A high occurrence of acquisition and/or expansion of C-CBL mutant clones in the progression of high-risk myelodysplastic syndrome to acute myeloid leukemia

Clonal dynamics of chronic myelomonocytic leukemia progression: paired-sample comparison

This study investigated the clonal evolution of chronic myelomonocytic leukemia (CMML) progression to secondary acute myeloid leukemia (sAML) by next-generation sequencing and pyrosequencing for variant allele frequency (VAF) of gene mutations and SNP microarray for copy neutral loss of heterozygosity (CN-LOH) in 38 paired samples from CMML/sAML patients of Taiwanese origin. The median interval between CMML and sAML samples collection was 14.9 months (1.0-89.6). RUNX1 (57%), TET2 (46%), SRSF2 (37%), and ASXL1 (28%) mutations were frequent at CMML diagnosis. Baseline VAF in epigenetic regulator genes was high (>35%) in 83% of mutational events at the CMML phase, remained stable in 78% (VAF changes <10%), and increased in 20% (increased VAF > 10%) during progression to sAML. Transcription factor genes showed high VAF (>35%) in 51% at the CMML phase, and stable VAF in 60% during progression. VAF of spliceosome genes was high (>35%) in 70% at CMML phase, and stable in 61% during progression. Activated signaling genes exhibited acquisition or loss during progression. TET2 mutations were often founding clones, and SRSF2, ASXL1, DNMT3A, EZH2, or spliceosome genes also acted as ancestral mutations. RUNX1 mutations were typically later events and occasionally ancestral hits or germline mutations. Acquisition of cytogenetic changes, signaling pathways genes (PTPN11, FLT3, NRAS, CBL), or AML-defined genes (NPM1, CEBPA, CBFB::MYH11) by linear or branching evolution occurred during sAML progression. CN-LOH was noted in EZH2, CBL, TET2, and DNMT3A genes. CEBPA mutation and concurrent biallelic TET2 with NRAS mutations at CMML diagnosis were risk factors for time to AML progression and overall survival. A characteristic ASXL1MT/RUNX1MT/SpliceosomeMT/signalingWT genetic profile was associated with monocyte counts of 0.5-1.0 × 109/l. This study highlights the complexity and heterogeneity of dynamic changes in clonal architecture during CMML progression, emphasizing its importance in pathogenesis, phenotype, risk stratification, and therapeutic strategy. © 2025 The Pathological Society of Great Britain and Ireland.

Recurrent cytogenetic abnormalities reveal alterations that promote progression and transformation in myelodysplastic syndrome

OBJECTIVE

To illustrate patterns of cytogenetic abnormalities that promote progression and/or transformation in myelodysplastic syndrome.

METHODS

In this study we evaluated three different data sets to identify recurrent cytogenetic abnormalities (RCAs) to delineate the cytogenetic evolutionary trajectories and their clinical significance.

RESULTS

Datasets 1 and 2 were 2402 cross sectional samples from Mitelman database of Chromosome Aberrations and Gene Fusions in Cancer; these were used to discover RCAs and to validate them. Dataset 3 was a cohort of 163 institutional patients with serial samples from 35 % of them. This was used to further validate RCAs identified in the cross-sectional data, and their clinical impact. We identified MDS subtype associated RCAs, and some exclusive RCAs (Xp-, 2q-, 17q-, 21q-) that led to disease progression or transformation to leukemia. Evolutionary pathway analysis had shown temporal acquisition of RCAs. Therefore, presence of two or more RCAs suggests cooperative or complementary role in disease progression or transformation. Patients with one or more of these RCAs had poor prognosis and high risk for transformation. Genes frequently altered in MDS are mapped to some of the RCAs and suggest a close correlation between RCAs and molecular alterations in MDS. Karyotypic complexity, clonal evolution, loss of 17p had poor clinical outcomes.

CONCLUSION

This study identified a unique combination of RCAs that are components in distinct cytogenetic trajectories. Some of these were primary changes while others were secondary or tertiary changes. Acquiring specific additional aberrations predicts progression or transformation to leukemia.

