Activation Of Wild-Type Hras Suppresses The Earliest Stages Of Pancreatic Cancer.

BACKGROUND

The RAS family of small GTPases is comprised of HRAS, NRAS, and KRAS. KRAS is invariably oncogenically mutated in pancreatic cancers, which is known to induce this disease. Beyond oncogenic KRAS, redox-dependent reactions have been implicated in the activation of the remaining wild-type RAS proteins in pancreatic cancer cell lines. These results suggest a possible involvement of wild-type RAS proteins in pancreatic cancer.

AIMS

To evaluate the impact of genetically suppressing wild-type RAS expression on pancreatic cancer.

METHODS

Hras homozygous null mice (Hras) were crossed into a Pdx-Cre; LSL-Kras (KC) murine background in which oncogenic Kras is activated in the pancreas to promote preinvasive pancreatic cancer. Tumor burden was then measured at different stages of disease.

RESULTS

HRas;KC mice exhibited more precancerous lesions in the pancreas and more off-target skin papillomas compared to their wild-type counterparts, suggesting that Hras suppresses early oncogenic Kras-driven tumorigenesis, possibly at the time of initiation. Loss of Hras also reduced the survival of mice engineered to develop aggressive pancreatic cancer by the additional disruption of one allele of the tumor suppressor p53 (Trp53). However, this survival advantage was lost when both alleles of Trp53 were mutated, suggesting that wild-type Hras inhibits tumorigenesis in a p53-dependent fashion.

CONCLUSIONS

Loss of wild-type Hras promotes the earliest stages of pancreatic tumorigenesis, and moreover results in more rapid progression of the disease. As such, mechanisms leading to activation of wild-type Ras proteins, including but not limited to redox-dependent reactions, may influence the development of pancreatic cancer.