Mammary tumorigenesis and metastasis caused by overexpression of insulin receptor substrate 1 (IRS-1) or IRS-2.

Insulin receptor substrates (IRSs) are signaling adaptors that play a major role in the metabolic and mitogenic actions of insulin and insulin-like growth factors. Reports have recently noted increased levels, or activity, of IRSs in many human cancers, and some have linked this to poor patient prognosis. We found that overexpressed IRS-1 was constitutively phosphorylated in vitro and in vivo and that transgenic mice overexpressing IRS-1 or IRS-2 in the mammary gland showed progressive mammary hyperplasia, tumorigenesis, and metastasis.

The growth hormone receptor antagonist pegvisomant blocks both mammary gland development and MCF-7 breast cancer xenograft growth.

Mammary gland development is dependent upon the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis, this same axis has also been implicated in breast cancer progression. In this study we investigated the effect of a GH antagonist, pegvisomant (Somavert, Pfizer), on normal mammary gland development and breast cancer xenograft growth. Intraperitoneal administration of pegvisomant resulted in a 60% suppression of hepatic IGF-I mRNA levels and upto a 70-80% reduction of serum IGF-I levels.

Scaffold attachment factor B1 functions in development, growth, and reproduction.

Scaffold attachment factor B1 (SAFB1) is a multifunctional protein that can bind both DNA and RNA and is involved in RNA processing and stress response. In addition, SAFB1 contains a transcriptional repression domain and can bind certain hormone receptors and repress their activity. To assess the role of SAFB1 in vivo, we generated SAFB1 mutant mice through targeted deletion in embryonic stem cells.

Relationship between insulin resistance and muscle triglyceride content in nonobese and obese experimental models of insulin resistance syndrome.

In nonobese hereditary hypertriglyceridemic (HTg) rats and obese HTg Koletsky SHROB/Kol rats, muscle triglyceride accumulation and its relationship to glucose homeostasis and tissue sensitivity to insulin action were examined. Soleus muscle and diaphragm triglyceride contents were markedly increased in HTg rats as compared with controls and were further increased in obese animals. On the other hand, glucose intolerance and impairment of insulin-stimulated in vitro glycogen synthesis were of a similar degree in nonobese as well as obese animals.