The Epidermal Growth Factor Receptor Antibody Cetuximab Induces Autophagy in Cancer Cells by Downregulating HIF-1α and Bcl-2 and Activating the Beclin 1/hVps34 Complex

Abstract

Autophagy is a regulated catabolic process triggered in cells deprived of nutrients or growth factors that govern nutrient uptake. Here, we report that autophagy is induced by cetuximab, a therapeutic antibody that blocks epidermal growth factor receptor function. Cancer cell treatment with cetuximab triggered autophagosome formation, conversion of microtubule-associated protein 1 light chain 3 from its cytoplasmic to membraneassociated form, and increased acidic vesicular organelle formation. Autophagy occurred when cetuximab inhibited the class I phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin pathway, but not when it inhibited only the mitogen-activated protein/extracellular signal-regulated kinase kinase/Erk pathway, and it was accompanied by decreased levels of hypoxia inducible factor-1 α (HIF-1α) and Bcl-2. Stable overexpression of a HIF-1α mutant prevented cetuximab-induced autophagy and decrease in Bcl-2 levels. Knockdown of autophagy regulator beclin 1 or cell treatment with autophagy inhibitor 3-methyladenine, a class III PI3K (hVps34) inhibitor, also inhibited cetuximab-induced autophagy. Furthermore, knockdown of beclin 1 or Atg7 or treatment with the lysosome inhibitor chloroquine sensitized cancer cells to cetuximab-induced apoptosis. Mechanistic analysis argued that cetuximab acted by promoting an association between beclin 1 and hVps34, which was inhibited by overexpression of Bcl-2. Our findings suggest that the autophagy protects cancer cells from the proapoptotic effects of cetuximab.

The autophagic paradox in cancer therapy

“…Autophagy is induced by different forms of cancer therapy, including conventional chemotherapeutic drugs, novel targeted cancer therapeutics and ionizing radiation, in various types of solid and hematological malignancies (Table 2) (Han et al, 2007(Han et al, , 2008Kim et al, 2007Kim et al, , 2008bKim et al, , 2009aMaiuri et al, 2007b;Kamitsuji et al, 2008;Meschini et al, 2008;Qadir et al, 2008;Turcotte et al, 2008;Fu et al, 2009;Lorin et al, 2009;Tormo et al, 2009;Fan et al, 2010;Gupta et al, 2010;Huang and Sinicrope, 2010;Li and Fan, 2010;Voss et al, 2010;Yacoub et al, 2010;Wu et al, 2010c;Lian et al, 2011;O'Donovan et al, 2011). In some circumstances, autophagy mediates the cytotoxic or cytostatic effect of anticancer agents, in which blockade of autophagy abolishes the therapeutic actions.…”

mTORC1-independent autophagy regulates receptor tyrosine kinase phosphorylation in colorectal cancer cells via an mTORC2-mediated mechanism

“…It has been proposed by us and others that in established tumours autophagy plays a pro-survival role, 28,39,41,42,45,46,57 in particular upon starvation or downstream inhibition of oncogenic kinase signalling, both of which result in inhibition of the main autophagy inhibitor, the PI3K/AKT/mTORC1 pathway. However, little is known on the role of autophagy and autophagy-like pathways in the presence of active PI3K/AKT/mTORC1 signalling in cancer cells, due to mutations in either PI3K or RAS pathway.…”

“…28,39,41,42,45,46 We set out to further investigate the RTK-autophagy pathway in the context of CRC, where RTK signalling is a factor implicated in tumour development and is being targeted clinically. In particular, several agents targeting EGFR and other members of the ErbB family are currently being tested in CRC trials.…”

“…In turn, pharmacological inhibition of autophagy potentiates OncTK/RTK targeted therapy. 2,28,[38][39][40][41] In particular, autophagy has been placed downstream of two RTKs with a known role in cancer, the Epidermal Growth Factor Receptor (EGFR) 17,19,[42][43][44][45][46][47][48][49][50] and the Hepatocyte Growth Factor Receptor (HGFR), c-MET. 51 EGFR has been suggested to regulate autophagy either directly 17,19 or indirectly through its downstream effectors.…”

Integration of Autophagy and Anoikis Resistance in Solid Tumors

“…Considering the important but complex role of autophagy in cancer, autophagy has been regarded as a complementary target to treat tumor. In fact, several anticancer drugs, such as EGFR inhibitor cetuximab (Li and Fan, 2010), HDAC inhibitors vorinostat as well as OSU-HDAC42 have been demonstrated to induce autophagy . The specific mechanism of these drugs may be involved in excessive autophagy leading to cell death which are effectively enhanced by pharmacological inhibitors of autophagy, including the early stage inhibitors 3-methyladenine (Kondo and Makita, 1997), wortamannin and LY294002, and late stage inhibitors chloroquine, hydroxychloroquine (HCQ), bafilomycin A1 and monensin .…”