The role of HOXB2 and HOXB3 in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a heterogeneous aggressive disease and the most common form of adult leukemia. Mutations in the type III receptor tyrosine kinase FLT3 are found in more than 30% of AML patients. Drugs against FLT3 have been developed for the treatment of AML, but they lack specificity, show poor response and lead to the development of a resistant phenotype upon treatment. Therefore, a deeper understanding of FLT3 signaling will facilitate identification of additional pharmacological targets in FLT3-driven AML. In this report, we identify HOXB2 and HOXB3 as novel regulators of oncogenic FLT3-ITD-driven AML. We show that HOXB2 and HOXB3 expression is upregulated in a group of AML patients carrying FLT3-ITD. Overexpression of HOXB2 or HOXB3 in mouse pro-B cells resulted in decreased FLT3-ITD-dependent cell proliferation as well as colony formation and increased apoptosis. Expression of HOXB2 or HOXB3 resulted in a significant decrease in FLT3-ITD-induced AKT, ERK, p38 and STAT5 phosphorylation. Our data suggest that HOXB2 and HOXB3 act as tumor suppressors in FLT3-ITD driven AML.

Brain-Expressed X-linked (BEX) proteins in human cancers.

The Brain-Expressed X-linked (BEX) family proteins are comprised of five human proteins including BEX1, BEX2, BEX3, BEX4 and BEX5. BEX family proteins are expressed in a wide range of tissues and are known to play a role in neuronal development. Recent studies suggest a role of BEX family proteins in cancers. BEX1 expression is lost in a subgroup of patients with acute myeloid leukemia (AML) and chronic myeloid leukemia (CML). Expression of BEX1 controls cell surface receptor signaling and restores imatinib response in resistant cells. BEX2 is overexpressed in a group of breast cancer patients and also in gliomas. Increased BEX2 expression led to enhanced NF-κB signaling as well as cell proliferation. Although BEX2 acts as tumor promoter in a subset of breast cancer, BEX3 expression displayed an opposite role. Overexpression of BEX3 resulted in inhibition of tumor formation in breast cancer mouse xenograft models. The role of BEX4 and BEX5 in cancer has not yet been defined. Collectively this suggests that BEX family members have distinct roles in cancers. While BEX1 and BEX3 act as tumor suppressors, BEX2 seems to act as an oncogene.

BEX1 acts as a tumor suppressor in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a heterogeneous disease of the myeloid lineage. About 35% of AML patients carry an oncogenic FLT3 mutant making FLT3 an attractive target for treatment of AML. Major problems in the development of FLT3 inhibitors include lack of specificity, poor response and development of a resistant phenotype upon treatment. Further understanding of FLT3 signaling and discovery of novel regulators will therefore help to determine additional pharmacological targets in FLT3-driven AML. In this report, we identified BEX1 as a novel regulator of oncogenic FLT3-ITD-driven AML. We showed that BEX1 expression was down-regulated in a group of AML patients carrying FLT3-ITD. Loss of BEX1 expression resulted in poor overall survival (hazard ratio, HR = 2.242, p = 0.0011). Overexpression of BEX1 in mouse pro-B and myeloid cells resulted in decreased FLT3-ITD-dependent cell proliferation, colony and tumor formation, and in increased apoptosis in vitro and in vivo. BEX1 localized to the cytosolic compartment of cells and significantly decreased FLT3-ITD-induced AKT phosphorylation without affecting ERK1/2 or STAT5 phosphorylation. Our data suggest that the loss of BEX1 expression in FLT3-ITD driven AML potentiates oncogenic signaling and leads to decreased overall survival of the patients.

Role of SRC-like adaptor protein (SLAP) in immune and malignant cell signaling.

SRC-like adaptor protein (SLAP) is an adaptor protein structurally similar to the SRC family protein kinases. Like SRC, SLAP contains an SH3 domain followed by an SH2 domain but the kinase domain has been replaced by a unique C-terminal region. SLAP is expressed in a variety of cell types. Current studies suggest that it regulates signaling of various cell surface receptors including the B cell receptor, the T cell receptor, cytokine receptors and receptor tyrosine kinases which are important regulator of immune and cancer cell signaling. SLAP targets receptors, or its associated components, by recruiting the ubiquitin machinery and thereby destabilizing signaling. SLAP directs receptors to ubiquitination-mediated degradation and controls receptors turnover as well as signaling. Thus, SLAP appears to be an important component in regulating signal transduction required for immune and malignant cells.

