Palmitoylation of the Alternative Amino Terminus of the BTK-C Isoform Controls Subcellular Distribution and Signaling.

BACKGROUND: The alternative transcriptional isoform of Bruton's tyrosine kinase, BTK-C, is expressed in a wide variety of epithelial tumor types where it impacts apoptosis resistance, therapeutic escape, and glucose uptake. The initial exon in BTK-C encodes a 34 amino acid extension of the amino terminus of the canonical BTK-A isoform. Its function is unknown. MATERIALS AND METHODS: Site-directed mutagenesis, acylation assays and expression studies in cancer cell lines were used to determine the effects that the BTK-C first exon sequence has on kinase activity, subcellular localization and cell physiology. Analysis of BTK-C expression in tumors was conducted using genomic databases. RESULTS: BTK-C is palmitoylated on two cysteine residues. BTK-C localization at the plasma membrane is dependent upon phosphatidylinositol 3,4,5-triphosphate (PIP3) levels as well as palmitoylation. In epithelial cancer cells, both BTK-A and BTK-C isoforms are recruited to the plasma membrane; however, BTK-A also localizes to the nucleus whereas BTK-C has a primarily perinuclear distribution. Transcription of the BTK-C isoform is inversely correlated with expression of commonly activated breast cancer signaling receptors in breast tumors. In MDA-MB-231 cells, BTK-C expression confers modest increases in proliferation and glucose uptake rates compared to BTK-A. CONCLUSION: Palmitoylation affects localization and regulation of BTK-C in epithelial tumor cells where it functions as an important survival factor. Expression of either palmitoylated or non-palmitoylated kinase isoforms that function in PI3K signaling may be a common regulatory feature as nine other soluble kinases in the human genome possess similarly encoded alternative N-termini (ANT).

Bruton's Tyrosine Kinase and Its Isoforms in Cancer.

Bruton's tyrosine kinase (BTK) is a soluble tyrosine kinase with central roles in the development, maturation, and signaling of B cells. BTK has been found to regulate cell proliferation, survival, and migration in various B-cell malignancies. Targeting BTK with recently developed BTK inhibitors has been approved by the Food and Drug Administration (FDA) for the treatment of several hematological malignancies and has transformed the treatment of several B-cell malignancies. The roles that BTK plays in B cells have been appreciated for some time. Recent studies have established that BTK is expressed and plays pro-tumorigenic roles in several epithelial cancers. In this review, we focus on novel isoforms of the BTK protein expressed in epithelial cancers. We review recent work on the expression, function, and signaling of these isoforms and their value as potential therapeutic targets in epithelial tumors.

The first cohort of Iranian patients with hyper immunoglobulin E syndrome: A long-term follow-up and genetic analysis.

BACKGROUND: Hyper-IgE syndromes (HIES) are distinct diseases characterized by recurrent cutaneous and lung infections, eczema, and elevated serum IgE level. METHODS: In this study, clinical manifestations, immunologic findings, and genetic studies of all patients with HIES in the Iranian national registry database were evaluated. RESULTS: A total of 129 HIES patients with a median age of 14.0 (9.0-24.0) years were followed up for a total of 307.8 patient-years. Genetic studies showed heterozygous STAT3 mutations in 19 patients and homozygous DOCK8 mutation in 16 patients. The mean of National Institutes of Health score in STAT3-deficient patients was higher than in patients with DOCK8 mutation (P = 0.001). It was shown that the presence of pneumatocele and hematologic complication were significantly frequent in STAT3-deficient cases compared to patients with DOCK8 deficiency (P = 0.001 and P = 0.002, respectively). Moreover, the median IgE serum levels were higher in patients with STAT3 gene mutation than in patients with DOCK8 gene mutation (P = 0.02). The eosinophils' count was enhanced in patients with DOCK8 deficiency than in patients with STAT3 gene defects (P = 0.02). CONCLUSION: Specific molecular study of STAT3 and DOCK8 mutations in patients with HIES clinical phenotype could help the physician to definitively characterize the disease. Since HIES showed the highest rate of unsolved combined immunodeficiency, investigation of other genetic and environmental factors could also help in understanding the mechanism of remaining patients as well as providing strategy into therapeutic modalities.

Global metabolite profiling analysis of lipotoxicity in HER2/neu-positive breast cancer cells.

Recent work has shown that HER2/neu-positive breast cancer cells rely on a unique Warburg-like metabolism for survival and aggressive behavior. These cells are dependent on fatty acid (FA) synthesis, show markedly increased levels of stored fats and disruption of the synthetic process results in apoptosis. In this study, we used global metabolite profiling and a multi-omics network analysis approach to model the metabolic changes in this physiology under palmitate-supplemented growth conditions to gain insights into the molecular mechanism and its relevance to disease prevention and treatment. Computational analyses were used to define pathway enrichment based on the dataset of significantly altered metabolites and to integrate metabolomics and transcriptomics data in a multi-omics network analysis. Network-predicted changes and functional relationships were tested with cell assays in vitro. Palmitate-supplemented growth conditions induce distinct metabolic alterations. Growth of HER2-normal MCF7 cells is unaffected under these conditions whereas HER2/neu-positive cells display unchanged neutral lipid content, AMPK activation, inhibition of fatty acid synthesis and significantly altered glutamine, glucose and serine/glycine metabolism. The predominant upregulated lipid species is the novel bioactive lipid N-palmitoylglycine, which is non-toxic to these cells. Limiting the availability of glutamine significantly ameliorates the lipotoxic effects of palmitate, reduces CHOP and XBP1(s) induction and restores the expression levels of HER2 and HER3. The study shows that HER2/neu-positive breast cancer cells change their metabolic phenotype in the presence of palmitate. Palmitate induces AMPK activation and inhibition of fatty acid synthesis that feeds back into glycolysis as well as anaplerotic glutamine metabolism.