Marcus B. Valentine

Bio: Marcus B. Valentine is an academic researcher from St. Jude Children's Research Hospital. The author has contributed to research in topics: Gene & Fluorescence in situ hybridization. The author has an hindex of 44, co-authored 74 publications receiving 9086 citations. Previous affiliations of Marcus B. Valentine include University of Toledo Medical Center & University of New Mexico.

Fusion of a Kinase Gene, ALK, to a Nucleolar Protein Gene, NPM, in Non-Hodgkin's Lymphoma

Abstract: The 2;5 chromosomal translocation occurs in most anaplastic large-cell non-Hodgkin's lymphomas arising from activated T lymphocytes. This rearrangement was shown to fuse the NPM nucleolar phosphoprotein gene on chromosome 5q35 to a previously unidentified protein tyrosine kinase gene, ALK, on chromosome 2p23. In the predicted hybrid protein, the amino terminus of nucleophosmin (NPM) is linked to the catalytic domain of anaplastic lymphoma kinase (ALK). Expressed in the small intestine, testis, and brain but not in normal lymphoid cells, ALK shows greatest sequence similarity to the insulin receptor subfamily of kinases. Unscheduled expression of the truncated ALK may contribute to malignant transformation in these lymphomas.

Targetable Kinase-Activating Lesions in Ph-like Acute Lymphoblastic Leukemia

Abstract: BACKGROUND Philadelphia chromosome–like acute lymphoblastic leukemia (Ph-like ALL) is characterized by a gene-expression profile similar to that of BCR–ABL1–positive ALL, alterations of lymphoid transcription factor genes, and a poor outcome. The frequency and spectrum of genetic alterations in Ph-like ALL and its responsiveness to tyrosine kinase inhibition are undefined, especially in adolescents and adults. METHODS We performed genomic profiling of 1725 patients with precursor B-cell ALL and detailed genomic analysis of 154 patients with Ph-like ALL. We examined the functional effects of fusion proteins and the efficacy of tyrosine kinase inhibitors in mouse pre-B cells and xenografts of human Ph-like ALL. RESULTS Ph-like ALL increased in frequency from 10% among children with standard-risk ALL to 27% among young adults with ALL and was associated with a poor outcome. Kinase-activating alterations were identified in 91% of patients with Ph-like ALL; rearrangements involving ABL1, ABL2, CRLF2, CSF1R, EPOR, JAK2, NTRK3, PDGFRB, PTK2B, TSLP, or TYK2 and sequence mutations involving FLT3, IL7R, or SH2B3 were most common. Expression of ABL1, ABL2, CSF1R, JAK2, and PDGFRB fusions resulted in cytokine-independent proliferation and activation of phosphorylated STAT5. Cell lines and human leukemic cells expressing ABL1, ABL2, CSF1R, and PDGFRB fusions were sensitive in vitro to dasatinib, EPOR and JAK2 rearrangements were sensitive to ruxolitinib, and the ETV6–NTRK3 fusion was sensitive to crizotinib. CONCLUSIONS Ph-like ALL was found to be characterized by a range of genomic alterations that activate a limited number of signaling pathways, all of which may be amenable to inhibition with approved tyrosine kinase inhibitors. Trials identifying Ph-like ALL are needed to assess whether adding tyrosine kinase inhibitors to current therapy will improve the survival of patients with this type of leukemia. (Funded by the American Lebanese Syrian Associated Charities and others.)

Inactivating mutations in an SH2 domain-encoding gene in X-linked lymphoproliferative syndrome

Abstract: X-linked lymphoproliferative syndrome (XLP) is an inherited immunodeficiency characterized by increased susceptibility to Epstein–Barr virus (EBV). In affected males, primary EBV infection leads to the uncontrolled proliferation of virus-containing B cells and reactive cytotoxic T cells, often culminating in the development of high-grade lymphoma. The XLP gene has been mapped to chromosome band Xq25 through linkage analysis and the discovery of patients harboring large constitutional genomic deletions. We describe here the presence of small deletions and intragenic mutations that specifically disrupt a gene named DSHP in 6 of 10 unrelated patients with XLP. This gene encodes a predicted protein of 128 amino acids composing a single SH2 domain with extensive homology to the SH2 domain of SHIP, an inositol polyphosphate 5-phosphatase that functions as a negative regulator of lymphocyte activation. DSHP is expressed in transformed T cell lines and is induced following in vitro activation of peripheral blood T lymphocytes. Expression of DSHP is restricted in vivo to lymphoid tissues, and RNA in situ hybridization demonstrates DSHP expression in activated T and B cell regions of reactive lymph nodes and in both T and B cell neoplasms. These observations confirm the identity of DSHP as the gene responsible for XLP, and suggest a role in the regulation of lymphocyte activation and proliferation. Induction of DSHP may sustain the immune response by interfering with SHIP-mediated inhibition of lymphocyte activation, while its inactivation in XLP patients results in a selective immunodeficiency to EBV.

