Multiple effects of glucocorticoids and hyperosmolality on isoenzyme expression in cultured KB cells

The KB cell line, though indicted as a HeLa-contamined line, is a useful in vitro model for the study of the regulation of isoenzyme expression. KB cells produced three isoenzymic forms of alkaline phosphatase. When KB cells were grown in the presence of prednisolone and/or in hyperosmolar medium, the total enzyme activity was reduced. This change in activity was coupled with specific alterations in the proportion of each isoenzyme. The slow-moving form (identified biochemically and immunologically as the heat-stable, placental, Regan isoenzyme) was substantially increased by the steroid hormone and/or hyperosmolality. The fast-moving form [identified as the intestine-like, amnion (FL) isoenzyme] was strikingly diminished by either treatment. The intermediate form (tentatively referred to as "hybrid," inasmuch as it shared properties of the other two isoenzymes) was decreased only when KB cells were grown in hyperosmolar medium containing prednisolone. These results corroborated the notion that these stimuli cause the induction of increased levels of the heat-stable Regan alkaline phosphatase only. They also point out the necessity of performing isoenzyme analysis when one is investigating the regulation of this enzyme.