TGFBR1 and carcinoma: Furthermore, in carcinoma cells, loss or very low levels of TβR‐V expression do not affect TGF‐β‐stimulated canonical signaling (TβR‐I/TβR‐II/Smad‐2/3/4), as evidenced by TGF‐β‐stimulated expression of PAI‐1 in these cells.10