The ras genes, including Harvey ras (H-ras) and Kirsten ras (K-ras), were among the first oncogenes discovered, and are the most commonly mutated oncogenes in human cancer. The H-ras and K-ras proteins are 85% identical and share considerable functional overlap. However, there is increasing evidence for functional differences between the two proteins that may impart different properties to tumors arising from mutations in these two genes. To study the functional differences between H-ras and K-ras in an in vivo setting, we used two different transgenic mouse tumor models, MMTV-H-ras and MMTV-K-ras mice. The MMTV-H-ras mice were originally developed in Dr. Leder's lab and have been well characterized with regard to tumor properties. We created a similar line of transgenic mice expressing mutant K-ras (G12V) under the control of the MMTV promoter. Female mice of both lines develop primarily mammary tumors. We compared differences between the H-ras and K-ras lines with regard to age of tumor onset, rate of tumor growth, and rates of tumor proliferation and apoptosis. The tumors were also characterized by microarray analysis to look for genes that are differentially expressed in the two tumor types. Finally, the response of tumors to two common chemotherapeutic agents, doxorubicin and taxol, was also measured. We found that tumors in the MMTV-H-ras and MMTV-K-ras mice were similar with respect to several tumor properties, including age of onset, histopathology, and proliferation and apoptotic indices. While tumors from mice of these two genotypes clustered separately in an unsupervised analysis of gene expression profiles, the differentially expressed genes did not fall within any well-defined signaling pathways. However, drug studies indicated differences in response to doxorubicin between the two isoforms, with H-ras tumors responding better than K-ras tumors. In conclusion, our studies point to specific differences between H-ras and K-ras that may represent novel signaling pathways not currently known to be regulated by Ras. In spite of the few differences in properties of tumors arising from H-ras and K-ras mutation, there might be differences in response to chemotherapeutic agents that could have clinical significance.

p53 is an important tumor suppressor gene which is mutated in ~50% of all human cancers. Some of the p53 mutants appear to have acquired novel functions beyond merely losing wild-type functions. To investigate these gain-of-function effects in vivo, we interbred MMTV-v-Ha-ras transgenic mice to either p53-/- knock-out mice or p53R172H/+ knock-in mice to generate mice of three different genotypes: MMTV-ras, MMTV-ras/p53-/-, and MMTV-ras/p53R172H/R172H. Male mice of each of these genotypes were characterized with regard to age of salivary tumor onset and the tumors were characterized with regard to mean growth rates, proliferation fraction, apoptotic levels, and tumor histopathology, as well as responses to doxorubicin treatment. Microarray analysis was also performed to profile gene expression.The MMTV-ras/p53-/- and MMTV-ras/p53R172H/R172H mice display similar properties in age of tumor onset, tumor growth rates, and tumor histopathology, as well as response to doxorubicin. However, a subset of genes show differential expression between the two groups of tumor , and do not appear to be regulated by wild-type p53. At the same time, the MMTV-ras/p53R172H/R172H and MMTV-ras/p53+/+ tumors share similar expression levels of a group of genes that are differentially expressed in the MMTV-ras/p53-/- tumors. Thus, the gain-of-function effects may be caused in part by perturbed regulation of genes not normally regulated by wild-type p53, in addition to imbalances in the regulation of normal p53 target genes.