The mammalian anx7 gene codes for a Ca 2؉ -activated GTPase, which supports Ca 2؉ ͞GTP-dependent secretion events and Ca 2؉ channel activities in vitro and in vivo. To test whether anx7 might be involved in Ca 2؉ signaling in secreting pancreatic ␤ cells, we knocked out the anx7 gene in the mouse and tested the insulinsecretory properties of the ␤ cells. The nullizygous anx7 (؊͞؊) phenotype is lethal at embryonic day 10 because of cerebral hemorrhage. However, the heterozygous anx7 (؉͞؊) mouse, although expressing only low levels of ANX7 protein, is viable and fertile. The anx7 (؉͞؊) phenotype is associated with a substantial defect in insulin secretion, although the insulin content of the islets, is 8-to 10-fold higher in the mutants than in the normal littermate control. We infer from electrophysiological studies that both glucose-stimulated secretion and voltage-dependent Ca 2؉ channel functions are normal. However, electrooptical recordings indicate that the (؉͞؊) mutation has caused a change in the ability of inositol 1,4,5-trisphosphate (IP3)-generating agonists to release intracellular calcium. The principle molecular consequence of lower anx7 expression is a profound reduction in IP3 receptor expression and function in pancreatic islets. The profound increase in islets, ␤ cell number, and size may be a means of compensating for less efficient insulin secretion by individual defective pancreatic ␤ cells. This is a direct demonstration of a connection between glucoseactivated insulin secretion and Ca 2؉ signaling through IP3-sensitive Ca 2؉ stores.

The ANX7 gene is located on human chromosome 10q21, a site long hypothesized to harbor a tumor suppressor gene(s) (TSG) associated with prostate and other cancers. To test whether ANX7 might be a candidate TSG, we examined the ANX7-dependent suppression of human tumor cell growth, stage-specific ANX7 expression in 301 prostate specimens on a prostate tissue microarray, and loss of heterozygosity (LOH) of microsatellite markers at or near the ANX7 locus. Here we report that human tumor cell proliferation and colony formation are markedly reduced when the wild-type ANX7 gene is transfected into two prostate tumor cell lines, LNCaP and DU145. Consistently, analysis of ANX7 protein expression in human prostate tumor microarrays reveals a significantly higher rate of loss of ANX7 expression in metastatic and local recurrences of hormone refractory prostate cancer as compared with primary tumors (P ‫؍‬ 0.0001). Using four microsatellite markers at or near the ANX7 locus, and laser capture microdissected tumor cells, 35% of the 20 primary prostate tumors show LOH. The microsatellite marker closest to the ANX7 locus showed the highest rate of LOH, including one homozygous deletion. We conclude that the ANX7 gene exhibits many biological and genetic properties expected of a TSG and may play a role in prostate cancer progression.cancer genetics ͉ chromosome 10q21 ͉ loss of heterozygosity T he gene for annexin 7 (ANX7 ‡ ‡ , synexin; refs. 1-6) is located on human chromosome 10q21, where potential tumor suppressor genes (TSGs) have been hypothesized to exist for prostate and other cancers (5, 7-15). However, the specific relevance of the ANX7 gene for cancer only became apparent after we created a knockout for this gene in the mouse (16). Although the homozygous Anx7(Ϫ͞Ϫ) deletion is embryonically lethal, the phenotype of the Anx7(ϩ͞Ϫ) heterozygote includes calcium signaling deficits and growth defects such as gigantism, and selective organomegaly. As these mice aged, we also began to observe a profoundly increased frequency of disparate spontaneous tumors in both male and female Anx7(ϩ͞Ϫ) mutants (17).Because of these observations, and the chromosomal location of the gene, we hypothesized that ANX7 might be a candidate TSG associated with 10q21 locus. Commonly, TSGs can suppress growth of tumor cells, in vitro, and are frequently inactivated by mutations, deletions, or loss of expression in tumors, in vivo. In addition, loss of heterozygosity (LOH) often is observed for these genes in clinical tumor specimens. Therefore, to test this hypothesis for the ANX7 gene, we analyzed the action of the ANX7 gene on colony formation by human tumor cell lines. We also examined the expression of the ANX7 protein in hundreds of prostate cancers by using tumor tissue microarray technology. Finally, we tested a panel of primary and metastatic prostate cancers for evidence of LOH.In this paper we show that the ANX7 gene suppresses the growth of the prostate tumor cell lines DU145 and LNCaP. Consistently, in a prostate tissue microarray, we...