KIT proto-oncogene exon 8 deletions at codon 419 are highly frequent in acute myeloid leukaemia with inv(16) in Indian population

Cryo-EM analyses of KIT and oncogenic mutants reveal structural oncogenic plasticity and a target for therapeutic intervention

The receptor tyrosine kinase KIT and its ligand stem cell factor (SCF) are required for the development of hematopoietic stem cells, germ cells, and other cells. A variety of human cancers, such as acute myeloid leukemia, gastrointestinal stromal tumor, and mast cell leukemia, are driven by somatic gain-of-function KIT mutations. Here, we report cryo electron microscopy (cryo-EM) structural analyses of full-length wild-type and two oncogenic KIT mutants, which show that the overall symmetric arrangement of the extracellular domain of ligand-occupied KIT dimers contains asymmetric D5 homotypic contacts juxtaposing the plasma membrane. Mutational analysis of KIT reveals in D5 region an "Achilles heel" for therapeutic intervention. A ligand-sensitized oncogenic KIT mutant exhibits a more comprehensive and stable D5 asymmetric conformation. A constitutively active ligand-independent oncogenic KIT mutant adopts a V-shaped conformation solely held by D5-mediated contacts. Binding of SCF to this mutant fully restores the conformation of wild-type KIT dimers, including the formation of salt bridges responsible for D4 homotypic contacts and other hallmarks of SCF-induced KIT dimerization. These experiments reveal an unexpected structural plasticity of oncogenic KIT mutants and a therapeutic target in D5.

Identification and in silico analysis of noval alteration Arg420Gly in KIT proto oncogene among acute myeloid leukemia patients

A number of studies have reported frequent incidence of c-kit gene mutations in association with core binding factor acute myeloid leukemia (CBF-AML). These genetic changes have become important prognostic predictors in patients with abnormal karyotype. Aim of this study was the detection of nucleotide alterations in newly diagnosed acute myeloid leukemia patients for three exons of c-kit gene, including cytogenetically normal patients. Thirty-one de novo AML patients were screened for any possible variations in exon 8, 11 and 17 sequences of c-kit proto-oncogene leading to amino acid substitutions or frame shift. Sanger sequencing method was employed followed by sequence analysis. Mutation data was then correlated with clinical and hematological parameters of patients and prognostic significance of genetic changes was assessed as well. The computational tools were then used to further understand the extent of damage caused by these mutations to c-kit protein. Fifteen (48.4%) mutant patients were observed with single, double or multiple mutations in one, two or all three exons studied. The analysis revealed eight new alterations which were not reported previously. Significant variation among mutant and non-mutant group of patients was observed with respect to FAB subtypes (x² = 12.524, p = 0.029), Spleen size (x² = 4.288, p = 0.038) and Red blood cell count (x² = 8.447, p = 0.007). The survival analysis indicates poor overall and event free survival outcomes in mutant individuals. Furthermore, the in silico analysis suggests that changes in nucleotide sequences can possibly damage the protein structure and effect it's function. This study emphasizes the need to consider screening of c-kit gene alterations not only in CBF-AML but in cytogenetically normal AML patients as well. In current investigation the effect of mutation Arg420Gly on structure and function of c-kit protein was investigated, as this was the most observed substitution in present cohort. Various bioinformatics tools and techniques were employed, which determined that Arg420Gly is possibly non-pathogenic mutation.

Distinct cellular properties of oncogenic KIT receptor tyrosine kinase mutants enable alternative courses of cancer cell inhibition

Large genomic sequencing analysis as part of precision medicine efforts revealed numerous activating mutations in receptor tyrosine kinases, including KIT. Unfortunately, a single approach is not effective for inhibiting cancer cells or treating cancers driven by all known oncogenic KIT mutants. Here, we show that each of the six major KIT oncogenic mutants exhibits different enzymatic, cellular, and dynamic properties and responds distinctly to different KIT inhibitors. One class of KIT mutants responded well to anti-KIT antibody treatment alone or in combination with a low dose of tyrosine kinase inhibitors (TKIs). A second class of KIT mutants, including a mutant resistant to imatinib treatment, responded well to a combination of TKI with anti-KIT antibodies or to anti-KIT toxin conjugates, respectively. We conclude that the preferred choice of precision medicine treatments for cancers driven by activated KIT and other RTKs may rely on clear understanding of the dynamic properties of oncogenic mutants.

Study of Cysteine-Rich Protein 61 Genetic Polymorphism in Predisposition to Fracture Nonunion: A Case Control

Background. Many factors are responsible for this impaired healing, especially in long bones, but a possible genetic predisposition for the development of this complication remains unknown till now. In the present study, we aim to examine the CYR61 gene polymorphism in fracture nonunion patients and the correlation with clinical findings. Materials and Methods. We performed SNP analysis of the CYR61 gene in 250 fracture nonunion patients and 250 healthy subjects were genotyped in this hospital-based case control study, and 56 cases were further evaluated for mRNA expression of CYR61 by real-time quantitative reverse-transcription PCR. Results. CYR61 gene TT, TG, and GG genotype frequencies of total fracture nonunion cases were 41.6%, 49.2%, and 9.20% and 54.4%, 39.2%, and 6.40% in healthy controls. Heterozygous TG genotype was found statistically significant in fracture nonunion cases compared with that in controls, whereas homozygous mutant GG genotype was not found significant. Moreover, we found that TG + GG genotypes were significantly different in serum expression of CYR61 mRNA when compared with cases (TT genotypes). Conclusions. Our result signifies that genotype of CYR61 affects the mRNA expression and acts as a risk factor that could synergistically increase the susceptibility of a patient to develop fracture nonunion.