The expression of differentiation stages in a murine epidermal cell transformation model has been investigated as a basis for studies of chemically-induced differentiation.
Antibodies in sera of patients with the
autoimmune diseases bullous pemphigoid and
pemphigus vulgaris exhibit specific reactivity to
antigenic determinants of basal and spinous cells, respectively, in sections of mouse and human epidermis. In addition, spinous cells in epidermis are reactive with a mouse
monoclonal antibody to
desmoplakin, a desmosomal component immunologically distinct from
pemphigus. These
antibodies were used to identify and attempt to quantify keratinocyte subpopulations in culture based on differentiation stage. Epidermal cell lines were cultured under conditions which favour proliferation (0.02 to 0.04 mM extracellular Ca2+, i.e. low Ca2+ conditions) or differentiation (0.1 mM to 1.4 mM Ca2+), as previously shown using primary cultures of mouse keratinocytes. Two independently-derived normal keratinocyte lines demonstrated Ca2(+)-dependent reactivity with
pemphigoid and
pemphigus antiserum, like that which has been observed in primary cultures. Furthermore, a Ca2+ and time-dependent reactivity with the three
antisera was also observed in a
papilloma cell line (derived from one of the normal cell lines
after treatment in vitro with 7,12-dimethylbenz[alpha]
anthracene).
Papilloma cells cultured under conditions of low extracellular Ca2+ were comprised of three subpopulations: cells reactive only with
pemphigoid anti-serum, cells reactive only with
desmoplakin antibody. However, like the normal cell lines,
papilloma cells underwent a transition to predominantly a spinous cell population (i.e. reactive with
pemphigus and
desmoplakin antibody) in response to extracellular Ca2+. A slower loss of
pemphigoid antibody reactivity was noted in
papilloma cells, consistent with an abnormal regulation of differentiation. The attempt to characterize these dynamic transitions from basal to spinous cell subpopulations in culture was considered to be prerequisite for the use of the model to investigate differentiation-inducing agents in
carcinoma therapy.