A Top-Down Proteomic Assay to Evaluate KRAS4B-Compound Engagement

Development of new targeted inhibitors for oncogenic KRAS mutants may benefit from insight into how a given mutation influences the accessibility of protein residues and how compounds interact with mutant or wild-type KRAS proteins. Targeted proteomic analysis, a key validation step in the KRAS inhibitor development process, typically involves both intact mass- and peptide-based methods to confirm compound localization or quantify binding. However, these methods may not always provide a clear picture of the compound binding affinity for KRAS, how specific the compound is to the target KRAS residue, and how experimental conditions may impact these factors. To address this, we have developed a novel top-down proteomic assay to evaluate in vitro KRAS4B-compound engagement while assessing relative quantitation in parallel. We present two applications to demonstrate the capabilities of our assay: maleimide-biotin labeling of a KRAS4BG12D cysteine mutant panel and treatment of three KRAS4B proteins (WT, G12C, and G13C) with small molecule compounds. Our results show the time- or concentration-dependence of KRAS4B-compound engagement in context of the intact protein molecule while directly mapping the compound binding site.

Heterotopic Ossification Secondary to Motor Vehicle Collision Trauma Leading to Femoroacetabular Impingement Syndrome: A Case Report

Introduction

A patient presented for recalcitrant right hip pain secondary to femoroacetabular impingement (FAI) after blunt motor vehicle trauma and following the development of a 12 cm heterotopic ossification (HO). FAI is an increasingly recognized diagnosis where the hip joint is exposed to repeated femoral microtrauma from high-level physical activity or trauma, often causing labral ossification, and perhaps underlying a similar biological mechanism to HO.

Case Report

In this case report, we have an otherwise healthy 49-year-old male who was involved in a high-speed motor vehicle collision who was diagnosed with right hip FAI secondary to HO (Brooker's Class IV) and indicated for surgical excision of the HO anterior to the right proximal femur. The care team and patient initially trialed non-operative conservative treatment with non-steroidal anti-inflammatories drugs (NSAIDs) and hypothesized therapeutic success using a non-surgical approach. Surgical resection was pursued with the patient after a failure of conservative measures. The patient reported a zero out of ten on a ten-point numerical rating scale for pain, he also stated improved quality of life, satisfaction with the procedure, and subsequent rehabilitation at 1-month post-operative follow-up.

Conclusion

HO with near complete ankylosis of the hip joint may be causative of FAI when untreated. Although this case demonstrates a rarely studied traumatic etiology of impingement secondary to HO, initial standard conservative anti-inflammatory treatment can still be pursued. By analyzing the periarticular impact of HO secondary to non-surgical trauma, we can utilize and make inferential correlations from the literature, studying HO and impingement in the setting of prior hip surgery to guide treatment and prognosis in those presenting with FAI symptoms secondary to blunt force trauma.

Structural dynamics of RAF1-HSP90-CDC37 and HSP90 complexes reveal asymmetric client interactions and key structural elements

RAF kinases are integral to the RAS-MAPK signaling pathway, and proper RAF1 folding relies on its interaction with the chaperone HSP90 and the cochaperone CDC37. Understanding the intricate molecular interactions governing RAF1 folding is crucial for comprehending this process. Here, we present a cryo-EM structure of the closed-state RAF1-HSP90-CDC37 complex, where the C-lobe of the RAF1 kinase domain binds to one side of the HSP90 dimer, and an unfolded N-lobe segment of the RAF1 kinase domain threads through the center of the HSP90 dimer. CDC37 binds to the kinase C-lobe, mimicking the N-lobe with its HxNI motif. We also describe structures of HSP90 dimers without RAF1 and CDC37, displaying only N-terminal and middle domains, which we term the semi-open state. Employing 1 μs atomistic simulations, energetic decomposition, and comparative structural analysis, we elucidate the dynamics and interactions within these complexes. Our quantitative analysis reveals that CDC37 bridges the HSP90-RAF1 interaction, RAF1 binds HSP90 asymmetrically, and that HSP90 structural elements engage RAF1's unfolded region. Additionally, N- and C-terminal interactions stabilize HSP90 dimers, and molecular interactions in HSP90 dimers rearrange between the closed and semi-open states. Our findings provide valuable insight into the contributions of HSP90 and CDC37 in mediating client folding.

Comparative analysis of KRAS4a and KRAS4b splice variants reveals distinctive structural and functional properties

KRAS, the most frequently mutated oncogene in human cancer, produces two isoforms, KRAS4a and KRAS4b, through alternative splicing. These isoforms differ in exon 4, which encodes the final 15 residues of the G-domain and hypervariable regions (HVRs), vital for trafficking and membrane localization. While KRAS4b has been extensively studied, KRAS4a has been largely overlooked. Our multidisciplinary study compared the structural and functional characteristics of KRAS4a and KRAS4b, revealing distinct structural properties and thermal stability. Position 151 influences KRAS4a's thermal stability, while position 153 affects binding to RAF1 CRD protein. Nuclear magnetic resonance analysis identified localized structural differences near sequence variations and provided a solution-state conformational ensemble. Notably, KRAS4a exhibits substantial transcript abundance in bile ducts, liver, and stomach, with transcript levels approaching KRAS4b in the colon and rectum. Functional disparities were observed in full-length KRAS variants, highlighting the impact of HVR variations on interaction with trafficking proteins and downstream effectors like RAF and PI3K within cells.

Revealing the mechanism of action of a first-in-class covalent inhibitor of KRASG12C (ON) and other functional properties of oncogenic KRAS by 31P NMR

Individual oncogenic KRAS mutants confer distinct differences in biochemical properties and signaling for reasons that are not well understood. KRAS activity is closely coupled to protein dynamics and is regulated through two interconverting conformations: state 1 (inactive, effector binding deficient) and state 2 (active, effector binding enabled). Here, we use 31P NMR to delineate the differences in state 1 and state 2 populations present in WT and common KRAS oncogenic mutants (G12C, G12D, G12V, G13D, and Q61L) bound to its natural substrate GTP or a commonly used nonhydrolyzable analog GppNHp (guanosine-5'-[(β,γ)-imido] triphosphate). Our results show that GppNHp-bound proteins exhibit significant state 1 population, whereas GTP-bound KRAS is primarily (90% or more) in state 2 conformation. This observation suggests that the predominance of state 1 shown here and in other studies is related to GppNHp and is most likely nonexistent in cells. We characterize the impact of this differential conformational equilibrium of oncogenic KRAS on RAF1 kinase effector RAS-binding domain and intrinsic hydrolysis. Through a KRAS G12C drug discovery, we have identified a novel small-molecule inhibitor, BBO-8956, which is effective against both GDP- and GTP-bound KRAS G12C. We show that binding of this inhibitor significantly perturbs state 1-state 2 equilibrium and induces an inactive state 1 conformation in GTP-bound KRAS G12C. In the presence of BBO-8956, RAF1-RAS-binding domain is unable to induce a signaling competent state 2 conformation within the ternary complex, demonstrating the mechanism of action for this novel and active-conformation inhibitor.