Cbl and Cbl-b ubiquitin ligases are essential for intestinal epithelial stem cell maintenance

Receptor tyrosine kinases (RTKs) control stem cell maintenance vs. differentiation decisions. Casitas B-lineage lymphoma (CBL) family ubiquitin ligases are negative regulators of RTKs, but their stem cell regulatory roles remain unclear. Here, we show that Lgr5+ intestinal stem cell (ISC)-specific inducible Cbl-knockout (KO) on a Cblb null mouse background (iDKO) induced rapid loss of the Lgr5 Hi ISCs with transient expansion of the Lgr5 Lo transit-amplifying population. LacZ-based lineage tracing revealed increased ISC commitment toward enterocyte and goblet cell fate at the expense of Paneth cells. Functionally, Cbl/Cblb iDKO impaired the recovery from radiation-induced intestinal epithelial injury. In vitro, Cbl/Cblb iDKO led to inability to maintain intestinal organoids. Single-cell RNA sequencing in organoids identified Akt-mTOR (mammalian target of rapamycin) pathway hyperactivation upon iDKO, and pharmacological Akt-mTOR axis inhibition rescued the iDKO defects. Our results demonstrate a requirement for Cbl/Cblb in the maintenance of ISCs by fine-tuning the Akt-mTOR axis to balance stem cell maintenance vs. commitment to differentiation.

Cbl and Cbl-b Ubiquitin Ligases are Essential for Intestinal Epithelial Stem Cell Maintenance

Among the signaling pathways that control the stem cell self-renewal and maintenance vs. acquisition of differentiated cell fates, those mediated by receptor tyrosine kinase (RTK) activation are well established as key players. CBL family ubiquitin ligases are negative regulators of RTKs but their physiological roles in regulating stem cell behaviors are unclear. While hematopoietic Cbl/Cblb knockout (KO) leads to a myeloproliferative disease due to expansion and reduced quiescence of hematopoietic stem cells, mammary epithelial KO led to stunted mammary gland development due to mammary stem cell depletion. Here, we examined the impact of inducible Cbl/Cblb double-KO (iDKO) selectively in the Lgr5-defined intestinal stem cell (ISC) compartment. Cbl/Cblb iDKO led to rapid loss of the Lgr5 Hi ISC pool with a concomitant transient expansion of the Lgr5 Lo transit amplifying population. LacZ reporter-based lineage tracing showed increased ISC commitment to differentiation, with propensity towards enterocyte and goblet cell fate at the expense of Paneth cells. Functionally, Cbl/Cblb iDKO impaired the recovery from radiation-induced intestinal epithelial injury. In vitro , Cbl/Cblb iDKO led to inability to maintain intestinal organoids. Single cell RNAseq analysis of organoids revealed Akt-mTOR pathway hyperactivation in iDKO ISCs and progeny cells, and pharmacological inhibition of the Akt-mTOR axis rescued the organoid maintenance and propagation defects. Our results demonstrate a requirement for Cbl/Cblb in the maintenance of ISCs by fine tuning the Akt-mTOR axis to balance stem cell maintenance vs. commitment to differentiation.

Co-mutation landscape and clinical significance of RAS pathway related gene mutations in patients with myelodysplastic syndrome

Single gene mutations in the RAS pathway are uncommon and of unknown significance in myelodysplastic syndrome (MDS) patients, RAS pathway-related gene mutations (RASway^mut ) as a whole may be significant and require further elucidation. The clinical and molecular data of 370 MDS patients who were newly diagnosed between 1 November 2016 and 31 August 2020 in our hospital were collected and retrospectively reviewed. RASway^mut were detected in 57 (15.41%) patients. Higher median percentage of marrow blasts (2% vs. 1%, P = 0.00), more co-mutated genes (4, interquartile range [IQR]: 2-5. vs. 2, IQR:1-4, P = 0.00), more higher risk patients according to international prognostic scoring system-revised (IPSS-R) (80.70% vs. 59.11%, P = 0.002) as well as higher acute myeloid leukemia transformation rate (35.09% vs. 14.38%, P = 0.02) were observed in patients with RASway^mut when compared to those with wild type RAS pathway-related genes (RASway^wt ). The most frequent co-mutated genes were ASXL1 (28.6%), TET2 (23.2%), U2AF1, RUNX1, TP53 (14.3%); DNMT3A (12.5%), among which ASXL1 mutation rate were significantly higher than those with RASway^wt (p < 0.05). RASway^mut had no significant effect on response to disease-modifying treatment in MDS patients. However, Overall survivals (OS) of RASway^mut patients were significantly shorter than those with RASway^wt (16.05 m. vs. 92.3 m, P = 0.00), especially in patients with marrow blasts less than 5% (P = 0.002), normal karyotype (P = 0.01) and lower risk (P = 0.00). While multivariate prognostic analysis showed that RASway^mut co-mutated with TET2 was an independent poor prognostic factor for all MDS patients (P = 0.00, hazrad ratio [HR] = 4.77 with 95% confidence interval [CI]: 2.4-9.51) and RASway^mut patients (P = 0.02, HR 2.76, 95% CI 1.21-6.29). In conclusion, RASway^mut was associated with higher IPSS-R risk, higher incidence of leukemic transformation thus shorter OS in MDS patients, it could be viewed as a whole to predict poor prognosis. Co-mutation with TET2 may promote disease progression and was an independent poor prognostic factor in MDS patients.

