Characterisation of the role of DRAM-related TMEM150 proteins in cancer cell survival, cell death and autophagy

Abstract

Autophagy, a cellular recycling mechanism, and apoptosis, a regulated mode of cell death, are two fundamental cellular processes that contribute to carcinogenesis and tumour growth as well as treatment sensitivity and resistance. The protein encoded by DRAM1, a p53-responsive gene, has previously been described as an autophagy and apoptosis modulator downstream of p53 activation. Furthermore, a family of DRAM1-related proteins has been uncovered by in silico analysis. Of the 5 members of this protein family, only DRAM1 and DRAM-2 had previously been tested for their roles in cell death and autophagy. Much less was known about the remaining three DRAM-family members TMEM150A/B/C (termed DRAM-5/-3/-4 by us for ‘DRAM-related/associated member-5/-3/-4’) and their potential roles in autophagy, cell death or cell survival in cancer cells. In this project, we therefore aimed to test whether these DRAM-family proteins could modulate autophagy, cell death or cell survival in in vitro cancer cell line systems. We used both retroviral, constitutive overexpression systems and CRISPR/Cas9-mediated gene disruption systems to study the effect of TMEM150 overexpression or TMEM150 ablation on these processes. In summary, we found that none of the TMEM150 genes were induced by p53, but starvation conditions increased TMEM150A and C transcript levels in some conditions. Moderate changes in TMEM150 protein levels showed no dramatic effect on cell growth and survival. Of the three TMEM150 proteins, only TMEM150B affected autophagy, while TMEM150A and C did not modulate autophagic processes in any of the assays performed. Moreover, we show that TMEM150B overexpression can improve cellular survival under glucose deprived conditions, while none of the other DRAM-family proteins seems capable of doing so. Additionally, serum or amino acid starvation did not show parallel effects. Lastly, we show that the influence of TMEM150B on autophagic processes is uncoupled from its ability to modulate survival in glucose-starved cells. Taken all together, with this work we provide an initial characterisation of the TMEM150 proteins, which may lay a foundation for future, expanded studies on the cellular functions of the DRAM-family