Lintula S, Stenman U H
Department of Clinical Chemistry, Helsinki University Central Hospital, Finland.
J Urol. 1997 May;157(5):1969-72.
Prostate-specific membrane antigen (PSM) and prostate-specific antigen (PSA) have been used as marker genes for detection of cancer cells in circulation of prostate cancer patients. However, PSA was recently found to be expressed in non-prostate cell lines and normal blood. To evaluate this phenomenon for PSM, we studied its mRNA expression in non-prostatic cells and cell lines, in blood from healthy donors and patients with prostate cancer.
We studied PSM expression by a highly sensitive reverse transcription-polymerase chain reaction (RT-PCR) in peripheral blood of 24 patients with cancer of the prostate (CAP) and 13 healthy young male and female donors, in four non-prostatic cell lines and in isolated blood cells. The identity of the RT-PCR product was confirmed by sequencing. Contamination of the samples with cDNA or prostatic RNA was rigorously excluded by subjecting each sample to PCR reaction without RT-enzyme and by RT-PCR with PSA primers, respectively.
We found PSM mRNA expression in blood from 18 of 24 CAP patients and 12 of 13 healthy donors and in the leukocyte fraction of normal blood cells. PSM expression could not be detected in erythroblasts, platelets, K-562, U-937, HL-60 or Jurkat cell lines.
Our results indicate that sensitive nested RT-PCR method detects PSM mRNA in the leukocyte fraction of normal blood. This "background" expression is probably caused by a leaky promoter of PSM. We conclude that it is necessary to develop quantitative RT-PCR assays to differentiate PSM mRNA expression derived from circulating cancer cells from background expression in blood cells.
前列腺特异性膜抗原（PSM）和前列腺特异性抗原（PSA）已被用作检测前列腺癌患者循环中癌细胞的标志物基因。然而，最近发现PSA在非前列腺细胞系和正常血液中表达。为了评估PSM的这种现象，我们研究了其在非前列腺细胞和细胞系、健康供体和前列腺癌患者血液中的mRNA表达。
我们采用高灵敏度逆转录聚合酶链反应（RT-PCR）研究了24例前列腺癌（CAP）患者和13名健康年轻男性及女性供体的外周血、四种非前列腺细胞系以及分离的血细胞中的PSM表达。通过测序确认RT-PCR产物的同一性。分别通过对每个样本进行无RT酶的PCR反应以及用PSA引物进行RT-PCR，严格排除样本被cDNA或前列腺RNA污染的情况。
我们在24例CAP患者中的18例、13名健康供体中的12例以及正常血细胞的白细胞部分中发现了PSM mRNA表达。在成红细胞、血小板、K-562、U-937、HL-60或Jurkat细胞系中未检测到PSM表达。
我们的结果表明，灵敏的巢式RT-PCR方法可检测到正常血液白细胞部分中的PSM mRNA。这种“背景”表达可能是由PSM的渗漏启动子引起的。我们得出结论，有必要开发定量RT-PCR检测方法，以区分循环癌细胞来源的PSM mRNA表达与血细胞中的背景表达。
