Multiple roles of mothers against decapentaplegic homolog 4 in tumorigenesis, stem cells, drug resistance, and cancer therapy

Figure 4 Role of mothers against decapentaplegic homolog 4 in autophagy and drug resistance induced by transforming growth factor-β. In cancer cells with decreased or absent expression of mothers against decapentaplegic homolog 4 (Smad4) (Smad4-negative cancer cells), Smad4 mutation combined with other autophagy inducing factors (autophagy inducers) activates autophagy via the transforming growth factor-β signaling pathway, so that cancer cells can obtain nutrition through autophagy, develop resistance to chemotherapy, and show enhanced proliferation, metastasis, and stemness. Smad4: Mothers against decapentaplegic homolog 4; TGF-β: Transforming growth factor-β.