Increase of Specific Activity, Electrophoretic Type-Transition and Gene Expression of Alkaline Phosphatase during...

In F9 mouse embryonal carcinoma cells, the specific activity of alkaline phosphatase (ALPase) increases markedly during endodermal differentiation induced by retinoic acid (RA) treatment, but the specific 5'-nucleotidase activity of a similar ecto-phosphatase increases only temporally. Polyacrylamide disc gel electrophoresis showed that F9 cells express only type I ALPase, whereas RA-treated F9 cells express both type I and type II ALPases. Type II ALPase is a minor form on day 1 of RA treatment and becomes the major form on day 4. RA-treated F9 cells also expressed mRNAs for endoderm cell-specific molecules, such as α-fetoprotein, type IV collagen and laminin B1 chain, but their expression of M2 -type pyruvate kinase mRNA of an essential non-ectoenzyme remains constant throughout endodermal differentiation. Northern blot analyses showed that type I ALPase was encoded by a liver (L)/bone (B)/kidney (K)/placenta (P)-type mRNA. The expression of L/B/K/P-type ALPase mRNA was induced in RA-treated F9 cells, but its increase preceded that of ALPase specific activity. These results suggest that the expression of L/B/K-type ALPase is regulated at the translational and/or post-translational level. The differential inhibition of ALPases by L-phenylalanine/L-homoarginine and the thermal inactivation (56°C for 60 min) inferred that type II ALPase was also an L/B/K-type isozyme.