This article considers the role of the adult epithelial stem cell, with particular reference to the intestinal epithelial stem cell. Although the potential of adult stem cells has been revealed in a number of recent publications, the organization and control of the stem cell hierarchy in epithelial tissues is still not fully understood. The intestinal epithelium is an excellent model in which to study such hierarchies, having a distinctive polarity and high rate of cell proliferation and migration. Studies on the small intestinal crypt provide insight into the characteristics of the stem cells in normal and regenerating circumstances and demonstrate why a thorough understanding of these cells is an essential pre-requisite for stem cell based therapeutic approaches.

The aim of this study was to characterize the activation of caspase-3 along the crypt/villus axis in the normal and irradiated intestine and to compare active caspase-3 expression with existing apoptosis detection techniques. Small and large intestine were removed from mice at various time points after exposure to 8 Gy gamma-radiation. Positive apoptotic cells stained with an antibody against active caspase-3, haematoxylin and eosin (H&E) or TUNEL were scored in histological sections of small and large intestinal crypts and villi. In the control intestine, active caspase-3 expression was rarely observed; however, expression was markedly increased following exposure to radiation and was predominantly confined to apoptotic bodies. Measurement of apoptosis in intestinal crypts using active caspase-3 expression gave similar results to apoptosis detected from H&E-stained sections. In the normal villus, active caspase-3 expression was observed infrequently and did not significantly increase following radiation, consistent with a lack of apoptotic body formation from H&E sections. This study indicates that caspase-3 is activated in intestinal crypts but not in villi following gamma-radiation. Active caspase-3 detection compared favourably with existing immunological techniques, suggesting that it is a suitable alternative method for apoptosis quantification.

High concentrations of statin were necessary to impair insulin-mediated glucose uptake (300 nM ‫؍‬ 33% ؎ 12% p < 0.05), and this process was not effected by farnesyl transferase inhibition. Gycosylation inhibitors mimicked the effect of statin treatment (tunicamycin p < 0.001, castanospermine p < 0.05, deoxymannojirimycin p < 0.05), and there was insulin proreceptor accumulation. These data imply that HMG-CoA reductase inhibitors disrupt IGF-I signaling by combined effects on Ras prenylation and IGF receptor glycosylation, whereas insulin signaling is only affected by disrupted receptor glycosylation.

231 ECM = extracellular matrix; EGF = epidermal growth factor; ER = oestrogen receptor; GH = growth hormone; GHR = growth hormone receptor; IFN = interferon; IGF = insulin-like growth factor; IGFBP = insulin-like growth factor-binding protein; IGF-IR = type I insulin-like growth factor receptor; IRS-1 = insulin-receptor substrate-1; K d = dissociation constant; MAPK = mitogen-activated protein kinase; PI3K = phosphatidylinositol 3-kinase; STAT-3 = signal transducer and activator of transcription-3; TEB = terminal end bud.Available online http://breast-cancer-research.com/content/4/6/231 IntroductionThe insulin-like growth factors (IGF)-I and -II are singlechain polypeptides that share 62% homology in their amino acid sequences. Although at least two receptors for IGFs exist, the primary signalling receptor through which both IGF-I and IGF-II exert their biological actions is the type I insulin-like growth factor receptor (IGF-IR). The IGF-IR binds IGF-I and IGF-II with high affinity (K d~1 -2 nM) and binds insulin with an affinity that is 500-1000 times lower. IGFs can also bind and activate the insulin receptor [1]. IGFs are synthesized and secreted by many tissues, and they can act locally as autocrine or paracrine factors, or as endocrine factors that circulate in the plasma.IGFs have both immediate and long-term effects on various cellular activities. For example, IGF-I exerts an acute anabolic action on protein and carbohydrate metabolism by increasing the cellular uptake of amino acids and glucose by stimulating glycogen and protein synthesis [2]. IGFs also have long-term impact on cell proliferation, differentiation, migration and survival (for general reviews on IGF function, see [3,4]).The actions of IGFs can be modulated by interaction with a family of six insulin-like growth factor-binding proteins (IGFBPs), IGFBP-1 to IGFBP-6, which share 40-60% amino acid identity. All six IGFBPs have 16-18 conserved cysteine residues in the amino and carboxy terminal regions. The majority of circulating IGFs (> 97%) are bound to IGFBPs, particularly to IGFBP-3, with an affinity equal to or greater than that of the IGF-IR [5]. By binding IGF-I and IGF-II, IGFBPs regulate the bioavailability of IGFs in the circulation; however, their functions at the cellular level are not fully understood. IGFBPs have been reported to both inhibit and enhance IGF-I action depending on the system under investigation and the IGFBP studied. Review Insulin-like growth factors and insulin-like growth factor binding proteins in mammary gland function AbstractInsulin-like growth factor (IGF)-mediated proliferation and survival are essential for normal development in the mammary gland during puberty and pregnancy. IGFs interact with IGF-binding proteins and regulate their function. The present review focuses on the role of IGFs and IGF-binding proteins in the mammary gland and describes how modulation of their actions occurs by association with hormones, other growth factors and the extracellular matrix. The review will also highlight the ...

Epithelial cell survival is dependent on extracellular signals provided by both soluble factors and by adhesion. In the mammary gland, extensive apoptosis of epithelial cells occurs rapidly when lactation ceases, but the mechanism of apoptosis induction is not known. In tissue culture, mammary epithelial cells require laminin as a survival ligand and specific ␤1 integrins are necessary to suppress apoptosis. To explore the possibility that dynamic changes in cell-matrix interactions contribute to the onset of apoptosis during mammary involution in vivo, a detailed immunohistochemical analysis of the expression of integrin subunits and their extracellular matrix ligands during mouse mammary gland development has been performed. The kinetics of apoptosis were determined by using tissue samples obtained from virgin, pregnant, lactating, and involuting gland. The maximal elevation of apoptosis occurred within 24 hr of weaning as determined by histologic analysis and caspase-3 staining. A wide variety of laminin subunits, together with nidogen-1 and -2, and perlecan were identified within the basement membrane region of epithelial ducts, lobules, and alveoli in both human and mouse mammary gland. However, no change in the distribution of any of the basement membrane proteins or their cognate integrin receptors was observed during the transition from lactation to apoptosis. Instead, we discovered that altered ligand-binding conformation of the ␤1 integrin to a nonbinding state coincided with the immediate onset of mammary apoptosis. This finding may provide a novel dynamic mechanism for inhibiting the transduction of extracellular matrix survival signals, thereby contributing to the onset of apoptosis in a developmental context in vivo.