| Abstrakt: |
It is well established that micrordament disintegration by cytochalasin D (CD) as well as latrunculin (LAT)-A and LAT B causes an inhibition of S phase entry of various nontransformed cell lines. Our experiments extended these observations to human embryonal diploid fibroblasts (Wi-38). To investigate the question whether this stop of DNA synthesis is due to a decline of the synthesis of proteins that are necessary for G1, progression and S phase entry, we examined the expression of two proto-oncogenes (c-fos, c-jun) and three cyclins (D1, E, A) after alter ing the microfilament system. Disintegration of micrordaments by CD, LAT-A, or LAT-B of asynchronously growing fibroblasts caused a strong dose-dependent and time-dependent inhibition of total protein synthesis. Expression of c-jun, cyclins D1, E, and A decreased by about the same percentage as total protein synthesis. The strong induction of total protein synthesis after reactivating serum-starved fibroblasts by adding fetal calf serum was suppressed, when CD or LAT-A were added to the culture medium during this reactivation process. While expression of cyclin E as well as cyclin A decreased by about the same percentage as total protein synthesis, cyclin D1 was more suppressed after micrordament disintegration. After reactivating growtharrested Wi-38 fibroblasts, cultured in suspension for 12 h, by transferring them to a rigid substratum they could adhere to, total protein synthesis was strongly induced. Again alteration of microfilaments by CD suppressed that increase. The expression of cyclin D1 was slightly more suppressed than total protein synthesis after addition of CD during that reactivation process. |
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