PAK isoform expression in thyroid cancer cells. Expression of PAK isoforms was examined by RT-PCR (A) and WB (B) in six established human thyroid cancer cell lines. (A) For the RT-PCR, negative controls were RT-negative reactions with RNA from each cell line and non-template control. The RNA from HEK293 cells transfected with PAK5 was used as a positive control, since HEK293 cells express all PAK isoforms except for PAK5. All PAK isoforms except PAK5 were expressed in all six human thyroid cancer cell lines. RT, reverse transcriptase; NTC, non-template control. (B) For WB, the protein was isolated from HEK293 cells transfected with each PAK isoform and used as positive controls. All six cell lines expressed all PAK1, PAK2, PAK3, and PAK4 isoforms, and no expression of PAK5 was seen. PAK6 protein was not detected in BCPAP and KTC1 cells.