C16orf72/HAPSTR1 is a molecular rheostat in an integrated network of stress response pathways

All cells contain specialized signaling pathways which enable adaptation to specific molecular stressors. Yet, whether these pathways are centrally regulated in complex physiological stress states remains unclear. Using genome-scale fitness screening data, we quantified the stress phenotype of 739 cancer cell lines, each representing a unique combination of intrinsic tumor stresses. Integrating dependency and stress perturbation transcriptomic data, we illuminate a network of genes with vital functions spanning diverse stress contexts. Analyses for central regulators of this network nominated C16orf72/HAPSTR1, an evolutionarily ancient gene critical for the fitness of cells reliant on multiple stress response pathways. We find that HAPSTR1 plays a pleiotropic role in cellular stress signaling, functioning to titrate various specialized cell-autonomous and paracrine stress response programs. This function, while dispensable to unstressed cells and nematodes, is essential for resilience in the presence of stressors ranging from DNA damage to starvation and proteotoxicity. Mechanistically, diverse stresses induce HAPSTR1, which encodes a protein expressed as two equally abundant isoforms. Perfectly conserved residues in a domain shared between HAPSTR1 isoforms mediate oligomerization and binding to the ubiquitin ligase HUWE1. We show that HUWE1 is a required cofactor for HAPSTR1 to control stress signaling, and that in turn, HUWE1 feeds back to ubiquitinate and destabilize HAPSTR1. Altogether, we propose that HAPSTR1 is a central rheostat in a network of pathways responsible for cellular adaptability, the modulation of which may have broad utility in human disease. Comparative RNA-seq profiling various cell lines after siRNA knockdown of HAPSTR1 and/or HUWE1 in the presence or absence of molecular stressors.

所有细胞均拥有特化的信号通路，介导其对特定分子应激源的适应性应答。然而，在复杂的生理应激状态下，这些通路是否受到中枢调控仍未阐明。本研究依托全基因组适应性筛选（genome-scale fitness screening）数据，对739株癌细胞系的应激表型（stress phenotype）进行了定量分析——每一株细胞系均对应一组独特的固有肿瘤应激组合。通过整合基因依赖数据与应激扰动转录组（stress perturbation transcriptomic）数据，本研究阐明了一个覆盖多种应激场景、具备核心功能的基因调控网络。针对该网络的中枢调控因子分析，筛选出了C16orf72/HAPSTR1——这是一个进化上高度保守的古老基因，对依赖多种应激应答通路的细胞的生存适合度至关重要。研究发现，HAPSTR1在细胞应激信号通路中发挥多效性调控作用，可精准调控多种特化的细胞自主性及旁分泌应激应答程序。该功能对未受应激的细胞及线虫（nematodes）而言并非必需，但在面对DNA损伤、饥饿、蛋白毒性应激（proteotoxicity）等多种应激源时，却是维持细胞存活的关键。从机制层面来看，多种应激均可诱导HAPSTR1的表达；该基因编码的蛋白存在两种丰度相当的剪接同工型。HAPSTR1两种同工型共有的结构域中存在完全保守的残基，这些残基可介导蛋白寡聚化（oligomerization）以及与泛素连接酶（ubiquitin ligase）HUWE1的结合。研究证实，HUWE1是HAPSTR1调控应激信号通路所必需的辅因子；反之，HUWE1也会通过反馈通路对HAPSTR1进行泛素化修饰，降低其稳定性。综上，本研究提出HAPSTR1是调控细胞适应性的通路网络中的核心调谐枢纽，对其进行干预有望在人类疾病治疗中具备广泛应用前景。本研究配套的数据集包含：在存在或缺失分子应激源的条件下，对经siRNA敲低HAPSTR1和/或HUWE1的多种细胞系开展的比较RNA测序（RNA-seq）转录组分析。