Functional interactions between neurofibromatosis tumor suppressors underlie Schwann cell tumor de-differentiation and treatment resistance

Schwann cell tumors are the most common cancers of the peripheral nervous system and can arise in patients with neurofibromatosis type-1 (NF-1) or neurofibromatosis type-2 (NF-2). Functional interactions between NF1 and NF2 and broader mechanisms underlying malignant transformation of the Schwann lineage are unclear. Here we integrate bulk and single-cell genomics, biochemistry, and pharmacology across human samples, cell lines, and mouse allografts to identify cellular de-differentiation mechanisms driving malignant transformation and treatment resistance. We find DNA methylation groups of Schwann cell tumors can be distinguished by differentiation programs that correlate with response to the MEK inhibitor selumetinib. Functional genomic screening in NF1-mutant tumor cells reveals NF2 loss and PAK activation underlie selumetinib resistance, and we find that concurrent MEK and PAK inhibition is effective in vivo. These data support a de-differentiation paradigm underlying malignant transformation and treatment resistance of Schwann cell tumors and elucidate a functional link between NF1 and NF2.

Progress in Targeting KRAS Directly

RAS research has entered the world of translational and clinical science. Progress has been based on our appreciation of the role of RAS mutations in different types of cancer and the effects of these mutations on the biochemical, structural, and biophysical properties of the RAS proteins themselves, particularly KRAS, on which most attention has been focused. This knowledge base, while still growing, has enabled creative chemical approaches to targeting KRAS directly. Our understanding of RAS signaling pathways in normal and cancer cells plays an important role for developing RAS inhibitors but also continues to reveal new approaches to targeting RAS through disruption of signaling complexes and downstream pathways.

Report From a Multidisciplinary Symposium on the Future of Living Kidney Donor Transplantation

Virtually all clinicians agree that living donor renal transplantation is the optimal treatment for permanent loss of kidney function. Yet, living donor kidney transplantation has not grown in the United States for more than 2 decades. A virtual symposium gathered experts to examine this shortcoming and to stimulate and clarify issues salient to improving living donation. The ethical principles of rewarding kidney donors and the limits of altruism as the exclusive compelling stimulus for donation were emphasized. Concepts that donor incentives could save up to 40 000 lives annually and considerable taxpayer dollars were examined, and survey data confirmed voter support for donor compensation. Objections to rewarding donors were also presented. Living donor kidney exchanges and limited numbers of deceased donor kidneys were reviewed. Discussants found consensus that attempts to increase living donation should include removing artificial barriers in donor evaluation, expansion of living donor chains, affirming the safety of live kidney donation, and assurance that donors incur no expense. If the current legal and practice standards persist, living kidney donation will fail to achieve its true potential to save lives.

RAS Signaling Gone Awry in the Skin: The Complex Role of RAS in Cutaneous Neurofibroma Pathogenesis, Emerging Biological Insights

Cutaneous neurofibromas (cNFs) are the most common tumor in people with the rasopathy neurofibromatosis type 1. They number in hundreds or even thousands throughout the body, and currently, there are no effective interventions to prevent or treat these skin tumors. To facilitate the identification of novel and effective therapies, essential studies including a more refined understanding of cNF biology and the role of RAS signaling and downstream effector pathways responsible for cNF initiation, growth, and maintenance are needed. This review highlights the current state of knowledge of RAS signaling in cNF pathogenesis and therapeutic development for cNF treatment.

Long-term ecological research in freshwaters enabled by regional biodiversity collections, stable isotope analysis, and environmental informatics

Biodiversity collections are experiencing a renaissance fueled by the intersection of informatics, emerging technologies, and the extended use and interpretation of specimens and archived databases. In this article, we explore the potential for transformative research in ecology integrating biodiversity collections, stable isotope analysis (SIA), and environmental informatics. Like genomic DNA, SIA provides a common currency interpreted in the context of biogeochemical principles. Integration of SIA data across collections allows for evaluation of long-term ecological change at local to continental scales. Challenges including the analysis of sparse samples, a lack of information about baseline isotopic composition, and the effects of preservation remain, but none of these challenges is insurmountable. The proposed research framework interfaces with existing databases and observatories to provide benchmarks for retrospective studies and ecological forecasting. Collections and SIA add historical context to fundamental questions in freshwater ecological research, reference points for ecosystem monitoring, and a means of quantitative assessment for ecosystem restoration.

RAS-dependent RAF-MAPK hyperactivation by pathogenic RIT1 is a therapeutic target in Noonan syndrome-associated cardiac hypertrophy

RIT1 is a RAS guanosine triphosphatase (GTPase) that regulates different aspects of signal transduction and is mutated in lung cancer, leukemia, and in the germline of individuals with Noonan syndrome. Pathogenic RIT1 proteins promote mitogen-activated protein kinase (MAPK) hyperactivation; however, this mechanism remains poorly understood. Here, we show that RAF kinases are direct effectors of membrane-bound mutant RIT1 necessary for MAPK activation. We identify critical residues in RIT1 that facilitate interaction with membrane lipids and show that these are necessary for association with RAF kinases and MAPK activation. Although mutant RIT1 binds to RAF kinases directly, it fails to activate MAPK signaling in the absence of classical RAS proteins. Consistent with aberrant RAF/MAPK activation as a driver of disease, we show that pathway inhibition alleviates cardiac hypertrophy in a mouse model of RIT1 mutant Noonan syndrome. These data shed light on the function of pathogenic RIT1 and identify avenues for therapeutic intervention.

Reduced dynamic complexity allows structure elucidation of an excited state of KRASG13D

Localized dynamics of RAS, including regions distal to the nucleotide-binding site, is of high interest for elucidating the mechanisms by which RAS proteins interact with effectors and regulators and for designing inhibitors. Among several oncogenic mutants, methyl relaxation dispersion experiments reveal highly synchronized conformational dynamics in the active (GMPPNP-bound) KRAS^G13D, which suggests an exchange between two conformational states in solution. Methyl and ³¹P NMR spectra of active KRAS^G13D in solution confirm a two-state ensemble interconverting on the millisecond timescale, with a major P^γ atom peak corresponding to the dominant State 1 conformation and a secondary peak indicating an intermediate state different from the known State 2 conformation recognized by RAS effectors. High-resolution crystal structures of active KRAS^G13D and KRAS^G13D-RAF1 RBD complex provide snapshots of the State 1 and 2 conformations, respectively. We use residual dipolar couplings to solve and cross-validate the structure of the intermediate state of active KRAS^G13D, showing a conformation distinct from those of States 1 and 2 outside the known flexible switch regions. The dynamic coupling between the conformational exchange in the effector lobe and the breathing motion in the allosteric lobe is further validated by a secondary mutation in the allosteric lobe, which affects the conformational population equilibrium.

