The Effects of Immunosuppressants Rapamycin and Cyclosporin A on the Proliferation, Cell Cycle, and Cyclin Expression of Cultured Human Keratinocyte Cell Line HaCaT Cells

Choi, Jee Ho; Suh, Ho Seok; Chung, Sung Tae; Suh, Chi Woo; Park, Eun Mi; Sung, Kyung Jeh

Abstract

BACKGROUND: Rapamycin and cyclosporin A display an immunosuppressive effect by inhibiting the proliferation of T lymphocytes. Both immunosuppressants are effective in the treatment of psoriasis which is considered to be a T-cell mediated immunological disease. The inhibition of helper T-cells by immunosuppressants is considered to be a therapeutic mechanism on psoriasis. Recent studies have demonstrated that rapamycin and cyclosporin A can directly inhibit the proliferation of many non-hematopoietic cells other than T lymphocytes direct inhibitory effect of two immunosuppressants on keratinocyte proliferation may be another anti-psoriatic mechanism.
OBJECTIVE
We investigated the direct inhibitory effects of rapamycin and cyclosporin A on the proliferation of cultured human keratinocyte cell line HaCaT cells without T-cell involvement, and also compared the effects of the two immunosuppressants on the cell cycle and cyclic expression of HaCaT cells.
METHODS
The effects of rapamycin and cyclosporin A on the proliferation of cultured human keratinocytes were examined by using the MTS {3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxy phenyl)-2-(4-sulfophenyl)-2H-tetrazolium} method and we also performed a flow cytometric study to determine whether the two immunosuppressants could affect the cell cycle and cyclic expression of HaCaT cells.
RESULTS
The results are summarized as follows: 1. Rapamycin and cyclosporin A significantly inhibited the proliferation of cultured human normal keratinocytes and HaCaT cells in a dose-dependent fashion(p<0.05), and the degree of suppression was more evident in normal keratinocytes than in HaCaT cells. 2. Both immunosuppressants reduced the number of HaCaT cells in the S phase and the number of S phase cells was decreased early (Dl) by cyclosporin 4, while rapamycin reduced S phase cells more slowly. 3. The expression of cyclic D2 was significantly inhibited after 16 hours of rapamycin treatment and after 2 hours of cyclosporin A treatment(p<0.05). The expression of cyclic A was significantly suppressed after 2 hours of both immunosuppressant treatments(p<0.05).
CONCLUSION
We have shown that rapamycin and cyclosporin A can directly inhibit the proliferation of keratinocytes without T-cell involvement by blocking cell cycle progression in the G1 phase through reducing the number of S phase cells and inhibition of cyclic D2 expression.