Correction: Fhit modulation of the Akt-survivin pathway in lung cancer cells: Fhit-tyrosine 114 (Y114) is essential.

After publication of this Article the authors noticed errors in several figures. In Fig. 2b the Gapdh panels are incorrect. The lysates are identical to those used in Fig. 1b, therefore the Gapdh panels should be the same in both figures. In Fig. 3b the Gapdh panels for Ad-Fhit-wt and Ad-Fhit-Y114F are incorrect and have been replaced with scans from original films. In Fig. 4A the Gapdh panels are incorrect. The lysates are identical to those used in Fig. 3b, therefore the Gapdh panels should be the same in both figures. In Fig. 4Bb the Gapdh panels for Fhit siRNA were incorrect and have been replaced with scans from original films. All resupplied figures are provided below. In Fig. 5C several panels are incorrect. The Authors were unable to locate the original films for all of these panels so Fig. 5c has been deleted. The scientific conclusions of this paper have not been affected.

Role of miR-15/16 in CLL.

B-cell chronic lymphocytic leukemia (CLL) is the most common adult leukemia. The most common chromosomal abnormalities detectable by cytogenetics include deletion at 13q (55%), 11q (18%), trisomy 12 (12-16%) and 17p (8%). In 2002, we discovered that a microRNA cluster miR-15a/miR-16-1 (miR-15/16) is the target of 13q deletions in CLL. MicroRNAs encoded by the miR-15/16 locus (miR-15 and miR-16) function as tumor suppressors. Expression of these miRNAs downregulated in CLL, melanoma, colorectal cancer, bladder cancer and other solid tumors. miR-15/16 cluster targets multiple oncogenes, including BCL2, Cyclin D1, MCL1 and others. The most important target of miR-15/16 in CLL is arguably BCL2, as BCL2 is overexpressed in almost all CLLs. In this review, we discuss the discovery, functions, clinical relevance and treatment opportunities related to miR-15/16.

CD5+CD23+ leukemic cell populations in TCL1 transgenic mice show significantly increased proliferation and Akt phosphorylation.

B-cell chronic lymphocytic leukemia (B-CLL) is the most common adult leukemia. Deregulation of the T-cell leukemia/lymphoma 1 (TCL1) oncogene in mouse B cells causes a CD5-positive leukemia similar to aggressive human B-CLLs. We recently reported that levels of TCL1 expression in B-CLL are regulated by miR-29 and miR-181 that target 3' UTR of TCL1. To determine whether treatment with microRNAs targeting TCL1 can inhibit B-CLL in mice, we generated TCL1 transgenic mice using a construct containing the 3' and 5' UTRs of TCL1 under B-cell-specific Emicro promoter (Emicro-TCL1FL). At the age of 16-20 months, these mice showed B-CLL-like disease. Immunophenotyping revealed accumulation of CD5+CD23+B220+ population in spleens and lymph nodes. Our results show that CD5+CD23+ B-cell populations from Emicro-TCL1FL mice actively proliferate and show significantly increased levels of phospho-Akt. Emicro-TCL1FL mice showed immunological abnormalities similar to human B-CLL, including hypoimmunoglobulinemia, abnormal levels of cytokines and impaired immune response. These findings revealed biochemical and immunological similarities between Tcl1-driven B-CLL in mice and human B-CLL.

Fhit modulation of the Akt-survivin pathway in lung cancer cells: Fhit-tyrosine 114 (Y114) is essential.

The Fhit tumor suppressor binds and hydrolyses diadenosine polyphosphates and the Fhit-substrate complex has been proposed as a proapoptotic effector, as determined by infection of susceptible cancer cells with adenoviruses carrying wild-type fragile histidine triad (FHIT) or catalytic site mutants. The highly conserved Fhit tyrosine 114 (Y114), within the unstructured loop C-terminal of the catalytic site, can be phosphorylated by Src family tyrosine kinases, although endogenous phospho-Fhit is rarely detected. To explore the importance of Y114 and identify Fhit-mediated signaling events, wild-type and Y114 mutant FHIT-expressing adenoviruses were introduced into two human lung cancer cell lines. Caspase-dependent apoptosis was effectively induced only by wild-type but not Y114 mutant Fhit proteins. By expression profiling of FHIT versus mutant FHIT-infected cells, we found that survivin, an Inhibitor of Apoptosis Protein (IAP) family member, was significantly decreased by wild-type Fhit. In addition, Fhit inhibited activity of Akt, a key effector in the phosphatidylinositol 3-OH kinase (PI3K) pathway; loss of endogenous Fhit expression caused increased Akt activity in vitro and in vivo, and overexpression of constitutively active Akt inhibited Fhit-induced apoptosis. The results indicate that the Fhit Y114 residue plays a critical role in Fhit-induced apoptosis, occurring through inactivation of the PI3K-Akt-survivin signal pathway.

