Topic 2

Inactivation of ABL Kinases Suppresses Lung Cancer Metastasis

Current therapies to treat non-small cell lung carcinoma (NSCLC) have proven ineffective due to transient, variable and incomplete responses. We found that ABL kinases, ABL1 and ABL2, promote metastasis of lung cancer cells harboring EGFR or KRAS mutations.

Pharmacological inhibition (Figure 1) or knockdown of both ABL kinases suppresses NSCLC metastasis (Figure 2). ABL kinases are required for expression of pro-metastasis genes in lung cancer cells. Further, ABL-mediated activation of the TAZ and β-catenin transcriptional co-activators is required for NSCLC metastasis. Notably, ABL kinases activate TAZ- and β-catenin by decreasing their interaction with the β-TrCP ubiquitin ligase leading to increased protein stability (model Figure 3).

Fig. 1 – (A) PC9M cells labeled with luciferase were delivered by intracardiac injection into nude mice. Mice were treated one day after injection with or without GNF5 at 100 mg/kg by oral gavage twice a day. Representative images taken at day 18 are shown. (B) Bioluminescent (BLI) counts of each mouse for the indicated groups (n=6 each group). (C) M4M5 cells labeled with luciferase were delivered by intracardiac injection into nude mice. Mice were treated 8 days after injection with or without GNF5 at 50 mg/kg by intra-peritoneal injection once a day. Representative images at 12 days after GNF5 treatment are shown. (D) BLI counts of each mouse for the indicated groups (control, n=7, GNF5 n=9). Data are represented as mean ± SEM. All P-values were determined by Student’s t-test. (E and F) Luciferase-labeled PC9M cells were delivered by intracardiac injection into nude mice. After 10 days, mice bearing metastatic tumors were divided into two groups, and treated with vehicle (E) or GNF5 (F) by oral gavage for 14 days. Representative BLI images (left); BLI counts of each individual mouse before and after treatment for the indicated groups (Right). (Control n=4, GNF5 treated n=7).

Fig. 2 – (A) PC9 cells labeled with luciferase were transduced with lentiviruses encoding either scrambled (SCR) or ABL1/ABL2-specific (AA) shRNAs, and cells were delivered by intracardiac injection into nude mice. Tumor metastasis was detected by Bioluminescent Imaging (BLI). Representative images at day 28 are shown. (B) BLI counts of each individual mouse for the indicated groups (SCR n=11, AA n=15). (C) Percentage of mice surviving over the indicated times (days). (D) Depletion of ABL1 and ABL2 proteins was confirmed by Western blotting. Data are represented as mean ± SEM. All P-values were determined by Student’s t-test or Log-rank test.

High-level expression of ABL1, ABL2 and a subset of ABL-dependent TAZ- and β-catenin-target genes correlates with shortened survival of lung adenocarcinoma patients. Thus, ABL-specific allosteric inhibitors might be effective to treat metastatic lung cancer with an activated ABL pathway signature. These data reveal novel signaling networks in lung cancer cells regulated by ABL kinases. This work was published in JCI Insight in December 22, 2016.

Fig. 3 – Active ABL kinases in lung cancer cells harboring mutant KRAS or EGFR promote metastasis by enhancing β-catenin and TAZ protein stability and downstream signaling leading to increased expression of genes required for NSCLC metastasis.

 

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