KRAS was recently identified to be potentially druggable by allele-specific covalent targeting of Cys-12 in vicinity to an inducible allosteric switch II pocket (S-IIP). Success of this approach requires active cycling of KRAS between its active-GTP and inactive-GDP conformations as accessibility of the S-IIP is restricted only to the GDP-bound state. This strategy proved feasible for inhibiting mutant KRAS in vitro; however, it is uncertain whether this approach would translate to in vivo. Here, we describe structure-based design and identification of ARS-1620, a covalent compound with high potency and selectivity for KRAS. ARS-1620 achieves rapid and sustained in vivo target occupancy to induce tumor regression. We use ARS-1620 to dissect oncogenic KRAS dependency and demonstrate that monolayer culture formats significantly underestimate KRAS dependency in vivo. This study provides in vivo evidence that mutant KRAS can be selectively targeted and reveals ARS-1620 as representing a new generation of KRAS-specific inhibitors with promising therapeutic potential.

SUMMARY The human gene PTPN11, which encodes the tyrosine phosphatase Shp2, may act as a proto-oncogene, as dominantly activating mutations have been detected in several types of leukemia. Herein we report a tumor suppressor function of Shp2. Hepatocyte-specific deletion of Shp2 promotes inflammatory signaling through the Stat3 pathway and hepatic inflammation/necrosis, resulting in regenerative hyperplasia and development of tumors in aged mice. Furthermore, Shp2 ablation dramatically enhanced diethylenenitrite (DEN)-induced hepatocellular carcinoma (HCC) development, which was abolished by concurrent deletion of Shp2 and Stat3 in hepatocytes. Decreased Shp2 expression was detected in a sub-fraction of human HCC specimens. Thus, in contrast to the leukemogenic effect of dominant active mutants, PTPN11/Shp2 has a tumor suppressor function in liver.

The stem cell factor (SCF)/Kit system has served as a classic model in deciphering molecular signaling events in the hematopoietic compartment, and Kit expression is a most critical marker for hematopoietic stem cells (HSCs) and progenitors. However, it remains to be elucidated how Kit expression is regulated in HSCs. Herein we report that a cytoplasmic tyrosine phosphatase Shp2, acting down- IntroductionThe quiescence and entry into cycling of hematopoietic stem cells (HSCs) are tightly controlled and maintained in postnatal hematopoiesis by cytokines/growth factors and other signals in the microenvironment. 1,2 Stem cell factor, SCF (also known as Kit ligand, mast cell factor, or Steel factor) is encoded by the mouse Steel locus, and its receptor Kit (also called c-Kit) is encoded by the mouse White locus. 3,4 The biologic significance of Kit in hematopoiesis was first revealed in the white spotting (W) mutant mice. 5 Several W mutations with different levels of Kit kinase deficiency were found to correlate with the phenotype severity. 6 W 37 mutation in the conserved tyrosine kinase domain leads to complete loss of the kinase activity, and W 37 -homozygous mutant mice are embryonic lethal because of severe macrocytic anemia. A similar phenotype was found in the mouse strain with mutations at the Steel locus. Recently Waskow et al 7 investigated mild W mutants, identifying a pivotal role of Kit in development of multiple hematopoietic lineages. Kit is highly expressed in HSCs and is currently used as a phenotypic marker for HSCs. 8 Studies in the viable primary W mutant mice or in mice after transplantation indicate the importance of Kit signaling in maintaining adult HSC quiescence and survival. [9][10][11] Despite the wealth of knowledge on SCF/Kit signaling, it is poorly understood how Kit expression is regulated in HSCs and progenitors.Shp2, a tyrosine phosphatase with 2 Src-homology 2 (SH2) domains, is highly expressed in hematopoietic cells and has been shown to physically associate with ligand-activated Kit and other cell surface receptors. 12 Germline-dominant active mutations in PTPN11/Shp2 are found in approximately 50% of Noonan syndrome patients, who have a high risk of juvenile myelomonocytic leukemia. 13,14 Somatic gain-of-function mutations in PTPN11 have also been detected in nonsyndromic juvenile myelomonocytic leukemia, pediatric acute myeloid leukemia, B-cell precursor acute lymphoblastic leukemia, and myelodysplastic syndromes. [15][16][17] The expression of activated Shp2 leads to lethal myeloproliferative disease in transgenic or knockin mouse models. [18][19][20] Thus, PTPN11 has been proposed as the first proto-oncogene that encodes a tyrosine phosphatase. 21 However, the physiologic function of Shp2 in normal hematopoiesis in adults remains to be elucidated.Here we report a functional requirement for Shp2 in adult HSC maintenance and functions. Notably, we observed a prominent ablation of the Kit-positive stem/progenitor cell subpopulations in Shp2 ⌬/⌬ BM. Further analyses suggest tha...

Summary Bile acid (BA) biosynthesis is tightly controlled by intrahepatic negative feedback signaling elicited by BA binding to farnesoid X receptor (FXR), and also by enterohepatic communication involving ileal BA reabsorption and FGF15/19 secretion. However, how these pathways are coordinated is poorly understood. We show here that non-receptor tyrosine phosphatase Shp2 is a critical player that couples and regulates the intrahepatic and enterohepatic signals for repression of BA synthesis. Ablating Shp2 in hepatocytes suppressed signal relay from FGFR4, receptor for FGF15/19, and attenuated BA activation of FXR signaling, resulting in elevation of systemic BA levels and chronic hepatobiliary disorders in mice. Acting immediately downstream of FGFR4, Shp2 associates with FRS2α and promotes the receptor activation and signal relay to several pathways. These results elucidate a molecular mechanism for the control of BA homeostasis by Shp2 through orchestration of multiple signals in hepatocytes.

The molecular mechanism underlying adipogenesis and the physiological functions of adipose tissue are not fully understood. We describe here a unique mouse model of severe lipodystrophy. Ablation of Ptpn11/Shp2 in adipocytes, mediated by aP2-Cre, led to premature death, lack of white fat, low blood pressure, compensatory erythrocytosis, and hepatic steatosis in Shp2 fat−/− mice. Fat transplantation partially rescued the lifespan and blood pressure in Shp2 fat−/− mice, and administration of leptin also restored partially the blood pressure of mutant animals with endogenous leptin deficiency. Consistently, homozygous deletion of Shp2 inhibited adipocyte differentiation from embryonic stem (ES) cells. Biochemical analyses suggest a Shp2-TAO2-p38-p300-PPARγ pathway in adipogenesis, in which Shp2 suppresses p38 activation, leading to stabilization of p300 and enhanced PPARγ expression. Inhibition of p38 restored adipocyte differentiation from Shp2 −/− ES cells, and p38signaling is also suppressed in obese patients and obese animals. These results illustrate an essential role of adipose tissue in mammalian survival and physiology and also suggest a common signaling mechanism involved in adipogenesis and obesity development.transduction | preadipocyte | dephosphorylation | substrate trapping