Epidermal cell‐shape regulation and subpopulation kinetics during butyrate‐induced terminal maturation of normal and SV40‐transformed human keratinocytes: Epithelial models of differentiation therapy

Recent data indicate that malignant human epidermal cells may be appropriate targets for sodium butyrate (NaB)-mediated differentiation therapy. The response of pre- and post-crisis populations of SV40-transformed human keratinocytes (SVKs) to this differentiation-inducing agent was assessed, therefore, within the framework of NaB-directed normal human keratinocyte (NHK) maturation. NaB augmented cornified envelope (CE) production in NHK and pre-crisis SVK cultures; the time-course and efficiency of induced maturation were similar in the 2 cell systems. In NHKs, the percentage of amplifying ("B" substate) cells decreased with time in NaB correlating with increases in both "C" stage keratinocytes and CEs. The latter formed over one or 2 layers of nucleated basal-like cells. Inductions were accompanied by immediate cell cycle blocks (in both the G1 and G2/M phases), reorganization within the actin cytoskeleton, and transient early increases in cellular actin content. Increased NHK and pre-crisis SVK cytoskeletal-associated actin reached a maximum approximately 48 hr after NaB addition and preceded development of CEs. The CE precursors, thus, probably reside in the "B" substate. Post-crisis SVKs, in contrast, were refractive to NaB-induced terminal maturation or cell-cycle perturbation, failed to initiate actin filament rearrangements, and retained a basal cell-like phenotype. Stable transformation of human SVKs in post-crisis phase, therefore, appears to be associated with loss of maturation "competence" within the "B" keratinocyte subpopulation.