CHANGES IN CELL-ADHESION AND CELL-PROLIFERATION ARE ASSOCIATED WITH EXPRESSION OF TISSUE NONSPECIFIC ALKALINE-PHOSPHATASE

Tissue non-specific alkaline phosphatase is a membrane-bound glycoprot ein enzyme which is characterized by its phosphohydrolytic, protein ph osphatase, and phosphotransferase activities. This enzyme is distribut ed virtually in all mammalian tissues, particularly during embryonic d evelopment. Its expression is stage-specific and can be demonstrated i n the developing embryo as early as the 2-cell stage. It has been sugg ested that tissue non-specific alkaline phosphatase might play a role in tissue formation. In the study reported here, a gene-transfer appro ach was employed to investigate possible roles for this enzyme by inse rting the cDNA for rat tissue non-specific alkaline phosphatase into C HO and LLC-PK1 cells. Permanently transfected cell-lines expressing va rying levels of alkaline phosphatase were estblished. The data showed that functional enzyme was expressed in the transfected cells. Cell sp reading and attachment were enhanced in transfected CHO cells expressi ng high levels of tissue non-specific alkaline phosphatase but not in the LLC-PK1 cells. Further, in CHO cells, proliferation was shown to b e inversely proportional to the level of the tissue non-specific alkal ine phosphatase expression. Homotypic cell association was demonstrate d in both alkaline phosphatase-positive and alkaline phosphatase-negat ive cells in both CHO and LLC-PK1 cell-lines. Taken together, these fi ndings suggest that in addition to a role in mineralization of bone, t issue nonspecific alkaline phosphatase might also play a role in other cell activities, including those related to differentiation, such as cell-cell or cell-substrate interaction and proliferation.