Metastasis is the principal event leading to death in individuals with cancer, yet its molecular basis is poorly understood. To explore the molecular differences between human primary tumors and metastases, we compared the gene-expression profiles of adenocarcinoma metastases of multiple tumor types to unmatched primary adenocarcinomas. We found a gene-expression signature that distinguished primary from metastatic adenocarcinomas. More notably, we found that a subset of primary tumors resembled metastatic tumors with respect to this gene-expression signature. We confirmed this finding by applying the expression signature to data on 279 primary solid tumors of diverse types. We found that solid tumors carrying the gene-expression signature were most likely to be associated with metastasis and poor clinical outcome (P < 0.03). These results suggest that the metastatic potential of human tumors is encoded in the bulk of a primary tumor, thus challenging the notion that metastases arise from rare cells within a primary tumor that have the ability to metastasize.

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A molecular signature of metastasis in primary solid tumors.

From the Departments of Genetics (E.R.M., L.D., V.J.M., R.K.W., T.J.L.), Medicine (R.E.R., P.W., M.H.T., S.H., W.D.S., D.C.L., M.J.W., T.A.G., J.F.D., T.J.L.), and Pathology and Immunology (J.E.P., M.A.W., R.N.); the Genome Center (E.R.M., L.D., D.J.D., D.E.L., M.D.M., K.C., D.C.K., R.S.F., K.D.D., S.D.M., L.A.F., D.P.L., V.J.M., R.M.A.,

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Recurring mutations found by sequencing an acute myeloid leukemia genome.

Causal Relationship between the Loss of RUNX3 Expression and Gastric Cancer

Children with Down syndrome have a 10–20-fold elevated risk of developing leukemia, particularly acute megakaryoblastic leukemia (AMKL)1. While a subset of pediatric AMKLs is associated with the 1;22 translocation and expression of a mutant fusion protein2,3, the genetic alterations that promote Down syndrome–related AMKL (DS-AMKL) have remained elusive. Here we show that leukemic cells from every individual with DS-AMKL that we examined contain mutations in GATA1, encoding the essential hematopoietic transcription factor GATA1 (GATA binding protein 1 or globin transcription factor 1). Each mutation results in the introduction of a premature stop codon in the gene sequence that encodes the amino-terminal activation domain. These mutations prevent synthesis of full-length GATA1, but not synthesis of a shorter variant that is initiated downstream. We show that the shorter GATA1 protein, which lacks the N-terminal activation domain, binds DNA and interacts with its essential cofactor Friend of GATA1 (FOG1; encoded by ZFPM1)4 to the same extent as does full-length GATA1, but has a reduced transactivation potential. Although some reports suggest that the activation domain is dispensable in cell-culture models of hematopoiesis5,6, one study has shown that it is required for normal development in vivo7. Together, these findings indicate that loss of wildtype GATA1 constitutes one step in the pathogenesis of AMKL in Down syndrome.

Acquired mutations in GATA1 in the megakaryoblastic leukemia of Down syndrome.

Embryonic development of multilineage hematopoiesis requires the precisely regulated expression of lineage-specific transcription factors, including AML-1 (encoded by Runx1; also known as CBFA-2 or PEBP-2αB)1,2,3,4,5. In vitro studies and findings in human diseases, including leukemias6,7, myelodysplastic syndromes8 and familial platelet disorder with predisposition to acute myeloid leukemia (AML)9, suggest that AML-1 has a pivotal role in adult hematopoiesis. However, this role has not been fully uncovered in vivo because of the embryonic lethality of Runx1 knockout in mice. Here we assess the requirement of AML-1/Runx1 in adult hematopoiesis using an inducible gene-targeting method10. In the absence of AML-1, hematopoietic progenitors were fully maintained with normal myeloid cell development. However, AML-1-deficient bone marrow showed inhibition of megakaryocytic maturation, increased hematopoietic progenitor cells and defective T- and B-lymphocyte development. AML-1 is thus required for maturation of megakaryocytes and differentiation of T and B cells, but not for maintenance of hematopoietic stem cells (HSCs) in adult hematopoiesis.

AML-1 is required for megakaryocytic maturation and lymphocytic differentiation, but not for maintenance of hematopoietic stem cells in adult hematopoiesis.

Familial platelet disorder with predisposition to acute myelogenous leukaemia (FPD/AML, MIM 601399) is an autosomal dominant disorder characterized by qualitative and quantitative platelet defects, and propensity to develop acute myelogenous leukaemia (AML). Informative recombination events in 6 FPD/AML pedigrees with evidence of linkage to markers on chromosome 21q identified an 880-kb interval containing the disease gene. Mutational analysis of regional candidate genes showed nonsense mutations or intragenic deletion of one allele of the haematopoietic transcription factor CBFA2 (formerly AML1) that co-segregated with the disease in four FPD/AML pedigrees. We identified heterozygous CBFA2 missense mutations that co-segregated with the disease in the remaining two FPD/AML pedigrees at phylogenetically conserved amino acids R166 and R201, respectively. Analysis of bone marrow or peripheral blood cells from affected FPD/AML individuals showed a decrement in megakaryocyte colony formation, demonstrating that CBFA2 dosage affects megakaryopoiesis. Our findings support a model for FPD/AML in which haploinsufficiency of CBFA2 causes an autosomal dominant congenital platelet defect and predisposes to the acquisition of additional mutations that cause leukaemia.

K. Gardiner

Papers

Haploinsufficiency of CBFA2 causes familial thrombocytopenia with propensity to develop acute myelogenous leukaemia