Development and Pilot Screen of Novel High Content Assay for Down Regulators of Expression of Heterogenous Nuclear Ribonuclear Protein H2.

BACKGROUND/AIMS: Despite recent advances in melanoma drug discovery, the average overall survival of patients with late-stage metastatic melanoma is approximately 3 years, suggesting a need for new approaches and melanoma therapeutic targets. Previously we identified heterogeneous nuclear ribonucleoprotein H2 as a potential target of anti-melanoma compound 2155-14 (Palrasu et al., Cell Physiol Biochem 2019;53:656-686). In the present study, we endeavored to develop an assay to enable a high throughput screening campaign to identify drug-like molecules acting via down regulation of heterogeneous nuclear ribonucleoprotein H2 that can be used for melanoma therapy and research. METHODS: We established a cell-based platform using metastatic melanoma cell line WM266-4 expressing hnRNPH2 conjugated with green fluorescent protein to enable assay development and screening. High Content Screening assay was developed and validated in 384 well plate format, followed by miniaturization to 1,536 well plate format. RESULTS: All plate-based QC parameters were acceptable: %CV = 6.7±0.3, S/B = 21±2.1, Z' = 0.75±0.04. Pilot screen of FDA-approved drug library (n=1,400 compounds) demonstrated hit rate of 0.5%. Two compounds demonstrated pharmacological response and were authenticated by western blot analysis. CONCLUSION: We developed a highly robust HTS-amenable high content screening assay capable of monitoring down regulation of hnRNPH2. This assay is thus capable of identifying authentic down regulators of hnRNPH1 and 2 in a large compound collection and, therefore, is amenable to a large-scale screening effort.

Cyclic GMP-AMP synthase promotes the inflammatory and autophagy responses in Huntington disease.

Huntington disease (HD) is caused by an expansion mutation of the N-terminal polyglutamine of huntingtin (mHTT). mHTT is ubiquitously present, but it induces noticeable damage to the brain's striatum, thereby affecting motor, psychiatric, and cognitive functions. The striatal damage and progression of HD are associated with the inflammatory response; however, the underlying molecular mechanisms remain unclear. Here, we report that cGMP-AMP synthase (cGAS), a DNA sensor, is a critical regulator of inflammatory and autophagy responses in HD. Ribosome profiling revealed that the cGAS mRNA has high ribosome occupancy at exon 1 and codon-specific pauses at positions 171 (CCG) and 172 (CGT) in HD striatal cells. Moreover, the protein levels and activity of cGAS (based on the phosphorylated STING and phosphorylated TBK1 levels), and the expression and ribosome occupancy of cGAS-dependent inflammatory genes (Ccl5 and Cxcl10) are increased in HD striatum. Depletion of cGAS diminishes cGAS activity and decreases the expression of inflammatory genes while suppressing the up-regulation of autophagy in HD cells. In contrast, reinstating cGAS in cGAS-depleted HD cells activates cGAS activity and promotes inflammatory and autophagy responses. Ribosome profiling also revealed that LC3A and LC3B, the two major autophagy initiators, show altered ribosome occupancy in HD cells. We also detected the presence of numerous micronuclei, which are known to induce cGAS, in the cytoplasm of neurons derived from human HD embryonic stem cells. Collectively, our results indicate that cGAS is up-regulated in HD and mediates inflammatory and autophagy responses. Thus, targeting the cGAS pathway may offer therapeutic benefits in HD.