TGF-β2 promotes autophagy-mediated resistance to doxorubicin in metastatic colon cancer cells via HMGB1.

Chemoresistance remains a major concern in combating cancer. Colorectal cancer progression is associated with augmented TGF-β serum level. The role of TGF-β2 in promoting doxorubicin resistance in Colo205 cell line was investigated by treating with dox ± TGF-β2 for 7-days. Cell viability, proliferation, cytotoxicity, rhodamine123 efflux, MDR1 expression at gene, surface, and total protein levels, apoptosis assay, induction of autophagy by acridine orange, monodansyl cadaverine staining, and LC3II/I protein ratio were examined. Expression of epithelial, mesenchymal, stem cell markers, regulation of Dab2 and HMGB1 (high mobility group box 1), activation of NF-κB (p65) were also evaluated. Cell proliferation was inhibited after day 1; while loss of viability and cytotoxicity occurred after day 3, with no comparable loss after 7 days. MDR1 protein and gene levels were significantly increased after day 1 in co-treated group alone while elevation in all treatments was noted after 3 and 7 days. Induction of autophagy, increased mesenchymal and stem cell markers, and downregulation of Dab2 protein was observed after 7 days. In TGF-β2 groups, HMGB1 level was significantly decreased, and arrest of NF-κB nuclear translocation was noted. Thus, the presence of TGF-β2 ligand might determine the dox resistance pathway in metastatic colon cancer cell line, Colo205 with smad4 mutation.