Expression of the Proto-Oncogene Axl in Renal Cell Carcinoma

Abstract

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.

Gain-of-Function Activity of Mutant p53 in Lung Cancer through Up-Regulation of Receptor Protein Tyrosine Kinase Axl

“…We analyzed mutant p53-induced genes for the overrepresentation of genes that contain putative p63 binding sites. The Axl gene was selected for further study based on the presence of a p63 binding site, its known role in oncogenesis, 34,40,43,46,47 and its potential role in mutant p53 GOF activities. We first verified the microarray data by performing RT-qPCR analysis of the Axl mRNA, confirming induction by mutant p53.…”

Axl as a potential therapeutic target in cancer: role of Axl in tumor growth, metastasis and angiogenesis

“…Axl overexpression has been reported in a variety of human cancers (Craven et al, 1995;Ito et al, 1999;Berclaz et al, 2001;Sun et al, 2004;Shieh et al, 2005), and is associated with invasiveness and metastasis in lung (Shieh et al, 2005), prostate (Sainaghi et al, 2005), breast (Meric et al, 2002), and gastric cancers (Wu et al, 2002) as well as in renal cell carcinoma (Chung et al, 2003) and glioblastoma (Hutterer et al, 2008). A recent study showed that Axl overexpression via a 'tyrosine kinase switch' leads to resistance to imatinib in gastrointestinal stromal tumors (Mahadevan et al, 2007).…”

An anti-Axl monoclonal antibody attenuates xenograft tumor growth and enhances the effect of multiple anticancer therapies

“…Dysregulation of Axl or its ligand Gas6 is implicated in the pathogenesis of a variety of human cancers. Overexpression of Axl has been reported in a wide array of human cancers (Craven et al, 1995;Ito et al, 1999;Berclaz et al, 2001;Sun et al, 2004;Shieh et al, 2005) and is associated with invasiveness and metastasis in lung (Shieh et al, 2005), prostate (Sainaghi et al, 2005), breast (Meric et al, 2002;Zhang et al, 2008), gastric (Wu et al, 2002) and pancreatic (Koorstra et al, 2009) cancers, renal cell carcinoma (Chung et al, 2003) as well as glioblastoma (Hutterer et al, 2008). Recently, by profiling of phosphotyrosine signaling, activated Axl protein was detected in about 5% primary tumors of non-small-cell lung cancer (NSCLC) (Rikova et al, 2007).…”