The tyrosine kinase Janus kinase 2 (JAK2) binds to the majority of the known members of the cytokine family of receptors. Ligand-receptor binding leads to activation of the associated JAK2 molecules, resulting in rapid autophosphorylation of multiple tyrosines within JAK2. Phosphotyrosines can then serve as docking sites for downstream JAK2 signaling molecules. Despite the importance of these phosphotyrosines in JAK2 function, only a few sites and binding partners have been identified. Using two-dimensional phosphopeptide mapping and a phosphospecific antibody, we identified tyrosine 813 as a site of JAK2 autophosphorylation of overexpressed JAK2 and endogenous JAK2 activated by growth hormone. Tyrosine 813 is contained within a YXXL sequence motif associated with several other identified JAK2 phosphorylation sites. We show that phosphorylation of tyrosine 813 is required for the SH2 domain-containing adapter protein SH2-B␤ to bind JAK2 and to enhance the activity of JAK2 and STAT5B. The homologous tyrosine in JAK3, tyrosine 785, is autophosphorylated in response to interleukin-2 stimulation and is required for SH2-B␤ to bind JAK3. Taken together these data strongly suggest that tyrosine 813 is a site of autophosphorylation in JAK2 and is the SH2-B␤-binding site within JAK2 that is required for SH2-B␤ to enhance activation of JAK2.The Janus kinase family of tyrosine kinases (JAK1, JAK2, JAK3, and Tyk2) plays an essential role in the signaling by all members of the cytokine receptor superfamily. The JAKs promote growth, proliferation, and/or differentiation of many cell types (1, 15). Activation of the JAKs occurs upon ligand binding to its receptor. Activation is thought to occur as a consequence of two JAK molecules being brought into close enough proximity to allow for rapid trans-phosphorylation of the activation loop of each kinase (15). The activated JAK molecules then phosphorylate multiple targets, including the JAKs themselves, the associated receptors, and multiple signaling molecules such as the signal transducers and activators of transcription (STATs) (4,10,16,17). Dysregulation of JAKs can lead to a host of physiological problems, including diseases of the immune system (6) and cancer (22,29,40).Among the JAKs, JAK2 is activated by more than two-thirds of the known cytokine receptor ligands, including growth hormone (GH), prolactin, erythropoietin, and leptin, making it the most studied of the JAK family members (14). Autophosphorylation of JAK2 is an important step in regulating signaling as it leads to activation of the kinase. Autophosphorylation also results in the production of potential docking sites for downstream signaling molecules containing phosphotyrosine binding Src homology 2 (SH2) domains, such as the adapter protein, SH2-B, and the JAK2 inhibitor suppressor of cytokine signaling 1 (SOCS-1). Identification of the autophosphorylation sites on JAK2, therefore, is critical for advancing our understanding of how these kinases signal, and could provide potential targets for pharmaceutical ...

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Background Detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA in blood, also known as RNAemia, has been reported, but its prognostic implications are poorly understood. This study aimed to determine the frequency of SARS-CoV-2 RNA in plasma and its association with coronavirus disease 2019 (COVID-19) clinical severity. Methods An analytical cross-sectional study was performed in a single-center tertiary care institution and included consecutive inpatients and outpatients with confirmed COVID-19. The prevalence of SARS CoV-2 RNAemia and the strength of its association with clinical severity variables were examined and included intensive care unit (ICU) admission, invasive mechanical ventilation, and 30-day all-cause mortality. Results Paired nasopharyngeal and plasma samples were included from 85 patients. The median age was 55 years, and individuals with RNAemia were older than those with undetectable SARS-CoV-2 RNA in plasma (63 vs 50 years; P = .04). Comorbidities were frequent including obesity (37.6%), hypertension (30.6%), and diabetes mellitus (22.4%). RNAemia was detected in 28/85 (32.9%) of patients, including 22/28 (78.6%) who required hospitalization. In models adjusted for age, RNAemia was detected more frequently in individuals who developed severe disease including ICU admission (32.1 vs 14.0%; P = .04) and invasive mechanical ventilation (21.4% vs 3.5%; P = .02). All 4 deaths occurred in individuals with detectable RNAemia. An additional 121 plasma samples from 28 individuals with RNAemia were assessed longitudinally, and RNA was detected for a maximum duration of 10 days. Conclusions This study demonstrated a high proportion of SARS-CoV-2 RNAemia, and an association between RNAemia and clinical severity suggesting the potential utility of plasma viral testing as a prognostic indicator for COVID-19.

A subset of myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) show complex karyotype (CK), and these cases include a relatively high proportion of cases of therapy-related myeloid neoplasms and TP53 mutations. We aimed to evaluate the clinicopathologic features of outcome of 299 AML and MDS patients with CK. Mutations were present in 287 patients (96%) and the most common mutation detected was in TP53 gene (83%). A higher frequency of TP53 mutations was present in therapy-related cases (p=0.008) with a trend for worse overall survival (OS) in therapy-related patients as compared with de novo (p=0.08) and within the therapy-related group, the presence of TP53 mutation strongly predicted for worse outcome (p=0.0017). However, there was no difference in survival between CK patients based on categorization of AML versus MDS, (p=0.96) or presence of absence of circulating blasts ≥1% (p=0.52). TP53 mutated patients presented with older age (p=0.06) and lower hemoglobin (p=0.004) and marrow blast (p=0.02) compared to those with CK lacking TP53 mutation. Multivariable analysis identified presence of multi-hit TP53 mutation as strongest predictor of worse outcome, while neither a diagnosis of AML versus MDS nor therapy-relatedness independently influenced OS. Our findings suggest that among patients with MDS and AML, the presence of TP53 mutation (in particular multi-hit TP53 mutation) in the context of CK identifies a homogeneously aggressive disease, irrespective of the blast count at presentation or therapy-relatedness. The current classification of these cases into different disease categories artificially separates a single biologic disease entity.