Noonan syndrome (MIM 163950) is characterized by short stature, facial dysmorphism and cardiac defects. Heterozygous mutations in PTPN11, which encodes SHP-2, cause approximately 50% of cases of Noonan syndrome. The SHP-2 phosphatase relays signals from activated receptor complexes to downstream effectors, including Ras. We discovered de novo germline KRAS mutations that introduce V14I, T58I or D153V amino acid substitutions in five individuals with Noonan syndrome and a P34R alteration in a individual with cardio-facio-cutaneous syndrome (MIM 115150), which has overlapping features with Noonan syndrome. Recombinant V14I and T58I K-Ras proteins show defective intrinsic GTP hydrolysis and impaired responsiveness to GTPase activating proteins, render primary hematopoietic progenitors hypersensitive to growth factors and deregulate signal transduction in a cell lineage-specific manner. These studies establish germline KRAS mutations as a cause of human disease and infer that the constellation of developmental abnormalities seen in Noonan syndrome spectrum is, in large part, due to hyperactive Ras.

Germ line PTPN11 mutations cause 50% of cases of Noonan syndrome (NS). Somatic mutations in PTPN11 occur in 35% of patients with de novo, nonsyndromic juvenile myelomonocytic leukemia (JMML). Myeloproliferative disorders (MPDs), either transient or more fulminant forms, can also occur in infants with NS (NS/MPD). We identified PTPN11 mutations in blood or bone marrow specimens from 77 newly reported patients with JMML (n ‫؍‬ 69) or NS/MPD (n ‫؍‬ 8). Together with previous reports, we compared the spectrum of PTPN11 mutations in 3 groups: (1) patients with JMML (n ‫؍‬ 107); (2) patients with NS/MPD (n ‫؍‬ 19); and (3) patients with NS (n ‫؍‬ 243). Glu76 was the most commonly affected residue in JMML (n ‫؍‬ 45), with the Glu76Lys alteration (n ‫؍‬ 29) being most frequent. Eight of 19 patients with NS/ MPD carried the Thr73Ile substitution. These data suggest that there is a genotype/phenotype correlation in the spectrum of PTPN11 IntroductionThe PTPN11 proto-oncogene encodes Src-homology tyrosine phosphatase 2 (SHP-2), a protein tyrosine phosphatase with a role in signal transduction and hematopoiesis. 1,2 Somatic PTPN11 mutations exist in 35% of juvenile myelomonocytic leukemia (JMML) specimens and are less frequent in other leukemias. 3-6 SHP-2 relays signals from activated growth factor receptors to Ras. PTPN11, KRAS2, NRAS, and NF1 mutations are found in mutually exclusive subsets of patients with JMML. 3,4 These data support the hypothesis that hyperactive Ras signaling plays a central role in JMML.Germ-line PTPN11 mutations cause approximately 50% of cases of Noonan syndrome (NS), 7,8 a congenital disorder characterized by facial anomalies, short stature, and heart defects. 9 Whereas NS is frequently inherited as an autosomal dominant condition, almost half of the constitutional PTPN11 mutations found in NS arise sporadically. Germ-line PTPN11 mutations are also found in patients with multiple lentigene syndrome (LS), a rare developmental disorder clinically related to NS. 9 Infants with NS are predisposed to developing a myeloproliferative disorder (NS/MPD), which may regress without treatment or follow an aggressive clinical course similar to JMML. 10-14 By contrast, cases of JMML that arise in patients without NS have a poor prognosis without hematopoietic stem cell transplantation. [15][16][17][18] Recent studies show that children with JMML have improved outcomes when they are treated aggressively early in the course of disease. 18 Therefore, differentiating JMML from NS/MPD and identifying patients with NS/MPD who will require aggressive treatment are important clinical questions. We identify PTPN11 mutations in 77 newly reported patients with JMML and NS/MPD, and compare the mutational spectrum in JMML, NS/MPD, and NS/LS to determine if genotype-phenotype correlations exist that may help guide diagnosis and clinical management. Study designTissue samples (bone marrow, peripheral blood, and, rarely, buccal swab and skin fibroblasts) from patients with JMML and NS/MPD were collected under Institutional...

SummaryWhen Trypanosoma brucei differentiates from the bloodstream form to the procyclic form, there are decreases in the levels of many mRNAs encoding proteins required for the glycolytic pathway, and the mRNA encoding the RNA recognition motif protein RBP10 decreases in parallel. We show that RBP10 is a cytoplasmic protein that is specific to bloodstreamform trypanosomes, where it is essential. Depletion of RBP10 caused decreases in many bloodstream-formspecific mRNAs, with increases in mRNAs associated with the early stages of differentiation. The changes were similar to, but more extensive than, those caused by glucose deprivation. Conversely, forced RBP10 expression in procyclics induced a switch towards bloodstream-form mRNA expression patterns, with concomitant growth inhibition. Forced expression of RBP10 prevented differentiation of bloodstream forms in response to cis-aconitate, but did not prevent expression of key differentiation markers in response to glucose deprivation. RBP10 was not associated with heavy polysomes, showed no detectable in vivo binding to RNA, and was not stably associated with other proteins. Tethering of RBP10 to a reporter mRNA inhibited translation, and halved the abundance of the bound mRNA. We suggest that RBP10 may prevent the expression of regulatory proteins that are specific to the procyclic form.

Granulomas are immune cell aggregates formed in response to persistent inflammatory stimuli. Granuloma macrophage subsets are diverse and carry varying copy numbers of their genomic information. The molecular programs that control the differentiation of such macrophage populations in response to a chronic stimulus, though critical for disease outcome, have not been defined. Here, we delineate a macrophage differentiation pathway by which a persistent Toll-like receptor (TLR) 2 signal instructs polyploid macrophage fate by inducing replication stress and activating the DNA damage response. Polyploid granuloma-resident macrophages formed via modified cell divisions and mitotic defects and not, as previously thought, by cell-to-cell fusion. TLR2 signaling promoted macrophage polyploidy and suppressed genomic instability by regulating Myc and ATR. We propose that, in the presence of persistent inflammatory stimuli, pathways previously linked to oncogene-initiated carcinogenesis instruct a long-lived granuloma-resident macrophage differentiation program that regulates granulomatous tissue remodeling.