- The hepatitis B virus encoded oncoprotein pX amplifies TGF-beta family signaling through direct interaction with Smad4: potential mechanism of hepatitis B virus-induced liver fibrosis. Lee, D.K., Park, S.H., Yi, Y., Choi, S.G., Lee, C., Parks, W.T., Cho, H., de Caestecker, M.P., Shaul, Y., Roberts, A.B., Kim, S.J. Genes Dev. (2001)