The PTPN11 gene encodes SHP-2 (Src homology 2 domain-containing protein tyrosine Phosphatase), a nonreceptor tyrosine protein tyrosine phosphatase (PTPase) that relays signals from activated growth factor receptors to p21 Ras (Ras) and other signaling molecules. Mutations in PTPN11 cause Noonan syndrome (NS), a developmental disorder characterized by cardiac and skeletal defects. NS is also associated with a spectrum of hematologic disorders, including juvenile myelomonocytic leukemia (JMML). To test the hypothesis that PTPN11 mutations might contribute to myeloid leukemogenesis, we screened the entire coding region for mutations in 51 JMML specimens and in selected exons from 60 patients with other myeloid malignancies. Missense mutations in PTPN11 were detected in 16 of 49 JMML specimens from patients without NS, but they were less common in other myeloid malignancies. RAS, NF1, and PTPN11 mutations are largely mutually exclusive in JMML, which suggests that mutant SHP-2 proteins deregulate myeloid growth through Ras. However, although Ba/F3 cells engineered to express leukemia-associated SHP-2 proteins cells showed enhanced growth factor-independent survival, biochemical analysis failed to demonstrate hyperactivation of the Ras effectors extracellular-regulated kinase (ERK) or Akt. We conclude that SHP-2 is an important cellular PTPase that is mutated in myeloid malignancies. Further investigation is required to clarify how these mutant proteins interact with Ras and other effectors to deregulate myeloid growth. (Blood.

National Heart, Lung, and Blood Institute.

A challenge in biology is to understand how complex molecular networks in the cell execute sophisticated regulatory functions. Here we explore the idea that there are common and general principles that link network structures to biological functions, principles that constrain the design solutions that evolution can converge upon for accomplishing a given cellular task. We describe approaches for classifying networks based on abstract architectures and functions, rather than on the specific molecular components of the networks. For any common regulatory task, can we define the space of all possible molecular solutions? Such inverse approaches might ultimately allow the assembly of a design table of core molecular algorithms that could serve as a guide for building synthetic networks and modulating disease networks.

The influence of caloric restriction (CR) initiated at 17 months of age was investigated on selected age-associated measures in skeletal muscle. Tissue from young (3-4 months) ad libitum-fed, old (30-32 months) restricted (35% and 50% CR, designated CR35 and CR50, respectively), and old ad libitum-fed rats (29 months) was studied. CR preserved fiber number and fiber type composition in the vastus lateralis muscle of the CR50 rats. In the old rats from all groups, individual fibers were found with either no detectable cytochrome c oxidase activity (COX-), hyperreactivity for succinate dehydrogenase activity (SDH++; also known as ragged red fibers [RRF]), or both COX- and SDH++. Muscle from the CR50 rats contained significantly fewer COX- and SDH++ fibers than did the muscle from CR35 rats. CR50 rats also had significantly lower numbers of mtDNA deletion products in two (adductor longus and soleus) of the four muscles examined compared to CR35 rats. These data indicate that CR begun in late middle age can retard age-associated fiber loss and fiber type changes, as well as increases in the number of skeletal muscle fibers showing mitochondrial enzyme abnormalities. CR also decreased the accumulation of mtDNA deletions.