The Ribosomal S6 Kinase 2 (RSK2)-SPRED2 complex regulates phosphorylation of RSK substrates and MAPK signaling

Sprouty-related EVH-1 domain-containing (SPRED) proteins are a family of proteins that negatively regulate the RAS-MAPK pathway, which is involved in the regulation of the mitogenic response and cell proliferation. However, the mechanism by which these proteins affect RAS-MAPK signaling has not been fully elucidated. Patients with mutations in SPRED give rise to unique disease phenotypes, thus we hypothesized that distinct interactions across SPRED proteins may account for alternative nodes of regulation. To characterize the SPRED interactome and evaluate how members of the SPRED family function through unique binding partners, here we performed affinity purification mass spectrometry. We identified 90-kDa ribosomal S6 kinase 2 (RSK2) as a specific interactor of SPRED2, but not SPRED1 or SPRED3. We identified that the N-terminal kinase domain of RSK2 mediates interaction between amino acids 123-201 of SPRED2. Using X-ray crystallography, we determined the structure of the SPRED2-RSK2 complex and identified the SPRED2 motif, F145A, as critical for interaction. Additionally, we found that formation of this interaction is regulated by MAPK signaling events. We also find that that this interaction between SPRED2 and RSK2 has functional consequences, whereby knockdown of SPRED2 resulted in increased phosphorylation of RSK substrates, YB1 and CREB. Furthermore, SPRED2 knockdown hindered phospho-RSK membrane and nuclear subcellular localization. Lastly, we report that disruption of the SPRED2-RSK complex has effects on RAS-MAPK signaling dynamics. Overall, our analysis reveals that members of the SPRED family have unique protein binding partners and describes the molecular and functional determinants of SPRED2-RSK2 complex dynamics.

Projecting the Economic Impact of Compensating Living Kidney Donors in the United States: Cost-Benefit Analysis Demonstrates Substantial Patient and Societal Gains

OBJECTIVES

The aim of this study was to show how the US government could save approximately 47 000 patients with chronic kidney failure each year from suffering on dialysis and premature death by compensating living kidney donors enough to completely end the kidney shortage.

METHODS

Supply and demand analysis was used to estimate the number of donated kidneys needed to end the kidney shortage and the level of compensation required to encourage this number of donations. These results were then input into a detailed cost-benefit analysis to estimate the economic value of kidney transplantation to (1) the average kidney recipient and their caregiver, (2) taxpayers, and (3) society in general.

RESULTS

We estimate half of patients diagnosed with kidney failure each year-approximately 62 000 patients-could be saved from suffering on dialysis and premature death if they could receive an average of 1½ kidney transplants. However, currently there are only enough donated kidneys to save approximately 15 000 patients. To encourage sufficient donations to save the other 47 000 patients, the government would have to compensate living kidney donors approximately $77 000 (±50%) per donor. The value of transplantation to an average kidney recipient (and caregiver) would be approximately $1.5 million, and the savings from the recipient not needing expensive dialysis treatments would be approximately $1.2 million.

CONCLUSIONS

This analysis reveals the huge benefit that compensating living kidney donors would provide to patients with kidney failure and their caregivers and, conversely, the huge cost that is being imposed on these patients and their families by the current legal prohibition against such compensation.

DDDR-06. NEUROFIBROMATOSIS TUMOR SUPPRESSORS COOPERATIVELY DRIVE TUMOR DE-DIFFERENTIATION AND MEK INHIBITOR RESISTANCE IN PERIPHERAL NERVOUS SYSTEM TUMORS

Schwann cell derived tumors comprising schwannomas, neurofibromas, and malignant peripheral nerve sheath tumors (MPNSTs) are the most common cancers of the peripheral nervous system and often arise in patients with neurofibromatosis type-1 (NF-1) or type-2 (NF-2). NF-1 is caused by loss of NF1, a negative regulator of Ras signaling, and NF-2 is caused by loss of NF2, a pleiotropic tumor suppressor with numerous functions including inhibition of PAK signaling. However, whether functional interactions exist between the NF1 and NF2 tumor suppressors remain unclear. More broadly, there are currently no effective molecular therapies for patients with Schwann cell tumors beyond the MEK inhibitor selumetinib to treat neurofibromas in patients with NF-1. Here, we integrate DNA methylation profiling, whole exome sequencing, bulk and single-cell RNA sequencing, biochemistry, and pharmacology across human samples, cell lines, and mouse xenografts to identify cellular de-differentiation as a driver of malignant transformation and selumetinib resistance. Single nuclear RNA-sequencing of human neurofibromas (n = 3) or MPNSTs (n = 3) revealed a total of 13 cell types with increased proliferating, de-differentiated tumor cell populations in MPNST samples. Single cell RNA-sequencing of MPNST mouse xenografts revealed persistence of de-differentiated cell populations in selumetinib treated samples compared to vehicle control, suggesting cellular de-differentiation underlies treatment resistance. A genome-wide CRISPRi screen for mediators of selumetinib response in NF1 deficient neurofibroma cells revealed NF2 loss drives selumetinib resistance. Consistently, NF2 suppression in NF1 deficient neurofibroma cells caused Schwann cell de-differentiation and activation of PAK, a serine threonine kinase. Translationally, a small molecule PAK inhibitor in combination with selumetinib formed an effective therapy in mouse MPNST xenografts. In sum, we elucidate a paradigm of de-differentiation driving malignant transformation and treatment resistance in Schwann cell tumors, uncovering a functional link between the NF1 and NF2 tumor suppressors that sheds light on a novel therapeutic vulnerability.

Structure of the SHOC2-MRAS-PP1C complex provides insights into RAF activation and Noonan syndrome

SHOC2 acts as a strong synthetic lethal interactor with MEK inhibitors in multiple KRAS cancer cell lines. SHOC2 forms a heterotrimeric complex with MRAS and PP1C that is essential for regulating RAF and MAPK-pathway activation by dephosphorylating a specific phosphoserine on RAF kinases. Here we present the high-resolution crystal structure of the SHOC2-MRAS-PP1C (SMP) complex and apo-SHOC2. Our structures reveal that SHOC2, MRAS, and PP1C form a stable ternary complex in which all three proteins synergistically interact with each other. Our results show that dephosphorylation of RAF substrates by PP1C is enhanced upon interacting with SHOC2 and MRAS. The SMP complex forms only when MRAS is in an active state and is dependent on SHOC2 functioning as a scaffolding protein in the complex by bringing PP1C and MRAS together. Our results provide structural insights into the role of the SMP complex in RAF activation and how mutations found in Noonan syndrome enhance complex formation, and reveal new avenues for therapeutic interventions.

