MODULATION OF INVOLUCRIN AND ENVELOPE COMPETENCE IN HUMAN KERATINOCYTES BY HYDROCORTISONE, RETINYL ACETATE, AND GROWTH ARREST

Abstract

Involucrin accumulation and ionophore-assisted envelope formation, markers of keratinocyte differentiation, were highly dependent on culture conditions in the malignant epidermal keratinocyte line, SCC-13, derived from a human squamous cell carcinoma. In confluent cultures, .apprx. 1/2 of the cells were competent to form envelopes when grown in medium without hydrocortisone or retinyl acetate supplementation. Addition of hydrocortisone to the medium during growth resulted in up to 90% competence; addition of retinyl acetate instead resulted in as low as 10% competence. Hydrocortisone partially antagonized the effect of retinyl acetate when both agents were added together. Involucrin levels, measured by radioimmunoassay, were modulated essentially in parallel with envelope competence under the various conditions tested. When the cells were grown in medium supplemented with hydrocortisone, the levels shortly after confluence were over 50-fold higher than in sparse cultures. Regardless of hydrocortisone or retinyl acetate addition, < 1% of the cells were competent in sparse cultures of growing cells, but up to 90% exhibited this property after growth arrest in serum-free medium containing hydrocortisone. High levels of competence were correlated with cessation of cell division but not with loss of colony-forming efficiency; under optimal conditions, 2/3 of the cells were capable of envelope formation and colony initiation. Normal human epidermal cells showed a 4- to 5-fold increase in envelope competence from sparse to confluent culture, but were insensitive to the suppressive effect of retinyl acetate. Some potential differentiated character of malignant keratinocytes may be suppressed in vivo by physiological agents such as vitamin A.