Abstract
Genetic alterations in the MMAC1 tumor suppressor gene (also referred to as PTEN or TEP1) occur in several types of human cancers including glioblastoma. Growth suppression induced by overexpression of MMAC1 in cells with mutant MMAC1 alleles is thought to be mediated by the inhibition of signaling through the phosphatidylinositol 3-kinase pathway. However, the exact biochemical mechanisms by which MMAC1 exerts its growth-inhibitory effects are still unknown. Here we report that recombinant adenovirus-mediated overexpression of MMAC1 in three different MMAC1-mutant glioblastoma cell lines blocked progression from G0/G1 to S phase of the cell cycle. Cell cycle arrest correlated with the recruitment of the cyclin-dependent kinase (CDK) inhibitor, p27Kip1, to cyclin E immunocomplexes, which resulted in a reduction in CDK2 kinase activities and a decrease in levels of endogenous phosphorylated retinoblastoma protein. CDK4 kinase activities were unaffected, as were the levels of the CDK inhibitor p21Cip1 present in cyclin E immunocomplexes. Therefore, overexpression of MMAC1 via adenovirus-mediated gene transfer suppresses tumor cell growth through cell cycle inhibitory mechanisms, and as such, represents a potential therapeutic approach to treating glioblastomas.
MeSH terms
-
Adenoviruses, Human / genetics
-
Antigen-Antibody Complex / metabolism
-
CDC2-CDC28 Kinases*
-
Cell Cycle / physiology
-
Cell Cycle Proteins*
-
Cell Division / drug effects
-
Cyclin E / immunology
-
Cyclin E / metabolism*
-
Cyclin-Dependent Kinase 2
-
Cyclin-Dependent Kinase 4
-
Cyclin-Dependent Kinase Inhibitor p21
-
Cyclin-Dependent Kinase Inhibitor p27
-
Cyclin-Dependent Kinases / metabolism*
-
Cyclins / analysis
-
Genetic Vectors / genetics
-
Glioblastoma / pathology*
-
Humans
-
Macromolecular Substances
-
Microtubule-Associated Proteins / metabolism*
-
Neoplasm Proteins / metabolism*
-
Neoplasm Proteins / physiology*
-
PTEN Phosphohydrolase
-
Phosphoric Monoester Hydrolases / genetics
-
Phosphoric Monoester Hydrolases / physiology*
-
Phosphorylation
-
Protein Processing, Post-Translational
-
Protein Serine-Threonine Kinases / metabolism*
-
Proto-Oncogene Proteins*
-
Recombinant Fusion Proteins / physiology
-
Retinoblastoma Protein / metabolism
-
S Phase / physiology*
-
Signal Transduction
-
Transfection
-
Tumor Cells, Cultured
-
Tumor Suppressor Proteins*
Substances
-
Antigen-Antibody Complex
-
CDKN1A protein, human
-
Cell Cycle Proteins
-
Cyclin E
-
Cyclin-Dependent Kinase Inhibitor p21
-
Cyclins
-
Macromolecular Substances
-
Microtubule-Associated Proteins
-
Neoplasm Proteins
-
Proto-Oncogene Proteins
-
Recombinant Fusion Proteins
-
Retinoblastoma Protein
-
Tumor Suppressor Proteins
-
Cyclin-Dependent Kinase Inhibitor p27
-
Protein Serine-Threonine Kinases
-
CDC2-CDC28 Kinases
-
CDK2 protein, human
-
CDK4 protein, human
-
Cyclin-Dependent Kinase 2
-
Cyclin-Dependent Kinase 4
-
Cyclin-Dependent Kinases
-
Phosphoric Monoester Hydrolases
-
PTEN Phosphohydrolase
-
PTEN protein, human