Autophagy mediates degradation of nuclear lamina

In response to cancer-associated stress, autophagy machinery mediates degradation of nuclear lamina components in mammals, suggesting that cells might degrade nuclear components to prevent tumorigenesis. Autophagy in action in the nucleus Much is known about degradation of the cytoplasmic content by the process of autophagy. Shelly Berger and colleagues provide evidence that the nuclear content is also subject to such cellular clearance. The authors show that, in response to cancer-associated stress such as the activated oncogene RAS, the autophagy protein LC3 interacts with the nuclear lamina protein lamin B1 and binds to lamin-associated domains on chromatin. Lamin B1 is then shuttled to the cytoplasm for degradation within lysosomes. Inhibiting this process led to delay in oncogene-induced senescence, hinting that cells might degrade nuclear components to prevent tumorigenesis. Macroautophagy (hereafter referred to as autophagy) is a catabolic membrane trafficking process that degrades a variety of cellular constituents and is associated with human diseases 1 , 2 , 3 . Although extensive studies have focused on autophagic turnover of cytoplasmic materials, little is known about the role of autophagy in degrading nuclear components. Here we report that the autophagy machinery mediates degradation of nuclear lamina components in mammals. The autophagy protein LC3/Atg8, which is involved in autophagy membrane trafficking and substrate delivery 4 , 5 , 6 , is present in the nucleus and directly interacts with the nuclear lamina protein lamin B1, and binds to lamin-associated domains on chromatin. This LC3–lamin B1 interaction does not downregulate lamin B1 during starvation, but mediates its degradation upon oncogenic insults, such as by activated RAS. Lamin B1 degradation is achieved by nucleus-to-cytoplasm transport that delivers lamin B1 to the lysosome. Inhibiting autophagy or the LC3–lamin B1 interaction prevents activated RAS-induced lamin B1 loss and attenuates oncogene-induced senescence in primary human cells. Our study suggests that this new function of autophagy acts as a guarding mechanism protecting cells from tumorigenesis.