DNA-SYNTHESIS AND FOS AND JUN PROTEIN EXPRESSION IN MITOTIC AND POSTMITOTIC WI-38 FIBROBLASTS IN-VITRO

Normal human embryonic lung fibroblasts WI-38 differentiate spontaneou sly along the cell lineage mitotic fibroblasts (MF) I, II, and III and postmitotic fibroblasts (PMF) IV, V, VI, and VII in the fibroblast st em cell system in vitro, when appropriate methods are applied. The mit otic fibroblasts can be induced to shift to postmitotic fibroblasts by two treatments with mitomycin C (2X MMC) in a short period of time co mpared to spontaneous development. Mitotic and postmitotic fibroblast cell types have specific morphological and biochemical properties, e.g ., [S-35]methionine polypeptide markers in 2D PAGE. Spontaneously aris en and experimentally induced (2X MMC) PMF have the same morphological and biochemical characteristics. Mitotic fibroblasts have 2n DNA and undergo DNA synthesis for reduplication. Postmitotic cells undergo, on average, two rounds of DNA synthesis for endoreduplication (polyploid ization). Spontaneously arisen and experimentally induced postmitotic populations are composed of postmitotic fibroblasts PMF IV, V, and VI with 2n, 4n, and 8n DNA. DNA synthesis of mitotic and postmitotic WI-3 8 cell populations may be regulated by the expression of Fos and Jun p roteins. The Fos level of MFs was higher by a factor of 15-24 and the Jun level of MFs by a factor of 4.2-6.3 than those of spontaneously ar isen PMFs. In 2X MMC-induced PMFs, the Fos level was about 4.4-7.5 tim es higher and the Jun level 1.7-3.3 times higher than that of spontane ously arisen PMFs. The down-regulation of these two parameters is a no rmal event in the development of mitotic to postmitotic WI-38 fibrobla sts in the fibroblast stem cell system and is not related to cellular aging. (C) 1994 Academic Press, Inc.