Chronic lymphocytic leukemia: molecular genetics and animal models.

Chronic lymphocytic leukemia accounts for almost 30% of all adult leukemia cases in the United States and Western Europe. Although several common genomic abnormalities in CLL have been identified, mutational and functional analysis of corresponding genes so far have not proved their involvement in CLL. Our latest studies demonstrated functional involvement of Tcl1 oncoprotein and microRNA genes in the pathogenesis of CLL. Deregulated expression of Tcl1 in transgenic mice resulted in CLL. These CLL tumors showed abnormalities in expression of murine microRNA genes mmu-mir-15a and mmu-mir-16-1. Interestingly, human homologs of these genes, mir-15a and mir-16-1, located at the chromosome 13q14 are also deleted in human CLL samples. In this review we summarize and discuss these new developments. These recently emerged insights into the molecular mechanisms of CLL will allow for the development of new approaches to treat this disease.

Molecular basis of mature T-cell leukemia.

T-cell chronic lymphocytic/prolymphocytic leukemia (T-CLL/T-PLL) is a lymphoproliferative disease derived from immunocompetent post-thymic T cells. Activation (initiation of expression) of the TCL1 locus at chromosome 14q32.1 appears to be the causal event in the pathogenesis of these mature T-cell leukemias. This activation occurs as a result of translocations or inversions that cause rearrangement of the TCL1 (T-cell leukemia/lymphoma 1) locus with regulatory elements of T-cell receptor genes. To describe the molecular events that take part in the leukemogenesis of mature T-cell leukemias, we reviewed the literature and our own data on the molecular basis of mature T-cell leukemia. This data search revealed that 4 genes have been identified at the TCL1 locus: TCL1, TCL1b, TNG1, and TNG2. The expression of these genes is substantially increased following rearrangements involving 14q32.1. Functional analysis of the Tcl1 protein revealed its involvement in an Akt (protein kinase B) prosurvival pathway through its interaction with the Akt kinase, which promotes translocation of Akt to the nucleus and increases Akt's enzymatic activity. The available data provide important insights into the molecular mechanisms of T-cell leukemogenesis that may lead to the development of new drugs for treatment of mature T-cell leukemia.

Fhit protein expression in oral epithelium: immunohistochemical evaluation of three antisera.

BACKGROUND: A number of studies have shown that the Fhit tumour suppressor protein is abundantly expressed in normal epithelial cells of human organs and that this expression is lost or reduced in the majority of cancers arising in these epithelial tissues. A variety of antiFhit sera have been used but a systematic comparison of the different antisera has not yet been reported. MATERIALS AND METHODS: We compared the Fhit expression pattern in the epithelium of fibrous epuli, oral lichen planus, oral epithelial dysplasia and oral squamous cell carcinomas (OSCC) using three different Fhit antisera. RESULTS: The antigstFhit sera from two sources gave very similar results for all types of oral lesions except for lichen planus and showed that about 60% of OSCCs have lost Fhit expression. CONCLUSION: Although different staining patterns were found for the three antisera, all three could be used for evaluation of Fhit expression in OSCC.

The role of TCL1 in human T-cell leukemia.

The TCL1 locus on human chromosome 14q32.1 is activated in T-cell leukemias by translocations and inversions that juxtapose it to regulatory elements of T-cell receptor genes. We isolated and characterized four genes at this locus, TCL1 and TCL1b (T-cell leukemia/lymphoma 1 and 1b), and TNG1 and TNG2 (TCL neighboring genes 1 and 2) all of which are overexpressed following rearrangements involving 14q32.1. TCL1 and TCL1b show 60% similarity and are represented in the mouse by a cluster of six homologous genes. In humans TCL1 and TCL1b show similar expression patterns: They are expressed mainly in CD4-/CD8- immature T-cells, pre B-cells and virgin B-cells. Expression decreases significantly at more mature stages of B-cell development. Activation of TCL1 and/or TCL1b in mature T-cells causes T-cell leukemia in humans. The oncogenic nature of TCL1 was confirmed by the analysis of a transgenic mouse model. Functional analysis of Tcl1 revealed its involvement in a PI3-kinase dependent Akt (PKB) pro-survival pathway through its interaction with the Akt kinase which increases Akt's enzymatic activity and promotes translocation of Akt to the nucleus.