Structure-function analysis of the SHOC2-MRAS-PP1C holophosphatase complex

Receptor tyrosine kinase (RTK)-RAS signalling through the downstream mitogen-activated protein kinase (MAPK) cascade regulates cell proliferation and survival. The SHOC2-MRAS-PP1C holophosphatase complex functions as a key regulator of RTK-RAS signalling by removing an inhibitory phosphorylation event on the RAF family of proteins to potentiate MAPK signalling1. SHOC2 forms a ternary complex with MRAS and PP1C, and human germline gain-of-function mutations in this complex result in congenital RASopathy syndromes2-5. However, the structure and assembly of this complex are poorly understood. Here we use cryo-electron microscopy to resolve the structure of the SHOC2-MRAS-PP1C complex. We define the biophysical principles of holoenzyme interactions, elucidate the assembly order of the complex, and systematically interrogate the functional consequence of nearly all of the possible missense variants of SHOC2 through deep mutational scanning. We show that SHOC2 binds PP1C and MRAS through the concave surface of the leucine-rich repeat region and further engages PP1C through the N-terminal disordered region that contains a cryptic RVXF motif. Complex formation is initially mediated by interactions between SHOC2 and PP1C and is stabilized by the binding of GTP-loaded MRAS. These observations explain how mutant versions of SHOC2 in RASopathies and cancer stabilize the interactions of complex members to enhance holophosphatase activity. Together, this integrative structure-function model comprehensively defines key binding interactions within the SHOC2-MRAS-PP1C holophosphatase complex and will inform therapeutic development .

Impaired proteolysis of non-canonical RAS proteins drives clonal hematopoietic transformation

Recently, screens for mediators of resistance to FLT3 and ABL kinase inhibitors in leukemia resulted in the discovery of LZTR1 as an adaptor of a Cullin-3 RING E3 ubiquitin ligase complex responsible for degradation of RAS GTPases. In parallel, dysregulated LZTR1 expression via aberrant splicing and mutations were identified in clonal hematopoietic conditions. Here we identify that loss of LZTR1, or leukemia-associated mutants in the LZTR1 substrate and RAS GTPase RIT1 which escape degradation, drive hematopoietic stem cell (HSC) expansion and leukemia in vivo. While RIT1 stabilization was sufficient to drive hematopoietic transformation, transformation mediated by LZTR1 loss required MRAS. RAS targeting bioPROTACs or reduction of GTP-loaded RAS overcomes LZTR1 loss-mediated resistance to FLT3 inhibitors. These data reveal proteolysis of non-canonical RAS proteins as novel regulators of HSC self-renewal, define the function of RIT1 and LZTR1 mutations in leukemia, and identify means to overcome drug resistance due to LZTR1 downregulation.

More to the RAS Story: KRASG12C Inhibition, Resistance Mechanisms, and Moving Beyond KRASG12C

Despite the discovery of RAS oncogenes in human tumor DNA 40 years ago, the development of effective targeted therapies directed against RAS has lagged behind those more successful advancements in the field of therapeutic tyrosine kinase inhibitors targeting other oncogenes such as EGFR, ALK, and ROS1. The discoveries that (1) malignant RAS oncogenes differ from their wild-type counterparts by only a single amino acid change and (2) covalent inhibition of the cysteine residue at codon 12 of KRAS^G12C in its inactive GDP-bound state resulted in effective inhibition of oncogenic RAS signaling and have catalyzed a dramatic shift in mindset toward KRAS-driven cancers. Although the development of allele-selective KRAS^G12C inhibitors has changed a treatment paradigm, the clinical activity of these agents is more modest than tyrosine kinase inhibitors targeting other oncogene-driven cancers. Heterogeneous resistance mechanisms generally result in the restoration of RAS/mitogen-activated protein kinase pathway signaling. Many approaches are being evaluated to overcome this resistance, with many combinatorial clinical trials ongoing. Furthermore, because KRAS^G12D and KRAS^G12V are more prevalent than KRAS^G12C, there remains an unmet need for additional therapeutic strategies for these patients. Thus, our current translational standing could be described as "the end of the beginning," with additional discovery and research innovation needed to address the enormous disease burden imposed by RAS-mutant cancers. Here, we describe the development of KRAS^G12C inhibitors, the challenges of resistance to these inhibitors, strategies to mitigate that resistance, and new approaches being taken to address other RAS-mutant cancers.

Cross-species analysis of LZTR1 loss-of-function mutants demonstrates dependency to RIT1 orthologs

RAS GTPases are highly conserved proteins involved in the regulation of mitogenic signaling. We have previously described a novel Cullin 3 RING E3 ubiquitin ligase complex formed by the substrate adaptor protein LZTR1 that binds, ubiquitinates, and promotes proteasomal degradation of the RAS GTPase RIT1. In addition, others have described that this complex is also responsible for the ubiquitination of classical RAS GTPases. Here, we have analyzed the phenotypes of Lztr1 loss-of-function mutants in both fruit flies and mice and have demonstrated a biochemical preference for their RIT1 orthologs. Moreover, we show that Lztr1 is haplosufficient in mice and that embryonic lethality of the homozygous null allele can be rescued by deletion of Rit1. Overall, our results indicate that, in model organisms, RIT1 orthologs are the preferred substrates of LZTR1.

