The role of Dlc1 isoform 2 in K-Ras2(G12D) induced thymic cancer.
The Deleted in liver cancer one (Dlc1) tumor suppressor gene encodes a RhoGTPase activating protein (RhoGAP). The Dlc1 gene has multiple transcriptional isoforms and we have previously established a mouse strain containing a gene trap (gt) insertion, which specifically reduces the expression of the 6.1 kb isoform (isoform 2). This gene trapped allele when homozygous results in embryonic lethality and the heterozygous gene trapped mice do not show an increased incidence of cancers, suggesting that cooperating oncogenic changes may be required for transformation. In the present work, we have studied the in vivo cooperation between oncogenic K-Ras2 and Dlc1 genes in tumourigenesis. We have observed an increase in invasive thymic cancers, including both thymomas and lymphomas, resulting in significantly shortened life spans in mice heterozygous for the gt Dlc1 allele and an inducible LSL-K-Ras2(G12D) allele compared with the LSL-K-Ras2(G12D) only mice. The heterozygous mice showed a high degree of metastasis in the lung. We have found tumour specific selective hypermethylation of the Dlc1 isoform 2 promoter and reduction of the corresponding protein expression in thymic lymphoma (TL) and thymic epithelial carcinoma (TEC) derived from the thymic tumours. The Dlc1 deficient thymic lymphoma cell lines exhibited increased trans-endothelial cell migration. TEC cell lines also exhibited increased stress fiber formation and Rho activity. Introduction of the three Dlc1 isoforms tagged with GFP into these cells resulted in different morphological changes. These results suggest that loss of expression of only isoform 2 may be sufficient for the development of thymic tumors and metastasis.
Manitoba Institute of Cell Biology, CancerCare Manitoba, Winnipeg, Manitoba, Canada.
Mohammad Golam
MG
Sabbir
Heather
H
Prieditis
Esther
E
Ravinsky
Michael R A
MR
Mowat
D000818:Animals; D001483:Base Sequence; D048430:Cell Shape; D022081:Cell Surface Extensions; D002874:Chromosome Mapping; D018899:CpG Islands; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D019175:DNA Methylation; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015972:Gene Expression Regulation, Neoplastic; D008175:Lung Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000556:secondary; D016399:Lymphoma, T-Cell / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D009374:Neoplasms, Experimental / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics; D022502:Stress Fibers / Q000378:metabolism; D013945:Thymoma / Q000235:genetics* / Q000378:metabolism / Q000556:secondary; D013953:Thymus Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D057705:Transendothelial and Transepithelial Migration; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D020741:rho GTP-Binding Proteins / Q000378:metabolism; D020742:rhoA GTP-Binding Protein
D050759:Cyclin-Dependent Kinase Inhibitor p21; C430864:DLC-1 (deleted in liver cancer) protein, mouse; D020690:GTPase-Activating Proteins; D020033:Protein Isoforms; D025521:Tumor Suppressor Proteins; C495971:Hras protein, mouse; D016283:Proto-Oncogene Proteins p21(ras); C526380:RhoA protein, mouse; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein