sFRP4-overexpression in an in vitro model of PC.


METHODS
Polyclonal antibodies were raised against a COOH-terminal peptide of sFRP4, characterized and used to assess sFRP4 protein expression in benign prostate tissue and 229 patients with clinically localized PC (median follow-up 77 months, range 1-156). In vitro studies of the function of sFRP4 overexpression were performed using PC3 cells transfected with sFRP4.


RESULTS
Benign and malignant prostate tissue demonstrated cytoplasmic sFRP4 immunoreactivity, but there was a decrease in the expression of membranous sFRP4 in PCs compared with the hyperplastic lesions (P < 0.0001). Kaplan-Meier analysis revealed that patients whose PC expressed membranous sFRP4 in >20% of cells had improved relapse-free survival compared with those with </=20% membranous expression (P = 0.002). Moreover, membranous sFRP4 expression (P = 0.04) was an independent predictor of relapse when modeled with Gleason score (P = 0.006), pathological stage (P = 0.002), and pre-operative prostate-specific antigen levels (P = 0.004). In addition, in vitro studies demonstrated a decrease in the proliferation rate of PC3 cells transfected with sFRP4 when compared with the control PC3-empty vector cells (P < 0.0001). Decreased levels of phosphorylated glycogen synthase kinase 3beta in PC3-sFRP4 cells suggested that this phenotype is mediated by the "Wnt/beta-catenin" pathway.


CONCLUSIONS
These data suggest that sFRP4 expression may be prognostic for localized PC, potentially as a consequence of an inhibitory effect on PC cell proliferation.
Horvath
Lisa G
LG
Cancer Research Program, Garvan Institute of Medical Research, St. Vincent's Hospital, Darlinghurst, Sydney, New South Wales, Australia.
Henshall
Susan M
SM
Kench
James G
JG
Saunders
Darren N
DN
Lee
C-Soon
CS
Golovsky
David
D
Brenner
Phillip C
PC
O'Neill
Gordon F
GF
Kooner
Raji
R
Stricker
Phillip D
PD
Grygiel
John J
JJ
Sutherland
Robert L
RL
D000293:Adolescent; D000328:Adult; D000368:Aged; D002455:Cell Division; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism*; D015331:Cohort Studies; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D018572:Disease-Free Survival; D005822:Genetic Vectors; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D066298:In Vitro Techniques; D008297:Male; D008856:Microscopy, Fluorescence; D008875:Middle Aged; D015999:Multivariate Analysis; D020411:Oligonucleotide Array Sequence Analysis; D010455:Peptides / Q000737:chemistry; D010641:Phenotype; D010766:Phosphorylation; D011379:Prognosis; D016016:Proportional Hazards Models; D011467:Prostate / Q000378:metabolism / Q000473:pathology; D011471:Prostatic Neoplasms / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis* / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D012008:Recurrence; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D051153:Wnt Proteins; D000094742:Secreted Frizzled-Related Proteins
D018076:DNA, Complementary; D038362:Glycogen Synthase Kinase 3; D000071679:Glycogen Synthase Kinase 3 beta; D010455:Peptides; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D051153:Wnt Proteins; C118723:SFRP4 protein, human; D000094742:Secreted Frizzled-Related Proteins; C000605506:GSK3B protein, human