Mechanism of autophagy initiation by transmembrane selective autophagy receptors

Selective autophagy ensures the targeted degradation of damaged or surplus cellular components, including organelles, thereby safeguarding cellular homeostasis. This process relies on selective autophagy receptors (SARs) that link specific cargo to the autophagy machinery. These receptors exist in two distinct forms: soluble SARs that are recruited to the cargo on demand, and transmembrane SARs that are stably embedded in the membranes of organelles they target. While both receptor types converge on the same autophagy core machinery, they differ in how they recognize cargo, are regulated, and recruit this machinery to the site of degradation. In this review, we explore the unique challenges and strategies associated with transmembrane SARs, including how their activity is suppressed under basal conditions and activated in response to stress. We compare their mode of action with that of soluble SARs, highlight key differences in kinase regulation, including the roles of TBK1, ULK1, CK2, and Src, and discuss emerging models of autophagy initiation. We further highlight fundamental principles of organelle-selective autophagy and identify open questions that will guide future research.