Uniform response of c-raf expression to differentiation induction and inhibition of proliferation in a rat rhabdomyosarcoma cell line.
The clonal rat rhabdomyosarcoma cell line BA-HAN-1C is composed of proliferating mononuclear cells, some of which spontaneously fuse to terminally differentiated myotube-like giant cells. Both the induction of differentiation by retinoic acid (RA) and by sodium butyrate (NaBut), as well as the inhibition of proliferation by fetal calf serum (FCS)-depleted medium uniformly resulted in the same effects. There was a significant (p less than 0.001) inhibition of proliferation and induction of cellular differentiation, as evidenced by a significant (p less than 0.05) increase in creatine kinase activity. Furthermore, after exposure to RA-supplemented or FCS-depleted medium, a significant (p less than 0.001) increase in the number of myotube-like giant cells was observed. These effects were preceded by a uniform enhancement of c-raf mRNA expression, which became evident 6 h after exposure to RA, NaBut and FCS-depleted media. C-raf mRNA expression persisted at an elevated level throughout the observation period of 5 days after exposure to RA or NaBut, whereas the increased expression of c-raf mRNA observed after FCS-depletion declined near to the basal level after only 24 h. Furthermore, a transient c-fos mRNA expression was observed 15 and 30 min after exposure to RA-supplemented and FCS-depleted medium but not after exposure to NaBut. The present results suggest a possible role of c-raf in the regulation of differentiation and proliferation of this cell line. Since all our experiments with RA, NaBut and FCS-depletion resulted in an early peak of c-raf mRNA expression, it is suggested that this early peak may be sufficient to trigger events crucial for differentiation and proliferation of BA-HAN-1C tumor cells.
Ramp
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Department of Pathology, University of Mainz, Federal Republic of Germany.
Gerharz
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Doehmer
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J
Oster
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O
Gabbert
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HE
D000818:Animals; D015152:Blotting, Northern; D002087:Butyrates / Q000494:pharmacology; D020148:Butyric Acid; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002459:Cell Fusion / Q000187:drug effects; D003402:Creatine Kinase / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D008854:Microscopy, Electron; D011519:Proto-Oncogenes / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis; D012334:RNA, Neoplasm / Q000096:biosynthesis; D051381:Rats; D012208:Rhabdomyosarcoma / Q000235:genetics* / Q000473:pathology / Q000648:ultrastructure; D014212:Tretinoin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D002087:Butyrates; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D020148:Butyric Acid; D014212:Tretinoin; D003402:Creatine Kinase