FLCN loss is characterized by SQSTM1/p62 accumulation despite functional autophagy flux in Birt-Hogg-Dubé syndrome-associated kidney cancer
ABSTRACT Birt-Hogg-Dubé syndrome (BHD) is an autosomal, dominant condition caused by Folliculin (FLCN) mutation and characterized by enhanced risk for kidney tumors. Previous studies have shown constitutive nuclear localization of the transcription factor TFEB and simultaneous hyperactivation of canonical MTORC1 signaling in the absence of FLCN. Here we assess the impact on autophagy under the situation of combined anabolic and catabolic activation. Using an established BHD patient-derived kidney cancer cell line, we confirmed that TFEB was permanently localized in the nucleus combined with an increase in canonical MTORC1 signaling, whereas bulk autophagy flux and LC3 lipidation were unaffected by FLCN status. However, we found that the autophagy receptor SQSTM1/p62 accumulated in enlarged puncta in the absence of FLCN. Finally, we recapitulate aberrant p62 accumulation in a Norwegian cohort of BHD kidney tumor samples. Our results demonstrate that FLCN loss is characterized by SQSTM1/p62 accumulation, although SQSTM1/p62 appears dispensable for anchorage-independent growth in cell models.