Galectin-3 sensitized melanoma cell lines to vemurafenib (PLX4032) induced cell death through prevention of autophagy

// Silvina Odete Bustos 1 , Gustavo Jose da Silva Pereira 2 , Renata de Freitas Saito 1 , Cristiane Damas Gil 3 , Daniela Bertolli Zanatta 1 , Soraya Soubhi Smaili 2 and Roger Chammas 1 1 Instituto do Câncer do Estado de Sao Paulo, Faculdade de Medicina de Sao Paulo, Sao Paulo, Brazil 2 Department of Pharmacology, Federal University of Sao Paulo, Sao Paulo, Brazil 3 Laboratory of Histology, Department of Morphology and Genetics, Federal University of Sao Paulo, Sao Paulo, Brazil Correspondence to: Roger Chammas, email: rchammas@usp.br Keywords: autophagy; galectin-3; melanoma; vemurafenib; starvation Received: October 20, 2017      Accepted: February 10, 2018      Epub: February 16, 2018      Published: March 06, 2018 ABSTRACT Melanoma is a current worldwide problem, as its incidence is increasing. In the last years, several studies have shown that melanoma cells display high levels of autophagy, a self-degradative process that can promote survival leading to drug resistance. Consequently, autophagy regulation represents a challenge for cancer therapy. Herein, we showed that galectin-3 (Gal-3), a β-galactoside binding lectin which is often lost along melanoma progression, is a negative regulator of autophagy in melanoma cells. Our data demonstrated that Gal-3 low/negative cells were more resistant to the inhibition of the activity of the cancer driver gene BRAF V600E by vemurafenib (PLX4032). Interestingly, in these cells, starvation caused further LC3-II accumulation in cells exposed to chloroquine, which inhibits the degradative step in autophagy. In addition, Gal-3 low/negative tumor cells accumulated more LC3-II than Gal-3 high tumor cells in vivo . Resistance of Gal-3 low/negative cells was associated with increased production of superoxide and activation of the Endoplasmic Reticulum (ER) stress response, as evaluated by accumulation of GRP78. Pharmacological inhibition of autophagy with bafilomycin A reversed the relative resistance of Gal-3 low/negative cells to vemurafenib treatment. Taken together, these results show that the autophagic flux is dependent on Gal-3 levels, which attenuate the prosurvival role of autophagy.