The development of intratumoral hypoxia is a universal hallmark of rapidly growing solid tumors. Adaptation to the hypoxic environment, which is critical for tumor cell survival and growth, is mediated primarily through a hypoxia-inducible factor (HIF)-dependent transcriptional program. HIF activates genes that facilitate crucial adaptive mechanisms including increased glucose uptake and glycolysis and tumor angiogenesis, making it an important therapeutic target. However, the HIF-dependent transcriptional mechanism remains incompletely understood, and targeting HIF is a difficult endeavor. Here, we show that the orphan nuclear receptor estrogen-related receptors (ERRs) physically interact with HIF and stimulate HIF-induced transcription. Importantly, ERRs appear to be essential for HIF's function. Transcriptional activation of hypoxic genes in cells cultured under hypoxia is largely blocked by suppression of ERRs through expression of a dominant negative form of ERR or treatment with a pharmacological ERR inhibitor, diethylstilbestrol. Systematic administration of diethylstilbestrol severely diminished growth and angiogenesis of tumor xenografts in vivo. Because nuclear receptors are outstanding targets for drug discovery, the findings not only may offer mechanistic insights into HIF-mediated transcription but also may open new avenues for targeting the HIF pathway for cancer therapy.angiogenesis ͉ energy metabolism ͉ nuclear hormone receptor R apidly growing solid tumors tend to outstrip the supply of oxygen and nutrients provided by blood vessels, resulting in regions of low oxygen levels (hypoxia). Cancer cells undergo adaptation to persist in the hostile hypoxic environment. The adaptive response to hypoxia is controlled primarily by the hypoxia-inducible factor (HIF), a master regulator of hypoxic gene expression and oxygen homeostasis (1-3). HIF is a heterodimeric transcription factor comprising an oxygen-regulated ␣-subunit (HIF1␣ or -2␣) and a constitutively expressed and stable ␤-subunit (HIF␤). Under normal oxygen tension, the HIF␣ subunit is subjected to prolyl hydroxylation catalyzed by a set of oxygen-and ferrous ion-dependent prolyl hydroxylases. Hydroxylated HIF␣ is recognized by the tumor-suppressor protein von Hippel-Lindau (VHL), a component of an E3 ubiquitin ligase complex. Subsequently, HIF␣ becomes polyubiquitinated and is targeted for rapid degradation by the proteasomal system. Oxygen deprivation, or administration of iron chelators or cobaltous ion (a classic hypoxia mimetic, which competes with ferrous ion), suppresses hydroxylase activity, allowing HIF␣ to escape the VHL-mediated destruction and to accumulate and dimerize with the constitutively present HIF␤. The binding of the HIF␣-HIF␤ heterodimer along with the transcriptional coactivator p300/CBP to the cognate hypoxia-responsive element (HRE) augments the expression of a plethora of hypoxic genes that carry such elements within their promoters or enhancers (4). The HIF-orchestrated transcriptional program is directly responsible ...

Background Minimal Change Disease (MCD) in relapse is associated with increased podocyte CD80 expression and elevated urinary CD80 excretion, whereas focal segmental glomerulosclerosis (FSGS) has mild or absent CD80 podocyte expression and normal urinary CD80 excretion. Methods One patient with MCD, one patient with primary FSGS and three patients with recurrent FSGS after transplantation received CD80 blocking antibodies (abatacept or belatacept). Urinary CD80 and CTLA-4 were measured by ELISA. Glomeruli were stained for CD80. Results After abatacept, urinary CD80 became undetectable with concomitant transient resolution of proteinuria in the MCD patient. In contrast, proteinuria remained unchanged after abatacept or belatacept therapy in one patient with primary FSGS and in two recurrent FSGS subjects despite the presence of mild CD80 glomerular expression but normal urinary CD80 excretion. One patient with recurrent FSGS after transplantation had elevated urinary CD80 excretion immediately after surgery which fell spontaneously before abatacept. After Abatacept, his proteinuria remained unchanged for 5 days despite normal urinary CD80 excretion. Conclusion These observations are consistent with a role of podocyte CD80 in the development of proteinuria in MCD. In contrast, CD80 may not play a role in recurrent FSGS since urinary CD80 is only increased transiently after surgery and normalization of urinary CD80 did not result in resolution of proteinuria.

Estrogen signaling plays a critical role in the pathogenesis of breast cancer. Because the majority of breast carcinomas express the estrogen receptor ERα, endocrine therapy that impedes estrogen-ER signaling reduces breast cancer mortality and has become a mainstay of breast cancer treatment. However, patients remain at continued risk of relapse for many years after endocrine treatment. It has been proposed that cancer recurrence may be attributed to cancer stem cells (CSCs)/tumor-initiating cells (TICs). Previous studies in breast cancer have shown that such cells can be enriched and propagated in vitro by culturing the cells in suspension as mammospheres/tumorspheres. Here we established tumorspheres from ERα-positive human breast cancer cell line MCF7 and investigated their response to antiestrogens Tamoxifen and Fulvestrant. The tumorsphere cells express lower levels of ERα and are more tumorigenic in xenograft assays than the parental cells. Both 4-hydroxytamoxifen (4-OHT) and Fulvestrant attenuate tumorsphere cell proliferation, but only 4-OHT at high concentrations interferes with sphere formation. However, treated tumorsphere cells retain the self-renewal capacity. Upon withdrawal of antiestrogens, the treated cells resume tumorsphere formation and their tumorigenic potential remains undamaged. Depletion of ERα shows that ERα is dispensable for tumorsphere formation and xenograft tumor growth in mice. Surprisingly, ERα-depleted tumorspheres display heightened sensitivity to 4-OHT and their sphere-forming capacity is diminished after the drug is removed. These results imply that 4-OHT may inhibit cellular targets besides ERα that are essential for tumorsphere growth, and provide a potential strategy to sensitize tumorspheres to endocrine treatment.