Effects of filaggrin breakdown products on the growth and maturation of keratinocytes.

Filaggrin is degraded to amino acids in the stratum corneum. We tested the hypothesis that the resulting high concentrations of amino acids might be involved in the control of keratinocyte maturation. An amino acid mixture, with the composition of the filaggrin breakdown products, inhibited the growth of cultured human keratinocytes at 0.1 M. Inhibition of protein synthesis was progressive with time. After 24-h exposure, 50% inhibition occurred at 0.3-0.4 M amino acids. When the cultures were incubated with the amino acids for 7 days, the concentration giving half-inhibition was reduced to 0.2 M. No change was observed in the pattern of keratin synthesis, although synthesis of protein with Mr of 36,000 was disproportionately inhibited. It is concluded that filaggrin breakdown products are not involved in the control of keratinocyte differentiation.