Inhibition of Id proteins by a peptide aptamer induces cell-cycle arrest and apoptosis in ovarian cancer cells.
BACKGROUND
Inhibitors of DNA-binding proteins (Id1-4), lacking the basic DNA-binding domain, function as dominant inhibitors of cell-cycle regulators. Overexpression of Id proteins promotes cancer cell proliferation and resistance against apoptosis. Level of Id protein expression, especially of Id1, correlates with poor differentiation, enhanced malignant potential and more aggressive clinical behaviour of ovarian tumours. Although overexpression of Ids has been found and shown to correlate with poor clinical outcome, their inhibition at protein level has never been studied.


METHODS
A peptide aptamer, Id1/3-PA7, targeting Id1 and Id3, was isolated from a randomised combinatorial expression library using yeast and mammalian two-hybrid systems. Id1/3-PA7 was fused, expressed and purified with a cell-penetrating protein transduction domain.


RESULTS
Intracellular-delivered Id1/3-PA7 colocalised to Id1 and Id3. It induced cell-cycle arrest and apoptosis in ovarian cancer cells ES-2 and PA-1. It activated the E-box promoter and increased the expression level of cyclin-dependent kinase inhibitor (CDKN2A) in a dose-dependent manner that is paralleled by the cleavage of poly-ADP ribose polymerase. These effects were counteracted by ectopically overexpressed Id1 and Id3.


CONCLUSIONS
Id1/3-PA7 could represent an exogenous anti-tumour agent that can significantly trigger cell-cycle arrest and apoptosis in ovarian cancer.
Mern
D S
DS
Helmholtz-University Group Molecular Epidemiology, German Cancer Research Center, Im Neuenheimer Feld 581, D-69120 Heidelberg, Germany. d.mern@dkfz-heidelberg.de
Hasskarl
J
J
Burwinkel
B
B
D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D052158:Aptamers, Peptide / Q000378:metabolism / Q000493:pharmacokinetics / Q000494:pharmacology*; D002277:Carcinoma / Q000235:genetics / Q000473:pathology*; D002453:Cell Cycle / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D019942:Genes, p16 / Q000187:drug effects; D006801:Humans; D051798:Inhibitor of Differentiation Protein 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D051796:Inhibitor of Differentiation Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D010051:Ovarian Neoplasms / Q000235:genetics / Q000473:pathology*; D014018:Tissue Distribution; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D052158:Aptamers, Peptide; D051798:Inhibitor of Differentiation Protein 1; D051796:Inhibitor of Differentiation Proteins; D009363:Neoplasm Proteins; C075640:ID3 protein, human