Prognosis in Myelodysplastic Syndromes: The Clinical Challenge of Genomic Integration

Myelodysplastic syndromes (MDS) are a group of clonal hematopoietic neoplasms characterized by ineffective hematopoiesis and myelodysplasia with a variable spectrum of clinical-biological features that can be used to build a prognostic estimation. This review summarizes the current most widely used prognostic scoring systems and gives a general view of the prognostic impact of somatic mutations in MDS patients.

A continuous-time Markov model approach for modeling myelodysplastic syndromes progression from cross-sectional data

The integration of both genomics and clinical data to model disease progression is now possible, thanks to the increasing availability of molecular patients' profiles. This may lead to the definition of novel decision support tools, able to tailor therapeutic interventions on the basis of a "precise" patients' risk stratification, given their health status evolution. However, longitudinal analysis requires long-term data collection and curation, which can be time demanding, expensive and sometimes unfeasible. Here we present a clinical decision support framework that combines the simulation of disease progression from cross-sectional data with a Markov model that exploits continuous-time transition probabilities derived from Cox regression. Trajectories between patients at different disease stages are stochastically built according to a measure of patient similarity, computed with a matrix tri-factorization technique. Such trajectories are seen as realizations drawn from the stochastic process driving the transitions between the disease stages. Eventually, Markov models applied to the resulting longitudinal dataset highlight potentially relevant clinical information. We applied our method to cross-sectional genomic and clinical data from a cohort of Myelodysplastic syndromes (MDS) patients. MDS are heterogeneous clonal hematopoietic disorders whose patients are characterized by different risks of Acute Myeloid Leukemia (AML) development, defined by an international score. We computed patients' trajectories across increasing and subsequent levels of risk of developing AML, and we applied a Cox model to the simulated longitudinal dataset to assess whether genomic characteristics could be associated with a higher or lower probability of disease progression. We then used the learned parameters of such Cox model to calculate the transition probabilities of a continuous-time Markov model that describes the patients' evolution across stages. Our results are in most cases confirmed by previous studies, thus demonstrating that simulated longitudinal data represent a valuable resource to investigate disease progression of MDS patients.

Consequences of mutant TET2 on clonality and subclonal hierarchy

Somatic mutations in TET2 are common in myelodysplastic syndromes (MDS), myeloproliferative, and overlap syndromes. TET2 mutant (TET2^MT) clones are also found in asymptomatic elderly individuals, a condition referred to as clonal hematopoiesis of indeterminate potential (CHIP). In various entities of TET2^MT neoplasia, we examined the phenotype in relation to the strata of TET2 hits within the clonal hierarchy. Using deep sequencing, 1781 mutations were found in 1205 of 4930 patients; 40% of mutant cases were biallelic. Hierarchical analysis revealed that of TET2^MT cases >40% were ancestral, e.g., representing 8% of MDS. Higher (earlier) TET2 lesion rank within the clonal hierarchy (greater clonal burden) was associated with impaired survival. Moreover, MDS driven by ancestral TET2^MT is likely derived from TET2^MT CHIP with a penetrance of ~1%. Following ancestral TET2 mutations, individual disease course is determined by secondary hits. Using multidimensional analyses, we demonstrate how hits following the TET2 founder defect induces phenotypic shifts toward dysplasia, myeloproliferation, or progression to AML. In summary, TET2^MT CHIP-derived MDS is a subclass of MDS that is distinct from de novo disease.

