Autophagosome formation requires multiple autophagy‐related (ATG) factors. However, we find that a subset of autophagy substrates remains robustly targeted to the lysosome in the absence of several core ATGs, including the LC3 lipidation machinery. To address this unexpected result, we performed genome‐wide CRISPR screens identifying genes required for NBR1 flux in ATG7^KO cells. We find that ATG7‐independent autophagy still requires canonical ATG factors including FIP200. However, in the absence of LC3 lipidation, additional factors are required including TAX1BP1 and TBK1. TAX1BP1's ability to cluster FIP200 around NBR1 cargo and induce local autophagosome formation enforces cargo specificity and replaces the requirement for lipidated LC3. In support of this model, we define a ubiquitin‐independent mode of TAX1BP1 recruitment to NBR1 puncta, highlighting that TAX1BP1 recruitment and clustering, rather than ubiquitin binding per se, is critical for function. Collectively, our data provide a mechanistic basis for reports of selective autophagy in cells lacking the lipidation machinery, wherein receptor‐mediated clustering of upstream autophagy factors drives continued autophagosome formation.

中文翻译：

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受体介导的 FIP200 聚集绕过了 LC3 脂化在自噬中的作用

自噬体的形成需要多种自噬相关（ATG）因子。然而，我们发现在没有几个核心 ATG（包括 LC3 脂化机制）的情况下，一部分自噬底物仍然强烈靶向溶酶体。为了解决这个意想不到的结果，我们进行了全基因组 CRISPR 筛选，鉴定了ATG7 ^{KO中 NBR1 通量所需的基因}细胞。我们发现不依赖 ATG7 的自噬仍然需要经典的 ATG 因子，包括 FIP200。然而，在没有 LC3 脂化的情况下，需要额外的因子，包括 TAX1BP1 和 TBK1。TAX1BP1 将 FIP200 聚集在 NBR1 货物周围并诱导局部自噬体形成的能力增强了货物特异性并取代了对脂化 LC3 的要求。为了支持这个模型，我们定义了一种不依赖泛素的 TAX1BP1 募集到 NBR1 puncta 的模式，强调 TAX1BP1 募集和聚集，而不是泛素结合本身，对功能至关重要。总的来说，我们的数据为缺乏脂化机制的细胞中的选择性自噬报告提供了机制基础，其中受体介导的上游自噬因子聚集驱动持续的自噬体形成。