Activation of cellular p21 ras by myristoylation

Abstract

p21ras is palmitoylated on a cysteine residue near the C-terminus. Changing Cys-186 to Ser in oncogenic forms produces a non-palmitoylated protein that fails to associate with membranes and does not transform NIH 3T3 cells. To examine whether palmitate acts in a general way to increase ras protein hydrophobicity, or is involved in more specific interactions between p21ras and membranes, we constructed genes that encode non-palmitoylated ras proteins containing myristic acid at their N-termini. Myristoylated, activated ras, without palmitate (61Leu/186Ser) exhibited both efficient membrane association and full transforming activity. Unexpectedly, we found that myristoylated forms of normal cellular ras were also potently transforming. Myristoylated c-ras retained the high GTP binding and GTPase characteristic of the cellular protein and, moreover, bound predominantly GDP in vivo. This implied that it continued to interact with GAP (GTPase-activating protein). While the membrane binding induced by myristate permitted transformation, only palmitate produced a normal (non-transforming) association of ras with membranes and must therefore regulate ras function by some unique property that myristate does not mimic. Myristoylation thus represents a novel mechanism by which the ras proto-oncogene protein can become transforming.

Inherited predispositions and hyperactive Ras in myeloid leukemogenesis

“…The germline PTPN11 mutations found in NS constitutively activate SHP‐2 phosphatase activity by destabilizing auto‐inhibitory interactions between the N‐SH2 and PTP domains of the molecule. Even before the discovery of PTPN11 mutations in NS, the crystal structure of SHP‐2 suggested 35 that Asp61 and Glu76 were critical inhibitory contact points between these domains, and studies of Glu76 → Ala mutants in a Xenopus animal cap assay demonstrated a phenotype consistent with hyperactivation of the Ras/ERK pathway 36. The association between NS and JMML and the key roles of SHP‐2 in Ras signaling and hematopoiesis suggested that PTPN11 might be mutated in patients with JMML.…”