Keratin 19 expression correlates with poor prognosis in breast cancer.

Breast cancer expression profiling has been used for determining biomarkers. Using gene expression profiles of 2,400 patients we identified keratin 19 (KRT19) as a highly deregulated gene in breast cancer. KRT19 expression is independent of patient race but correlates with disease grade, and ER, PR or HER2 expression. Expression of TPD52, GATA3 and KRT18 was increased in KRT19 expressing patients. Furthermore, KRT19 expression was associated with ER up-regulation and Luminal B gene signatures, as well as a constitutive RAF1 signaling pathway. Finally, KRT19 expression correlated with poor overall survival. Taken together, our results suggest that KRT19 expression can be used as a prognostic marker.

SOCS6 is a selective suppressor of receptor tyrosine kinase signaling.

The suppressors of cytokine signaling (SOCS) are well-known negative regulators of cytokine receptor signaling. SOCS6 is one of eight members of the SOCS family of proteins. Similar to other SOCS proteins, SOCS6 consists of an uncharacterized extended N-terminal region followed by an SH2 domain and a SOCS box. Unlike other SOCS proteins, SOCS6 is mainly involved in negative regulation of receptor tyrosine kinase signaling. SOCS6 is widely expressed in many tissues and is found to be downregulated in many cancers including colorectal cancer, gastric cancer, lung cancer, ovarian cancer, stomach cancer, thyroid cancer, hepatocellular carcinoma, and pancreatic cancer. SOCS6 is involved in negative regulation of receptor signaling by increasing degradation mediated by ubiquitination of receptors or substrate proteins and induces apoptosis by targeting mitochondrial proteins. Therefore, SOCS6 turns out as an important regulator of survival signaling and its activity is required for controlling receptor tyrosine kinase signaling.

SOCS proteins in regulation of receptor tyrosine kinase signaling.

Receptor tyrosine kinases (RTKs) are a family of cell surface receptors that play critical roles in signal transduction from extracellular stimuli. Many in this family of kinases are overexpressed or mutated in human malignancies and thus became an attractive drug target for cancer treatment. The signaling mediated by RTKs must be tightly regulated by interacting proteins including protein-tyrosine phosphatases and ubiquitin ligases. The suppressors of cytokine signaling (SOCS) family proteins are well-known negative regulators of cytokine receptors signaling consisting of eight structurally similar proteins, SOCS1-7, and cytokine-inducible SH2-containing protein (CIS). A key feature of this family of proteins is the presence of an SH2 domain and a SOCS box. Recent studies suggest that SOCS proteins also play a role in RTK signaling. Activation of RTK results in transcriptional activation of SOCS-encoding genes. These proteins associate with RTKs through their SH2 domains and subsequently recruit the E3 ubiquitin machinery through the SOCS box, and thereby limit receptor stability by inducing ubiquitination. In a similar fashion, SOCS proteins negatively regulate mitogenic signaling by RTKs. It is also evident that RTKs can sometimes bypass SOCS regulation and SOCS proteins can even potentiate RTKs-mediated mitogenic signaling. Thus, apart from negative regulation of receptor signaling, SOCS proteins may also influence signaling in other ways.

Grb10 is a dual regulator of receptor tyrosine kinase signaling.

The adaptor protein Grb10 is a close homolog of Grb7 and Grb14. These proteins are characterized by an N-terminal proline-rich region, a Ras-GTPase binding domain, a PH domain, an SH2 domain and a BPS domain in between the PH and SH2 domains. Human Grb10 gene encodes three splice variants. These variants show differences in functionality. Grb10 associates with multiple proteins including tyrosine kinases in a tyrosine phosphorylation dependent or independent manner. Association with multiple proteins allows Grb10 to regulate different signaling pathways resulting in different biological consequences.

Protein kinase C (PKC) as a drug target in chronic lymphocytic leukemia.

