LSL-K-ras G12C Mice

Catalog Number: C001409

Strain Name: C57BL/6JCya-Krastm1(LSL-G12C)/Cya

Genetic Background: C57BL/6JCya

Reproduction: Heterozygote x WT

 

Strain Description

The Kirsten rat sarcoma viral oncogene homolog (KRAS) is a proto-oncogene encoding the K-Ras protein, a membrane-associated GTPase, and a key member of the RAS gene family. K-Ras protein plays a crucial role in the RAS/MAPK signaling pathway by regulating the interconversion between GTP and GDP, transmitting extracellular signals to the nucleus, and thus influencing cell growth, proliferation, and differentiation [1]. KRAS is among the most frequently mutated genes in cancer, with mutations at codons 12, 13, and 61 leading to constitutive activation of the K-Ras protein. These alterations interact with multiple effector molecules and activate downstream signaling pathways, resulting in uncontrolled cellular proliferation and oncogenesis [2]. Approximately 30% of cancer patients harbor KRAS mutations. Specifically, 90% of pancreatic cancers, 50% of colorectal cancers, 25% of lung cancers, and 20–30% of non-small cell lung cancers (NSCLC) exhibit KRAS mutations. The G12C mutation is one of the most common KRAS mutations, accounting for 33% of all KRAS mutations, and is particularly prevalent in NSCLC. The G12C mutation is also present in approximately 14% of pancreatic cancers, 3–4% of colorectal cancers, and 1–2% of cholangiocarcinomas [3].

This strain is a conditional expression model of K-ras G12C, generated by introducing the G12C point mutation into the mouse Kras gene. Under normal conditions, the expression of K-ras G12C is blocked by an upstream loxP-Stop-loxP cassette. Expression is achieved only upon crossing with Cre mice, where Cre recombinase-mediated loxP site recombination removes the blocking sequence. This enables precise temporal and spatial control of K-ras G12C expression and tumorigenesis. By mating with tissue-specific Cre mice, this model can conditionally express K-ras G12C in specific tissues, making it a valuable tool for constructing cancer models in various tissues and organs. Homozygous LSL-K-ras G12C mice are nonviable.

Strain Strategy


Figure 1. Gene editing strategy of LSL-K-ras G12C mice. Using gene-editing technology, the sequence “loxP-Ad SA-3*SV40 pA-Neo cassette (PGK-Neo-BGH pA)-Stop-loxP” was inserted into intron 1 of the mouse Kras gene. Additionally, the G12C point mutation was introduced into exon 2.

Strain Application

This strain can be crossed with tissue-specific Cre mice to construct tumor models for various tissues or organs. It is suitable for applications such as drug screening and pharmacodynamic evaluations.

Validation Data

1. Construction of a Lung Tumor Model


Figure 2. Lung morphology and histopathology comparison between the lung tumor model constructed using LSL-K-ras G12C mice and wild-type (WT) mice. LSL-K-ras G12C mice were crossed with the Sftpc-CreERT2 mice (an alveolar epithelial cell-specific Cre strain). The resulting double heterozygous offspring (21 weeks old) were dissected and subjected to histopathological analysis. Gross examination revealed white nodules in the lungs of LSL-K-ras G12C [KI/+];Sftpc-CreERT2 [TG/+] double heterozygous mice, while WT lungs appeared normal. H&E staining showed no pathological changes in WT lungs, whereas double heterozygous lungs displayed nodules at the periphery characterized by well-demarcated epithelial cell-dense areas (solid growth) compressing surrounding tissues. Rare mitotic figures were observed. The lesion was diagnosed as pulmonary adenoma, a proliferative neoplastic lesion. A trend toward an indistinct boundary between adenomatous and normal tissues suggested a potential risk of malignancy.

Note: The Sftpc-CreERT2 mouse is a tamoxifen-inducible Cre strain. However, in this strain, leaky expression of Cre recombinase occurs even without tamoxifen induction. Therefore, in this study, LSL-K-ras G12C [KI/+]; Sftpc-CreERT2 [TG/+] mice were not treated with tamoxifen.

 

References
[1]Zebisch A, Czernilofsky AP, Keri G, Smigelskaite J, Sill H, Troppmair J. Signaling through RAS-RAF-MEK-ERK: from basics to bedside. Curr Med Chem. 2007;14(5):601-23.
[2]Downward J. Targeting RAS signalling pathways in cancer therapy. Nat Rev Cancer. 2003 Jan;3(1):11-22.
[3]Li S, Balmain A, Counter CM. A model for RAS mutation patterns in cancers: finding the sweet spot. Nat Rev Cancer. 2018 Dec;18(12):767-777.