NMR 1H, 13C, 15N backbone resonance assignments of the T35S and oncogenic T35S/Q61L mutants of human KRAS4b in the active, GppNHp-bound conformation

RAS proteins cycling between the active-form (GTP-bound) and inactive-form (GDP-bound) play a key role in cell signaling pathways that control cell survival, proliferation, and differentiation. Mutations at codon 12, 13, and 61 in RAS are known to attenuate its GTPase activity favoring the RAS active state and constitutively active downstream signaling. This hyperactivation accounts for various malignancies including pancreatic, lung, and colorectal cancers. Active KRAS is found to exist in equilibrium between two rapidly interconverting conformational states (State1-State2) in solution. Due to this dynamic feature of the protein, the ¹H-¹⁵N correlation cross-peak signals of several amino acid (AA) residues of KRAS belonging to the flexible loop regions are absent from its 2D ¹H-¹⁵N HSQC spectrum within and near physiological solution pH. A threonine to serine mutation at position 35 (T35S) shifts the interconverting equilibrium to State1 conformation and enables the emergence of such residues in the 2D ¹H-¹⁵N HSQC spectrum due to gained conformational rigidity. We report here the ¹H^N, ¹⁵N, and ¹³C backbone resonance assignments for the 19.2 kDa (AA 1-169) protein constructs of KRAS-GppNHp harboring T35S mutation (KRAS^T35S/C118S-GppNHp) and of its oncogenic counterpart harboring the Q61L mutation (KRAS^{T35S/Q61L/C118S}-GppNHp) using heteronuclear, multidimensional NMR spectroscopy at 298 K. High resolution NMR data allowed the unambiguous assignments of ¹H-¹⁵N correlation cross-peaks for all the residues except for Met1. Furthermore, 2D ¹H-¹⁵N HSQC overlay of two proteins assisted in determination of Q61L mutation-induced chemical shift perturbations for select residues in the regions of P-loop, Switch-II, and helix α3.

Insights into the Cross Talk between Effector and Allosteric Lobes of KRAS from Methyl Conformational Dynamics

KRAS is the most frequently mutated RAS protein in cancer patients, and it is estimated that about 20% of the cancer patients in the United States carried mutant RAS proteins. To accelerate therapeutic development, structures and dynamics of RAS proteins had been extensively studied by various biophysical techniques for decades. Although 31P NMR studies revealed population equilibrium of the two major states in the active GMPPNP-bound form, more complex conformational dynamics in RAS proteins and oncogenic mutants subtly modulate the interactions with their downstream effectors. We established a set of customized NMR relaxation dispersion techniques to efficiently and systematically examine the ms-μs conformational dynamics of RAS proteins. This method allowed us to observe varying synchronized motions that connect the effector and allosteric lobes in KRAS. We demonstrated the role of conformational dynamics of KRAS in controlling its interaction with the Ras-binding domain of the downstream effector RAF1, the first kinase in the MAPK pathway. This allows one to explain, as well as to predict, the altered binding affinities of various KRAS mutants, which was neither previously reported nor apparent from the structural perspective.

A brief history of RAS and the RAS Initiative

In this review, I provide a brief history of the discovery of RAS and the GAPs and GEFs that regulate its activity from a personal perspective. Much of this history has been driven by technological breakthroughs that occurred concurrently, such as molecular cloning, cDNA expression to analyze RAS proteins and their structures, and application of PCR to detect mutations. I discuss the RAS superfamily and RAS proteins as therapeutic targets, including recent advances in developing RAS inhibitors. I also describe the role of the RAS Initiative at Frederick National Laboratory for Cancer Research in advancing development of RAS inhibitors and providing new insights into signaling complexes and interaction of RAS proteins with the plasma membrane.

Cost Structures of US Organ Procurement Organizations

BACKGROUND

The goal is to provide a national analysis of organ procurement organization (OPO) costs.

METHODS

Five years of data, for 51 of the 58 OPOs (2013-2017, a near census) were obtained under a FOIA. OPOs are not-for-profit federal contractors with a geographic monopoly. A generalized 15-factor cost regression model was estimated with adjustments to precision of estimates (P) for repeated observations. Selected measures were validated by comparison to IRS forms.

RESULTS

Decease donor organ procurement is a $1B/y operation with over 26 000 transplants/y. Over 60% of the cost of an organ is overhead. Profits are $2.3M/OPO/y. Total assets are $45M/OPO and growing at 9%/y. "Tissue" (skin, bones) generates $2-3M profit/OPO/y. A comparison of the highest with the lower costing OPOs showed our model explained 75% of the cost difference. Comparing costs across OPOs showed that highest-cost OPOs are smaller, import 44% more kidneys, face 6% higher labor costs, report 98% higher compensation for support personnel, spend 46% more on professional education, have 44% fewer assets, compensate their Executive Director 36% less, and have a lower procurement performance (SDRR) score.

CONCLUSIONS

Profits and assets suggest that OPOs are fiscally secure and OPO finances are not a source of the organ shortage. Asset accumulation ($45M/OPO) of incumbents suggests establishing a competitive market with new entrants is unlikely. Kidney-cost allocations support tissue procurements. Professional education spending does not reduce procurement costs. OPO importing of organs from other OPOs is a complex issue possibly increasing cost ($6K/kidney).

CSIG-01. EPIGENETIC REPROGRAMMING DRIVES MALIGNANT PERIPHERAL NERVE SHEATH TUMOR (MPNST) DE-DIFFERENTIATION AND TREATMENT RESISTANCE

Schwann cell derived tumors comprising schwannomas, neurofibromas, and malignant peripheral nerve sheath tumors are the most common malignancies of the peripheral nervous system. While schwannomas and neurofibromas are benign, MPNSTs are malignant, metastasize, and respond poorly to treatment. Neurofibromas and MPNSTs are associated with loss of NF1, a tumor suppressor that inhibits Ras/MEK signaling, and MPNSTs alone are distinguished by loss of the Polycomb Repressive Complex 2 (PRC2), an epigenetic regulator of methylation. To understand the genomic mechanisms of Schwann cell tumorigenesis and treatment resistance, we performed DNA methylation profiling, RNA-sequencing, and whole exome sequencing of primary Schwann cell tumor resection specimens (n=119 total: n=66 schwannoma, n=13 neurofibroma, n=40 MPNSTs). Hierarchical clustering identified three epigenetic Schwann cell tumor groups with transcriptional differences in PRC2 target genes associated with Schwann cell differentiation. Integrating biochemical and genomic approaches in primary human tumor cell lines from NF1 intact peripheral nerve, NF1 mutant neurofibromas, and MPNSTs, we found MPNST and neurofibroma cell lines with CRISPR knockout SUZ12 or EZH1/2 neurofibroma cell lines demonstrated repression of Schwann cell differentiation genes and induction of Ras signaling target genes. Further, MPNST cells deficient in PRC2 and NF1 exhibited increased basal active Ras-GTP levels, and therapeutically, PRC2 deficient MPNST cell lines were more resistant to the MEK inhibitor selumetinib and radiotherapy when compared to NF1-deficient neurofibroma cells. Single cell RNA sequencing analysis suggested distinct mechanisms of selumetinib resistance in PRC2 intact neurofibroma cells compared to PRC2-deficient MPNST cells. Taken together, our data demonstrate the importance of epigenetic dysregulation in malignant Schwann cell transformation and suggest differentiation status underlies a novel mechanism of MEK inhibitor resistance.