Molecular and Cellular Mechanisms of Myelodysplastic Syndrome: Implications on Targeted Therapy

Myelodysplastic syndrome (MDS) is a group of heterogeneous clonal hematopoietic stem cell disorders characterized by cytopenia, ineffective hematopoiesis, and progression to secondary acute myeloid leukemia in high-risk cases. Conventional prognostication relies on clinicopathological parameters supplemented by cytogenetic information. However, recent studies have shown that genetic aberrations also have critical impacts on treatment outcome. Moreover, these genetic alterations may themselves be a target for treatment. The mutation landscape in MDS is shaped by gene aberrations involved in DNA methylation (TET2, DNMT3A, IDH1/2), histone modification (ASXL1, EZH2), the RNA splicing machinery (SF3B1, SRSF2, ZRSR2, U2AF1/2), transcription (RUNX1, TP53, BCOR, PHF6, NCOR, CEBPA, GATA2), tyrosine kinase receptor signaling (JAK2, MPL, FLT3, GNAS, KIT), RAS pathways (KRAS, NRAS, CBL, NF1, PTPN11), DNA repair (ATM, BRCC3, DLRE1C, FANCL), and cohesion complexes (STAG2, CTCF, SMC1A, RAD21). A detailed understanding of the pathogenetic mechanisms leading to transformation is critical for designing single-agent or combinatorial approaches in target therapy of MDS.

Mutations of c-Cbl in myeloid malignancies

Next generation sequencing has shown the frequent occurrence of point mutations in the ubiquitin E3 ligase c-Cbl in myeloid malignancies. Mouse models revealed a causal contribution of c-Cbl for the onset of such neoplasms. The point mutations typically cluster in the linker region and RING finger domain and affect both alleles by acquired uniparental disomy. The fast progress in the detection of c-Cbl mutations is contrasted by our scarce knowledge on their functional consequences. The c-Cbl protein displays several enzymatic functions by promoting the attachment of differentially composed ubiquitin chains and of the ubiquitin-like protein NEDD8 to its target proteins. In addition, c-Cbl functions as an adapter protein and undergoes phosphorylation-dependent inducible conformation changes. Studies on the impact of c-Cbl mutations on its functions as a dynamic and versatile adapter protein, its interactomes and on its various enzymatic activities are now important to allow the identification of druggable targets within the c-Cbl signaling network.

Cigarette Smoking and the Risk of Adult Myeloid Disease: A Meta-Analysis

Background

The adult myeloid diseases, myelodysplastic syndrome and acute myeloid leukemia, have been reported to be associated with cigarette smoking, but the results have been conflicting. Previous studies may have ignored the relationship between myelodysplastic syndrome and acute myeloid leukemia, where approximately one-third of myelodysplastic syndrome cases will progress to acute myeloid leukemia, which could induce a serious bias in independent analyses. For the purposes of researching pathogenesis, we suggest that myelodysplastic syndrome and acute myeloid leukemia should be regarded as a single class of adult myeloid disease, and herein assessed the relationship between cigarette smoking and the risk of adult myeloid disease.

Methods

The PubMed, Cochrane Library, EBSCO, and EMBASE databases were systematically searched for reports published from 1990 to 2015. Two authors independently assessed the methodological quality and the extracted data. The odds ratios and adjusted odds ratios (OR), a sensitivity analysis, and the publication bias were analyzed using the CMA v2 (Comprehensive Meta Analysis Version 2) software program.

Results

Twenty-five studies were included in this meta-analysis. The publication dates ranged from 1990 to 2014. The pooled OR in current smokers and ever-smokers showed an increased risk of adult myeloid disease, with ORs of 1.45 (95% CI, 1.30–1.62; p<0.001) and 1.23 (95% CI 1.15–1.32; p<0.001) versus non-smokers, respectively. In the subset analyses, the OR of adult myeloid disease was increased regardless of the form of disease, geographical region, NOS (Newcastle Ottawa Scale) score, and source of controls. The smoking status was divided into <20 and ≥20 cigarettes per day, and these groups had ORs of developing adult myeloid disease of 1.24 (95% CI, 1.09–1.40; p = 0.001) and 1.32 (95% CI, 1.14–1.53; p<0.001), respectively. In the groups divided based on the number of years the subjects had smoked (<20 and ≥20 years), the ORs were 1.05 (95% CI, 0.90–1.23; p = 0.25) and 1.30 (95% CI, 1.16–1.45; p<0.001), respectively. Similarly, <20 and ≥20 pack-years were associated with ORs of 1.15 (95% CI, 1.03–1.29; p = 0.017) and 1.34 (95% CI, 1.18–1.52; p<0.001), respectively.

