Abstract 3389: Targeting SALL4 in lung cancer through a novel Cbl-b/IGF1R&EGFR axis
Authors: Li Ailing , Ou Wenbin , Fletcher Jonathan , Yong Kol Jia , Yang Henry , Soo Ross , Tenen Daniel , Chai Li 
Published: May 2015

Lung cancer is the leading cause of cancer deaths in the United States with an estimated &gt;160,000 deaths and &gt;200,000 newly diagnosed cases each year. Over the past 20 years, the survival rate for patients remains extremely poor (∼15% over 5 years). Discovery of novel pathway involved in the pathogenesis of the lung cancer can provide new therapeutic opportunities. Stem cell factor SALL4 has recently merged to be a diagnostic tool and therapeutic target for acute myeloid leukemia and liver cancer. However, very little is known on its role in lung cancer.

In order to investigate the functional role of SALL4 in lung cancer tumorigenesis and progression, we first performed gene expression profile analysis and revealed that SALL4 expression level was significant higher in all types of non-small cell lung cancer samples compared to normal lung tissue control, which was validated by IHC. Furthermore, we performed loss of function study using multiple shRNAs. Our data showed that knockdown of SALL4 could induce dramatic cell growth arrest in multiple lung cell lines including large cell carcinoma H661 and adenocarcinoma H522, H292 and PC9, but not in HCC827 cells with none/low SALL4 level. In order to elucidate the downstream pathway of SALL4 in lung cancer, we first conducted gene expression microarray using SALL4 knockdown H661 cells and cells treated with scramble control vectors. Combination of one-way ANOVA analysis and pathway analysis using Pathway Interaction Database (PID) showed that both the EGFR and IGF1R signaling pathways were affected by SALL4 knockdown in H661 lung cancer cells. Using western blot, we further validated that SALL4 depletion could lead to a decrease in both EGFR and IGF1R protein expressions in lung cancer cells. However, we did not observe any changes at the mRNA level for these two receptors upon SALL4 depletion. This leads us to wonder whether SALL4 could affect these two molecules indirectly. It has been well established that receptor tyrosine kinase (RTK) including EGFR and IGF1R can be negatively regulated by Cbl RING ubiquitin ligases. Of interest, our microarray data also showed that loss of SALL4 led to a dramatic upregulation of Cbl-b, a member of Cbl RING ligases, which was further validated by using real-time RT-PCR. In addition, SALL4 downregulation also dramatically increased Cbl-b protein expression in these lung cancer cells. Therefore, we propose that SALL4 can indirectly positively affect the expression of EGFR and IGF1R proteins through Cbl-b.

In summary, we have demonstrated that SALL4 expression is aberrantly elevated in non-small cell lung cancer cells. Furthermore our data suggested that SALL4 plays an essential role in lung cancer tumor growth and maintenance by affecting both EGFR and IGFR signaling pathways via regulating Cbl-b expression.

Citation Format: Ailing Li, Wenbin Ou, Jonathan Fletcher, Kol Jia Yong, Henry Yang, Ross Soo, Daniel Tenen, Li Chai. Targeting SALL4 in lung cancer through a novel Cbl-b/IGF1R&EGFR axis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3389. doi:10.1158/1538-7445.AM2014-3389