Transforming growth factor-β1 acts cooperatively with sodium n-butyrate to induce differentiation of normal human keratinocytes

Abstract

Growth factors with established biological activity toward cultured normal human epidermal keratinocytes (NHEKs) (e.g., transforming growth factor-β, TGF-β; retinoic acid, RA) initiate programmed changes in cellular maturation which differ with regard to the specific differentiation pathway (normal or abnormal) analyzed. Sodium butyrate (NaB) initiates one form of epidermal differentiation leading to enhanced cornified envelope (CE) formation which involves abrogation of the normally inhibitory effect of RA on NHEK maturation. NaB also induces TGF-β mRNA in the maturing suprabasal compartment, suggesting that TGF-β may play a role in NaB-initiated NHEK differentiation. Treatment with TGF-β1 alone, however, only marginally increased (by twofold) the number of detergent-resistant CEs compared to control NHEKs and did not alter the prevalence of fully mature enucleated CEs. TGF-β1 was quite effective in inducing significant levels of CE expression when used simultaneously with suboptimal concentrations of NaB. The cooperative action of suboptimal NaB and TGF-β1 generated numbers of CEs which, in fact, exceeded the incidence of mature CEs formed in response to optimal levels of NaB alone. Neutralizing antibodies to TGF-β, moreover, effectively reduced the incidence of CE formation in cultures treated with optimal NaB concentrations, further implicating endogenous TGF-β activity in the NaB-initiated NHEK differentiation model. It is suggested, therefore, that within the NaB-induced pathway of NHEK differentiation, TGF-β can positively modulate expression of the differentiated phenotype but alone is insufficient for generation of mature CEs.