title: Inhibition of Mer and Axl receptor tyrosine kinases in astrocytoma cells leads to increased apoptosis and improved chemosensitivity.
abstract: Astrocytomas account for the majority of malignant brain tumors diagnosed in both adult and pediatric patients. The therapies available to treat these neoplasms are limited, and the prognosis associated with high-grade lesions is extremely poor. Mer (MerTK) and Axl receptor tyrosine kinases (RTK) are expressed at abnormally high levels in a variety of malignancies, and these receptors are known to activate strong antiapoptotic signaling pathways that promote oncogenesis. In this study, we found that Mer and Axl mRNA transcript and protein expression were elevated in astrocytic patient samples and cell lines. shRNA-mediated knockdown of Mer and Axl RTK expression led to an increase in apoptosis in astrocytoma cells. Apoptotic signaling pathways including Akt and extracellular signal-regulated kinase 1/2, which have been shown to be activated in resistant astrocytomas, were downregulated with Mer and Axl inhibition whereas poly(ADP-ribose) polymerase cleavage was increased. Furthermore, Mer and Axl shRNA knockdown led to a profound decrease of astrocytoma cell proliferation in soft agar and a significant increase in chemosensitivity in response to temozolomide, carboplatin, and vincristine treatment. Our results suggest Mer and Axl RTK inhibition as a novel method to improve apoptotic response and chemosensitivity in astrocytoma and provide support for these oncogenes as attractive biological targets for astrocytoma drug development.
authors.affiliation: Department of Pediatrics, University of Colorado Denver, Aurora, CO 80045, USA. Amy.Keating@UCDenver.edu
authors.forename: Amy K
authors.initials: AK
authors.lastname: Keating
authors.forename: Grace K
authors.initials: GK
authors.lastname: Kim
authors.forename: Ashley E
authors.initials: AE
authors.lastname: Jones
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Donson
authors.forename: Kathryn
authors.initials: K
authors.lastname: Ware
authors.forename: Jean M
authors.initials: JM
authors.lastname: Mulcahy
authors.forename: Dana B
authors.initials: DB
authors.lastname: Salzberg
authors.forename: Nicholas K
authors.initials: NK
authors.lastname: Foreman
authors.forename: Xiayuan
authors.initials: X
authors.lastname: Liang
authors.forename: Andrew
authors.initials: A
authors.lastname: Thorburn
authors.forename: Douglas K
authors.initials: DK
authors.lastname: Graham
mesh_terms: D000328:Adult; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D001254:Astrocytoma / Q000188:drug therapy / Q000235:genetics / Q000473:pathology*; D001932:Brain Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000473:pathology*; D049109:Cell Proliferation / Q000187:drug effects; D002648:Child; D004353:Drug Evaluation, Preclinical; D019008:Drug Resistance, Neoplasm / Q000187:drug effects* / Q000235:genetics; D055785:Gene Knockdown Techniques; D006801:Humans; D047428:Protein Kinase Inhibitors / Q000008:administration & dosage / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D034741:RNA, Small Interfering / Q000008:administration & dosage / Q000494:pharmacology*; D020794:Receptor Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics; D014407:Tumor Cells, Cultured; D000076202:c-Mer Tyrosine Kinase; D000094963:Axl Receptor Tyrosine Kinase
chemical_list: D047428:Protein Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; C097072:MERTK protein, human; D020794:Receptor Protein-Tyrosine Kinases; D000076202:c-Mer Tyrosine Kinase; D000094963:Axl Receptor Tyrosine Kinase; C000722289:AXL protein, human