Giorgio Inghirami

BRAF Mutations in Hairy-Cell Leukemia

BACKGROUND Hairy-cell leukemia (HCL) is a well-defined clinicopathological entity whose underlying genetic lesion is still obscure. METHODS We searched for HCL-associated mutations by performing massively parallel sequencing of the whole exome of leukemic and matched normal cells purified from the peripheral blood of an index patient with HCL. Findings were validated by Sanger sequencing in 47 additional patients with HCL. RESULTS Whole-exome sequencing identified five missense somatic clonal mutations that were confirmed on Sanger sequencing, including a heterozygous mutation in BRAF that results in the BRAF V600E variant protein. Since BRAF V600E is oncogenic in other tumors, further analyses were focused on this genetic lesion. The same BRAF mutation was noted in all the other 47 patients with HCL who were evaluated by means of Sanger sequencing. None of the 195 patients with other peripheral B-cell lymphomas or leukemias who were evaluated carried the BRAF V600E variant, including 38 patients with splenic marginal-zone lymphomas or unclassifiable splenic lymphomas or leukemias. In immunohistologic and Western blot studies, HCL cells expressed phosphorylated MEK and ERK (the downstream targets of the BRAF kinase), indicating a constitutive activation of the RAF-MEK-ERK mitogen-activated protein kinase pathway in HCL. In vitro incubation of BRAF-mutated primary leukemic hairy cells from 5 patients with PLX-4720, a specific inhibitor of active BRAF, led to a marked decrease in phosphorylated ERK and MEK. CONCLUSIONS; The BRAF V600E mutation was present in all patients with HCL who were evaluated. This finding may have implications for the pathogenesis, diagnosis, and targeted therapy of HCL. (Funded by Associazione Italiana per la Ricerca sul Cancro and others.).

The anaplastic lymphoma kinase in the pathogenesis of cancer

Tyrosine kinases are involved in the pathogenesis of most cancers. However, few tyrosine kinases have been shown to have a well-defined pathogenetic role in lymphomas. The anaplastic lymphoma kinase (ALK) is the oncogene of most anaplastic large cell lymphomas (ALCL), driving transformation through many molecular mechanisms. In this Review, we will analyse how translocations or deregulated expression of ALK contribute to oncogenesis and how recent genetic or pharmacological tools, aimed at neutralizing its activity, can represent the basis for the design of powerful combination therapies.

β4 Integrin Amplifies ErbB2 Signaling to Promote Mammary Tumorigenesis

Amplification of the ErbB2 locus, which encodes a receptor tyrosine kinase, is common in aggressive breast tumors and correlates with poor prognosis. The mechanisms underlying ErbB2-mediated breast carcinoma progression remain incompletely defined. To examine the role of the signaling and cell-adhesion receptor beta 4 integrin during ErbB2-mediated tumorigenesis, we introduced a targeted deletion of the beta 4 signaling domain into a mouse model of ErbB2-induced mammary carcinoma. Loss of beta 4 signaling suppresses mammary tumor onset and invasive growth. Ex vivo studies indicate that beta 4 forms a complex with ErbB2 and enhances activation of the transcription factors STAT3 and c-Jun. STAT3 contributes to disruption of epithelial adhesion and polarity, while c-Jun is required for hyperproliferation. Finally, deletion of the beta 4 signaling domain enhances the efficacy of ErbB2-targeted therapy. These results indicate that beta 4 integrin promotes tumor progression by amplifying ErbB2 signaling and identify beta 4 as a potential target for molecular therapy of breast cancer.

Stat3 is required for ALK-mediated lymphomagenesis and provides a possible therapeutic target

Anaplastic large cell lymphomas (ALCLs) are caused by chromosomal translocations that juxtapose the anaplastic lymphoma kinase (ALK) proto-oncogene to a dimerization partner, resulting in constitutive expression of ALK and ALK tyrosine kinase activity. One substrate of activated ALK in human ALCLs is the transcription factor Stat3, and its phosphorylation is accurately recapitulated in a new nucleophosmin (NPM)-ALK transgenic mouse model of lymphomagenesis. Here we show by gene targeting that Stat3 is required for the transformation of mouse embryonic fibroblasts in vitro, for the development of B-cell lymphoma in transgenic mice and for the growth and survival of both human and mouse NPM-ALK–transformed B and T cells. Ablation of Stat3 expression by antisense oligonucleotides significantly (P < 0.0001) impaired the growth of human and mouse NPM-ALK tumors in vivo. Pharmacological ablation of Stat3 represents a new candidate approach for the treatment of human lymphoma.

Anaplastic lymphoma kinase (ALK) activates Stat3 and protects hematopoietic cells from cell death.