Inhibition of MET Signaling with Ficlatuzumab in Combination with Chemotherapy in Refractory AML: Clinical Outcomes and High-Dimensional Analysis

Acute myeloid leukemia patients refractory to induction therapy or relapsed within one year have poor outcomes. Autocrine production of hepatocyte growth factor by myeloid blasts drives leukemogenesis in pre-clinical models. A phase Ib trial evaluated ficlatuzumab, a first-in-class anti-HGF antibody, in combination with cytarabine in this high-risk population. Dose-limiting toxicities were not observed, and 20 mg/kg was established as the recommended phase II dose. The most frequent treatment-related adverse event was febrile neutropenia. Among 17 evaluable patients, the overall response rate was 53%, all complete remissions. Phospho-proteomic mass cytometry showed potent on-target suppression of p-MET after ficlatuzumab treatment and that attenuation of p-S6 was associated with clinical response. Multiplexed single cell RNA sequencing using prospectively acquired patient specimens identified interferon response genes as adverse predictive factors. The ficlatuzumab and cytarabine combination is well-tolerated with favorable efficacy. High-dimensional analyses at single-cell resolution represent promising approaches for identifying biomarkers of response and mechanisms of resistance in prospective clinical studies.

RAS interaction with Sin1 is dispensable for mTORC2 assembly and activity

RAS proteins are molecular switches that interact with effector proteins when bound to guanosine triphosphate, stimulating downstream signaling in response to multiple stimuli. Although several canonical downstream effectors have been extensively studied and tested as potential targets for RAS-driven cancers, many of these remain poorly characterized. In this study, we undertook a biochemical and structural approach to further study the role of Sin1 as a RAS effector. Sin1 interacted predominantly with KRAS isoform 4A in cells through an atypical RAS-binding domain that we have characterized by X-ray crystallography. Despite the essential role of Sin1 in the assembly and activity of mTORC2, we find that the interaction with RAS is not required for these functions. Cells and mice expressing a mutant of Sin1 that is unable to bind RAS are proficient for activation and assembly of mTORC2. Our results suggest that Sin1 is a bona fide RAS effector that regulates downstream signaling in an mTORC2-independent manner.

Oncogenic mutant RAS signaling activity is rescaled by the ERK/MAPK pathway

Activating mutations in RAS are present in ~ 30% of human tumors, and the resulting aberrations in ERK/MAPK signaling play a central role in oncogenesis. However, the form of these signaling changes is uncertain, with activating RAS mutants linked to both increased and decreased ERK activation in vivo. Rationally targeting the kinase activity of this pathway requires clarification of the quantitative effects of RAS mutations. Here, we use live‐cell imaging in cells expressing only one RAS isoform to quantify ERK activity with a new level of accuracy. We find that despite large differences in their biochemical activity, mutant KRAS isoforms within cells have similar ranges of ERK output. We identify roles for pathway‐level effects, including variation in feedback strength and feedforward modulation of phosphatase activity, that act to rescale pathway sensitivity, ultimately resisting changes in the dynamic range of ERK activity while preserving responsiveness to growth factor stimuli. Our results reconcile seemingly inconsistent reports within the literature and imply that the signaling changes induced by RAS mutations early in oncogenesis are subtle.

Targeted mass spectrometry-based assays enable multiplex quantification of receptor tyrosine kinase, MAP Kinase, and AKT signaling

SUMMARY

A primary goal of the US National Cancer Institute's Ras initiative at the Frederick National Laboratory for Cancer Research is to develop methods to quantify RAS signaling to facilitate development of novel cancer therapeutics. We use targeted proteomics technologies to develop a community resource consisting of 256 validated multiple reaction monitoring (MRM)-based, multiplexed assays for quantifying protein expression and phosphorylation through the receptor tyrosine kinase, MAPK, and AKT signaling networks. As proof of concept, we quantify the response of melanoma (A375 and SK-MEL-2) and colorectal cancer (HCT-116 and HT-29) cell lines to BRAF inhibition by PLX-4720. These assays replace over 60 Western blots with quantitative mass spectrometry-based assays of high molecular specificity and quantitative precision, showing the value of these methods for pharmacodynamic measurements and mechanism of action studies. Methods, fit-for-purpose validation, and results are publicly available as a resource for the community at assays.cancer.gov.

MOTIVATION

A lack of quantitative, multiplexable assays for phosphosignaling limits comprehensive investigation of aberrant signaling in cancer and evaluation of novel treatments. To alleviate this limitation, we sought to develop assays using targeted mass spectrometry for quantifying protein expression and phosphorylation through the receptor tyrosine kinase, MAPK, and AKT signaling networks. The resulting assays provide a resource for replacing over 60 Western blots in examining cancer signaling and tumor biology with high molecular specificity and quantitative rigor.

A Covalent Calmodulin Inhibitor as a Tool to Study Cellular Mechanisms of K-Ras-Driven Stemness

Recently, the highly mutated oncoprotein K-Ras4B (hereafter K-Ras) was shown to drive cancer cell stemness in conjunction with calmodulin (CaM). We previously showed that the covalent CaM inhibitor ophiobolin A (OphA) can potently inhibit K-Ras stemness activity. However, OphA, a fungus-derived natural product, exhibits an unspecific, broad toxicity across all phyla. Here we identified a less toxic, functional analog of OphA that can efficiently inactivate CaM by covalent inhibition. We analyzed a small series of benzazulenones, which bear some structural similarity to OphA and can be synthesized in only six steps. We identified the formyl aminobenzazulenone 1, here named Calmirasone1, as a novel and potent covalent CaM inhibitor. Calmirasone1 has a 4-fold increased affinity for CaM as compared to OphA and was active against K-Ras in cells within minutes, as compared to hours required by OphA. Calmirasone1 displayed a 2.5–4.5-fold higher selectivity for KRAS over BRAF mutant 3D spheroid growth than OphA, suggesting improved relative on-target activity. Importantly, Calmirasone1 has a 40–260-fold lower unspecific toxic effect on HRAS mutant cells, while it reaches almost 50% of the activity of novel K-RasG12C specific inhibitors in 3D spheroid assays. Our results suggest that Calmirasone1 can serve as a new tool compound to further investigate the cancer cell biology of the K-Ras and CaM associated stemness activities.

