Figure 5. Surface TβRIII interacts with GTP bound Cdc42 in a TβRII and TβRI independent manner.

(A) Mink lung epithelial cell lines MV1Lu (wild type), R1b (TβRI−/−) and DR (TβRI−/− and TβRII−/−) were serum starved for 14 hours and subjected to ¹²⁵I-TGF-β₁ binding and cross-linking followed by GST-CRIB pulldown assay (PD) with GST only as a control. Expression level of TβRI, TβRII and TβRIII of MV1Lu, R1b and DR cells were detected by ¹²⁵I-TGF-β₁ binding and cross-linking (right panel). A representative of two independent replicates is presented. β-actin was used as a loading control. Integrated density, normalized to total TβRIII, is presented below and fold integrated density of TβRIII for each cell line relative to MV1Lu cells is presented below. (B) COS7 cells infected with adenovirus expressing either GFP or TβRIII followed by transfection with empty vector, TβRII-HA or kinase dead TβRII (TβRIIKD-HA) were subjected to ¹²⁵I-TGF-β₁ binding and cross- linking followed by GST-CRIB pulldown assay. 5% of total cell lysate was used for input to immunoblot against TβRIII, β-actin and anti-TβRII using Odyssey infrared imaging system to determine expression of transfected receptors. Control TβRIII intensity was subtracted from each condition, normalized to total TβRIII and fold TβRIII intensity bound to GST-CRIB relative to TβRIII only condition is presented. Quantified data represent the average of five independent experiments. ANOVA; p<0.0001; one sample t-test and two sample t-test: *p<0.005