(a) mRNA expression determined by RT-PCR of some genes up- or downregulated in mammary tissue of MK-PTEN mice as compared with that of WT mice. These results are representative of two WT and two MK-PTEN mice different from those used to perform the microarray experiment. (b) Immunohistochemical localization of IGFBP-5 in the mammary gland of MK-PTEN and WT mice. Sections from mammary glands removed from mice lactating for 2 days were analyzed by immunohistochemistry as described in Methods. (c) An IGFBP-5–blocking peptide reduces the level of the apoptotic mammary epithelial cells of MK-PTEN mice. Following incubation of mammary epithelial cells from WT and MK-PTEN mice in DMEM with serum for 48 hours, the cells were untreated or treated with 5 or 10 μg/ml of an IGFBP-5–blocking peptide. Apoptotic cells were detected by TUNEL assay and caspase-3 activity was determined by the ApoAlert colorimetric assay as described in Methods. The data are representative of three independent experiments performed in triplicates.