a, Left, total levels of PDGFRβ and EGFR. A431, an EGFR-amplified cell line. Tubulin levels, loading control. Right, whole-cell extracts were incubated on the RTK antibody arrays, and phosphorylation status was determined by subsequent incubation with anti-phosphotyrosine horseradish peroxidase (each RTK spotted in duplicate, positive controls in corners, gene identity below). b, Anti-PDGFRβ immunohistochemistry of formalin-fixed, paraffin-embedded tissues. Prostate, negative control; placenta, positive control. Black bar, 50 μm. c, Relative RNA levels of PDGFRβ in M229 P/R5 and Pt48 R as determined by real-time, quantitative PCR (average of duplicates). d, Total PDGFRβ (left) and p-RTK (right) levels in Pt48 R versus M229 R5.