Relationship between gastric carcinoma and intestinal metaplasia from the aspect of the expression of placental alkaline phosphatase messenger RNA

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Intestinal metaplasia of the gastric mucosa has been suggested to represent a precancerous state. However, how it is related to carcinogenesis remains controversial. We developed specific monoclonal antibodies (MAbs) against placental alkaline phosphatase (PLAP). Imnninohistochemical study with the specific MAb showed that expression of PLAP was apt to occur in more highly differentiated gastric carcinoma, and was highly specific for carcinoma. Therefore, we attempted to elucidate the expression of PLAP MRNA with the RT-PCR method in various benign and malignant gastric diseases. Each RNA was extracted from KATO-III cells (gastric cancer), intestinal mucosal tissue, BeWo cells (chorionic carcinoma), and placental tissue. Primer pairs were selected as synthetic 25 oligonucleotides which detected the PLAP cDNA region (2l4 bp) which was widely different from intestinal alkaline phosphatase cDNA (IAP cDNA). The results of RT-PCR showed that 214 bp band appeared in samples from KATO-III cells, BeWo cells, intestinal mucosal tissue as well as placental tissue. On the other hand, PLAP cDNA is very similar to IAP cDNA. These results indicated that primer pairs probably reacted with both PLAP mRNA and IAP mRNA. Futhermore, the amplified PLAPcDNA region in the sample of KATO- III was recognized as a slightly small weight band in electrophoresis and therefore several base pairs of the amplified region might be deleted in KATO- III cells. To clarify these points, further investigations continue.