Conclusions

This meta-analysis, for the first time, combined myelodysplastic syndrome with acute myeloid leukemia to assess the overall risk of adult myeloid disease, and it demonstrated that cigarette smoking is associated with a significantly increased risk of adult myeloid disease.

Molecular mechanisms of the progression of myelodysplastic syndrome to secondary acute myeloid leukaemia and implication for therapy

Myelodysplastic syndrome (MDS) includes a heterogeneous group of clonal haematological stem cell disorders characterized by dysplasia, cytopenias, ineffective haematopoiesis, and an increased risk of progression to acute myeloid leukaemia (AML), which is also called secondary AML (sAML). Approximately one-third of patients with MDS will progress to sAML within a few months to a few years, and this type of transformation is more common and rapid in patients with high-risk MDS (HR-MDS). However, the precise mechanisms underlying the evolution of MDS to sAML remain unclear. Currently, chemotherapy for sAML has minimal efficacy. The only method of curing patients with sAML is allogeneic haematopoietic stem cell transplantation (Allo-HSCT). Unfortunately, only a few patients are appropriate for transplantation because this disease primarily affects older adult patients. Additionally, compared to de novo AML, sAML is more difficult to cure, and the prognosis is often worse. Therefore, it is important to clarify the molecular mechanisms of the progression of MDS to sAML and to explore the potent drugs for clinical use. This review will highlight several molecular mechanisms of the progression of MDS to sAML and new therapeutic strategies of this disease.

Cancer subclonal genetic architecture as a key to personalized medicine

The future of personalized oncological therapy will likely rely on evidence-based medicine to integrate all of the available evidence to delineate the most efficacious treatment option for the patient. To undertake evidence-based medicine through use of targeted therapy regimens, identification of the specific underlying causative mutation(s) driving growth and progression of a patient's tumor is imperative. Although molecular subtyping is important for planning and treatment, intraclonal genetic diversity has been recently highlighted as having significant implications for biopsy-based prognosis. Overall, delineation of the clonal architecture of a patient's cancer and how this will impact on the selection of the most efficacious therapy remain a topic of intense interest.

Five important advances in hematopathology

CONTEXT

Hematopathology is a dynamic field that has always been on the frontier of clinical research within the scope of pathology. Several recent developments in hematopathology will likely affect its practice clinically.

OBJECTIVE

To review 5 important recent advances in hematopathology: (1) detection and prognostic implication of MYC in diffuse large B-cell lymphomas, (2) determining origin and prognosis through immunoglobulin gene usage in mature B-cell neoplasms, (3)detecting minimal residual disease in multiple myeloma, (4) using genome-wide analysis in myelodysplastic syndromes, and (5) employing whole-genome sequencing in acute myeloid leukemias.

DATA SOURCES

Literature review and the authors' experiences in an academic center.

CONCLUSIONS

These advances will bring hematopathology into a new molecular era and help us to better understand the molecular, pathologic mechanisms of lymphomas, leukemias, myelomas, and myelodysplastic syndromes. They will help us to identify diagnostic and prognostic markers and eventually provide new therapeutic targets and treatments for these diseases.

The need for additional genetic markers for myelodysplastic syndrome stratification: what does the future hold for prognostication?

Myelodysplastic syndromes (MDS) constitute a heterogeneous group of clonal hematopoietic disorders. Metaphase cytogenetics has been the gold standard for genetic testing in MDS, but it detects clonal cytogenetic abnormalities in only 50% of cases. New karyotyping tests include FISH, array-based comparative genomic hybridization and single-nucleotide polymorphism arrays. These techniques have increased the detected genetic abnormalities in MDS, many of which confer prognostic significance to overall and leukemia-free survival. This has eventually increased our understanding of MDS genetics. With the help of new technologies, we anticipate that the existing prognostic scoring systems will incorporate mutational data into their parameters. This review discusses the progress in MDS diagnosis through the use of array-based technologies. The authors also discuss the recently investigated genetic mutations in MDS and revisit the MDS classification and prognostic scoring systems.

