PUROMYCIN-INDUCED NECROSIS OF CRYPT CELLS OF THE SMALL INTESTINE OF MOUSE

Chemical and radioautographic analysis of the small intestine of mice injected intraperitoneally with puromycin revealed an immediate decrease of precursor incorporation into DNA and protein and a delayed decrease of precursor incorporation into RNA. In addition to this decrease of precursor incorporation, damage to the crypt cells, but not to the cells of the villus of the small intestine, was observed. Further examination of other dividing cells (spleen) and nondividing cells (liver and heart) of these mice showed again that only cells of actively dividing tissues were damaged. The metabolic inhibitors actinomycin D, cytosine arabinoside, actidione, and puromycin aminonucleoside were used in an attempt to clarify the mechanism of cell damage by puromycin. The results showed that there was no clear correlation between cell necrosis and the pattern of inhibition of synthesis of DNA, RNA, or protein

Micro RNA 145 targets the insulin receptor substrate-1 and inhibits the growth of colon cancer cells

The insulin receptor substrate-1 (IRS-1), a docking protein for both the type 1 insulin-like growth factor receptor (IGF-IR) and the insulin receptor, is known to send a mitogenic, anti-apoptotic, and anti-differentiation signal. Several micro RNAs (miRs) are suggested by the data base as possible candidates for targeting IRS-1. We show here that one of the miRs predicted by the data base, miR145, whether transfected as a synthetic oligonucleotide or expressed from a plasmid, causes down-regulation of IRS-1 in human colon cancer cells. IRS-1 mRNA is not decreased by miR145, while it is down-regulated by an siRNA targeting IRS-1. Targeting of the IRS-1 3\u27-untranslated region (UTR) by miR145 was confirmed using a reporter gene (luciferase) expressing the miR145 binding sites of the IRS-1 3\u27-UTR. In agreement with the role of IRS-1 in cell proliferation, we show that treatment of human colon cancer cells with miR145 causes growth arrest comparable to the use of an siRNA against IRS-1. Taken together, these results identify miR145 as a micro RNA that down-regulates the IRS-1 protein, and inhibits the growth of human cancer cells