Characterization of the 13q14 tumor suppressor locus in CLL: identification of ALT1, an alternative splice variant of the LEU2 gene.

Chromosome 13q14 deletions constitute the most common genetic abnormality in chronic lymphocytic leukemia (CLL). To identify the putative tumor suppressor gene targeted by 13q14 genomic loss, we completely sequenced and characterized a segment of 790 kb at 13q14 spanning the minimal region of loss in CLL. Transcribed sequences in the region were identified through database homology searches and exon-prediction analysis. Two-hundred kb at the centromeric end of the sequence contain five CpG islands, three previously identified genes LEU5/RFP2, LEU2, and LEU1, seven of seven EST clusters composed of >10 ESTs, and a large number of predicted exons. Homology searches against the mouse EST database have allowed us to identify a highly conserved alternative first exon of the LEU2 gene, giving rise to a novel transcript, ALT1 (GenBank accession no. AF380424), which originates within a G+C region in the vicinity of the D13S272 marker. Two novel 3' exons of LEU2 were also identified and are present in both LEU2 and ALT1 transcripts. However, we have not identified any mutations in leukemia cases, or alterations in expression of mRNAs in the region, that might directly implicate these mRNAs in the pathology of CLL. The centromeric end of the sequence, where all reported genes are located, contains twice the expected amount of ALU repeats, whereas the telomeric end is LINE1 rich and contains four LINE1 elements longer than 4 kb, including two full-length LINE1 sequences. This feature of the sequence may favor the occurrence of chromosomal rearrangements and may confer instability to the region, resulting in deletions that may inactivate an as yet unidentified tumor suppressor.

Akt phosphorylates and regulates the orphan nuclear receptor Nur77.

The immediate early gene NUR77 (also called NGFI-B) is required for T cell antigen receptor-mediated cell death and is induced to very high levels in immature thymocytes and T cell hybridomas undergoing apoptosis. The Akt (PKB) kinase is a key player in transduction of anti-apoptotic and proliferative signals in T cells. Because Nur77 has a putative Akt phosphorylation site at Ser-350, and phosphorylation of this residue is critical for the transactivation activity of Nur77, we investigated whether Akt regulates Nur77. Coimmunoprecipitation experiments showed the detection of Nur77 in Akt immune complexes, suggesting that Nur77 and Akt physically interact. We further show that Akt specifically phosphorylates Ser-350 of the Nur77 protein within its DNA-binding domain in vitro and in vivo in 293 and NIH 3T3 cells. Because phosphorylation of Ser-350 of Nur77 is critical for its function as a transcription factor, we examined the effect of Akt on this function. By using luciferase assay experiments, we showed that phosphorylation of Nur77 by Akt decreased the transcriptional activity of Nur77 by 50--85%. Thus, we show that Akt interacts with Nur77 and inactivates Nur77 by phosphorylation at Ser-350 in a phosphatidylinositol 3-kinase-dependent manner, connecting the phosphatidylinositol 3-kinase-dependent Akt pathway and a nuclear receptor pathway.

Crystal structure of the worm NitFhit Rosetta Stone protein reveals a Nit tetramer binding two Fhit dimers.

BACKGROUND: The nucleotide-binding protein Fhit, among the earliest and most frequently inactivated proteins in lung cancer, suppresses tumor formation by inducing apoptosis. In invertebrates, Fhit is encoded as a fusion protein with Nit, a member of the nitrilase superfamily. In mice, the Nit1 and Fhit genes have nearly identical expression profiles. According to the Rosetta Stone hypothesis, if the separate Nit and Fhit genes could be shown to occur in the same subset of genomes (that is, to share a phylogenetic profile), then the existence of a fusion protein in invertebrates and the coordinated expression of separate mRNAs in mouse suggest that Nit and Fhit function in the same pathway and that the structure of invertebrate NitFhit may reflect the nature of Nit-Fhit interactions. RESULTS: To satisfy the phylogenetic profile criterion for functional significance of protein fusion events, we cloned additional Nit homologs from organisms with Fhit homologs. We used fluorescent nucleotide analogs of ApppA to follow the purification and to characterize the nucleotide specificity of NitFhit from Caenorhabditis elegans, crystallized the 200 kDa tetrameric complex, and solved the structure of NitFhit from a single mercury derivative phased by two-wavelength anomalous diffraction. CONCLUSIONS: Nit monomers possess a new alpha-beta-beta-alpha sandwich fold with a presumptive Cys-Glu-Lys catalytic triad. Nit assembles into a tetrameric, 52-stranded beta box that binds Fhit dimers at opposite poles and displays Nit active sites around the middle of the complex. The most carboxy-terminal beta strand of each Nit monomer exits the core of the Nit tetramer and interacts with Fhit. Residence in the NitFhit complex does not alter the nucleotide specificity of Fhit dimers, which are oriented with ApppA-binding surfaces away from Nit.

