P311 inhibits TGF-β1 and TGF-βR2 in NIH 3T3 and C3H10 T1/2 cells and decreases collagen 1 and 3 expression. (a) RT-PCR and immunoprecipitation followed by immunoblotting (lower panels) showing downregulation of TGF-β1 in P311-expressing cells compared with controls. (b) RT-PCR and Western blotting demonstrating P311-induced downregulation of TGF-βR2 but not of TGF-βR1 in NIH 3T3 (upper panels) and C3H10 T1/2 (lower panels). Untreated (untreat) cells were used as an additional control for C3H10 T1/2 cells in the lower panels. (c) RT-PCR showing significant collagen 1 (CN1) and 3 (CN3) downregulation in P311-expressing cells (upper panels) and inhibition of MMP-2 and MMP-9, which participate in TGF-β1 activation and inhibition of MMP-1 that is upregulated by TGF-β1. (d) RT-PCR performed on control and P311-expressing NIH 3T3 cells after 48 hours in culture with or without TGF-β1 treatment demonstrating reversal of P311-induced downregulation in collagen expression by exogenous TGF-β1.