Structural and functional consequences of c-N-Ras constitutively associated with intact mitochondria.

We demonstrate that both c-N-Ras and c-K(B)-Ras are constitutively associated with purified mitochondria. c-K(B)-Ras is associated with the mitochondrial outer membrane, and c-N-Ras is associated with both the outer membrane and inner mitochondrial compartments. The mitochondrial morphology is abnormal in both c-N-Ras negative and K-Ras negative cells.

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.

K-ras regulates the steady-state expression of matrix metalloproteinase 2 in fibroblasts.

Fibroblasts constitutively express matrix metalloproteinase 2 (MMP-2), which specifically cleaves type IV collagen, a major structural component of basement membranes. The level of MMP-2 expression was not altered by serum withdrawal, suggesting that MMP-2 expression is regulated by a series of steady-state conditions that impinge on the MMP-2 promoter. Expression of a dominant-negative Ras protein significantly inhibited MMP-2 transcription, thereby suggesting a role for steady-state Ras function in the regulation of MMP-2 expression.

Cellular N-Ras promotes cell survival by downregulation of Jun N-terminal protein kinase and p38.

Cellular N-Ras provides a steady-state antiapoptotic signal, at least partially through the regulation of phosphorylated Akt and Bad levels. Fibroblasts lacking c-N-Ras expression are highly sensitive to the induction of apoptosis by a variety of agents. Reduction of pBad and pAkt levels using a phosphatidylinositol 3-kinase inhibitor was not sufficient to sensitize the control cell population to the high level of apoptosis observed in the N-Ras knockout cell lines, suggesting that c-N-Ras provides at least one other antiapoptotic signal.