Growth factor-dependent AKT activation and cell migration requires the function of c-K(B)-Ras versus other cellular Ras isoforms

K-Ras-negative fibroblasts are defective in their steady- state expression of MMP-2. This occurs through c- K( B)- Ras dependent regulation of basal levels of AKT activity. In this report, we have extended those studies to demonstrate that in the absence of K- Ras expression, PDGF- BB fails to induce significant AKT activation, although this was not the case in N- Ras- negative cells. This phenotype was directly linked to PDGF- dependent cell migration. All of the independently immortalized K-Ras-negative cells failed to migrate upon the addition of PDGF. Only ectopic expression of c- K( B)- Ras, not c- K( A)- Ras nor oncogenic N- Ras, could restore both PDGF- dependentAKTactivation and cell migration. Since most Ras binding partners can interact with all Ras isoforms, the specificity of PDGF- dependent activation of AKT and enhanced cell migration suggests that these outcomes are likely to be regulated through a c- K( B)- Ras- specific binding partner. Others have published that of the four Ras isoforms, only K( B)- Ras can form a stable complex with calmodulin ( CaM). Along those lines, we provide evidence that 1) PDGF addition results in increased levels of a complex between c- K( B)Ras and CaM and 2) the biological outcomes that are strictly dependent on c- K( B)- Ras ( AKT activation and cell migration) are blocked by CaM antagonists. The PDGF- dependent activation of ERK is unaffected by the absence of K( B)- Ras and presence of CaM antagonists. This is the first example of a linkage between a specific biological outcome, cell migration, and the activity of a single Ras isoform, c- K( B)- Ras.