Centrosome Amplification in Cancer Disrupts Autophagy and Sensitizes to Autophagy Inhibition

Amplified centrosomes-more than just a threat

Centrosomes are major organizing components of the tubulin-based cytoskeleton. In recent years, we have gained extensive knowledge about their structure, biogenesis, and function from single cells, cell-cell interactions to tissue homeostasis, including their role in human diseases. Centrosome abnormalities are linked to, among others primary microcephaly, birth defects, ciliopathies, and tumorigenesis. Centrosome amplification, a state where two or more centrosomes are present in the G1 phase of the cell cycle, correlates in cancer with karyotype alterations, clinical aggressiveness, and lymph node metastasis. However, amplified centrosomes also appear in healthy tissues and, independent of their established role, in multi-ciliation. One example is the liver where hepatocytes carry amplified centrosomes owing to whole-genome duplication events during organogenesis. More recently, amplified centrosomes have been found in neuronal progenitors and several cell types of hematopoietic origin in which they enhance cellular effector functions. These findings suggest that extra centrosomes do not necessarily pose a risk for genome integrity and are harnessed for physiological processes. Here, we compare established and emerging 'non-canonical functions' of amplified centrosomes in cancerous and somatic cells and discuss their role in cellular physiology.

Centrosome amplification promotes cell invasion via cell-cell contact disruption and Rap-1 activation

Centrosome amplification (CA) is a prominent feature of human cancers linked to tumorigenesis in vivo. Here, we report mechanistic contributions of CA induction alone to tumour architecture and extracellular matrix (ECM) remodelling. CA induction in non-tumorigenic breast cells MCF10A causes cell migration and invasion, with underlying disruption of epithelial cell-cell junction integrity and dysregulation of expression and subcellular localisation of cell junction proteins. CA also elevates expression of integrin β-3, its binding partner fibronectin-1 and matrix metalloproteinase enzymes, promoting cell-ECM attachment, ECM degradation, and a migratory and invasive cell phenotype. Using a chicken embryo xenograft model for in vivo validation, we show that CA-induced (+CA) MCF10A cells invade into the chick mesodermal layer, with inflammatory cell infiltration and marked focal reactions between chorioallantoic membrane and cell graft. We also demonstrate a key role of small GTPase Rap-1 signalling through inhibition using GGTI-298, which blocked various CA-induced effects. These insights reveal that in normal cells, CA induction alone (without additional oncogenic alterations) is sufficient to confer early pro-tumorigenic changes within days, acting through Rap-1-dependent signalling to alter cell-cell contacts and ECM disruption.

The fate of extra centrosomes in newly formed tetraploid cells: should I stay, or should I go?

An increase in centrosome number is commonly observed in cancer cells, but the role centrosome amplification plays along with how and when it occurs during cancer development is unclear. One mechanism for generating cancer cells with extra centrosomes is whole genome doubling (WGD), an event that occurs in over 30% of human cancers and is associated with poor survival. Newly formed tetraploid cells can acquire extra centrosomes during WGD, and a generally accepted model proposes that centrosome amplification in tetraploid cells promotes cancer progression by generating aneuploidy and chromosomal instability. Recent findings, however, indicate that newly formed tetraploid cells in vitro lose their extra centrosomes to prevent multipolar cell divisions. Rather than persistent centrosome amplification, this evidence raises the possibility that it may be advantageous for tetraploid cells to initially restore centrosome number homeostasis and for a fraction of the population to reacquire additional centrosomes in the later stages of cancer evolution. In this review, we explore the different evolutionary paths available to newly formed tetraploid cells, their effects on centrosome and chromosome number distribution in daughter cells, and their probabilities of long-term survival. We then discuss the mechanisms that may alter centrosome and chromosome numbers in tetraploid cells and their relevance to cancer progression following WGD.

Centrosome instability: when good centrosomes go bad

The centrosome is a tiny cytoplasmic organelle that organizes and constructs massive molecular machines to coordinate diverse cellular processes. Due to its many roles during both interphase and mitosis, maintaining centrosome homeostasis is essential to normal health and development. Centrosome instability, divergence from normal centrosome number and structure, is a common pathognomonic cellular state tightly associated with cancers and other genetic diseases. As novel connections are investigated linking the centrosome to disease, it is critical to understand the breadth of centrosome functions to inspire discovery. In this review, we provide an introduction to normal centrosome function and highlight recent discoveries that link centrosome instability to specific disease states.

Endoplasmic reticulum acetyltransferases Atase1 and Atase2 differentially regulate reticulophagy, macroautophagy and cellular acetyl-CoA metabolism

Nε-lysine acetylation in the ER lumen is a recently discovered quality control mechanism that ensures proteostasis within the secretory pathway. The acetyltransferase reaction is carried out by two type-II membrane proteins, ATase1/NAT8B and ATase2/NAT8. Prior studies have shown that reducing ER acetylation can induce reticulophagy, increase ER turnover, and alleviate proteotoxic states. Here, we report the generation of Atase1-/- and Atase2-/- mice and show that these two ER-based acetyltransferases play different roles in the regulation of reticulophagy and macroautophagy. Importantly, knockout of Atase1 alone results in activation of reticulophagy and rescue of the proteotoxic state associated with Alzheimer's disease. Furthermore, loss of Atase1 or Atase2 results in widespread adaptive changes in the cell acetylome and acetyl-CoA metabolism. Overall, our study supports a divergent role of Atase1 and Atase2 in cellular biology, emphasizing ATase1 as a valid translational target for diseases characterized by toxic protein aggregation in the secretory pathway.

Centrosome amplification mediates small extracellular vesicle secretion via lysosome disruption

Bidirectional communication between cells and their surrounding environment is critical in both normal and pathological settings. Extracellular vesicles (EVs), which facilitate the horizontal transfer of molecules between cells, are recognized as an important constituent of cell-cell communication. In cancer, alterations in EV secretion contribute to the growth and metastasis of tumor cells. However, the mechanisms underlying these changes remain largely unknown. Here, we show that centrosome amplification is associated with and sufficient to promote small extracellular vesicle (SEV) secretion in pancreatic cancer cells. This is a direct result of lysosomal dysfunction, caused by increased reactive oxygen species (ROS) downstream of extra centrosomes. We propose that defects in lysosome function could promote multivesicular body fusion with the plasma membrane, thereby enhancing SEV secretion. Furthermore, we find that SEVs secreted in response to amplified centrosomes are functionally distinct and activate pancreatic stellate cells (PSCs). These activated PSCs promote the invasion of pancreatic cancer cells in heterotypic 3D cultures. We propose that SEVs secreted by cancer cells with amplified centrosomes influence the bidirectional communication between the tumor cells and the surrounding stroma to promote malignancy.

Centrosome-phagy: implications for human diseases

Autophagy is a prominent mechanism to preserve homeostasis and the response to intracellular or extracellular stress. Autophagic degradation can be selectively targeted to dysfunctional subcellular compartments. Centrosome homeostasis is pivotal for healthy proliferating cells, but centrosome aberration is a hallmark of diverse human disorders. Recently, a process called centrosome-phagy has been identified. The process involves a panel of centrosomal proteins and centrosome-related pathways that mediate the specific degradation of centrosomal components via the autophagic machinery. Although autophagy normally mediates centrosome homeostasis, autophagy defects facilitate ageing and multiple human diseases, such as ciliopathies and cancer, which benefit from centrosome aberration. Here, we discuss the molecular systems that trigger centrosome-phagy and its role in human disorders.