For DNA microarray screening and analysis, we used the same protocol as described previously [12] [13] [14] [15] [16] . Briefly, RNA was extracted from cells by using RNAzol. Ten micrograms of total RNA was used for each sample. cDNA was synthesized by using Superscript II (Life Technologies, Invitrogen, Milano, Italy) and amino-allyl dUTP (Sigma-Aldrich). Monoreactive Cy3 and Cy5 esters (Amersham Pharmacia, Little Chalfont, UK) were used for indirect cDNA labeling. RNA extracted from untreated cells was labeled with Cy3 and used as control against the Cy5-labeled treated (PG) cDNA in the first experiment and then switched. For 20 K human DNA microarrays slides (MWG Biotech AG, Ebersberg, Germany), 100 lL of the sample and control cDNAs in DIG Easy hybridization solution (Roche, Basel, Switzerland) were used in a sandwich hybridization of the two slides, constituting the 20 K set at 37°C overnight. Washing was performed three times for 10 minutes with 19 saline sodium citrate (SSC) and 0.1% sodium dodecyl sulfate at 42°C and three times for 5 minutes with 0.19 SSC at room temperature. Slides were dried by centrifugation for 2 minutes at 2000 rpm. Hybridized arrays were scanned with a GenePix 4000 scanner (Axon Instruments) at variable photomultiplier tube (PMT) voltage to obtain maximal signal intensities with less than 1% probe saturation.