Overcoming intratumor heterogeneity of polygenic cancer drug resistance with improved biomarker integration

Improvements in technology and resources are helping to advance our understanding of cancer-initiating events as well as factors involved with tumor progression, adaptation, and evasion of therapy. Tumors are well known to contain diverse cell populations and intratumor heterogeneity affords neoplasms with a diverse set of biologic characteristics that can be used to evolve and adapt. Intratumor heterogeneity has emerged as a major hindrance to improving cancer patient care. Polygenic cancer drug resistance necessitates reconsidering drug designs to include polypharmacology in pursuit of novel combinatorial agents having multitarget activity to overcome the diverse and compensatory signaling pathways in which cancer cells use to survive and evade therapy. Advances will require integration of different biomarkers such as genomics and imaging to provide for more adequate elucidation of the spatially varying location, type, and extent of diverse intratumor signaling molecules to provide for a rationale-based personalized cancer medicine strategy.

Flt3 inhibitor AC220 is a potent therapy in a mouse model of myeloproliferative disease driven by enhanced wild-type Flt3 signaling

High levels of expression of wild-type Flt3 characterize many hematopoietic proliferative diseases and neoplasms, providing a potential therapeutic target. Using the c-Cbl RING finger mutant mouse as a model of a myeloproliferative disease (MPD) driven by wild-type Flt3, in the present study, we show that treatment with the Flt3 kinase inhibitor AC220 blocks MPD development by targeting Flt3+ multipotent progenitors (MPPs). We found that daily administration of AC220 caused a marked reduction in Flt3 expression, induction of quiescence, and a significant loss of MPPs within 4 days. Unexpectedly, a robust Flt3 ligand–associated proliferative recovery response soon followed, preventing further loss of MPPs. However, continued AC220 treatment limited MPP recovery and maintained reduced, steady-state levels of cycling MPPs that express low levels of Flt3. Therefore, a finely tuned balance between the opposing forces of AC220 and Flt3 ligand production was established; whereas the Flt3 ligand blunted the inhibitory effects of AC220, the disease was held in remission for as long as therapy was continued. The net effect is a potent therapy indicating that patients with c-Cbl mutations, or those with similarly enhanced Flt3 signaling, may respond well to AC220 even after the induction of high levels of Flt3 ligand.

Protein tyrosine kinase regulation by ubiquitination: critical roles of Cbl-family ubiquitin ligases

Protein tyrosine kinases (PTKs) coordinate a broad spectrum of cellular responses to extracellular stimuli and cell-cell interactions during development, tissue homeostasis, and responses to environmental challenges. Thus, an understanding of the regulatory mechanisms that ensure physiological PTK function and potential aberrations of these regulatory processes during diseases such as cancer are of broad interest in biology and medicine. Aside from the expected role of phospho-tyrosine phosphatases, recent studies have revealed a critical role of covalent modification of activated PTKs with ubiquitin as a critical mechanism of their negative regulation. Members of the Cbl protein family (Cbl, Cbl-b and Cbl-c in mammals) have emerged as dominant "activated PTK-selective" ubiquitin ligases. Structural, biochemical and cell biological studies have established that Cbl protein-dependent ubiquitination targets activated PTKs for degradation either by facilitating their endocytic sorting into lysosomes or by promoting their proteasomal degradation. This mechanism also targets PTK signaling intermediates that become associated with Cbl proteins in a PTK activation-dependent manner. Cellular and animal studies have established that the relatively broadly expressed mammalian Cbl family members Cbl and Cbl-b play key physiological roles, including their critical functions to prevent the transition of normal immune responses into autoimmune disease and as tumor suppressors; the latter function has received validation from human studies linking mutations in Cbl to human leukemia. These newer insights together with embryonic lethality seen in mice with a combined deletion of Cbl and Cbl-b genes suggest an unappreciated role of the Cbl family proteins, and by implication the ubiquitin-dependent control of activated PTKs, in stem/progenitor cell maintenance. Future studies of existing and emerging animal models and their various cell lineages should help test the broader implications of the evolutionarily-conserved Cbl family protein-mediated, ubiquitin-dependent, negative regulation of activated PTKs in physiology and disease.

