Growth inhibition of glioblastoma cells by human Purα

Pura is a multifunctional DNA- and RNA-binding protein implicated in a variety of biological events including transcription and replication. Further, this protein has the ability to form a complex with several cellular proteins which are important for cell proliferation including the transcription factor, E2F-1. Pur alpha has a modular structure highlighted by alternating three basic aromatic class I and two acidic leucine-rich class II repeats in the central region of the protein. Here, we demonstrate that ectopic overexpression of Pur alpha suppresses proliferation of a variety of transformed and tumor cells including human glioblastoma. By utilizing various deletion mutants of Pur alpha in colony formation assay, we identified the region spanning the first class II repeat (residues 107-131) and the second class I repeat (residues 148-170) of Pur alpha which participate in growth inhibitory action of Pur alpha. Results from protein transduction experiments using the synthetic peptides representing residues 109-131 and 123-154 of Pur alpha in fusion with the arginine rich domain of HIV-1 Tat revealed cellular internalization and nuclear appearance of the Tat-Pur alpha fusion peptide after 2 h and its detection in nuclei up to 24 h after treatment. Glioblastoma cells treated with Tat-Pur alpha (109-131) and Tat-Pur alpha (123-154) exhibited 41 and 47% decrease, respectively, in proliferation. Altogether these results illustrate the efficacy of Pur alpha in suppressing glioblastoma cell growth and provide evidence for the potential use of this protein and its derivative(s) in blocking proliferation of tumor cells. (C) 2001 Wiley-Liss, Inc.