Autophagy: Renovation of Cells and Tissues

The integrin family of cell adhesion receptors regulates a diverse array of cellular functions crucial to the initiation, progression and metastasis of solid tumours. The importance of integrins in several cell types that affect tumour progression has made them an appealing target for cancer therapy. Integrin antagonists, including the alphavbeta3 and alphavbeta5 inhibitor cilengitide, have shown encouraging activity in Phase II clinical trials and cilengitide is currently being tested in a Phase III trial in patients with glioblastoma. These exciting clinical developments emphasize the need to identify how integrin antagonists influence the tumour and its microenvironment.

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Integrins in cancer: biological implications and therapeutic opportunities

Autophagy and Aging

We present a high-quality genome sequence of a Neanderthal woman from Siberia. We show that her parents were related at the level of half-siblings and that mating among close relatives was common among her recent ancestors. We also sequenced the genome of a Neanderthal from the Caucasus to low coverage. An analysis of the relationships and population history of available archaic genomes and 25 present-day human genomes shows that several gene flow events occurred among Neanderthals, Denisovans and early modern humans, possibly including gene flow into Denisovans from an unknown archaic group. Thus, interbreeding, albeit of low magnitude, occurred among many hominin groups in the Late Pleistocene. In addition, the high-quality Neanderthal genome allows us to establish a definitive list of substitutions that became fixed in modern humans after their separation from the ancestors of Neanderthals and Denisovans.

http://dash.harvard.edu/bitstream/handle/1/12717373/4031459.pdf?sequence=1

The complete genome sequence of a Neanderthal from the Altai Mountains

Mounting evidence suggests that autophagy is a more selective process than originally anticipated. The discovery and characterization of autophagic adapters, like p62 and NBR1, has provided mechanistic insight into this process. p62 and NBR1 are both selectively degraded by autophagy and able to act as cargo receptors for degradation of ubiquitinated substrates. A direct interaction between these autophagic adapters and the autophagosomal marker protein LC3, mediated by a so-called LIR (LC3-interacting region) motif, their inherent ability to polymerize or aggregate as well as their ability to specifically recognize substrates are required for efficient selective autophagy. These three required features of autophagic cargo receptors are evolutionarily conserved and also employed in the yeast cytoplasm-to-vacuole targeting (Cvt) pathway and in the degradation of P granules in C. elegans. Here, we review the mechanistic basis of selective autophagy in mammalian cells discussing the degradation of misfolded proteins, p62 bodies, aggresomes, mitochondria and invading bacteria. The emerging picture of selective autophagy affecting the regulation of cell signaling with consequences for oxidative stress responses, tumorigenesis and innate immunity is also addressed.

Selective autophagy mediated by autophagic adapter proteins

Autophagy is a highly conserved cellular process by which cytoplasmic components are sequestered in autophagosomes and delivered to lysosomes for degradation. As a major intracellular degradation and recycling pathway, autophagy is crucial for maintaining cellular homeostasis as well as remodeling during normal development, and dysfunctions in autophagy have been associated with a variety of pathologies including cancer, inflammatory bowel disease and neurodegenerative disease. Stem cells are unique in their ability to self-renew and differentiate into various cells in the body, which are important in development, tissue renewal and a range of disease processes. Therefore, it is predicted that autophagy would be crucial for the quality control mechanisms and maintenance of cellular homeostasis in various stem cells given their relatively long life in the organisms. In contrast to the extensive body of knowledge available for somatic cells, the role of autophagy in the maintenance and function of stem cells is only beginning to be revealed as a result of recent studies. Here we provide a comprehensive review of the current understanding of the mechanisms and regulation of autophagy in embryonic stem cells, several tissue stem cells (particularly hematopoietic stem cells), as well as a number of cancer stem cells. We discuss how recent studies of different knockout mice models have defined the roles of various autophagy genes and related pathways in the regulation of the maintenance, expansion and differentiation of various stem cells. We also highlight the many unanswered questions that will help to drive further research at the intersection of autophagy and stem cell biology in the near future.

https://www.tandfonline.com/doi/pdf/10.4161/auto.24132

Autophagy in stem cells

Neural-specific deletion of FIP200 leads to cerebellar degeneration caused by increased neuronal death and axon degeneration

Focal adhesion kinase (FAK) has been implicated in the development of cancers, including those of the breast. Nevertheless, the molecular and cellular mechanisms by which FAK promotes mammary tumorigenesis in vivo are not well understood. Here, we show that targeted deletion of FAK in mouse mammary epithelium significantly suppresses mammary tumorigenesis in a well-characterized breast cancer model. Ablation of FAK leads to the depletion of a subset of bipotent cells in the tumor that express both luminal marker keratin 8/18 and basal marker keratin 5. Using mammary stem/progenitor markers, including aldehyde dehydrogenase, CD24, CD29, and CD61, we further revealed that ablation of FAK reduced the pool of cancer stem/progenitor cells in primary tumors of FAK-targeted mice and impaired their self-renewal and migration in vitro. Finally, through transplantation in NOD-SCID mice, we found that cancer stem/progenitor cells isolated from FAK-targeted mice have compromised tumorigenicity and impaired maintenance in vivo. Together, these results show a novel function of FAK in maintaining the mammary cancer stem/progenitor cell population and provide a novel mechanism by which FAK may promote breast cancer development and progression.

https://cancerres.aacrjournals.org/content/canres/69/2/466.full.pdf

Mammary Epithelial-Specific Ablation of the Focal Adhesion Kinase Suppresses Mammary Tumorigenesis by Affecting Mammary Cancer Stem/Progenitor Cells

Despite recent studies showing that inhibition of autophagy depletes the hematopoietic stem cell pool and increases intracellular reactive oxygen species (ROS), it remains unknown whether autophagy is essential in the maintenance of other stem cells. Moreover, it is unclear whether and how the aberrant ROS increase causes depletion of stem cells. Here we report that ablation of FIP200 (also known as Rb1cc1), a gene essential for autophagy induction in mammalian cells, results in a progressive loss of neural stem cells (NSCs) and impairment in neuronal differentiation specifically in the postnatal brain, but not the embryonic brain, in mice. The defect in maintaining the postnatal NSC pool was caused by p53-dependent apoptotic responses and cell cycle arrest. However, the impaired neuronal differentiation was rescued by treatment with the antioxidant N-acetylcysteine but not by p53 inactivation. These data reveal that FIP200-mediated autophagy contributes to the maintenance and functions of NSCs through regulation of oxidative state.

Chenran Wang

Papers

Autophagy in stem cells

Neural-specific deletion of FIP200 leads to cerebellar degeneration caused by increased neuronal death and axon degeneration

Mammary Epithelial-Specific Ablation of the Focal Adhesion Kinase Suppresses Mammary Tumorigenesis by Affecting Mammary Cancer Stem/Progenitor Cells

FIP200 is required for maintenance and differentiation of postnatal neural stem cells

Regulation of Integrin β1 Recycling to Lipid Rafts by Rab1a to Promote Cell Migration