Somatostatin limits cell growth by inhibiting the proliferative activity of growth factor receptors. In this study, it is shown that in pituitary tumor cells, the somatostatin analogue octreotide produces its antiproliferative action by inducing the expression the tumor suppressor gene Zac1. ZAC/Zac1 induces cell cycle arrest and apoptosis and is highly expressed in normal pituitary, mammary, and ovarian glands but is down-regulated in pituitary, breast, and ovarian tumors. Knocking down Zac1 by RNA interference abolished the antiproliferative effect of octreotide in pituitary tumor cells, indicating that Zac1 is necessary for the action of octreotide. The effect of octreotide on Zac1 expression was pertussis toxin sensitive and was abolished after transfection with a dominant negative vector for SHP-1. Zac1 is a target of the phosphatidylinositol 3-kinase (PI3K) survival pathway. Octreotide treatment decreased the tyrosine phosphorylation levels of the PI3K regulatory subunit p85, induced dephosphorylation of phosphoinositidedependent kinase 1 (PDK1) and Akt, and activated glycogen synthase kinase 3B (GSKB). Therefore, in pituitary tumor cells, somatostatin analogues produce their antiproliferative action by acting on the PI3K/Akt signaling pathway and increasing

SUMMARY Red blood cell production is a finely tuned process that requires coordinated oxygen- and iron-dependent regulation of cell differentiation and iron metabolism. Here we show that translational regulation of HIF-2α synthesis by IRP1 is critical for controlling erythrocyte number. IRP1 null mice (Irp1−/−) display a marked transient polycythemia. HIF-2α mRNA is derepressed in kidney of Irp1−/− but not Irp2−/− mice leading to increased renal erythropoietin (Epo) mRNA and inappropriately elevated serum Epo levels. Expression of the iron transport genes DCytb, DMT1 and ferroportin as well as other HIF-2α targets is enhanced in IRP1−/− duodenum. Analysis of mRNA translation state in liver revealed IRP1-dependent dysregulation of HIF-2α mRNA translation while IRP2 deficiency derepressed translation of all other known 5′ IRE-containing mRNAs expressed in liver. These results uncover separable physiological roles of each IRP and identify IRP1 as a therapeutic target for manipulating HIF-2α action in hematologic, oncologic and other disorders.

Age-associated central arterial wall stiffness is linked to extracellular matrix (ECM) remodeling, including fibrosis and vascular calcification. Angiotensin II induces both matrix metalloproteinase type 2 (MMP2) and calpain-1 expression and activity in the arterial wall. But the role of calpain-1 in MMP2 activation and ECM remodeling remains unknown. Dual histo-immunolabeling demonstrates co-localization of calpain-1 and MMP2 within old rat vascular smooth muscle cells. Over-expression of calpain-1 induces MMP2 transcripts, protein levels and activity, in part, by increasing the ratio of membrane-type 1 MMPs to tissue inhibitor of metalloproteinases 2. These effects of calpain-1 over-expression-induced MMP2 activation are linked to increased collagen I and III production and vascular calcification. In addition, over-expression of calpain-1 also induces transforming growth factor-β1/Smad signaling, elastin degradation, alkaline phosphatase activation and total calcium content, but reduces the expression of calcification inhibitors, osteopontin and osteonectin, in cultured vascular smooth muscle cells in vitro and in carotid artery rings ex vivo. Furthermore, both calpain-1 and collagen II increase with aging within human aortic intima. Interestingly, in aged human aortic wall, both calpain-1 and collagen II are highly expressed in arteriosclerotic plaque areas compared to grossly normal areas. Cross-talk of two proteases, calpain-1 and MMP2, leads to secretion of active MMP2, which modulates ECM remodeling via enhancing collagen production and facilitating vascular calcification. These results establish calpain-1 as a novel molecular candidate to retard age-associated ECM remodeling and its attendant risk for hypertension and atherosclerosis.