Loss of ATG4B and ATG4A results in two-stage cell cycle defects in pancreatic ductal adenocarcinoma cells.

Pancreatic ductal adenocarcinoma (PDAC) exhibits elevated levels of autophagy, which promote tumor progression and treatment resistance. ATG4B is an autophagy-related cysteine protease under consideration as a potential therapeutic target, but it is largely unexplored in PDAC. Here, we investigated the clinical and functional relevance of ATG4B expression in PDAC. Using two PDAC patient cohorts, we found that low ATG4B mRNA or protein expression is associated with worse patient survival outcomes, poorly differentiated PDAC tumors and a lack of survival benefit from adjuvant chemotherapy. In PDAC cell lines, ATG4B knockout reduced proliferation, abolished processing of LC3B (also known as MAP1LC3B), and reduced GABARAP and GABARAPL1 levels, but increased ATG4A levels. ATG4B and ATG4A double knockout lines displayed a further reduction in proliferation, characterized by delays in G1-S phase transition and mitosis. Pro-LC3B accumulated aberrantly at the centrosome with a concomitant increase in centrosomal proteins PCM1 and CEP131, which was rescued by exogenous ATG4B. The two-stage cell cycle defects following ATG4B and ATG4A loss have important therapeutic implications for PDAC.

Inhibition of glutamine-dependent autophagy increases t-PA production in CHO cell fed-batch processes.

Understanding the cellular responses caused by metabolic stress is crucial for the design of robust fed-batch bioprocesses that maximize the expression of recombinant proteins. Chinese hamster ovary cells were investigated in chemically defined, serum-free cultures yielding 10(7) cells/mL and up to 500 mg/L recombinant tissue-plasminogen activator (t-PA). Upon glutamine depletion increased autophagosome formation and autophagic flux were observed, along with decreased proliferation and high viability. Higher lysosomal levels correlated with decreased productivity. Chemical inhibition of autophagy with 3-methyl adenine (3-MA) increased the t-PA yield by 2.8-fold. Autophagy-related MAP1LC3 and LAMP2 mRNA levels increased continuously in all cultures. Analysis of protein quality revealed that 3-MA treatment did not alter glycan antennarity while increasing fucosylation, galactosylation, and sialylation. Taken together, these findings indicate that inhibition of autophagy can considerably increase the yield of biotechnology fed-batch processes, without compromising the glycosylation capacity of cells. Monitoring or genetic engineering of autophagy provides novel avenues to improve the performance of cell culture-based recombinant protein production.

Raman microspectroscopy of live cells under autophagy-inducing conditions.

The role of autophagy in numerous physiological responses triggered by a variety of mechanisms both in states of health and disease has raised considerable interest in this cellular process. However, the current analytical tools to study autophagy are either invasive or require genetic manipulation. Raman microspectroscopy is a potentially quantitative analytical method that has been shown to be useful for the label-free, non-destructive analysis of living biological cells and tissues. We present in this study initial efforts to study autophagy using Raman spectroscopy. The response of adherent mouse and human cancer cells to starvation conditions (glutamine deprivation and amino acid deprivation) was probed by Raman spectroscopy and compared to fluorescence microscopy results using autophagy-specific markers. We also demonstrate the capability of Raman spectroscopy to monitor the recovery dynamics of starved cells and to probe the heterogeneity in the response to starvation that can arise in cell populations. Finally, this work suggests that the 718 cm(-1) Raman line associated with phospholipids may be a useful spectral marker indicative of an autophagic response to starvation stimuli. Overall, this study establishes the utility of Raman spectroscopy to non-invasively detect biologically relevant changes in live cells exposed to conditions known to trigger autophagy.

Effects of cysteine, asparagine, or glutamine limitations in Chinese hamster ovary cell batch and fed-batch cultures.