The retinoblastoma protein binds to a family of E2F transcription factors.

Abstract: E2F is a transcription factor that helps regulate the expression of a number of genes that are important in cell proliferation. Recently, several laboratories have isolated a cDNA clone that encodes an E2F-like protein, known as E2F-1. Subsequent characterization of this protein showed that it had the properties of E2F, but it was difficult to account for all of the suggested E2F activities through the function of this one protein. Using low-stringency hybridization, we have isolated cDNA clones that encode two additional E2F-like proteins, called E2F-2 and E2F-3. The chromosomal locations of the genes for E2F-2 and E2F-3 were mapped to 1p36 and 6q22, respectfully, confirming their independence from E2F-1. However, the E2F-2 and E2F-3 proteins are closely related to E2F-1. Both E2F-2 and E2F-3 bound to wild-type but not mutant E2F recognition sites, and they bound specifically to the retinoblastoma protein in vivo. Finally, E2F-2 and E2F-3 were able to activate transcription of E2F-responsive genes in a manner that was dependent upon the presence of at least one functional E2F binding site. These observations suggest that the E2F activities described previously result from the combined action of a family of proteins.

Coamplification of the CDK4 Gene with MDM2 and GLI in Human Sarcomas

Abstract: The 34-kilodalton cyclin-dependent kinase, p34cdk4, is a major catalytic subunit of mammalian D-type cyclins, which act during the G1 phase of the cell cycle to enforce the decision of cells to enter S phase. A murine complementary DNA clone was used to clone the cognate human CDK4 gene, which was localized to human chromosome 12, band q13, by fluorescence in situ hybridization. Because this chromosomal band contains the GLI and MDM2 genes, which are frequently amplified in human sarcomas, we analyzed CDK4 copy number and expression in a panel of sarcoma cell lines. An osteosarcoma cell line, OsACL, manifested a 25-fold increased copy number of CDK4 , amplified concordantly with both GLI and MDM2 , whereas a rhabdomyosarcoma cell line, SJRH30, was found to have an amplicon that included CDK4 and GLI but not MDM2. CDK4 mRNA and protein were overexpressed in both cell lines, and nucleotide sequencing analysis indicated that the gene had not sustained mutations. These observations provide the first evidence for amplification of a gene encoding a cell division cycle protein kinase, complement recent data indicating that genes encoding D-type cyclins are targets of chromosomal rearrangement and gene amplification in tumor cells, and suggest that CDK4 amplification might contribute to oncogenesis.

Identification of a Cancer Stem Cell in Human Brain Tumors

Abstract: Most current research on human brain tumors is focused on the molecular and cellular analysis of the bulk tumor mass. However, there is overwhelming evidence in some malignancies that the tumor clone is heterogeneous with respect to proliferation and differentiation. In human leukemia, the tumor clone is organized as a hierarchy that originates from rare leukemic stem cells that possess extensive proliferative and self-renewal potential, and are responsible for maintaining the tumor clone. We report here the identification and purification of a cancer stem cell from human brain tumors of different phenotypes that possesses a marked capacity for proliferation, self-renewal, and differentiation. The increased self-renewal capacity of the brain tumor stem cell (BTSC) was highest from the most aggressive clinical samples of medulloblastoma compared with low-grade gliomas. The BTSC was exclusively isolated with the cell fraction expressing the neural stem cell surface marker CD133. These CD133+ cells could differentiate in culture into tumor cells that phenotypically resembled the tumor from the patient. The identification of a BTSC provides a powerful tool to investigate the tumorigenic process in the central nervous system and to develop therapies targeted to the BTSC.

Identification of the transforming EML4–ALK fusion gene in non-small-cell lung cancer

Abstract: Improvement in the clinical outcome of lung cancer is likely to be achieved by identification of the molecular events that underlie its pathogenesis. Here we show that a small inversion within chromosome 2p results in the formation of a fusion gene comprising portions of the echinoderm microtubule-associated protein-like 4 (EML4) gene and the anaplastic lymphoma kinase (ALK) gene in non-small-cell lung cancer (NSCLC) cells. Mouse 3T3 fibroblasts forced to express this human fusion tyrosine kinase generated transformed foci in culture and subcutaneous tumours in nude mice. The EML4-ALK fusion transcript was detected in 6.7% (5 out of 75) of NSCLC patients examined; these individuals were distinct from those harbouring mutations in the epidermal growth factor receptor gene. Our data demonstrate that a subset of NSCLC patients may express a transforming fusion kinase that is a promising candidate for a therapeutic target as well as for a diagnostic molecular marker in NSCLC.