Detection of cyclin D1 and p21Cip1 in tumors and in cultured cells. (a) Tumor sections from mice bearing MDA-MB-231/secreted Frizzled-related protein 1 (sFRP1)-P1 and control tumors were stained with cyclin D1-specific antiserum. Signal intensities, shown in the bar graph, reflect data collected from six MDA-MB-231/sFRP1-P1 tumors and eight control tumors ± standard error of the mean (SEM). *P < 0.05. (b) Cyclin D1 detected in lysates from in vitro cultured MDA-MB-231/sFRP1-P1 cells and control cells by immunoblotting. Bar graph: levels were quantified from three MDA-MB-231/sFRP1 and three control clones (from Figure 1a). Average ± SEM, n.s. = not significant. (c) p21Cip1 detected in tumor lysates from five MDA-MB-231/sFRP1-P1 tumors and three control tumors. (d) Lysates from in vitro cultured MDA-MB-231/sFRP1-P1 and control-P1 cells had no detectable p21Cip1. Lysates from MCF7 control and siRNA-mediated p21Cip1 knockdown tumor cells served as positive and negative controls, respectively; α-tubulin served as loading control.