Tcl1 enhances Akt kinase activity and mediates its nuclear translocation.

The TCL1 oncogene at 14q32.1 is involved in the development of human mature T-cell leukemia. The mechanism of action of Tcl1 is unknown. Because the virus containing the v-akt oncogene causes T-cell lymphoma in mice and Akt is a key player in transduction of antiapoptotic and proliferative signals in T-cells, we investigated whether Akt and Tcl1 function in the same pathway. Coimmunoprecipitation experiments showed that endogenous Akt1 and Tcl1 physically interact in the T-cell leukemia cell line SupT11; both proteins also interact when cotransfected into 293 cells. Using several AKT1 constructs in cotransfection experiments, we determined that this interaction occurs through the pleckstrin homology domain of the Akt1 protein. We further demonstrated that, in 293 cells transfected with TCL1, the endogenous Akt1 bound to Tcl1 is 5-10 times more active compared with Akt1 not bound to Tcl1. The intracellular localization of Tcl1 and Akt1 in mouse fibroblasts was investigated by immunofluorescence. When transfected alone, Akt1 was found only in cytoplasm whereas Tcl1 was localized in the cytoplasm and in the nucleus. Interestingly, Akt1 was also found in the nucleus when AKT1 was cotransfected with TCL1, suggesting that Tcl1 promotes the transport of Akt1 to the nucleus. These findings were supported by the intracellular localization of Akt1 or Tcl1 when Tcl1 or Akt1, respectively, were confined to the specific cellular compartments. Thus, we demonstrate that Tcl1 is a cofactor of Akt1 that enhances Akt1 kinase activity and promotes its nuclear transport.

Genomic analysis of human and mouse TCL1 loci reveals a complex of tightly clustered genes.

TCL1 and TCL1b genes on human chromosome 14q23.1 are activated in T cell leukemias by translocations and inversions at 14q32.1, juxtaposing them to regulatory elements of T cell receptor genes. In this report we present the cloning, mapping, and expression analysis of the human and murine TCL1/Tcl1 locus. In addition to TCL1 and TCL1b, the human locus contains two additional genes, TCL1-neighboring genes (TNG) 1 and 2, encoding proteins of 141 and 110 aa, respectively. Both genes show no homology to any known genes, but their expression profiles are very similar to those of TCL1 and TCL1b. TNG1 and TNG2 also are activated in T cell leukemias with rearrangements at 14q32.1. To aid in the development of a mouse model we also have characterized the murine Tcl1 locus and found five genes homologous to human TCL1b. Tcl1b1-Tcl1b5 proteins range from 117 to 123 aa and are 65-80% similar, but they show only a 30-40% similarity to human TCL1b. All five mouse Tcl1b and murine Tcl1 mRNAs are abundant in mouse oocytes and two-cell embryos but rare in various adult tissues and lymphoid cell lines. These data suggest a similar or complementary function of these proteins in early embryogenesis.

FHIT loss of function in human primary breast cancer correlates with advanced stage of the disease.

The FHIT gene, encompassing the FRA3B fragile site at chromosome 3p14.2, is a tumor suppressor gene involved in different tumor types. We have assessed 29 human primary breast carcinomas for both the presence of abnormal FHIT transcripts and the Fhit protein levels as compared with the normal breast epithelium of the same patients. In addition, we have also examined a second retrospective series of 156 consecutive breast carcinomas for the expression of the Fhit protein. In nine (31%) cases of the first series, FHIT transcripts were either aberrant or absent as determined by reverse transcription-PCR, and Fhit protein levels in tumors were low or absent as determined immunohistochemically. In 11 other cases (38%), only normal FHIT transcripts were detected by PCR, paralleled by the reduction or absence of Fhit protein. In the remaining nine cases (31%), the presence of the normal FHIT transcript corresponded to protein levels that were similar in tumor and normal breast epithelia. Thus, alterations in FHIT transcripts were detected in 31% of the patients, but reduction or absence of Fhit protein occurred in 69% of the breast carcinoma samples examined. These data suggest that alteration in Fhit expression in breast carcinomas is a frequent event. Analysis of correlation between Fhit expression and pathological, clinical, and biological parameters in these 29 tumors and in a second retrospective series of 156 consecutive primary breast carcinomas indicated that a decrease or an absence of Fhit protein expression is associated with high proliferation and large tumor size.

