Axl and growth arrest-specific gene 6 are frequently overexpressed in human gliomas and predict poor prognosis in patients with glioblastoma multiforme.
OBJECTIVE
The receptor tyrosine kinase Axl has recently been identified as a critical element in the invasive properties of glioma cell lines. However, the effect of Axl and its ligand growth arrest--specific gene 6 (Gas6) in human gliomas is still unknown.


METHODS
Axl and Gas6 expression was studied in 42 fresh-frozen and 79 paraffin-embedded glioma specimens by means of reverse transcription-PCR and immunohistochemistry. The prognostic value of Axl and Gas6 expression was evaluated using a population-based tissue microarray derived from a cohort of 55 glioblastoma multiforme (GBM) patients.


RESULTS
Axl and Gas6 were detectable in gliomas of malignancy grades WHO 2 to 4. Moderate to high Axl mRNA expression was found in 61%, Axl protein in 55%, Gas6 mRNA in 81%, and Gas6 protein in 74% of GBM samples, respectively. GBM patients with high Axl expression and Axl/Gas6 coexpression showed a significantly shorter time to tumor progression and an association with poorer overall survival. Comparative immunohistochemical studies showed that Axl staining was most pronounced in glioma cells of pseudopalisades and reactive astrocytes. Additionally, Axl/Gas6 coexpression was observed in glioma cells and tumor vessels. In contrast, Axl staining was not detectable in nonneoplastic brain tissue and Gas6 was strongly expressed in neurons.


CONCLUSIONS
In human gliomas, Axl and Gas6 are frequently overexpressed in both glioma and vascular cells and predict poor prognosis in GBM patients. Our results indicate that specific targeting of the Axl/Gas6 signaling pathway may represent a potential new approach for glioma treatment.
Hutterer
Markus
M
Clinical Department of Neurology, Innsbruck Medical University, Innsbruck, Austria. Markus.Hutterer@i-med.ac.at
Knyazev
Pjotr
P
Abate
Ariane
A
Reschke
Markus
M
Maier
Hans
H
Stefanova
Nadia
N
Knyazeva
Tatjana
T
Barbieri
Verena
V
Reindl
Markus
M
Muigg
Armin
A
Kostron
Herwig
H
Stockhammer
Guenther
G
Ullrich
Axel
A
D001932:Brain Neoplasms / Q000378:metabolism / Q000401:mortality / Q000473:pathology*; D018572:Disease-Free Survival; D005260:Female; D015870:Gene Expression; D005909:Glioblastoma / Q000378:metabolism / Q000401:mortality / Q000473:pathology*; D006801:Humans; D007150:Immunohistochemistry; D036341:Intercellular Signaling Peptides and Proteins / Q000096:biosynthesis*; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D015513:Oncogene Proteins / Q000096:biosynthesis*; D011379:Prognosis; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000032:analysis; D020794:Receptor Protein-Tyrosine Kinases / Q000096:biosynthesis*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016019:Survival Analysis; D046888:Tissue Array Analysis; D000094963:Axl Receptor Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6
D036341:Intercellular Signaling Peptides and Proteins; D015513:Oncogene Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D020794:Receptor Protein-Tyrosine Kinases; D000094963:Axl Receptor Tyrosine Kinase; D000099255:Growth Arrest-Specific Protein 6; C000722289:AXL protein, human