By reverse transcriptase-polymerase chain reaction (RT-PCR) and quantitative RT-PCR (Q-RT-PCR) they were found unable to silence RET/PTC1.     ///    Three efficient siRNAs previously designed in our laboratory in a model of murine PTC (RP-1 cells) were used to knockdown RET/PTC1 in the TPC-1 cells.     ///    The downregulation of RET/PTC1 modified the cell cycle and induced an apoptotic response.     ///    A mutation was found by sequencing within the H4 part of the RET/PTC1 junction leading to a ????T?G substitution.     ///    The specificity of the siRNARET/PTC1 was confirmed by the absence of a silencing effect on the human breast MCF-7 and BT-474 cells without RET/PTC1 and the murine RP-1 with ????G?T mutation.     ///    "Our aims were (i) to target the RET/PTC1 oncogene by siRNAs, (ii) to assess the knockdown effects on cell growth and cell cycle regulation, and (iii) to identify genes affected by the RET/PTC1 silencing. "    ///    "After sequencing, we redesigned an siRNA against RET/PTC1 (siRNARET/PTC1) and compared it for its efficiency and specificity with an siRNA against RET (siRNARET) in the TPC-1 cells, in human cell lines that expressed RET (MCF-7 and BT-474 cells), and in the murine RP-1 cells. "    ///    Effects of silencing RET/PTC1 junction oncogene in human papillary thyroid carcinoma cells..     ///    The E2F2 gene regulation would have a biological significance and seems to be directly mediated by RET/PTC1..     ///    Genes affected by the RET/PTC1 knockdown were identified by microarray analysis followed by Q-RT-PCR validation. 