SIRT3 regulates cellular iron metabolism and cancer growth by repressing iron regulatory protein 1.

Iron metabolism is essential for many cellular processes, including oxygen transport, respiration and DNA synthesis, and many cancer cells exhibit dysregulation in iron metabolism. Maintenance of cellular iron homeostasis is regulated by iron regulatory proteins (IRPs), which control the expression of iron-related genes by binding iron-responsive elements (IREs) of target mRNAs. Here, we report that mitochondrial SIRT3 regulates cellular iron metabolism by modulating IRP1 activity. SIRT3 loss increases reactive oxygen species production, leading to elevated IRP1 binding to IREs. As a consequence, IRP1 target genes, such as the transferrin receptor (TfR1), a membrane-associated glycoprotein critical for iron uptake and cell proliferation, are controlled by SIRT3. Importantly, SIRT3 deficiency results in a defect in cellular iron homeostasis. SIRT3 null cells contain high levels of iron and lose iron-dependent TfR1 regulation. Moreover, SIRT3 null mice exhibit higher levels of iron and TfR1 expression in the pancreas. We found that the regulation of iron uptake and TfR1 expression contribute to the tumor-suppressive activity of SIRT3. Indeed, SIRT3 expression is negatively correlated with TfR1 expression in human pancreatic cancers. SIRT3 overexpression decreases TfR1 expression by inhibiting IRP1 and represses proliferation in pancreatic cancer cells. Our data uncover a novel role of SIRT3 in cellular iron metabolism through IRP1 regulation and suggest that SIRT3 functions as a tumor suppressor, in part, by modulating cellular iron metabolism.

The structure and growth of the statocyst in the Australian crayfish Cherax destructor.

The morphology of the statocyst of the Australian crayfish Cherax destructor was examined using scanning electron microscopy. It resembles in general structure, size, and position the statocysts of crayfish described previously, and the size and distribution of the fields of setae on the floor of the capsule are similar but not the same. Over the size range examined, the relationship between the carapace length, the length of the basal antennular segment, the diameter of the statocyst capsule, and the total number of setae are all linear. The number and position of setae on the floor of the statocyst capsule were mapped for animals in two size classes (small, ca. 20 mm; large, ca. 50 mm) to test for changes in their arrangement during growth. The change in the ratio of setal number to statocyst size between the two size classes was about three times greater for the anterior setal field than for the other fields. We propose that differential development of the setal fields may be related to changes in the force-monitoring requirements of the animals as they increase in size, but this remains to be experimentally tested.

Managing health care costs: strategies available to small businesses.

Although health care costs continue to rise at an alarming rate, small businesses can take steps to help moderate these costs. First, business firms must restructure benefits so that needless surgery is eliminated and inpatient hospital care is minimized. Next, small firms should investigate the feasibility of partial self-insurance options such as risk pooling and purchasing preferred premium plans. Finally, small firms should investigate the cost savings that can be realized through the use of alternative health care delivery systems such as HMOs and PPOs. Today, competition is reshaping the health care industry by creating more options and rewarding efficiency. The prospect of steadily rising prices and more choices makes it essential that small employers become prudent purchasers of employee health benefits. For American businesses, the issue is crucial. Unless firms can control health care costs, they will have to keep boosting the prices of their goods and services and thus become less competitive in the global marketplace. In that event, many workers will face a prospect even more grim than rising medical premiums: losing their jobs.