Amino acid availability is a key factor that can be controlled to optimize the productivity of fed-batch cultures. To study amino acid limitation effects, a serum-free chemically defined basal medium was formulated to exclude the amino acids that became depleted in batch culture. The effect of limiting glutamine, asparagine, and cysteine on the cell growth, metabolism, antibody productivity, and product glycosylation was investigated in three Chinese hamster ovary (CHO) cell lines (CHO-DXB11, CHO-K1SV, and CHO-S). Cysteine limitation was detrimental to both cell proliferation and productivity for all three CHO cell lines. Glutamine limitation reduced growth but not cell specific productivity, whereas asparagine limitation had no significant effect on either growth or cell specific productivity. Neither glutamine nor asparagine limitation significantly affected antibody glycosylation. Replenishing the CHO-DXB11 culture with cysteine after 1 day of cysteine limitation allowed the cells to partially recover their growth and productivity. This recovery was not observed after 2 days of cysteine limitation. Based on these findings, a fed-batch protocol was developed using single or mixed amino acid supplementation. Although cell density and antibody concentration were lower compared to a commercial feed, the feeds based on cysteine supplementation yielded comparable cell specific productivity. Overall, this study showed that different amino acid limitations have varied effects on the performance of CHO cell cultures and that maintaining cysteine availability is a critical process parameter for the three cell lines investigated.

Autophagy: from structure to metabolism to therapeutic regulation.

Multidisciplinary approaches are increasingly being used to elucidate the role of autophagy in health and disease and to harness it for therapeutic purposes. The broad range of topics included in the program of the Vancouver Autophagy Symposium (VAS) 2013 illustrated this multidisciplinarity: structural biology of Atg proteins, mechanisms of selective autophagy, in silico drug design targeting ATG proteins, strategies for drug screening, autophagy-metabolism interplay, and therapeutic approaches to modulate autophagy. VAS 2013 took place at the British Columbia Cancer Research Centre, and was hosted by the CIHR Team in Investigating Autophagy Proteins as Molecular Targets for Cancer Treatment. The program was designed as a day of research exchanges, featuring two invited keynote speakers, internationally recognized for their groundbreaking contributions in autophagy, Dr Ana Maria Cuervo (Albert Einstein College of Medicine, Bronx, NY) and Dr Jayanta Debnath (University of California, San Francisco). By bringing together international and local experts in cell biology, drug discovery, and clinical translation, the symposium facilitated rich interdisciplinary discussions focused on multiple forms of autophagy and their regulation and modulation in the context of cancer.

Fed-batch CHO cell t-PA production and feed glutamine replacement to reduce ammonia production.

Industrial therapeutic protein production has been greatly improved through fed-batch development. In this study, improvement to the productivity of a tissue-plasminogen activator (t-PA) expressing Chinese hamster ovary (CHO) cell line was investigated in shake flask culture through the optimization of the fed-batch feed and the reduction of ammonia generation by glutamine replacement. The t-PA titer was increased from 33 mg/L under batch conditions to 250 mg/L with daily feeding starting after three days of culture. A commercially available fed-batch feed was supplemented with cotton seed hydrolysate and the four depleted amino acids, aspartic acid, asparagine, cysteine, and tyrosine. The fed-batch operation increased the generation of by-products such as lactate and ammonia that can adversely affect the fed-batch performance. To reduce the ammonia production, a glutamine-containing dipeptide, pyruvate, glutamate, and wheat gluten hydrolysate, were investigated as glutamine substitutes. To minimize the lag phase as the cells adjusted to the new energy source, a feed glutamine replacement process was developed where the cells were initially cultured with a glutamine containing basal medium to establish cell growth followed by feeding with a feed containing the glutamine substitutes. This two-step feed glutamine replacement process not only reduced the ammonia levels by over 45% but, in the case of using wheat gluten hydrolysate, almost doubled the t-PA titer to over 420 mg/L without compromising the t-PA product quality or glycosylation pattern. The feed glutamine replacement process combined with optimizing other feed medium components provided a simple, practical, and effective fed-batch strategy that could be applied to the production of other recombinant therapeutic proteins.