In order to increase our understanding of the molecular events underlying osteosarcoma progression, the expression of approximately 950 genes was examined in 24 primary and metastatic osteosarcoma tumor specimens. A gene, RMO1, was isolated with decreased expression in metastatic samples. Real-Time PCR corroborated this pattern, revealing lower expression in the primary sample in 6 of 7 cases for which both primary and metastatic osteosarcoma samples were available from the same patient (p ؍ 0.034). RMO1 is located at 2q33, a region of frequent loss of heterozygosity in cancer, and exhibited loss of heterozygosity in 6 out of 9 primary osteosarcoma tumor samples (67%). Loss of heterozygosity is evident in primary tumors while the decrease in gene expression is seen in the metastatic samples, indicating that these 2 events are separately implicated in cancer progression. Cloning of RMO1 revealed an open reading frame with multiple splice forms with significant homology to GRB7, 10 and 14 and MIG10 in the region containing a Pleckstrin homology domain and a Ras association domain, suggestive of a role in cell signaling and migration. Northern blot analysis indicated that RMO1 mRNA is ubiquitously expressed in tissues except for peripheral blood leukocytes. These data suggest that RMO1 may be a candidate for a protein involved in inhibiting tumor progression. © 2004 Wiley-Liss, Inc. Key words: osteosarcoma; metastasis; RMO1; mRNA expression; loss of heterozygosity A number of genes have been shown to play a role in the pathogenesis of osteosarcoma, including the tumor suppressor genes p53 and Rb, and the proto-oncogenes CDK4 and MDM2. [1][2][3] However, cytogenetic and comparative genomic hybridization studies indicate that additional genes are also involved in the initiation and progression of this disease. 1,4 Osteosarcomas have many complex chromosomal alterations including translocations, deletions and amplifications. Whereas the tumor suppressor genes Rb and p53 are likely to be the targets of the frequent deletions at 13q and 17p in osteosarcoma, the genes associated with allelic loss at regions such as 2q, 5q, 6q, 8p, 9, 10, and 18q remain unknown. 1,4 -9 Deletion at 2q33 is commonly observed in cervical carcinoma, oral squamous cell carcinoma, head and neck squamous cell carcinoma, esophageal squamous cell carcinoma, neuroblastoma and lung cancer, suggesting that the target of this deletion is involved in the development of numerous types of cancer. 10 -15 Inactivation of tumor suppressor genes and activation of oncogenes can lead to their altered expression. For example, decreased gene expression of the tumor suppressor gene BRCA1 correlates with loss of heterozygosity (LOH) and the expression of the protooncogene CDK4 is significantly higher in samples with gene amplification. 3,16,17 The isolation of tumor suppressor genes and oncogenes can therefore be accomplished through a comparison of mRNA expression between tumor samples at different stages of development, such as primary tumor and metastase...
