Expression of prostate-specific membrane antigen (PSMA), increases cell folate uptake and proliferation and suggests a novel role for PSMA in the uptake of the non-polyglutamated folate, folic acid.
BACKGROUND
Prostate specific membrane antigen (PSMA) is a unique folate hydrolase that is significantly upregulated in prostate cancer. In a mouse model, PSMA is able to facilitate prostate carcinogenesis, however, little is known about the mechanism by which this occurs. As PSMA is able to hydrolyze polyglutamated folates, and cancer cells proliferate directly in response to available folate, we examined if expression of human PSMA in PC-3 cells confers a proliferative advantage in a microenvironment with physiologically relevant folate levels.


METHODS
Proliferation and folate uptake of PC-3 prostate cancer cells expressing human-PSMA or vector alone was assessed in media containing low (LF; 1 nM), physiological (PF; 25 nM), or high (HF; 2.3 microM) folate with or without poly-gamma-glutamated folate (Pte-Glu(5)) or folic acid, and a specific inhibitor of the enzymatic activity of PSMA, 2-(phosphonomethyl)-pentanedioic acid (2-PMPA). Folic acid was tested for its ability to competitively inhibit the enzymatic activity of PSMA.


RESULTS
Proliferation of PC-3-PSMA cells grown in the presence of poly-gamma-glutamated folate, was significantly higher than that of PC-3-vector cells, an advantage which was attenuated by the addition of 2-PMPA. In media containing physiologic levels of folate, PSMA expression increased folic acid uptake approximately twofold over non-expressing cells. Folic acid was able to inhibit hydrolysis of N-[4-(phenylazo)-benzoyl]-glutamyl-gamma-glutamic acid (PABGgG) by PSMA in a competitive inhibition assay.


CONCLUSIONS
These findings implicate PSMA in both the metabolism of polyglutamated folates, and in the uptake of monoglutamated folates. Under conditions of LF or PF levels, PSMA gives cells expressing it a proliferative advantage.
Yao
Veronica
V
Department of Urology, University of Pittsburgh, Pittsburgh, PA 15232, USA.
Berkman
Clifford E
CE
Choi
Joseph K
JK
O'Keefe
Denise S
DS
Bacich
Dean J
DJ
D000954:Antigens, Surface / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004151:Dipeptides / Q000378:metabolism; D005492:Folic Acid / Q000493:pharmacokinetics* / Q000494:pharmacology; D043425:Glutamate Carboxypeptidase II / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis / Q000187:drug effects; D008297:Male; D009943:Organophosphorus Compounds / Q000494:pharmacology; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000473:pathology*; D011624:Pteroylpolyglutamic Acids / Q000494:pharmacology
C402107:2-(phosphonomethyl)pentanedioic acid; D000954:Antigens, Surface; D004151:Dipeptides; C547476:N-(4-(phenylazo)benzoyl)glutamyl-gamma-glutamic acid; D009943:Organophosphorus Compounds; D011624:Pteroylpolyglutamic Acids; D005492:Folic Acid; C473848:FOLH1 protein, human; D043425:Glutamate Carboxypeptidase II