Temporal Dissection of the Biological Function of K-RAS Mutant in Lung Tumor Formation and Maintenance

Animal models which allow the temporal regulation of gene activities have been proved to be valuable for the dissection of gene function in tumorigenesis. Recently, a team of researchers, led by JI Hongbin and LIU Xinyuan at Shanghai Institute of Biochemistry and Cell Biology (SIBCB), CAS, and Dr. Kwok-Kin Wong at Dana-Farber Cancer Institute constructed a conditional inducible K-ras^G12D knock-in mice allele that allows temporally switching on or off the K-ras oncogenic mutant through tamoxifen administration.

 

Studies using mice embryonic fibroblast (MEF) show that tamoxifen induces K-ras^G12D activation promotes cell proliferation, anchor-independent cell growth, cell transformation and cell invasion. K-ras^G12D activation results in activation of the downstream MAPK pathway and cell cycle progression. Continuous activation of K-ras^G12D in vivo by tamoxifen treatment is sufficient to drive lung cancer formation in mice. Tamoxifen withdrawal from transformed MEFs leads to a recovery of normal cell state through shutting off the K-ras^G12D activation. More importantly, tamoxifen withdrawal after the tumor development results in dramatic regression accompanied with growth arrest and apoptosis in mice. Collectively, these data have convincingly demonstrated that K-ras mutant is essential for neoplastic transformation as well as tumor maintenance and this animal model may provide an ideal platform for further detailed characterization of the role of K-ras oncogenic mutant during different stages of lung tumorigenesis.

 

This study entitled “Temporal dissection of K-ras^G12D mutant in vitro and in vivo using a regulatable K-ras^G12D mouse allele” was published online in PLoS One on May 11^th, 2012.

 

The work is supported by grants from the Ministry of Science and Technology and the National Natural Science Foundation of China.

 

AUTHOR CONTACT:

JI Hongbin

Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences Shanghai, China

Phone: 86-21-54921108; E-mail: hbji@sibs.ac.cn

 

Figure 1. A regulatable K-ras^G12D mouse allele allows the temporal dissection of K-ras^G12D mutant in lung cancer formation as well as tumor maintenance. A) Construction of Loxp-Stop-Loxp-ER-K-ras^G12D mice allele. The Stop codon were flanked with two LoxP sites; the Neo cassette is flanked with two FRT sites; Positive selection cassette contains the gene for a viral Neo cassette and negative selection cassette contains the gene for a viral thymidine kinase (TK). The original mice were then crossed with β-actin-Flpe to delete the Neo cassette. Thymidine kinase (TK) ; BamH I (B); Kpn I (K); Not I (N); Xba I (Xb); Sph I (S); ER, estrogen receptor cDNA; * , GGT to GAT mutation at codon 12; B) Continuous tamoxifen treatment of the P53L/L, LSL-ER-K-rasG12D mice for 12 weeks after Ad-Cre treatment results in lung tumor formation. Tamoxifen withdrawal afterwards led to significant tumor regression accompanied with apoptosis indicated by cleaved caspase-3 positive immunostaining.