Immune profiling of COVID-19 patients has identified numerous alterations in both innate and adaptive immunity. However, whether those changes are specific to SARS-CoV-2 or driven by a general inflammatory response shared across severely ill pneumonia patients remains unknown. Here, we compared the immune profile of severe COVID-19 with non-SARS-CoV-2 pneumonia ICU patients using longitudinal, high-dimensional single-cell spectral cytometry and algorithm-guided analysis. COVID-19 and non-SARS-CoV-2 pneumonia both showed increased emergency myelopoiesis and displayed features of adaptive immune paralysis. However, pathological immune signatures suggestive of T cell exhaustion were exclusive to COVID-19. The integration of single-cell profiling with a predicted binding capacity of SARS-CoV-2-petides to the patients’ HLA profile further linked the COVID-19 immunopathology to impaired virus recognition. Towards clinical translation, circulating NKT cell frequency was identified as a predictive biomarker for patient outcome. Our comparative immune map serves to delineate treatment strategies to interfere with the immunopathologic cascade exclusive to severe COVID-19.
Son of Sevenless 1 (SOS1) is a dual guanine nucleotide exchange factor (GEF) that activates the small GTPases RAC and RAS. While the molecular mechanisms of RAS GEF catalysis have been unveiled, how SOS1 acquires RAC GEF activity and what is the physio-pathological relevance of this activity is much less understood. Here, we show that SOS1 is tyrosine phosphorylated on Y1196 by ABL. Phosphorylation of Y1196 controls SOS1 inter-molecular interaction, is required to promote the exchange of nucleotides on RAC in vitro, and for PDGF activation of RAC and RAC-dependent actin remodeling and cell migration. SOS1 is also phosphorylated on Y1196 by BCR-ABL in chronic myelogenous leukemic (CML) cells. Importantly, in these cells, SOS1 is required for BCR-ABL-mediated activation of RAC, cell proliferation and transformation in vitro and in a xenograft mouse model. Finally, genetic removal of Sos1 in bone marrow derived cells (BMDC) from Sos1fl/fl mice and infected with BCR-ABL causes a significant delay in the onset of leukemogenesis once BMDC are injected into recipient, lethally irradiated mice. Thus, SOS1 is required for full transformation and critically contribute to the leukemogenic potential of BCR-ABL.
Activating mutations in FMS-like tyrosine kinase receptor-3 (FLT3) and Nucleophosmin-1 (NPM1) are most frequent alterations in acute myeloid leukemia (AML), and are often coincidental. The mutational status of NPM1 has strong prognostic relevance to patients with point mutations of the FLT3 tyrosine kinase domain (TKD), but the biological mechanism underlying this effect remains unclear. In the present study, we investigated the effect of the coincidence of NPM1c and FLT3-TKD. Although expression of FLT3-TKD is not sufficient to induce a disease in mice, coexpression with NPM1c rapidly leads to an aggressive myeloproliferative disease in mice with a latency of 31.5 days. Mechanistically, we could show that FLT3-TKD is able to activate the downstream effector molecule signal transducer and activator of transcription 5 (STAT5) exclusively in the presence of mutated NPM1c. Moreover, NPM1c alters the cellular localization of FLT3-TKD from the cell surface to the endoplasmic reticulum, which might thereby lead to the aberrant STAT5 activation. Importantly, aberrant STAT5 activation occurs not only in primary murine cells but also in patients with AML with combined FLT3-TKD and NPM1c mutations. Thus, our data indicate a new mechanism, how NPM1c mislocalizes FLT3-TKD and changes its signal transduction ability.
Background: NIPA is involved in timing mitotic entry and is inactivated by phosphorylation. The kinase responsible for NIPA phosphorylation at G 2 /M is unknown. Results: We show that cell cycle-dependent phosphorylation of NIPA is mediated by ERK2. Conclusion: NIPA is identified as one of the very few ERK2-specific substrates at the G 2 /M transition. Significance: This demonstrates divergent functions of ERK1 and ERK2 in cell cycle regulation.
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