PTEN Physically Interacts with and Regulates E2F1-mediated Transcription in Lung Cancer

PTEN phosphorylation at its C-terminal (C-tail) serine/threonine cluster negatively regulates its tumor suppressor function. However, the consequence of such inhibition and its downstream effects in driving lung cancer remain unexplored. Herein, we ascertain the molecular mechanisms by which phosphorylation compromises PTEN function, contributing to lung cancer. Replacement of the serine/threonine residues with alanine generated PTEN-4A, a phosphorylation-deficient PTEN mutant, which suppressed lung cancer cell proliferation and migration. PTEN-4A preferentially localized to the nucleus where it suppressed E2F1-mediated transcription of cell cycle genes. PTEN-4A physically interacted with the transcription factor E2F1 and associated with chromatin at gene promoters with E2F1 DNA-binding sites, a likely mechanism for its transcriptional suppression function. Deletion analysis revealed that the C2 domain of PTEN was indispensable for suppression of E2F1-mediated transcription. Further, we uncovered cancer-associated C2 domain mutant proteins that had lost their ability to suppress E2F1-mediated transcription, supporting the concept that these mutations are oncogenic in patients. Consistent with these findings, we observed increased PTEN phosphorylation and reduced nuclear PTEN levels in lung cancer patient samples establishing phosphorylation as a bona fide inactivation mechanism for PTEN in lung cancer. Thus, use of small molecule inhibitors that hinder PTEN phosphorylation is a plausible approach to activate PTEN function in the treatment of lung cancer.
AbbreviationsAKT
V-Akt Murine Thymoma Viral Oncogene
CACancer adjacent
CDK1Cyclin dependent kinase 1
CENPC-CCentromere Protein C
ChIPChromatin Immunoprecipitation
co-IPCo-immunoprecipitation
COSMICCatalog of Somatic Mutations In Cancer
CREBcAMP Responsive Element Binding Protein
C-tailCarboxy terminal tail
E2F1E2F Transcription Factor 1
ECISElectric Cell-substrate Impedance Sensing
EGFREpidermal Growth Factor Receptor
GSIGamma Secretase Inhibitor
HDAC1Histone Deacetylase 1
HP1Heterochromatin protein 1
KAP1/TRIM28KRAB-Associated Protein 1/Tripartite Motif Containing 28
MAF1Repressor of RNA polymerase III transcription MAF1 homolog
MCM2Minichromosome Maintenance Complex Component 2
miRNAmicro RNA
MTF1Metal-Regulatory Transcription Factor 1
PARPPoly(ADP-Ribose) Polymerase
PD-1Programmed Cell Death 1
PD-L1Programmed Cell Death 1 Ligand 1
PI3KPhosphatidylinositol-4,5-Bisphosphate 3-Kinase
PLKPolo-like Kinase
pPTENPhosphorylated PTEN
PTENPhosphatase and Tensin Homolog deleted on chromosome ten
PTMPost Translational Modification
Rad51RAD51 Recombinase
Rad52RAD52 Recombinase
RPA1Replication protein A
SILACStable Isotope Labeling with Amino Acids in Cell Culture
SRFSerum Response Factor
TKITyrosine Kinase inhbitors
TMATissue Microarray
TOP2ADNA Topoisomerase 2A

V-Akt Murine Thymoma Viral Oncogene
Cancer adjacent
Cyclin dependent kinase 1
Centromere Protein C
Chromatin Immunoprecipitation
Co-immunoprecipitation
Catalog of Somatic Mutations In Cancer
cAMP Responsive Element Binding Protein
Carboxy terminal tail
E2F Transcription Factor 1
Electric Cell-substrate Impedance Sensing
Epidermal Growth Factor Receptor
Gamma Secretase Inhibitor
Histone Deacetylase 1
Heterochromatin protein 1
KRAB-Associated Protein 1/Tripartite Motif Containing 28
Repressor of RNA polymerase III transcription MAF1 homolog
Minichromosome Maintenance Complex Component 2
micro RNA
Metal-Regulatory Transcription Factor 1
Poly(ADP-Ribose) Polymerase
Programmed Cell Death 1
Programmed Cell Death 1 Ligand 1
Phosphatidylinositol-4,5-Bisphosphate 3-Kinase
Polo-like Kinase
Phosphorylated PTEN
Phosphatase and Tensin Homolog deleted on chromosome ten
Post Translational Modification
RAD51 Recombinase
RAD52 Recombinase
Replication protein A
Stable Isotope Labeling with Amino Acids in Cell Culture
Serum Response Factor
Tyrosine Kinase inhbitors
Tissue Microarray
DNA Topoisomerase 2A