TGFBR1 and renal cell carcinoma: After treatment with TGF-β1, the mRNA level of TGFBR2 was down-regulated in all RCC cells, while TGFBR1 levels were rather increased or not regulated in these cells with the exception of MZ2733RC, in which a down-regulation of TGFBR1 mRNA levels was detected (Figure 2A).