Abstract 1844: A CD70 antibody-drug conjugate is highly active and induces long term remission in patient-derived xenograft mouse models of cutaneous T cell lymphoma

Cutaneous T cell lymphoma (CTCL) is a type of non-Hodgkin's lymphoma in which malignant T cells initially home to the skin followed by systemic dissemination as the disease progresses. CD70 is rarely expressed in normal tissues but is overexpressed in activated T and B lymphocytes. From archival diagnostic specimens of 37 patients, we demonstrate that CD70 is highly expressed in subtypes of mature TCL, especially CTCL. SGNCD70A is a new anti-CD70 antibody-drug conjugate combining a monoclonal antibody to CD70 with a DNA-damaging agent. SGNCD70A inhibited cell growth and induced apoptosis of CD70+ CTCL cell lines and primary tumors from patient-derived xenograft (PDX) mice, but had no inhibitory effect on CD70- lymphoblastic TCL cells and normal T cells. Next, we examined the anti-tumor activity of SGNCD70A in CTCL PDX model. One week after tumor inoculation, mice were treated intraperitoneally with single-dosing of PBS, 100 μg/kg (SGN70A100) or 300 μg/kg (SGN70A300) of SGN-CD70A. SGN-CD70A prolonged survival of treated mice in a dose-dependent fashion compared to untreated mice. Median survival was 21 days, 27.5 days (P=0.041), and 57 days (p<0.01) for the PBS control, SGN70A100 and SGN70A300 group, respectively. To confirm that survival was dictated by disease progression, rather than drug toxicity of SGN-CD70A, we measured tumor burden by cell-free DNA (cfDNA) throughout the course of treatment. We demonstrated that cfDNA paralleled the disease progression and peaked before death of the animals. In contrast, in surviving mice, cfDNA remained at the background level. Importantly, we discovered relapse occurred in SGN70A300 group (3 of 4, 75%) due to persistent disease, not due to acquired resistance to SGN-CD70A. Thus, we investigated whether multiple dosing could lead to complete regression of tumors in PDX model. We treated PDX mice with SGN70A300 weekly (SGN70A300x3) for 3 consecutive weeks. In the SGN70A300x3 group, three of four mice survived beyond day 90 (median >85 days), resulting in markedly prolonged survival compared to the single-dose- and PBS-treated mice with a median survival of 39 days, (P<0.01) and 20 days (P<0.01), respectively. Compared to PBS group, both SGN70A300 and SGN70A300x3 treated mice had delayed tumor growth and cfDNA rise. Furthermore, in SGN70A300 group, cfDNA started to rise seven days before the endpoint of the mice in a range of 30-42 days, while three surviving mice in SGN70A300x3 remained at background cfDNA levels until day 85, indicating that multiple doses of SGN-CD70A decreased overall tumor burden and the occurrence of relapse in CTCL. Our results showed that CD70 is highly expressed in mature TCL, especially in CTCL. Using CTCL PDX models, SGN-CD70A has marked anti-tumor activity, leading to long-term survival of treated mice. Our results provide a rationale for clinical investigation of SGN-CD70A in patients with TCL.

Citation Format: Chi-Heng Wu, Chen-Yen Yang, Linlin Wang, Ryan Gill, Frank McCormick, Weiyun Z. Ai. A CD70 antibody-drug conjugate is highly active and induces long term remission in patient-derived xenograft mouse models of cutaneous T cell lymphoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1844.

Ancient DNA, lipid biomarkers and palaeoecological evidence reveals construction and life on early medieval lake settlements

Direct evidence of ancient human occupation is typically established through archaeological excavation. Excavations are costly and destructive, and practically impossible in some lake and wetland environments. We present here an alternative approach, providing direct evidence from lake sediments using DNA metabarcoding, steroid lipid biomarkers (bile acids) and from traditional environmental analyses. Applied to an early Medieval Celtic settlement in Ireland (a crannog) this approach provides a site chronology and direct evidence of human occupation, crops, animal farming and on-site slaughtering. This is the first independently-dated, continuous molecular archive of human activity from an archeological site, demonstrating a link between animal husbandry, food resources, island use. These sites are under threat but are impossible to preserve in-situ so this approach can be used, with or without excavation, to produce a robust and full site chronology and provide direct evidence of occupation, the use of plants and animals, and activities such as butchery.

Minor intron retention drives clonal hematopoietic disorders and diverse cancer predisposition

Most eukaryotes harbor two distinct pre-mRNA splicing machineries: the major spliceosome, which removes >99% of introns, and the minor spliceosome, which removes rare, evolutionarily conserved introns. Although hypothesized to serve important regulatory functions, physiologic roles of the minor spliceosome are not well understood. For example, the minor spliceosome component ZRSR2 is subject to recurrent, leukemia-associated mutations, yet functional connections among minor introns, hematopoiesis and cancers are unclear. Here, we identify that impaired minor intron excision via ZRSR2 loss enhances hematopoietic stem cell self-renewal. CRISPR screens mimicking nonsense-mediated decay of minor intron-containing mRNA species converged on LZTR1, a regulator of RAS-related GTPases. LZTR1 minor intron retention was also discovered in the RASopathy Noonan syndrome, due to intronic mutations disrupting splicing and diverse solid tumors. These data uncover minor intron recognition as a regulator of hematopoiesis, noncoding mutations within minor introns as potential cancer drivers and links among ZRSR2 mutations, LZTR1 regulation and leukemias.

Sensitivity of Oncogenic KRAS-Expressing Cells to CDK9 Inhibition

Oncogenic forms of KRAS proteins are known to be drivers of pancreatic, colorectal, and lung cancers. The goal of this study is to identify chemical leads that inhibit oncogenic KRAS signaling. We first developed an isogenic panel of mouse embryonic fibroblast (MEF) cell lines that carry wild-type RAS, oncogenic KRAS, and oncogenic BRAF. We validated these cell lines by screening against a tool compound library of 1402 annotated inhibitors in an adenosine triphosphate (ATP)-based cell viability assay. Subsequently, this MEF panel was used to conduct a high-throughput phenotypic screen in a cell viability assay with a proprietary compound library. All 126 compounds that exhibited a selective activity against mutant KRAS were selected and prioritized based on their activities in secondary assays. Finally, five chemical clusters were chosen. They had specific activity against SW620 and LS513 over Colo320 colorectal cancer cell lines. In addition, they had no effects on BRAF^V600E, MEK1, extracellular signal-regulated kinase 2 (ERK2), phosphoinositide 3-kinase alpha (PI3Kα), AKT1, or mammalian target of rapamycin (mTOR) as tested in in vitro enzymatic activity assays. Biophysical assays demonstrated that these compounds did not bind directly to KRAS. We further identified the mechanism of action and showed that three of them have CDK9 inhibitory activity. In conclusion, we have developed and validated an isogenic MEF panel that was used successfully to identify RAS oncogenic or wild-type allele-specific vulnerabilities. Furthermore, we identified sensitivity of oncogenic KRAS-expressing cells to CDK9 inhibitors, which warrants future studies of treating KRAS-driven cancers with CDK9 inhibitors.