PTPN11 encodes the protein tyrosine phosphatase SHP-2, which relays signals from growth factor receptors to Ras and other effectors. Germline PTPN11 mutations underlie about 50% of Noonan syndrome (NS), a developmental disorder that is associated with an elevated risk of juvenile myelomonocytic leukemia (JMML). Somatic PTPN11 mutations were recently identified in about 35% of patients with JMML; these mutations introduce amino acid substitutions that are largely distinct from those found in NS.We assessed the functional consequences of leukemia-associated PTPN11 mutations in murine hematopoietic cells. Expressing an E76K SHP-2 protein induced a hypersensitive pattern of granulocyte-macrophage colony-forming unit (CFU-GM) colony growth in response to granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 3 (IL-3) that was dependent on SHP-2 catalytic activity. E76K SHP-2 expression also enhanced the growth of immature progenitor cells with high replating potential, perturbed erythroid growth, and impaired normal differentiation in liquid cultures. In addition, leukemia-associated SHP-2 mutations conferred a stronger phenotype than a germline mutation found in patients with NS. Mutant SHP-2 proteins induce aberrant growth in multiple hematopoietic compartments, which supports a primary role of hyperactive Ras in the pathogenesis of JMML. IntroductionThe PTPN11 gene encodes SHP-2, a nonreceptor tyrosine phosphatase (PTPase) that relays signals from activated growth factor receptors to p21 ras (Ras), Src family kinases, and other signaling molecules (for reviews, see Barford and Neel 1 and Neel et al 2 ). SHP-2 contains 2 Src homology 2 (SH2) domains and a catalytic PTPase domain. The SHP-2 crystal structure predicts that binding of the N-SH2 domain to phosphotyrosyl peptides results in a conformational shift that relieves inhibition of the PTPase and activates SHP-2 function. 3 Missense mutations in PTPN11 underlie about 50% of cases of Noonan syndrome (NS), a developmental disorder characterized by cardiac defects, facial dysmorphism, and skeletal malformations. 4 Most of the PTPN11 mutations found in NS introduce amino acid substitutions within the N-SH2 and PTPase domains. 4,5 Molecular modeling and biochemical data infer that exon 3 mutations dominantly activate SHP-2 phosphatase activity by altering critical N-SH2 amino acids that lie on the interface with the PTPase domain. 4,5 Infants with NS show a spectrum of hematologic abnormalities that includes isolated monocytosis as well as myeloid disorders with features of chronic myelomonocytic leukemia that may remit spontaneously. [6][7][8] Patients with NS are also predisposed to juvenile myelomonocytic leukemia (JMML), an aggressive myeloproliferative disorder (MPD) characterized by leukocytosis, tissue infiltration, and hypersensitivity to granulocyte-macrophage colonystimulating factor (GM-CSF). 9,10 Studies of JMML specimens and experiments in mutant strains of mice strongly implicate aberrant Ras signaling in response to GM-CSF and othe...

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Organoids derived from stem cells or tissues in culture can develop into structures that resemble the in vivo anatomy and physiology of intact organs. Human organoid cultures provide the potential to study human development and model disease processes with the same scrutiny and depth of analysis customary for research with nonhuman model organisms. Resembling the complexity of the actual tissue or organ, patient-derived human organoid studies may accelerate medical research, creating new opportunities for tissue engineering and regenerative medicine, generating knowledge and tools for preclinical studies, including drug development and testing. Biologists are drawn to this system as a new “model organism” to study complex disease phenotypes and genetic variability among individuals using patient-derived tissues. The American Society for Cell Biology convened a task force to report on the potential, challenges, and limitations for human organoid research. The task force suggests ways to ease the entry for new researchers into the field and how to facilitate broader use of this new model organism within the research community. This includes guidelines for reproducibility, culturing, sharing of patient materials, patient consent, training, and communication with the public.

We have identified a novel mitochondrial targeting signal in the precursor of the DNA helicase Hmi1p of Saccharomyces cerevisiae that is located at the C terminus of the protein. Similar to classical N-terminal presequences, this C-terminal targeting signal consists of a stretch of positively charged amino acids that has the potential to form an amphipathic ␣-helix. Deletion of the C-terminal 36 amino acids of helicase resulted in loss of import into mitochondria, while deletion of the N-terminal 40 amino acids had no effect. When C-terminal regions of the helicase were placed at the C terminus of a passenger protein, dihydrofolate reductase, the resulting fusion proteins were directed into the mitochondrial matrix, and the C-terminal region of helicase became proteolytically processed. Import of helicase occurs in a C-to N-terminal direction; it requires a membrane potential and the TIM17-23 translocase together with mitochondrial Hsp70. Helicase is the only mitochondrial matrix protein identified thus far with a cleavable targeting signal at its C terminus.