No abstract

We report here a cancer drug therapy use of a gene involved in Down's syndrome. Using bioinformatics approaches, we recently predicted Single Minded 2 gene (SIM2) from Down's syndrome critical region to be specific to certain solid tumors. Involvement of SIM2 in solid tumors has not previously been reported. Intrigued by a possible association between a Down's syndrome gene and solid tumors, we monitored SIM2 expression in solid tumors. Isoform-specific expression of SIM2 short-form (SIM2-s) was seen selectively in colon, prostate, and pancreatic carcinomas but not in breast, lung, or ovarian carcinomas nor in most normal tissues. In colon tumors, SIM2-s expression was seen in early stages. Antisense inhibition of SIM2-s expression in a colon cancer cell line caused inhibition of gene expression, growth inhibition, and apoptosis. The administration of the antisense, but not the control, oligonucleotides caused a pronounced inhibition of tumor growth in nude mice with no major toxicity. Our findings provide a strong rationale for the genesto-drugs paradigm, establish SIM2-s as a molecular target for cancer therapeutics, and may further understanding of the cancer risk of Down's syndrome patients.

at the Down's syndrome critical region, which in triplication is associated with diverse phenotypic characteristics of Down's syndrome (1). Patients with Down's syndrome show various neurological symptoms and a high incidence of leukemia (1, 2). Members of the SIM family include SIM1 and SIM2, which map to 6q16.3-q21 and 21q22.2, respectively (3), and belong to a family of transcription factors containing a basic helix-loop-helix motif, two period homologue (PER)͞ARNT͞SIM (ARNT, aryl hydrocarbon receptor nuclear translocator) domains, and the HIF1␣͞SIM͞TRH domains (4-6). In Drosophila, SIM is a master regulator of fruit-fly neurogenesis, regulating midline gene expression (6, 7). The SIM2 gene exists in two distinct forms, the long and short forms (SIM2-l and SIM2-s), due to alternative splicing (3). A putative cancer-related role of the SIM family of genes is their ability to transcriptionally regulate key metabolic enzymes to inactivate carcinogens (8). Binding of carcinogens to the aryl hydrocarbon receptor (AhR), which is kept sequestered in the cytoplasm by heat-shock protein (HSP) 90 (9), dissociates HSP 90. The ligand-bound AhR is then translocated into the nucleus, where it can dimerize with ARNT (10). This complex binds to the xenobiotic response element, present in the promoters of key oxidative enzymes, and activates gene transcription (8, 11), thus causing inactivation of the carcinogen. The SIM proteins can inhibit the dimerization of the ligandbound AhR͞ARNT complex (12) and hence prevent carcinogen metabolism, leading to cumulative DNA damage and cancer.The growth arrest and DNA damage (GADD) family of genes was originally isolated from UV radiation-treated cells and subsequently grouped according to their coordinate regulation by growth arrest and DNA damage (13). The GADD family members include GADD34, -45␣, -45␤, -45␥, and -153 (14, 15). These are stressresponse genes induced by both genotoxic and nongenotoxic stresses (16)(17)(18). GADD45␣ is the most extensively studied member of the family and is regulated in both a p53-dependent and -independent manner (13,19). GADD45␣-mediated apoptosis may involve activation of JNK and͞or p38 mitogen-activated protein kinase (MAPK) signaling pathways (14,20).We have recently demonstrated that the SIM2 short-form (SIM2-s) gene is specifically expressed in distinct solid tumors, including colon, pancreas, and prostate, but not in the corresponding normal tissues (21-23). Antisense inhibition of SIM2-s expression caused apoptosis in colon and pancreatic cancer-derived cells. In an effort to understand the molecular mechanism underlying the role of SIM2-s in tumor cell growth, we have embarked on mapping the key pathways linked to SIM2-s. We show that apoptosis is tumor cell-selective and requires GADD45␣ function. Further, we demonstrate that key pathways, including caspase, p38 MAPK activities, and WT p53 status, are critical to apoptosis. Our results link apoptosis to induction of tumor cell-selective differentiation. MethodsCell Culture. Isogenic colon ca...