Trastuzumab resistance siRNA screen identifies PPM1H. Trastuzumab resistance siRNA screen identifies PPM1H. A, knockdown of the top 7 screen hits in an assay of cell proliferation in BT474M1 cells with and without trastuzumab (mean ± SEM). % knockdown by qRT-PCR is noted for each gene. B, PPM1H or control shRNA was transfected with a GFP vector or a GFP-PPM1H-SM vector harboring silent mutations in the shRNA binding region. GFP-positive cells were quantified (mean ± SEM). C, PPM1H knockdown with and without trastuzumab treatment was tested in 3D culture using a doxycycline-inducible BT474M1-PPM1H shRNA cell line. Data with a negative control shLacZ cell line are shown in Supplemenary Fig. 3A. Colony area is represented by box and whisker plot (whiskers represent 5th and 95th percentiles). Si Tuen Lee-Hoeflich et al. Cancer Discovery 2011;1:326-337 ©2011 by American Association for Cancer Research