Profile of placental alkaline phosphatase expression in human malignancies: Effect of tumour cell activation on alkaline phosphatase expression

Cellular alkaline phosphatases (ALP) are increasingly recognised as importa nt markers for monitoring tumour cell behaviour in human malignancies. Colo rimetric, flow-cytometric, and immunocytochemical assays were employed to a ssess the influence of activation on expression of cellular ALP in human tu mour cell lines. The results showed the following: (1) Testis tumour biopsi es (16/16) unlike bladder (0/14) and head and neck (0/16) tumours showed po sitive staining for ALP, particularly the placental type, i.e. PLAP, althou gh this was not always present on all the cells of non-seminoma biopsies. ( 2) The intensity of ALP expression differed widely in tumour cell lines. Ba sed on biochemical analysis, the profile of ALP fell into two categories: ( a) low expressing (MW 70 kD, placental type ALP) like Hep2 and KB lines, an d (b) those expressing both low and high molecular (MW 95 kD) bands like te stis lines Tera II and Ep2102. In ail cases treatment of tumour cell lysate s with heat prior to biochemical analysis showed the disappearance of the h igher and sharpening of the lower molecular weight ALP band. (3) Exposure o f tumour cells to epidermal growth factor (EGF) expressing EGF receptor led to a decreased ALP expression by as much as 54% as assessed by biochemical or flow-cytometric techniques. These data demonstrated that testis tumour tissues and cell lines expressed ALP which were different from others. The data also showed that exposure of tumour cell lines expressing EGFr to EGF resulted in suppression of ALP expression. These observations are consisten t with the notion that EGFr and PLAP expression may be taken as a marker of proliferation and differentiation in human malignancies, respectively. Cop yright (C) 2000 S. Karger AG, Basel.