ATG7 is a haploinsufficient repressor of tumor progression and promoter of metastasis.

Abstract

The role of autophagy in cancer is complex. Both tumor-promoting and tumor-suppressive effects are reported, with tumor type, stage and specific genetic lesions dictating the role. This calls for analysis in models that best recapitulate each tumor type, from initiation to metastatic disease, to specifically understand the contribution of autophagy in each context. Here, we report the effects of deleting the essential autophagy gene <i>Atg7</i> in a model of pancreatic ductal adenocarcinoma (PDAC), in which mutant <i>Kras^G12D</i> and mutant <i>Trp53^172H</i> are induced in adult tissue leading to metastatic PDAC. This revealed that <i>Atg7</i> loss in the presence of <i>Kras^G12D</i>^/+ and <i>Trp53^172H</i>^/+ was tumor promoting, similar to previous observations in tumors driven by embryonic <i>Kras^G12D</i>^/+ and deletion of <i>Trp53</i>. However, <i>Atg7</i> hemizygosity also enhanced tumor initiation and progression, even though this did not ablate autophagy. Moreover, despite this enhanced progression, fewer <i>Atg7</i> hemizygous mice had metastases compared with animals wild type for this allele, indicating that ATG7 is a promoter of metastasis. We show, in addition, that <i>Atg7</i>^+/- tumors have comparatively lower levels of succinate, and that cells derived from <i>Atg7</i>^+/- tumors are also less invasive than those from <i>Atg7</i>^+/+ tumors. This effect on invasion can be rescued by ectopic expression of <i>Atg7</i> in <i>Atg7</i>^+/- cells, without affecting the autophagic capacity of the cells, or by treatment with a cell-permeable analog of succinate. These findings therefore show that ATG7 has roles in invasion and metastasis that are not related to the role of the protein in the regulation of autophagy.