VICKZ1 Enhances Tumor Progression and Metastasis in Lung Adenocarcinomas in Mice by Enhancing Kras Signaling.

Introduction:

The VICKZ family of RNA binding proteins regulate RNA function at many levels, including intracellular RNA localization, stability, and translational control. One or more of the three VICKZ paralogs are upregulated in many different types of cancers and is usually correlated with poor prognosis.

Material and method:

Cell culture: The LKR-M cell line is a murine lung carcinoma line expressing a constitutively active mutant Kras G12D and selected for its ability to migrate to the lung when implanted in the flanks of syngeneic mice. In vitro studies of cell migration, growth in soft agar, wound healing and immune-precipitation were performed on stably infected LKR-M cells expressing VICKZ1, Dominant negative VICKZ1 (DN-VICKZ1) or GFP.

Mice models: The respective LKR-M cell lines expressing VICKZ1, DN-VICKZ1 or GFP were implanted in the flanks of syngeneic mice. 5 weeks post injection mice were sacrificed, and lungs were analyzed by H&E and IHC staining.

In the second model system, nasal administration of an adeno-Cre retrovirus was given to mice expressing both a conditional VICKZ transgene and a conditional Kras G12D transgene. Enabling us to test whether VICKZ1 can synergize with the constitutively active Kras mutant to enhance tumor development in the lungs.

Results and discussion:

We show that VICKZ1 enhances, and DN-VICKZ1 inhibits, cell migration, growth in soft agar, and wound healing in a mouse lung adenocarcinoma cell line containing a constitutively active, mutant Kras. Similarly, modulation of VICKZ1 activity promotes or inhibits metastases upon implantation of these cells into syngeneic mice. To test these effects in a genetic model system, we generated a mouse with an inducible VICKZ1 transgene and found that isolated overexpression of VICKZ1 in the lungs had no noticeable effect. Remarkably, when VICKZ1 overexpression was combined with mutant Kras overexpression in the lungs, tumor growth was accelerated and pulmonary adenocarcinomas were formed. In lung adenocarcinoma cells, VICKZ1-containing ribonucleoprotein complexes are highly enriched in Kras mRNA, and Kras signaling is enhanced in these cells by overexpression of VICKZ1.

An analysis of TCGA RNAseq data from lung adenocarcinoma patients shows that elevated VICKZ1 expression is not only associated with poor survival but also strikingly reduces life span in those patients who carry a Kras mutation.

Conclusion:

These results suggest a mechanism by which expression of VICKZ proteins, activated during oncogenic transformation, synergizes with mutant Kras to promote tumor progression and metastasis in lung adenocarcinomas, making it a promising target for directed therapy.