p21Ras downstream effectors are increased in activity or expression in mouse liver tumors but do not differ between ras-mutated and ras-wild-type lesions.
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| Abstract |
Mouse liver tumors frequently harbor activating ras gene mutations. Downstream effector molecules of p21Ras include Raf-1 kinase which mediates external signals via kinase signaling pathways to nuclear transcription factors including c-Fos and c-Jun. Mouse liver tumors with differing ras-mutational status were analyzed for alterations in Ras/Raf-1 signal transduction. Tumors were characterized with respect to the presence of base substitutions in the 3 known hot-spot positions at codons 12, 13, and 61 of Ha-ras, Ki-ras, and N-ras. Ha-ras codon 61 or Ki-ras codon 13 mutations, but no N-ras mutations, were detected in 23 out of 33 tumors analyzed, while no ras-mutations were found in 10 of the tumors. There was no significant difference in the expression of p21RaS proteins between ras-mutated tumors and tumors without detectable ras mutations. To allow for determination of Raf-1 kinase activity in tumors, a sensitive and specific assay was developed for measurements with tissue homogenates. Raf-1 kinase activity was increased about four-fold in liver tumors as compared with normal liver tissue. No significant differences in kinase activity, however, were evident between ras-mutated and ras-wild-type tumors. The same was true with respect to the levels of c-fos and c-jun mRNAs. Moreover, there were no significant differences in cell division (5-bromo-2'-deoxyuridine-labeling indices) of hepatocytes from ras-mutated and ras-wild-type tumors. The similar degree of constitutive activation of the Ras/Raf-1 signaling pathway in liver tumors, with and without detectable ras mutations, suggests that other molecules within the signaling pathway may substitute for ras-mutations during oncogenic conversion of ras-wild-type hepatocytes.
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| Authors | A Kalkuhl, J Troppmair, A Buchmann, S Stinchcombe, C L Buenemann, U R Rapp, K Kaestner, M Schwarz |
| Journal | Hepatology (Baltimore, Md.) (Hepatology) Vol. 27 Issue 4 Pg. 1081-8 (Apr 1998) ISSN: 0270-9139 [Print] United States |
| PMID | 9537449 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't) |
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