The anaplastic lymphoma kinase (ALK) gene is characteristically translocated in Anaplastic Large Cell Lymphomas (ALCL) and the juxtaposion of the ALK gene to multiple partners results in its constitutive protein tyrosine kinase activity. We show here that expression of activated ALK induces the constitutive phosphorylation of Stat3 in transfected cells as well as in primary human ALCLs. Furthermore, immunohistochemical studies demonstrate that among distinct human B and T cell lymphomas, activation of Stat3 nuclear translocation is uniquely associated with ALK expression. NPM-ALK also binds and activates Jak3; however, Jak3 is not required for Stat3 activation or for cell transformation in vitro. Moreover, src family kinases are not necessary for NPM-ALK-mediated Stat3 activation or transformation, suggesting that Stat3 may be phosphorylated directly by ALK. To evaluate relevant targets of ALK-activated Stat3, we investigated the regulation of the anti-apoptotic protein Bcl-xL and its role in cell survival in NPM-ALK positive cells. NPM-ALK expression caused enhanced Bcl-xL transcription, largely mediated by Stat3. Increased expression of Bcl-xL provided sufficient anti-apoptotic signals to protect cells from treatment with specific inhibitors of the Jaks/Stat pathway or the Brc-Abl kinase. These studies support a pathogenic mechanism whereby stimulation of anti-apoptotic signals through activation of Stat3 contributes to the successful outgrowth of ALK positive tumor cells.

Role of the F-box protein Skp2 in lymphomagenesis

The F-box protein Skp2 (S-phase kinase-associated protein 2) positively regulates the G1-S transition by controlling the stability of several G1 regulators, such as the cell cycle inhibitor p27. We show here that Skp2 expression correlates directly with grade of malignancy and inversely with p27 levels in human lymphomas. To directly evaluate the potential of Skp2 to deregulate growth in vivo, we generated transgenic mice expressing Skp2 targeted to the T-lymphoid lineage as well as double transgenic mice coexpressing Skp2 and activated N-Ras. A strong cooperative effect between these two transgenes induced T cell lymphomas with shorter latency and higher penetrance, leading to significantly decreased survival when compared with control and single transgenic animals. Furthermore, lymphomas of Nras single transgenic animals often expressed higher levels of endogenous Skp2 than tumors of double transgenic mice. This study provides evidence of a role for an F-box protein in oncogenesis and establishes SKP2 as a protooncogene causally involved in the pathogenesis of lymphomas.

Stromal contribution to the colorectal cancer transcriptome

Recent studies identified a poor-prognosis stem/serrated/mesenchymal (SSM) transcriptional subtype of colorectal cancer (CRC). We noted that genes upregulated in this subtype are also prominently expressed by stromal cells, suggesting that SSM transcripts could derive from stromal rather than epithelial cancer cells. To test this hypothesis, we analyzed CRC expression data from patient-derived xenografts, where mouse stroma supports human cancer cells. Species-specific expression analysis showed that the mRNA levels of SSM genes were mostly due to stromal expression. Transcriptional signatures built to specifically report the abundance of cancer-associated fibroblasts (CAFs), leukocytes or endothelial cells all had significantly higher expression in human CRC samples of the SSM subtype. High expression of the CAF signature was associated with poor prognosis in untreated CRC, and joint high expression of the stromal signatures predicted resistance to radiotherapy in rectal cancer. These data show that the distinctive transcriptional and clinical features of the SSM subtype can be ascribed to its particularly abundant stromal component.

The coding genome of splenic marginal zone lymphoma: activation of NOTCH2 and other pathways regulating marginal zone development

Notch2 mutations represent the most frequent lesion in splenic marginal zone lymphoma.

A targeted mutational landscape of angioimmunoblastic T-cell lymphoma

The genetics of angioimmunoblastic T-cell lymphoma (AITL) are very poorly understood. We defined the mutational landscape of AITL across 219 genes in 85 cases from the United States and Europe. We identified ≥2 mutations in 34 genes, nearly all of which were not previously implicated in AITL. These included loss-of-function mutations in TP53 (n = 4), ETV6 (n = 3), CCND3 (n = 2), and EP300 (n = 5), as well as gain-of-function mutations in JAK2 (n = 2) and STAT3 (n = 4). TET2 was mutated in 65 (76%) AITLs, including 43 that harbored 2 or 3 TET2 mutations. DNMT3A mutations occurred in 28 (33%) AITLs; 100% of these also harbored TET2 mutations (P < .0001). Seventeen AITLs harbored IDH2 R172 substitutions, including 15 with TET2 mutations. In summary, AITL is characterized by high frequencies of overlapping mutations in epigenetic modifiers and targetable mutations in a subset of cases.

Functional validation of the anaplastic lymphoma kinase signature identifies CEBPB and Bcl2A1 as critical target genes

Anaplastic large cell lymphomas (ALCLs) represent a subset of lymphomas in which the anaplastic lymphoma kinase (ALK) gene is frequently fused to the nucleophosmin (NPM) gene. We previously demonstrated that the constitutive phosphorylation of ALK chimeric proteins is sufficient to induce cellular transformation in vitro and in vivo and that ALK activity is strictly required for the survival of ALK-positive ALCL cells. To elucidate the signaling pathways required for ALK-mediated transformation and tumor maintenance, we analyzed the transcriptomes of multiple ALK-positive ALCL cell lines, abrogating their ALK-mediated signaling by inducible ALK RNA interference (RNAi) or with potent and cell-permeable ALK inhibitors. Transcripts derived from the gene expression profiling (GEP) analysis uncovered a reproducible signature, which included a novel group of ALK-regulated genes. Functional RNAi screening on a set of these ALK transcriptional targets revealed that the transcription factor C/EBPbeta and the antiapoptotic protein BCL2A1 are absolutely necessary to induce cell transformation and/or to sustain the growth and survival of ALK-positive ALCL cells. Thus, we proved that an experimentally controlled and functionally validated GEP analysis represents a powerful tool to identify novel pathogenetic networks and validate biologically suitable target genes for therapeutic interventions.