MTDH/SND1 Protein Complex in ERG-mediated Transformation and Therapeutic Resistance

I found the first time that ERG could interact with SND1/MTDH protein complex in prostate cancer cell. Here I used coimmunoprecipitation and proximity ligation assays to demonstrate that ERG interacts with SND1/MTDH complex in prostate cancer cells. I also identified the protein domains in both ERG and SND1 responsible for binding between ERG andSND1/MTDH complex. Overexpression of ERG promotes transformation of RWPE-1 immortalized human prostatic epithelial cells. I found that SND1 is necessary for ERG-mediated transformation of RWPE-1 cells. In prostate cancer VCaP cells, both ERG and SND1 are required for normal rates of VCaP cell proliferation; however, they do not show an additive effect and overexpression of SND1 partially rescues the effects of ERG knockdown, suggesting that in these cells ERG and SND1 are working in the same signaling pathway. Our in vivo mouse studies also revealed that SND1 is required for ERG/Pten KO mediated prostate tumorigenesis. I also performed RNA-Seq experiments to analyze if SND1 is involved in ERG-regulated transcriptional program. I observed highly statistically significant overlap between genes regulated by ERG and SND1 in VCaP cells and mouse prostates in our genetic mouse model. Moreover, SND1 was necessary for ERG-mediated activation of some of its gene targets. Utilizing mouse prostate organoid model, I also found that SND1 is necessary for ERG-mediated growth of mouse cells in 3D cultures. While ERG is a nuclear protein, endogenous SND1/MTDH are primarily localized to the cytoplasm. Our nuclear/cytosol fractionation experiments revealed that nuclear SND1/MTDH is increased and cytoplasmic SND1/MTDH is decreased in RWPE-1 cells overexpressing ERG.