Estimated impact of novel coronavirus-19 and transplant center inactivity on end-stage renal disease-related patient mortality in the United States

To predict whether the COVID‐19 pandemic and transplant center responses could have resulted in preventable deaths, we analyzed registry information of the US end‐stage renal disease (ESRD) patient population awaiting kidney transplantation. Data were from the Organ Procurement and Transplantation Network (OPTN), the US Centers for Disease Control and Prevention, and the United States Renal Data System. Based on 2019 OPTN reports, annualized reduction in kidney transplantation of 25%–100% could result in excess deaths of wait‐listed (deceased donor) transplant candidates from 84 to 337 and living donor candidate excess deaths from 35 to 141 (total 119–478 potentially preventable deaths of transplant candidates). Changes in transplant activity due to COVID‐19 varied with some centers shutting down while others simply heeded known or suspected pandemic risks. Understanding potential excess mortality for ESRD transplant candidates when circumstances compel curtailment of transplant activity may inform policy and procedural aspects of organ transplant systems allowing ways to best inform patients and families as to potential risks in shuttering organ transplant activity. Considering that more than 700 000 Americans have ESRD with 100 000 awaiting a kidney transplant, our highest annual estimate of 478 excess total deaths from postponing kidney transplantation seems modest.

The Metabolic Landscape of RAS-Driven Cancers from biology to therapy

Our understanding of how the RAS protein family, and in particular mutant KRAS promote metabolic dysregulation in cancer cells has advanced significantly over the last decade. In this Review, we discuss the metabolic reprogramming mediated by oncogenic RAS in cancer, and elucidating the underlying mechanisms could translate to novel therapeutic opportunities to target metabolic vulnerabilities in RAS-driven cancers.

Promoting Ethical Payment in Human Infection Challenge Studies

To prepare for potential human infection challenge studies (HICS) involving SARS-CoV-2, we convened a multidisciplinary working group to address ethical questions regarding whether and how much SARS-CoV-2 HICS participants should be paid. Because the goals of paying HICS participants, as well as the relevant ethical concerns, are the same as those arising for other types of clinical research, the same basic framework for ethical payment can apply. This framework divides payment into reimbursement, compensation, and incentives, focusing on fairness and promoting adequate recruitment and retention as counterweights to concerns about undue inducement. Within the basic framework, several factors are especially salient for HICS, and for SARS-CoV-2 HICS in particular, including the nature of participant confinement, anticipated discomfort, risks and uncertainty, participant motivations, and trust. These factors are reflected in a payment worksheet created to help sponsors, researchers, and ethics reviewers systematically develop and assess ethically justifiable payment amounts.

DoMY-Seq: A yeast two-hybrid-based technique for precision mapping of protein-protein interaction motifs

Interactions between proteins are fundamental for every biological process and especially important in cell signaling pathways. Biochemical techniques that evaluate these protein-protein interactions (PPIs), such as in vitro pull downs and coimmunoprecipitations, have become popular in most laboratories and are essential to identify and validate novel protein binding partners. Most PPIs occur through small domains or motifs, which are challenging and laborious to map by using standard biochemical approaches because they generally require the cloning of several truncation mutants. Moreover, these classical methodologies provide limited resolution of the interacting interface. Here, we describe the development of an alternative technique to overcome these limitations termed "Protein Domain mapping using Yeast 2 Hybrid-Next Generation Sequencing" (DoMY-Seq), which leverages both yeast two-hybrid and next-generation sequencing techniques. In brief, our approach involves creating a library of fragments derived from an open reading frame of interest and enriching for the interacting fragments using a yeast two-hybrid reporter system. Next-generation sequencing is then subsequently employed to read and map the sequence of the interacting fragment, yielding a high-resolution plot of the binding interface. We optimized DoMY-Seq by taking advantage of the well-described and high-affinity interaction between KRAS and CRAF, and we provide high-resolution domain mapping on this and other protein-interacting pairs, including CRAF-MEK1, RIT1-RGL3, and p53-MDM2. Thus, DoMY-Seq provides an unbiased alternative method to rapidly identify the domains involved in PPIs by advancing the use of yeast two-hybrid technology.

SPRED proteins and their roles in signal transduction, development, and malignancy

The roles of SPRED proteins in signaling, development, and cancer are becoming increasingly recognized. SPRED proteins comprise an N-terminal EVH-1 domain, a central c-Kit-binding domain, and C-terminal SROUTY domain. They negatively regulate signaling from tyrosine kinases to the Ras-MAPK pathway. SPRED1 binds directly to both c-KIT and to the RasGAP, neurofibromin, whose function is completely dependent on this interaction. Loss-of-function mutations in SPRED1 occur in human cancers and cause the developmental disorder, Legius syndrome. Genetic ablation of SPRED genes in mice leads to behavioral problems, dwarfism, and multiple other phenotypes including increased risk of leukemia. In this review, we summarize and discuss biochemical, structural, and biological functions of these proteins including their roles in normal cell growth and differentiation and in human disease.

Evidence-Based Physical Examination for the Diagnosis of Subscapularis Tears: A Systematic Review

CONTEXT

There is a renewed interest in diagnosing and treating subscapularis tears, but there is a paucity of clinical guidance to optimize diagnostic decision-making.

OBJECTIVE

To perform a literature review to evaluate advanced maneuvers and special tests in the diagnosis of subscapularis tears and create a diagnostic algorithm for subscapularis pathology.

DATA SOURCES

PubMed, MEDLINE, Ovid, and Cochrane Reviews databases.

STUDY SELECTION

Inclusion criteria consisted of level 1 and 2 studies published in peer-reviewed scientific journals that focused on physical examination.

STUDY DESIGN

Systematic review.

LEVEL OF EVIDENCE

Level 2.

DATA EXTRACTION

Individual test characteristics (bear hug, belly press, lift-off, Napoleon, and internal rotation lag sign) were combined in series and in parallel to maximize clinical sensitivity and specificity for any special test evaluated in at least 2 studies. A secondary analysis utilized subjective pretest probabilities to create a clinical decision tree algorithm and provide posttest probabilities.

RESULTS

A total of 3174 studies were identified, and 5 studies met inclusion criteria. The special test combination of the bear hug and belly press demonstrated the highest positive likelihood ratio (18.29). Overall, 3 special test combinations in series demonstrated a significant impact on posttest probabilities. With parallel testing, the combination of bear hug and belly press had the highest sensitivity (84%) and lowest calculated negative likelihood ratio (0.21).

CONCLUSION

The combined application of the bear hug and belly press physical examination maneuvers is an optimal combination for evaluating subscapularis pathology. Positive findings using this test combination in series with a likely pretest probability yield a 96% posttest probability; whereas, negative findings tested in parallel with an unlikely pretest probability yield a 12% posttest probability.