Oncogene database

558

AXL

AXL receptor tyrosine kinase;AXL;AXL receptor tyrosine kinase

AXL oncogene|AXL transforming sequence/gene|tyrosine-protein kinase receptor UFO

19q13.1

protein-coding

In this investigation, we examined the role of the Axl proto-oncogene in renal cell carcinoma (RCC). Axl is a tyrosine kinase receptor implicated in myeloid leukogenesis, and has been found to be overexpressed in lung cancers and breast cancers. Axl has been described to act as a mitogenic factor along with its ligand Gas-6. Axl has also shown to have a role in apoptosis, cell adhesion, and chemotaxis. The differential expression of the Axl RNA transcript was examined in 20 pairs of matched normal kidney and clear cell RCC patient samples. We found that there was a significant increase in the steady-state levels of Axl mRNA in the RCC compared with the normal kidney pair (Student s paired t-test P < 0.001). There was also a significant increase in Axl expression overall in RCC compared to normal kidney (P < 0.03). Western blotting was utilized to determine Axl protein levels in six out of the 20 pairs of the normal/RCC matched pairs. Overall, the level of expression was not significantly different between the paired normal kidneys and kidney tumors, but the detected Axl protein appeared to be at slightly different molecular weights. Primers were constructed for the two known Axl variant, RT-PCR performed, but no differences were observed in the expression of each variant. Next, we performed a gene silencing experiment utilizing double-stranded RNA constructed to silence the Axl gene in the 293 transformed kidney cell line. There was a 50% decrease in Axl gene expression in the RNAi transfected over control cells. In addition, flow cytometry performed to determine DNA content showed a 30% increase in G1/G0 cells, which were transfected with axl RNAi compared to control. Altogether, these findings suggest an overexpression of Axl as part of a proliferative phenotype in RCC.

Epithelial-to-mesenchymal transition (EMT) is a critical event in the progression toward cancer metastasis. The intermediate filament protein vimentin is an important marker of EMT and a requisite regulator of mesenchymal cell migration. However, it is not known how vimentin functionally contributes to cancer cell invasion. Here, we report that ectopic expression of oncogenic H-Ras-V12G and Slug induces vimentin expression and migration in pre-malignant breast epithelial cells. Conversely, vimentin expression is necessary for Slug- or H-Ras-V12G-induced EMT-associated migration. Furthermore, silencing of vimentin in breast epithelial cells results in specific changes in invasiveness-related gene expression including upregulation of RAB25 (small GTPase Rab25) and downregulation of AXL (receptor tyrosine kinase Axl), PLAU (plasminogen activator, urokinase) and ITGB4 (integrin beta4-subunit). Importantly, gene expression profiling analyses reveal that vimentin expression correlates positively/negatively with these genes also in multiple breast cancer cell lines and breast cancer patient samples. Focusing on the tyrosine kinase Axl, we show that induction of vimentin by EMT is associated with upregulation of Axl expression and that Axl enhances the migratory activity of pre-malignant breast epithelial cells. Using null and knock-down cells and overexpression models, we also show that regulation of breast cancer cell migration in two- and three-dimensional matrices by vimentin is Axl- dependent and that Axl functionally contributes to lung extravasation of breast cancer cells in mice. In conclusion, our data show that vimentin functionally contributes to EMT and is required for induction of Axl expression. Moreover, these results provide a molecular explanation for vimentin-dependent cancer cell migration during EMT by identifying Axl as a key proximal component in this process.

The receptor tyrosine kinases Axl and Mer, belonging to the Tyro3, Axl and Mer (TAM) receptor family, are expressed in a number of tumor cells and have well-characterized oncogenic roles. The therapeutic targeting of these kinases is considered an anticancer strategy, and various inhibitors are currently under development. At the same time, Axl and Mer are expressed in dendritic cells and macrophages and have an essential function in limiting inflammation. Inflammation is an enabling characteristic of multiple cancer hallmarks. These contrasting oncogenic and anti-inflammatory functions of Axl and Mer posit a potential paradox in terms of anticancer therapy. Here we demonstrate that azoxymethane (AOM) and dextran sulfate sodium (DSS)-induced inflammation-associated cancer is exacerbated in mice lacking Axl and Mer. Ablation of Axl and Mer signaling is associated with increased production of proinflammatory cytokines and failure to clear apoptotic neutrophils in the intestinal lamina propria, thereby favoring a tumor-promoting environment. Interestingly, loss of these genes in the hematopoietic compartment is not associated with increased colitis. Axl and Mer are expressed in radioresistant intestinal macrophages, and the loss of these genes is associated with an increased inflammatory signature in this compartment. Our results raise the possibility of potential adverse effects of systemic anticancer therapies with Axl and Mer inhibitors, and underscore the importance of understanding their tissue and cell type-specific functions in cancer.