K-ras Asp12 mutant neither interacts with Raf, nor signals through Erk and is less tumorigenic than K-ras Val12

Abstract

Different mutant amino acids in the Ras proteins lead to distinct transforming capacities and different aggressiveness in human tumors. K-Ras Asp12 (K12D) is more prevalent in benign than in malignant human colorectal tumors, whereas K-Ras Val12 (K12V) associates with more advanced and metastatic carcinomas, higher recurrence and decreased survival. Here, we tested, in a nude mouse xenograft model, whether different human K-Ras oncogenes mutated at codon 12 to Val, Asp or Cys would confer NIH3T3 fibroblasts distinct oncogenic phenotypes. We studied tumor histology and growth, apoptotic and mitotic rates, activation of signal transduction pathways downstream of Ras and regulation of the cell cycle and apoptotic proteins in tumors derived from the implanted transformants. We found that the K12V oncogene induces a more aggressive tumorigenic phenotype than the K12D oncogene, whereas K12C does not induce tumors in this model. Thus, K12V mutant tumors proliferate about seven times faster, and have higher cellularity and mitotic rates than the K12D mutant tumors. A molecular analysis of the induced tumors shows that the K12V mutant protein interacts with Raf-1 and transduces signals mainly through the Erk pathway. Unexpectedly, in tumors induced by the K12D oncogene, the K-Ras mutant protein does not interact with Raf-1 nor activates the Erk canonical pathway. Instead, it transduces signals through the PI3K/Akt, JNK, p38 and FAK pathways. Finally, the higher growth rate of the K12V tumors associates with enhanced Rb phosphorylation, and PCNA and cyclin B upregulation, consistent with faster G1/S and G2/M transitions, without alteration of apoptotic regulation.

Selective expression ofKrasG12Din granulosa cells of the mouse ovary causes defects in follicle development and ovulation

“…In these cells, KRAS G12D interacts with RAF1 and initially leads to increased phosphorylation of ERK1/2. These results support our recent study showing that RAS-GTP in rat granulosa cells interacts with RAF1 directly (Wayne et al, 2007), as well as the studies of others who have shown that KRAS G12D selectively activates RAF1 and/or PI3K in a cell-and context-specific manner Cespedes et al, 2006;Gupta et al, 2007;Tuveson et al, 2004). However, KRAS G12D -mediated ERK1/2 phosphorylation is transient and becomes markedly reduced in the mutant granulosa cells in vivo and in culture.…”

“…Activation of small G-proteins within the RAS superfamily impact multiple downstream signaling cascades, including RAF1/MEK/ERK1/2 and PI3K/AKT/FOXO, in many tissues in a cell-and context-specific manner Cespedes et al, 2006;Gupta et al, 2007;Rocks et al, 2006). In response to growth-regulatory molecules, transient activation of RAS can stimulate controlled proliferation as well as differentiation of cells.…”

CRM1-dependent p53 nuclear accumulation in lung lesions of a bitransgenic mouse lung tumor model

“…Whether these are due to differences intrinsic to the host or a result of differences in the effects of different rAs mutations remains to be determined. several laboratories have demonstrated mutation-specific effects of different mutagenic rAs alleles on lung tumorigenesis in a variety of murine and cell culture models (26)(27)(28)(29)(30)(31)(32)(33)(34). on the other hand, the data of p53 and crM1 alterations after curcumin treatment in the present study cannot exclude the possible protective effects of curcumin at the molecular levels against lung tumor progression.…”

Stimulated PI3K-AKT Signaling Mediated through Ligand or Radiation-Induced EGFR Depends Indirectly, but not Directly, on Constitutive K-Ras Activity

“…Conflicting data exist with respect to the role of K-Ras in activating PI3K-AKT signaling. Some reports indicate that K-Ras activity does directly modulate AKT phosphorylation through stimulation of PI3K (60,62), whereas others have not found a direct stimulation of AKT activity by mutated and constitutively active K-Ras protein (35, 58, 63). …”