Protein tyrosine kinase regulation by ubiquitination: critical roles of Cbl-family ubiquitin ligases

Protein tyrosine kinases (PTKs) coordinate a broad spectrum of cellular responses to extracellular stimuli and cell-cell interactions during development, tissue homeostasis, and responses to environmental challenges. Thus, an understanding of the regulatory mechanisms that ensure physiological PTK function and potential aberrations of these regulatory processes during diseases such as cancer are of broad interest in biology and medicine. Aside from the expected role of phospho-tyrosine phosphatases, recent studies have revealed a critical role of covalent modification of activated PTKs with ubiquitin as a critical mechanism of their negative regulation. Members of the Cbl protein family (Cbl, Cbl-b and Cbl-c in mammals) have emerged as dominant "activated PTK-selective" ubiquitin ligases. Structural, biochemical and cell biological studies have established that Cbl protein-dependent ubiquitination targets activated PTKs for degradation either by facilitating their endocytic sorting into lysosomes or by promoting their proteasomal degradation. This mechanism also targets PTK signaling intermediates that become associated with Cbl proteins in a PTK activation-dependent manner. Cellular and animal studies have established that the relatively broadly expressed mammalian Cbl family members Cbl and Cbl-b play key physiological roles, including their critical functions to prevent the transition of normal immune responses into autoimmune disease and as tumor suppressors; the latter function has received validation from human studies linking mutations in Cbl to human leukemia. These newer insights together with embryonic lethality seen in mice with a combined deletion of Cbl and Cbl-b genes suggest an unappreciated role of the Cbl family proteins, and by implication the ubiquitin-dependent control of activated PTKs, in stem/progenitor cell maintenance. Future studies of existing and emerging animal models and their various cell lineages should help test the broader implications of the evolutionarily-conserved Cbl family protein-mediated, ubiquitin-dependent, negative regulation of activated PTKs in physiology and disease.

Activating CBL mutations are associated with a distinct MDS/MPN phenotype

Activating point mutations in CBL have recently been identified in diverse subtypes of myeloid neoplasms. Because detailed clinical and hematological characteristics of CBL-mutated cases is lacking, we screened 156 BCR-ABL and JAK2 V617F negative patients with myeloproliferative neoplasms (MPN) and overlap syndromes between myelodysplastic syndrome (MDS) and MPN (MPS/MPN) for mutations in exons 8 and 9 of CBL by denaturing high-performance liquid chromatography and direct sequencing. CBL mutations were identified in 16/156 patients (10%), of which five also carried mutations in EZH2 (n = 3) and TET2 (n = 2). Comprehensive clinical and hematological characteristics were available from 13/16 patients (81%). In addition to splenomegaly (77%), striking common hematological features were CML-like left-shifted leukocytosis (85%) with monocytosis (85%), anemia (100%), and thrombocytopenia (62%). Thrombocytosis was not observed in any patient. Relevant bone marrow features (n = 12) included hypercellularity (92%) with marked granulopoiesis (92%), nonclustered microlobulated megakaryocytes (83%), and marrow fibrosis (83%). Nine deaths (progression to secondary acute myeloid leukemia/blast phase, n = 7; cytopenia complications, n = 2) were recorded. Three-year survival rate was 27%, possibly indicating poor prognosis of CBL mutated MDS/MPN patients.

The interconnectedness of cancer cell signaling

The elegance of fundamental and applied research activities have begun to reveal a myriad of spatial and temporal alterations in downstream signaling networks affected by cell surface receptor stimulation including G protein-coupled receptors and receptor tyrosine kinases. Interconnected biochemical pathways serve to integrate and distribute the signaling information throughout the cell by orchestration of complex biochemical circuits consisting of protein interactions and covalent modification processes. It is clear that scientific literature summarizing results from both fundamental and applied scientific research activities has served to provide a broad foundational biologic database that has been instrumental in advancing our continued understanding of underlying cancer biology. This article reflects on historical advances and the role of innovation in the competitive world of grant-sponsored research.