Inhibition of Single Minded 2 gene expression mediates tumor-selective apoptosis and differentiation in human colon cancer cells.
A Down's syndrome associated gene, Single Minded 2 gene short form (SIM2-s), is specifically expressed in colon tumors but not in the normal colon. Antisense inhibition of SIM2-s in a RKO-derived colon carcinoma cell line causes growth inhibition, apoptosis, and inhibition of tumor growth in a nude mouse tumoriginicity model. The mechanism of cell death in tumor cells is unclear. In the present study, we investigated the pathways underlying apoptosis. Apoptosis was seen in a tumor cell-specific manner in RKO cells but not in normal renal epithelial cells, despite inhibition of SIM2-s expression in both of these cells by the antisense. Apoptosis was depended on WT p53 status and was caspase-dependent; it was inhibited by a pharmacological inhibitor of mitogen-activated protein kinase activity. Expression of a key stress response gene, growth arrest and DNA damage gene (GADD)45alpha, was up-regulated in antisense-treated tumor cells but not in normal cells. In an isogenic RKO cell line expressing stable antisense RNA to GADD45alpha, a significant protection of the antisense-induced apoptosis was seen. Whereas antisense-treated RKO cells did not undergo cell cycle arrest, several markers of differentiation were deregulated, including alkaline phosphatase activity, a marker of terminal differentiation. Protection of apoptosis and block of differentiation showed a correlation in the RKO model. Our results support the tumor cell-selective nature of SIM2-s gene function, provide a direct link between SIM2-s and differentiation, and may provide a model to identify SIM2-s targets.
Aleman
Mireille J
MJ
Center for Molecular Biology and Biotechnology, Florida Atlantic University, 777 Glades Road, Boca Raton, FL 33431, USA.
DeYoung
Maurice Phil
MP
Tress
Matthew
M
Keating
Patricia
P
Perry
Gary W
GW
Narayanan
Ramaswamy
R
D017209:Apoptosis / Q000235:genetics*; D051792:Basic Helix-Loop-Helix Proteins; D002454:Cell Differentiation / Q000235:genetics*; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology*; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D009928:Organ Specificity; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D000097642:GADD45 Proteins
D051792:Basic Helix-Loop-Helix Proteins; D047908:Intracellular Signaling Peptides and Proteins; D014157:Transcription Factors; D000097642:GADD45 Proteins; C417032:SIM2 protein, human