Oncogene database

4004

LMO1

LIM domain only 1 (rhombotin 1);LMO1;LIM domain only 1 (rhombotin 1)

LIM domain only protein 1|LMO-1|T-cell translocation gene 1|T-cell translocation protein 1|cysteine-rich protein TTG-1|rhombotin-1

11p15

protein-coding

The T-cell oncogene rhombotin was first identified as a gene near a chromosomal translocation breakpoint in a human T-cell tumour and represents the first example of an oncogene carrying the duplicated cysteine-rich regions (CRR or LIM domains). Transgenic expression of a reporter gene under the control of one of the rhombotin gene promoters subsequently showed high levels of expression in the developing brain. These disparate sites of transcriptional activity suggested that the gene may have been activated de novo specifically in the T cell tumour via the translocation. Here, we assess this possibility by analysing rhombotin gene expression in mouse development by in situ hybridization of whole embryos, Northern filter hybridization, and a sensitive semiquantitative PCR method. The results show that the central nervous system is the major site of rhombotin mRNA production. Low level expression does, however, occur in other tissues including thymus. Furthermore, both promoters are active and differentially regulated during mouse embryogenesis in both brain and thymus. In subregions of the adult brain, different levels of rhombotin activity can be observed, with evidence for regional variation in promoter usage. A detailed analysis of mouse and human T-cell differentiation suggests that fluctuating promoter activities are related to a general T-cell differentiation process rather than to the differentiation of functionally distinct subsets of T-cells. These data suggest that the transforming activity of rhombotin in the T-cell with the chromosomal translocation was not due to de novo transcriptional activation, but rather to a quantitative or qualitative change in expression levels of this CRR-containing oncogene after chromosomal translocation.

Neuroblastoma is a childhood cancer of the sympathetic nervous system that accounts for approximately 10% of ALL paediatric oncology deaths. To identify genetic risk factors for neuroblastoma, we performed a genome-wide association study (GWAS) on 2,251 patients and 6,097 control subjects of European ancestry from four case series. Here we report a significant association within LIM domain only 1 (LMO1) at 11p15.4 (rs110419, combined P = 5.2 x 10(-16), odds ratio of risk allele = 1.34 (95% confidence interval 1.25-1.44)). The signal was enriched in the subset of patients with the most aggressive form of the disease. LMO1 encodes a cysteine-rich transcriptional regulator, and its paralogues (LMO2, LMO3 and LMO4) have each been previously implicated in cancer. In parallel, we analysed genome-wide DNA copy number alterations in 701 primary tumours. We found that the LMO1 locus was aberrant in 12.4% through a duplication event, and that this event was associated with more advanced disease (P < 0.0001) and survival (P = 0.041). The germline single nucleotide polymorphism (SNP) risk alleles and somatic copy number gains were associated with increased LMO1 expression in neuroblastoma cell lines and primary tumours, consistent with a gain-of-function role in tumorigenesis. Short hairpin RNA (shRNA)-mediated depletion of LMO1 inhibited growth of neuroblastoma cells with high LMO1 expression, whereas forced expression of LMO1 in neuroblastoma cells with low LMO1 expression enhanced proliferation. These data show that common polymorphisms at the LMO1 locus are strongly associated with susceptibility to developing neuroblastoma, but also may influence the likelihood of further somatic alterations at this locus, leading to malignant progression.

We previously identified a putative T cell oncogene on chromosome 11 near a translocation t(11;14)(p15;q11) in a human T cell tumour. The gene is transcribed from distinct promoters which have unrelated sequences, which occur within close but distinct methylation-free islands and which allow cell specific production of mRNA. The alternative first exons each contain a protein initiation codon from which two species of protein can be made, differing by only a single amino acid. The protein sequence is highly conserved between man and mouse (98%) and the same single codon difference between alternative first exons is also conserved. This is, therefore, a new form of eukaryotic gene organization from which similar proteins can be made from distinct mRNA species.