Protein kinase C (PKC) belongs to a family of ten serine/threonine protein kinases encoded by nine genes. This family of proteins plays critical roles in signal transduction which results in cell proliferation, survival, differentiation and apoptosis. Due to differential subcellular localization and tissue distribution, each member displays distinct signaling characteristics. In this review, we have summarized the roles of PKC family members in chronic lymphocytic leukemia (CLL). CLL is a heterogeneous hematological disorder with survival ranging from months to decades. PKC isoforms are differentially expressed in CLL and play critical roles in CLL pathogenesis. Thus, isoform-specific PKC inhibitors may be an attractive option for CLL treatment.

Deregulation of protein phosphatase expression in acute myeloid leukemia.

Acute myeloid leukemia (AML) is a highly malignant disease of myeloid cell line. AML is the most frequent adult leukemia with inadequate treatment possibility. The protein phosphatases are critical regulators of cell signaling, and deregulation of protein phosphatases always contribute to cell transformation. Although many studies established a relationship between protein phosphatases and leukemia, little is known about the role of this group of proteins in AML. To address this issue, we initially identified the complete catalog of human protein phosphatase genes and used this catalog to study deregulation of protein phosphatases in AML. Using mRNA expression data of AML patients, we show that 11 protein phosphatases are deregulated in AML within 174 protein phosphatases. The GO enrichment study suggests that these genes are involved in multiple biological processes other than protein de-phosphorylation. Expression of DUSP10, PTPRC, and PTPRE was significantly higher than average expression in AML, and a linear combination of DUSP10, MTMR11, PTPN4, and PTPRE expressions provides important information about disease subtypes. Our results provide an overview of protein phosphatase deregulation in AML.

Comparative analysis of human and bovine protein kinases reveals unique relationship and functional diversity.

Reversible protein phosphorylation by protein kinases and phosphatases is a common event in various cellular processes. The eukaryotic protein kinase superfamily, which is one of the largest superfamilies of eukaryotic proteins, plays several roles in cell signaling and diseases. We identified 482 eukaryotic protein kinases and 39 atypical protein kinases in the bovine genome, by searching publicly accessible genetic-sequence databases. Bovines have 512 putative protein kinases, each orthologous to a human kinase. Whereas orthologous kinase pairs are, on an average, 90.6% identical, orthologous kinase catalytic domain pairs are, on an average, 95.9% identical at the amino acid level. This bioinformatic study of bovine protein kinases provides a suitable framework for further characterization of their functional and structural properties.

Comparative analysis of human and bovine protein kinases reveals unique relationship and functional diversity

Reversible protein phosphorylation by protein kinases and phosphatases is a common event in various cellular processes. The eukaryotic protein kinase superfamily, which is one of the largest superfamilies of eukaryotic proteins, plays several roles in cell signaling and diseases. We identified 482 eukaryotic protein kinases and 39 atypical protein kinases in the bovine genome, by searching publicly accessible genetic-sequence databases. Bovines have 512 putative protein kinases, each orthologous to a human kinase. Whereas orthologous kinase pairs are, on an average, 90.6 percent identical, orthologous kinase catalytic domain pairs are, on an average, 95.9 percent identical at the amino acid level. This bioinformatic study of bovine protein kinases provides a suitable framework for further characterization of their functional and structural properties.

Bioinformatic prediction and analysis of eukaryotic protein kinases in the rat genome.

Eukaryotic protein kinases, containing a conserved catalytic domain, represent one of the largest superfamilies of the eukaryotic proteins and play distinct roles in cell signaling and diseases. Near completion of rat genome sequencing project enables the evaluation of a near complete set of rat protein kinases. Publicly accessible genetic sequence databases were searched for rat protein kinases, and 515 eukaryotic protein kinases, 40 atypical protein kinases and 45 kinase pseudogenes were identified. The rat has 509 putative protein kinases orthologous to human kinases. Unlike microtubule affinity-regulating kinases, the rat has a few more kinases, in addition to the orthologous pairs of mouse kinases. The comparison of 11 different eukaryotic species revealed the evolutionary conservation of this diverse family of proteins. The evolutionary rate studies of human disease and non-disease associated kinases suggested that relatively uniform selective pressures have been applied to these kinase classes. This bioinformatic study of the rat protein kinases provides a suitable framework for further characterization of the functional and structural properties of these protein kinases.