title: Differential SKIP expression in PTEN-deficient glioblastoma regulates cellular proliferation and migration.
abstract: Glioblastoma is the most common and lethal primary malignant brain tumor in adults. The tumor suppressor gene PTEN is deleted, mutated or hypermethylated in more than 60% of glioblastoma cases resulting in hyperactivation of the phosphoinositide 3-kinase pathway, which leads to sustained PI(3,4,5)P3 signaling, and thereby hyperactivation of Akt and other effectors. PI(3,4,5)P3 is also hydrolyzed to PI(3,4)P2 by inositol polyphosphate 5-phosphatases such as SKIP, but the role this pathway has in glioblastoma is unknown. Microarray expression profiling of SKIP in human glioblastoma has revealed both increased and decreased SKIP gene expression. Here we have screened PTEN-deficient glioblastoma for SKIP protein expression by immunohistochemistry and report that SKIP expression is increased in some cases or decreased relative to normal brain. Using the U-87MG PTEN-deficient cell line we show that SKIP knockdown did not further enhance cell proliferation or survival. However, SKIP overexpression in U-87MG cells suppressed anchorage-independent cell growth and growth factor-induced PI(3,4,5)P3/Akt signaling. Although, SKIP knockdown did not affect cell proliferation or survival, cell migration was significantly retarded, associated with significantly increased PI(4,5)P2 signals, and decreased phosphorylation of the actin-regulatory protein cofilin, a PI(4,5)P2-binding protein. Notably, overexpression of SKIP also inhibited migration of U-87MG cells to a similar degree as observed with PTEN reconstitution, however, via distinct mechanisms. PTEN reconstitution promoted sustained lamellipodia generation and focal adhesion formation. In contrast, SKIP overexpression reduced sustained lamellipodia formation, talin incorporation into focal adhesions and recruitment of PI(4,5)P2-binding proteins to the plasma membrane. Notably, analysis of two independent ONCOMINE microarray data sets revealed a significant correlation between increased SKIP mRNA expression in glioblastoma and improved long-term survival. Therefore, SKIP expression in glioblastoma may affect the local invasion of PTEN-deficient tumors.
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: E M
authors.initials: EM
authors.lastname: Davies
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: A M
authors.initials: AM
authors.lastname: Kong
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: A
authors.initials: A
authors.lastname: Tan
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: R
authors.initials: R
authors.lastname: Gurung
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: A
authors.initials: A
authors.lastname: Sriratana
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: P E
authors.initials: PE
authors.lastname: Bukczynska
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: L M
authors.initials: LM
authors.lastname: Ooms
authors.affiliation: Department of Anatomical Pathology, Alfred Hospital, Prahran, Victoria, Australia.
authors.forename: C A
authors.initials: CA
authors.lastname: McLean
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: T
authors.initials: T
authors.lastname: Tiganis
authors.affiliation: Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia.
authors.forename: C A
authors.initials: CA
authors.lastname: Mitchell
mesh_terms: D001932:Brain Neoplasms / Q000201:enzymology / Q000235:genetics / Q000473:pathology*; D045744:Cell Line, Tumor; D002465:Cell Movement; D049109:Cell Proliferation; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D005909:Glioblastoma / Q000201:enzymology / Q000235:genetics / Q000473:pathology*; D006801:Humans; D020935:MAP Kinase Signaling System; D020411:Oligonucleotide Array Sequence Analysis; D051059:PTEN Phosphohydrolase / Q000235:genetics*; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics* / Q000378:metabolism*; D016019:Survival Analysis
chemical_list: C471548:SKIP enzyme, human; D010744:Phosphoric Monoester Hydrolases; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human