LMO1 is a transcriptional regulator and a T-acute lymphoblastic leukaemia (T-ALL) oncogene. Although first identified in association with a chromosomal translocation in T-ALL, the ectopic expression of LMO1 occurs far more frequently in the absence of any known mutation involving its locus. Given that LMO1 is barely expressed in any haematopoietic lineage, and activation of transcriptional drivers in leukaemic cells is not well described, we investigated the regulation of this gene in normal haematopoietic and leukaemic cells. We show that LMO1 has two promoters that drive reporter gene expression in transgenic mice to neural tissues known to express endogenous LMO1. The LMO1 promoters display bivalent histone marks in multiple blood lineages including T-cells, and a 3 flanking region at LMO1 +57 contains a transcriptional enhancer that is active in developing blood cells in transgenic mouse embryos. The LMO1 promoters become activated in T-ALL together with the 3 enhancer, which is bound in primary T-ALL cells by SCL/TAL1 and GATA3. Taken together, our results show that LMO1 is poised for expression in normal progenitors, where activation of SCL/TAL1 together with a breakdown of epigenetic repression of LMO1 regulatory elements induces ectopic LMO1 expression that contributes to the development and maintenance of T-ALL.

Colorectal cancer (CRC) is the third leading cause of cancer mortality in the world. We report that one oncogene amplified on chromosome 3q26, LMO1, a master transcriptional regulator of stemness, operates to drive strong growth phenotype in CRC. The gene expression changes of LMO1 in human CRC tissues compared with noncancerous tissues were detected using real-time quantitative reverse transcriptase-polymerase chain reaction (QRT-PCR) analysis and immunohistochemistry, which identified the gene overexpression of LMO1 in CRC. Moreover, we discovered that LMO1 promoted cancer cell proliferation in vitro/in vivo and LMO1 expression correlated with elevated AKT phosphorylation in CRC while the AKT phosphorylation was required for oncogenic effects of LMO1. Next, our data point to the usefulness of LMO1 overexpression, as a new predictive marker for responsiveness to cetuximab. ALL in all, LMO1 is a commonly activated tumor promoter that activates AKT signaling in CRC and a new predictive marker for targeted therapy.

Non-small cell lung cancer (NSCLC) is the leading cause of cancer mortality in the world. We report that one oncogene amplified on chromosome 3q26, LMO1, a master transcriptional regulator of stemness, operates to drive strong growth phenotype in NSCLC. We first validate gene expression changes of LMO genes by real-time quantitative RT-PCR real-time quantitative reverse transcriptase-polymerase chain reaction analysis and immunohistochemistry, and we identified gene overexpression of LMO1 compared with non-cancerous tissues (p < 0.01). Next, we discovered that LMO1 promoted cancer cell proliferation in our in vitro/vivo cell proliferation assay, and our cell signaling experiments showed that LMO1 expression correlated with elevated AKT phosphorylation in NSCLC, while the AKT phosphorylation was required for LMO1 s oncogenic effects. In addition, we compared complete response rate, stable disease rate, disease progression rate, and the disease control rate of patient with different LMO1 gene expression which pointed to the usefulness of LMO1 overexpression, as a new predictive marker for responsiveness to cetuximab. ALL in all, LMO1 is a commonly activated tumor promoter that activates AKT signaling in NSCLC and a new predictive marker for targeted therapy.

The RBTN1 and RBTN2 genes are activated by distinct translocations involving chromosome 11 in some T cell acute leukaemias. The RBTN proteins belong to the LIM family which comprises proteins with one, two or three cysteine-rich LIM domains, sometimes together with homeodomains or protein kinase domains. The RBTN1 and RBTN2 proteins comprise only tandem LIM domains. We report that RBTN1 and RBTN2 proteins are capable of supporting transcriptional transactivation of specific reporter genes in transfection assays. The results, using intact proteins or fusions with the homeodomain of the heterologous protein Isl-1, show that this transcriptional activation ability resides in the NH2-terminal parts of both proteins. The use of yeast assays with RBTN2 shows that RBTN2 forms homodimers and that the NH2-terminal 27 amino acids are sufficient to facilitate transcriptional transactivation. These data expand the functional diversity of the LIM-domain protein family and they augment the previously defined relationship between chromosomal translocations and transcriptional activation.