Abnormalities at 14q32.1 in T cell malignancies involve two oncogenes.

The TCL1 oncogene on human chromosome 14q32.1 is involved in the development of T cell leukemia in humans. Its expression in these leukemias is activated by chromosomal translocations and inversions at 14q32.1. Here we report the isolation and characterization of a new member of the TCL1 gene family, TCL1b, located approximately 16 kb centromeric of TCL1. The 1.2-kb TCL1b cDNA encodes a 14-kDa protein of 128 aa and shows 60% similarity to Tcl1. Expression profiles of TCL1 and TCL1b genes are very similar: both genes are expressed at very low levels in normal bone marrow and peripheral lymphocytes but are activated in T cell leukemia by rearrangements of the 14q32.1 region. Thus, translocations and inversions at 14q32. 1 in T cell malignancies involve two oncogenes.

The murine Fhit locus: isolation, characterization, and expression in normal and tumor cells.

The murine Fhit locus maps near the centromere nu proximal Ptprg locus on mouse chromosome 14. The cDNA sequence and structure are similar to those of the human gene, with exons 5-9 encoding the protein. The predominant mRNA in the tissues and cell lines tested was an alternatively spliced form missing exon 3. Most murine cell lines tested, including lines established from normal mouse embryos and tumors, expressed very low or undetectable levels of Fhit mRNA. Most normal mouse tissues expressed wild-type Fhit mRNA, whereas approximately 40% of murine lung carcinomas expressed wild-type and aberrant Fhit RT-PCR products that lacked various exons. Several tumorigenic mouse cell lines exhibited homozygous deletions of Fhit exons. We conclude that the murine Fhit gene, like its human counterpart, is a target of alterations involved in murine carcinogenesis.

Absence or reduction of Fhit expression in most clear cell renal carcinomas.

The FHIT gene at human chromosome region 3p14.2 straddles the common fragile site, FRA3B, and numerous homozygous deletions in cancer cell lines and primary tumors. Also, the 3p14.2 chromosome breakpoint of the familial clear cell kidney carcinoma-associated translocation, t(3;8)(p14.2;q24), disrupts one FHIT allele between exons 3 and 4, fulfilling one criterion for a familial tumor suppressor gene: that one allele is constitutionally inactivated. Because the FHIT gene sustains biallelic intragenic deletions rather than mutations, there has not been evidence that the FHIT gene frequently plays a role in kidney cancer, although replacement of Fhit expression in a Fhit-negative renal carcinoma cell line suppressed tumor growth in nude mice. We have now assessed 41 clear cell renal carcinomas for expression of Fhit by immunohistochemistry. Normal renal tubule epithelial cells express Fhit uniformly and strongly, whereas 51% of the tumors are completely negative, 34% of tumors show a mixture of positive and negative cells, and 14% are uniformly positive, although usually less strongly positive than the normal epithelial cells. Most interestingly, there was a correlation between complete absence of Fhit and the G1 morphological grade and early clinical stage. Morphological grades G2 and G3 exhibited a mixture of positive and negative cells with a tendency for a higher fraction of negative cells in G3. Fhit inactivation is likely to be an early event in G1 tumors and may be associated with progression in G2 and G3 tumors.

Nitrilase and Fhit homologs are encoded as fusion proteins in Drosophila melanogaster and Caenorhabditis elegans.

The tumor suppressor gene FHIT encompasses the common human chromosomal fragile site at 3p14.2 and numerous cancer cell biallelic deletions. To study Fhit function we cloned and characterized FHIT genes from Drosophila melanogaster and Caenorhabditis elegans. Both genes code for fusion proteins in which the Fhit domain is fused with a novel domain showing homology to bacterial and plant nitrilases; the D. melanogaster fusion protein exhibited diadenosine triphosphate (ApppA) hydrolase activity expected of an authentic Fhit homolog. In human and mouse, the nitrilase homologs and Fhit are encoded by two different genes: FHIT and NIT1, localized on chromosomes 3 and 1 in human, and 14 and 1 in mouse, respectively. We cloned and characterized human and murine NIT1 genes and determined their exon-intron structure, patterns of expression, and alternative processing of their mRNAs. The tissue specificity of expression of murine Fhit and Nit1 genes was nearly identical. Because fusion proteins with dual or triple enzymatic activities have been found to carry out specific steps in a given biochemical or biosynthetic pathway, we postulate that Fhit and Nit1 likewise collaborate in a biochemical or cellular pathway in mammalian cells.