The
erythropoietin-producing hepatocellular (EPH)A2
receptor, tyrosine kinase, is overexpressed and phosphorylated in several types of human
tumors and has been associated with malignant transformation. A recent report, however, indicated that stimulation of the
EPHA2 receptor ligand, ephrinA1 (
EFNA1), inhibits the growth of EPHA2-expressing
breast cancer. The authors examined the expression of EPHA2 and
EFNA1 using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) in four
gastric cancer cell lines and 49 primary
gastric cancer samples, as well as in normal gastric tissue. EPHA2 was more highly expressed in
tumor tissue than in normal tissue in 27 cases (55%).
EFNA1 was overexpressed in
tumor tissue in 28 cases (57%). No significant correlation was detected between the expression levels and histologic features such as
tumor size, age, vessel invasion, or lymph node involvement. However, EPHA2 overexpression was more prominent in macroscopic type 3 and 4
tumors than in type 1 or 2 advanced
gastric cancer. The authors observed EPHA2 expression in three of the four
gastric cancer cell lines (AGS, KATO3, and MKN74) that were examined. In one cell line, TMK1, EPHA2 expression was barely detectable using northern blotting, RT-PCR, and western blotting. In contrast,
EFNA1 was detected in all cell lines. In the
gastric cancer cell lines that endogenously expressed EPHA2, stimulation with ephrinA1-Fc led to decreased
EPHA2 protein expression and increased EPHA2 phosphorylation. Finally, the growth of EPHA2-expressing cells was inhibited by repetitive stimulation with soluble ephrinA1-Fc. Taken together, these findings suggest that EPHA2 and
EFNA1 expression may influence the behavior of human
gastric cancer.