Predicting gene-level sensitivity to JAK-STAT signaling perturbation using a mechanistic-to-machine learning framework.

The Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway integrates complex cytokine signals via a limited number of molecular components, inspiring numerous efforts to clarify the diversity and specificity of STAT transcription factor function. We developed a computational framework to make global cytokine-induced gene predictions from STAT phosphorylation dynamics, modeling macrophage responses to interleukin (IL)-6 and IL-10, which signal through common STATs, but with distinct temporal dynamics and contrasting functions. Our mechanistic-to-machine learning model identified cytokine-specific genes associated with late pSTAT3 time frames and a preferential pSTAT1 reduction upon JAK2 inhibition. We predicted and validated the impact of JAK2 inhibition on gene expression, identifying genes that were sensitive or insensitive to JAK2 variation. Thus, we successfully linked STAT signaling dynamics to gene expression to support future efforts targeting pathology-associated STAT-driven gene sets. This serves as a first step in developing multi-level prediction models to understand and perturb gene expression outputs from signaling systems. A record of this paper's transparent peer review process is included in the supplemental information.

Isoform-specific optical activation of kinase function reveals p38-ERK signaling crosstalk.

Evolution has diversified the mammalian proteome by the generation of protein isoforms that originate from identical genes, e.g., through alternative gene splicing or post-translational modifications, or very similar genes found in gene families. Protein isoforms can have either overlapping or unique functions and traditional chemical, biochemical, and genetic techniques are often limited in their ability to differentiate between isoforms due to their high similarity. This is particularly true in the context of highly dynamic cell signaling cascades, which often require acute spatiotemporal perturbation to assess mechanistic details. To that end, we describe a method for the selective perturbation of the individual protein isoforms of the mitogen-activated protein kinase (MAPK) p38. The genetic installation of a photocaging group at a conserved active site lysine enables the precise light-controlled initiation of kinase signaling, followed by investigation of downstream events. Through optical control, we have identified a novel point of crosstalk between two major signaling cascades: the p38/MAPK pathway and the extracellular signal-regulated kinase (ERK)/MAPK pathway. Specifically, using the photoactivated p38 isoforms, we have found the p38γ and p38δ variants to be positive regulators of the ERK signaling cascade, while confirming the p38α and p38ß variants as negative regulators.

Predicting gene level sensitivity to JAK-STAT signaling perturbation using a mechanistic-to-machine learning framework.

The JAK-STAT pathway integrates complex cytokine signals via a limited number of molecular components, inspiring numerous efforts to clarify the diversity and specificity of STAT transcription factor function. We developed a computational workflow to make global cytokine-induced gene predictions from STAT phosphorylation dynamics, modeling macrophage responses to IL-6 and IL-10, which signal through common STATs, but with distinct temporal dynamics and contrasting functions. Our mechanistic-to-machine learning model identified select cytokine-induced gene sets associated with late pSTAT3 timeframes and a preferential pSTAT1 reduction upon JAK2 inhibition. We predicted and validated the impact of JAK2 inhibition on gene expression, identifying dynamically regulated genes that were sensitive or insensitive to JAK2 variation. Thus, we successfully linked STAT signaling dynamics to gene expression to support future efforts targeting pathology-associated STAT-driven gene sets. This serves as a first step in developing multi-level prediction models to understand and perturb gene expression outputs from signaling systems.

SARS-CoV-2 ORF8 Mediates Signals in Macrophages and Monocytes through MyD88 Independently of the IL-17 Receptor.

SARS-CoV-2 has caused an estimated 7 million deaths worldwide to date. A secreted SARS-CoV-2 accessory protein, known as open reading frame 8 (ORF8), elicits inflammatory pulmonary cytokine responses and is associated with disease severity in COVID-19 patients. Recent reports proposed that ORF8 mediates downstream signals in macrophages and monocytes through the IL-17 receptor complex (IL-17RA, IL-17RC). However, generally IL-17 signals are found to be restricted to the nonhematopoietic compartment, thought to be due to rate-limiting expression of IL-17RC. Accordingly, we revisited the capacity of IL-17 and ORF8 to induce cytokine gene expression in mouse and human macrophages and monocytes. In SARS-CoV-2-infected human and mouse lungs, IL17RC mRNA was undetectable in monocyte/macrophage populations. In cultured mouse and human monocytes and macrophages, ORF8 but not IL-17 led to elevated expression of target cytokines. ORF8-induced signaling was fully preserved in the presence of anti-IL-17RA/RC neutralizing Abs and in Il17ra-/- cells. ORF8 signaling was also operative in Il1r1-/- bone marrow-derived macrophages. However, the TLR/IL-1R family adaptor MyD88, which is dispensable for IL-17R signaling, was required for ORF8 activity yet MyD88 is not required for IL-17 signaling. Thus, we conclude that ORF8 transduces inflammatory signaling in monocytes and macrophages via MyD88 independently of the IL-17R.

CISH attenuates homeostatic cytokine signaling to promote lung-specific macrophage programming and function.

Tissue-specific cytokine stimuli orchestrate specialized homeostatic functions of resident macrophages. In the lung, steady-state signaling by the cytokine GM-CSF is critical for alveolar macrophage (AM) development and function. Here, we showed that CISH, a suppressor of cytokine signaling (SOCS) family member that is acutely induced by diverse cytokine stimuli in many tissues, was expressed constitutively in AMs in response to steady-state GM-CSF signaling. Cish deficiency led to the generation of foamy AMs and the accumulation of pulmonary surfactant. These phenotypic changes were associated with enhanced activation of STAT5, AKT, and ERK and increased expression of the gene encoding the transcription factor GATA2. RNA-seq analysis of Cish−/− AMs revealed a set of dysregulated immune and lipid-process modules, including the increased expression of genes enriched for GATA2-binding motifs. Last, Cish-deficient, bone marrow­derived macrophages showed increased Gata2 expression and accumulated more lipid upon incubation with bronchoalveolar lavage fluid compared with Cish-sufficient cells. Thus, CISH is part of a feedback loop that constrains homeostatic cytokine signaling and Gata2 expression to maintain AM identity and function.

Peptide vaccine immunotherapy biomarkers and response patterns in pediatric gliomas.

Low-grade gliomas (LGGs) are the most common brain tumor affecting children. We recently reported an early phase clinical trial of a peptide-based vaccine, which elicited consistent antigen-specific T cell responses in pediatric LGG patients. Additionally, we observed radiologic responses of stable disease (SD), partial response (PR), and near-complete/complete response (CR) following therapy. To identify biomarkers of clinical response in peripheral blood, we performed RNA sequencing on PBMC samples collected at multiple time points. Patients who showed CR demonstrated elevated levels of T cell activation markers, accompanied by a cytotoxic T cell response shortly after treatment initiation. At week 34, patients with CR demonstrated both IFN signaling and Poly-IC:LC adjuvant response patterns. Patients with PR demonstrated a unique, late monocyte response signature. Interestingly, HLA-V expression, before or during therapy, and an early monocytic hematopoietic response were strongly associated with SD. Finally, low IDO1 and PD-L1 expression before treatment and early elevated levels of T cell activation markers were associated with prolonged progression-free survival. Overall, our data support the presence of unique peripheral immune patterns in LGG patients associated with different radiographic responses to our peptide vaccine immunotherapy. Future clinical trials, including our ongoing phase II LGG vaccine immunotherapy, should monitor these response patterns.