The mechanical stress-activated serum-, glucocorticoid-regulated kinase 1 contributes to neointima formation in vein grafts.

RATIONALE: Mechanical stress plays an important role in proliferation of venous smooth muscle cells (SMCs) in neointima, a process of formation that contributes to failure of vein grafts. However, it is unknown what intracellular growth signal leads to proliferation of venous SMCs. OBJECTIVE: The objective of this study is to identify mechanisms of mechanical stretch on neointima formation. METHODS AND RESULTS: By a microarray analysis, we found that mechanical cyclic stretch (15% elongation) stimulated the transcription of SGK-1 (serum-, glucocorticoid-regulated kinase-1). Mechanical stretch-induced SGK-1 mRNA expression was blocked by actinomycin D. The mechanism for the SGK-1 expression involved MEK1 but not p38 or JNK signaling pathway. SGK-1 activation in response to stretch is blocked by insulin-like growth factor (IGF)-1 receptor inhibitor and mammalian target of rapamycin complex (mTORC)2 inhibitor (Ku-0063794) but not mTORC1 inhibitor (rapamycin). Mechanical stretch-induced bromodeoxyuridine incorporation was reduced by 83.5% in venous SMCs isolated from SGK-1 knockout mice. In contrast, inhibition of Akt, another downstream signal of PI3K resulted in only partial inhibition of mechanical stretch-induced proliferation of venous SMCs. Mechanical stretch also induced phosphorylation and nuclear exportation of p27(kip1), whereas knockout of SGK-1 attenuated this effect of mechanical stretch on p27(kip1). In vivo, we found that placement of a vein graft into artery increased SGK-1 expression. Knockout of SGK-1 effectively prevented neointima formation in vein graft. There is significant lower level of p27(kip1) located in the nucleus of neointima cells in SGK-1 knockout mice compared with that of wild-type vein graft. In addition, we also found that wire injury of artery or growth factors in vitro increased expression of SGK-1. CONCLUSIONS: These results suggest that SGK-1 is an injury-responsive kinase that could mediate mechanical stretch-induced proliferation of vascular cells in vein graft, leading to neointima formation.

Serine-derivatized gadonanotubes as magnetic nanoprobes for intracellular labeling.

Gadonanotubes (GNTs), which are powerful new T(1)-weighted MRI contrast agents, were derivatized with serine amino acid substituents to produce water-soluble (2 mg ml(-1)) ser-gadonanotubes (ser-GNs) as magnetic nanoprobes for intracellular labeling. The ser-GNTs were used to efficiently label MCF-7 human breast cancer cells (1.5 x 10(9) Gd(3+) ions/cell) with no observable cytotoxicity. Cell pellets derived from the ser-GNT labeled cells give bright T(1)-weighted MR images, confirming that the ser-GNTs are a promising new nanoprobe technology for magnetic cell labeling and possibly for in vivo cellular trafficking.

Insulin receptor substrates (IRSs) and breast tumorigenesis.

Insulin receptor substrate (IRS)-1 and IRS-2 are adaptor proteins in the insulin-like growth factor I (IGF-I)/IGF-I receptor (IGF-IR) pathway that mediate cell proliferation, migration, and survival. In addition to their role as scaffolding proteins in the cytoplasm, they are able to translocate into the nucleus and regulate gene transcription. IRS levels are developmentally and hormonally regulated in the normal mammary gland and both are essential for normal mammary gland bud formation and lactation. Both IRS-1 and IRS-2 are transforming oncogenes, and induce transformation and metastasis in vitro and in vivo. In breast cancer IRSs have unique functions, with IRS-1 being mainly involved in cell proliferation and survival, whereas IRS-2 has clear roles in cell migration and metastasis. In this review we will discuss the roles of IRSs in mammary gland development and breast cancer.