Estrogen prevents sustained COLO-205 human colon cancer cell growth by inducing apoptosis, decreasing c-myb protein, and decreasing transcription of the anti-apoptotic protein bcl-2.

The proto-oncogene c-myb is overexpressed in human colon cancer cells. c-myb is known to be affected by estrogen in some breast cancers and leukemias. However, the mechanism of c-myb regulation via estrogen in colon cancer requires further investigation. Human COLO-205 colon cancer cells were cultured and treated with beta-estradiol for 24 h. Apoptosis was quantified using acridine orange/propidium iodide labeling and confirmed with DNA fragmentation gel electrophoresis. Expression of c-myb protein was assessed via SDS-PAGE and immunoblotting and RT-PCR was used to quantify bcl-2 RNA. Protein and RNA expression levels were also assayed after c-myb siRNA treatment for 24 h. We demonstrate an increase in apoptosis after 24 h of beta-estradiol treatment of human COLO-205 colon cancer cells. Estrogen treatment also decreases c-myb protein levels as well as expression of its transcriptional target bcl-2. Suppression of c-myb protein also results in increased apoptosis and decreases bcl-2 expression. These results indicate that estrogen has a protective effect from sustained colon cancer cell growth at least partly through suppression of c-myb and bcl-2.

Insulin receptor substrate-1 deficiency promotes apoptosis in the putative intestinal crypt stem cell region, limits Apcmin/+ tumors, and regulates Sox9.

Reduced apoptosis of crypt stem/progenitor cells and elevated insulin and IGFs are linked to colon cancer risk. Insulin receptor substrate-1 (IRS-1) mediates the actions of insulin, IGF-I, and IGF-II, but the role of endogenous IRS-1 in crypt apoptosis and cancer is undefined. Using IRS-1(-/-), IRS-1(+/-), and IRS-1(+/+) mice, we tested the hypothesis that reduced IRS-1 expression increases apoptosis of intestinal crypt cells and protects against Apc(min/+) (Min)/beta-catenin-driven intestinal tumors. Expression of Sox9, a transcriptional target of Tcf/beta-catenin and putative biomarker of crypt stem cells, was assessed in intestine of different IRS-1 genotypes and cell lines. Irradiation-induced apoptosis was significantly increased in the crypts and crypt stem cell region of IRS-1-deficient mice. Tumor load was significantly reduced by 31.2 +/- 14.6% in IRS-1(+/-)/Min and by 64.1 +/- 7.6% in IRS-1(-/-)/Min mice, with more prominent reductions in tumor number than size. Compared with IRS-1(+/+)/Min, IRS-1(-/-)/Min mice had fewer Sox9-positive cells in intestinal crypts and reduced Sox9 mRNA in intestine. IRS-1 overexpression increased Sox9 expression in an intestinal epithelial cell line. We conclude that even small reductions in endogenous IRS-1 increase apoptosis of crypt stem or progenitor cells, protect against beta-catenin-driven intestinal tumors, and reduce Sox9, a Tcf/beta-catenin target and putative stem/progenitor cell biomarker.

Age- and size-related changes in the inner ear and hearing ability of the adult zebrafish (Danio rerio).

Fishes, unlike most other vertebrate groups, continue to add sensory hair cells to their ears for much of their lives. However, it is not clear whether the addition ever stops or how the addition of sensory cells impacts hearing ability. In this article, we tested both questions using the zebrafish, Danio rerio. Our results not only have important implications for understanding the consequences of adding sensory receptors, but these results for normal zebrafish also serve as valuable baseline information for future studies of select mutations on the ear and hearing of this species. Our results show that hair cell production continues in uncrowded zebrafish up to 10 months of age (about one-third of a normal life span), but despite this addition there is no change in hearing sensitivity or bandwidth. Therefore, hearing is not related to the number of sensory cells in the ear in juvenile and adult animals. We also show that despite no net addition of hair cells after about 10 months, hair cells are still being produced, but at a lower rate, presumably to replace cells that are dying. Moreover, crowding of zebrafish has a marked impact on the growth of the fish and on the addition of sensory cells to the ear. We also demonstrate that fish size, not age, is a better indicator of developmental state of zebrafish.

Reduction of spontaneous and irradiation-induced apoptosis in small intestine of IGF-I transgenic mice.

Insulin-like growth factor I (IGF-I) may promote survival of putative stem cells in the small intestinal epithelium. Mitosis and apoptosis were quantified in crypts of nonirradiated and irradiated IGF-I transgenic (TG) and wild-type (WT) littermates. The mean apoptotic index was significantly greater in WT vs. TG littermates. After irradiation, apoptotic indexes increased, and WT mice showed a more dramatic increase in apoptosis than TG mice at the location of putative stem cells. After irradiation, no mitotic figures were observed in WT crypts, whereas mitosis was maintained within the jejunal epithelium of TG mice. The abundance and localization of Bax mRNA did not differ between nonirradiated littermates. However, there was more Bax mRNA in TG vs. WT mice after irradiation. Bax mRNA was located along the entire length of the irradiated crypt epithelium, but there was less Bax protein observed in the bottom third of TG mouse crypts compared with WT littermates. IGF-I regulates cell number by stimulating crypt cell proliferation and decreasing apoptosis preferentially within the stem cell compartment.