Vol. 58, Issue 5, 1057-1066, November 2000

Regulation of Cell Proliferation, Gene Expression, Production of Cytokines, and Cell Cycle Progression in Primary Human T Lymphocytes by Piperlactam S Isolated from Piper kadsura

Yuh-Chi Kuo, Nai-Shian Yang, Cheng-Jen Chou, Lie-Chwen Lin, and Wei-Jern Tsai

National Research Institute of Chinese Medicine (Y.-C.K., C.-J.C., L.-C.L., W.-J.T.), Institute of Biology (Y.-C.K., N.-S.Y.), Fu-Jen University, Taipei, Taiwan, Republic of China

Effects of piperlactam S (C₁₇H₁₃NO₄; mol. wt. 295) isolated from Piper kadsura on phytohemagglutinin (PHA) stimulated cell proliferation were studied in primary culture of human T cells. The results showed that piperlactam S suppressed T cell proliferation at about 0 to 12 h after stimulation with PHA. Synthesis of total cellular proteins and RNA in activated cell cultures was also suppressed. The inhibitory action of piperlactam S was not through direct cytotoxicity. Cell cycle analysis indicated that piperlactam S arrested the cell cycle progression of activated T cells from the G₁ transition to the S phase. In an attempt to further localize the point in the cell cycle at which arrest occurred, a set of key regulatory events leading to the G₁/S boundary, including gene expression of cytokines and c-Fos protein synthesis, was examined. Piperlactam S suppressed, in activated T lymphocytes, the production and mRNA expression of cytokines such as interleukin-2 (IL-2), IL-4, and interferon- in a dose-dependent manner. In addition, Western blot analysis indicated that c-Fos protein expressed in activated T lymphocytes was decreased by piperlactam S. Results of kinetic study indicated that inhibitory effects of piperlactam S on IL-2 mRNA expressed in T cells might be related to blocking c-Fos protein synthesis. Thus, the suppressant effects of piperlactam S on proliferation of T cells activated by PHA seemed to be mediated, at least in part, through inhibition of early transcripts of T cells, especially those of important cytokines, IL-2, IL-4, and arresting cell cycle progression in the cells.