Autophagy cooperates with PDGFRA to support oncogenic growth signaling.

Macroautophagy (referred to as autophagy hereafter) is a highly conserved catabolic process which sequesters intracellular substrates for lysosomal degradation. Autophagy-related proteins have been shown to be involved in various aspects of tumor development by engaging with multiple cellular substrates. We recently uncovered a novel role for autophagy in regulating the signaling and levels of PDGFRA, a receptor tyrosine kinase amplified in several cancers. We discovered that PDGFRA can be targeted to autophagic degradation by binding the autophagy cargo receptor SQSTM1. Surprisingly, PDGFRA-mediated signaling is perturbed in the absence of autophagy despite enhanced receptor levels. We show that this is due to disrupted trafficking of the receptor to late endosomes where signaling activity persists. Conversely, prolonged autophagy inhibition results in a transcriptional downregulation of Pdgfra as a result of inhibited signaling activity demonstrating that short- and long-term autophagy inhibition have opposing effects on receptor levels. We further investigated the consequence of PDGFRA regulation by autophagy using a mouse model for gliomagenesis where we observed a disruption in PDGFA-driven tumor formation when autophagy is inhibited. Activation of downstream signaling through Pten mutation overrides the need for autophagy during tumor development suggesting a genotype-specific role for autophagy during tumorigenesis. Altogether, our findings provide a novel mechanism through which autophagy can support tumor growth.

Autophagy supports PDGFRA-dependent brain tumor development by enhancing oncogenic signaling.

Autophagy is a conserved cellular degradation process. While autophagy-related proteins were shown to influence the signaling and trafficking of some receptor tyrosine kinases, the relevance of this during cancer development is unclear. Here, we identify a role for autophagy in regulating platelet-derived growth factor receptor alpha (PDGFRA) signaling and levels. We find that PDGFRA can be targeted for autophagic degradation through the activity of the autophagy cargo receptor p62. As a result, short-term autophagy inhibition leads to elevated levels of PDGFRA but an unexpected defect in PDGFA-mediated signaling due to perturbed receptor trafficking. Defective PDGFRA signaling led to its reduced levels during prolonged autophagy inhibition, suggesting a mechanism of adaptation. Importantly, PDGFA-driven gliomagenesis in mice was disrupted when autophagy was inhibited in a manner dependent on Pten status, thus highlighting a genotype-specific role for autophagy during tumorigenesis. In summary, our data provide a mechanism by which cells require autophagy to drive tumor formation.

Temozolomide sensitivity of malignant glioma cell lines - a systematic review assessing consistencies between in vitro studies.

BACKGROUND: Malignant glioma cell line models are integral to pre-clinical testing of novel potential therapies. Accurate prediction of likely efficacy in the clinic requires that these models are reliable and consistent. We assessed this by examining the reporting of experimental conditions and sensitivity to temozolomide in glioma cells lines. METHODS: We searched Medline and Embase (Jan 1994-Jan 2021) for studies evaluating the effect of temozolomide monotherapy on cell viability of at least one malignant glioma cell line. Key data items included type of cell lines, temozolomide exposure duration in hours (hr), and cell viability measure (IC50). RESULTS: We included 212 studies from 2789 non-duplicate records that reported 248 distinct cell lines. The commonest cell line was U87 (60.4%). Only 10.4% studies used a patient-derived cell line. The proportion of studies not reporting each experimental condition ranged from 8.0-27.4%, including base medium (8.0%), serum supplementation (9.9%) and number of replicates (27.4%). In studies reporting IC50, the median value for U87 at 24 h, 48 h and 72 h was 123.9 µM (IQR 75.3-277.7 µM), 223.1 µM (IQR 92.0-590.1 µM) and 230.0 µM (IQR 34.1-650.0 µM), respectively. The median IC50 at 72 h for patient-derived cell lines was 220 µM (IQR 81.1-800.0 µM). CONCLUSION: Temozolomide sensitivity reported in comparable studies was not consistent between or within malignant glioma cell lines. Drug discovery science performed on these models cannot reliably inform clinical translation. A consensus model of reporting can maximise reproducibility and consistency among in vitro studies.

The impact of autophagy during the development and survival of glioblastoma.

Glioblastoma is the most common and aggressive adult brain tumour, with poor median survival and limited treatment options. Following surgical resection and chemotherapy, recurrence of the disease is inevitable. Genomic studies have identified key drivers of glioblastoma development, including amplifications of receptor tyrosine kinases, which drive tumour growth. To improve treatment, it is crucial to understand survival response processes in glioblastoma that fuel cell proliferation and promote resistance to treatment. One such process is autophagy, a catabolic pathway that delivers cellular components sequestered into vesicles for lysosomal degradation. Autophagy plays an important role in maintaining cellular homeostasis and is upregulated during stress conditions, such as limited nutrient and oxygen availability, and in response to anti-cancer therapy. Autophagy can also regulate pro-growth signalling and metabolic rewiring of cancer cells in order to support tumour growth. In this review, we will discuss our current understanding of how autophagy is implicated in glioblastoma development and survival. When appropriate, we will refer to findings derived from the role of autophagy in other cancer models and predict the outcome of manipulating autophagy during glioblastoma treatment.