Polyamine-dependent post-translational modification of proteins in differentiating mouse epidermal cells

In order to get a better understanding of the role played by polyamines in calcium-induced epidermal cell differentiation, the time course of their metabolism was investigated. Results demonstrate that differentiating epidermal cells are characterized by time-dependent changes in polyamine concentrations. An early polyamine catabolic phase, characterized by increased total putrescine concentration and drastic reduction of both spermidine and spermine levels, is followed by active spermidine biosynthesis. The differences in putrescine and, in particular, spermidine metabolism are reflected in a time-dependent modulation of nd polyamine derivatives. In fact, upon addition of calcium to the culture medium, hypusine Nε-(4-amino-2-hydroxybutyllysine) is rapidly reduced to undetectable levels. The very low hypusine level is paralleled by an increase in γ-glutamyl putrescine derivatives and followed by a large increase in γ-glutamyl spermidine derivatives; in addition, there is a remarkable concomitant biosynthesis of transglutaminase-catalyzed mono and bis γ-glutamyl spermidine derivatives and ε(γ-glutamyl)lysine cross-links. The effect of TPA and RA on hypusine formation is also reported.