Adam J. Krieg

Regulation of the Histone Demethylase JMJD1A by Hypoxia-Inducible Factor 1α Enhances Hypoxic Gene Expression and Tumor Growth

ABSTRACT The hypoxia-inducible transcription factors (HIFs) directly and indirectly mediate cellular adaptation to reduced oxygen tensions. Recent studies have shown that the histone demethylase genes JMJD1A, JMJD2B, and JARID1B are HIF targets, suggesting that HIFs indirectly influence gene expression at the level of histone methylation under hypoxia. In this study, we identify a subset of hypoxia-inducible genes that are dependent on JMJD1A in both renal cell and colon carcinoma cell lines. JMJD1A regulates the expression of adrenomedullin (ADM) and growth and differentiation factor 15 (GDF15) under hypoxia by decreasing promoter histone methylation. In addition, we demonstrate that loss of JMJD1A is sufficient to reduce tumor growth in vivo, demonstrating that histone demethylation plays a significant role in modulating growth within the tumor microenvironment. Thus, hypoxic regulation of JMJD1A acts as a signal amplifier to facilitate hypoxic gene expression, ultimately enhancing tumor growth.

AXL Is an Essential Factor and Therapeutic Target for Metastatic Ovarian Cancer

The receptor tyrosine kinase AXL is thought to play a role in metastasis; however, the therapeutic efficacy of an AXL-targeting agent remains largely untested in metastatic disease. In this study, we defined AXL as a therapeutic target for metastatic ovarian cancer. AXL is primarily expressed in metastases and advanced-stage human ovarian tumors but not in normal ovarian epithelium. Genetic inhibition of AXL in human metastatic ovarian tumor cells is sufficient to prevent the initiation of metastatic disease in vivo. Mechanistically, inhibition of AXL signaling in animals with metastatic disease results in decreased invasion and matrix metalloproteinase activity. Most importantly, soluble human AXL receptors that imposed a specific blockade of the GAS6/AXL pathway had a profound inhibitory effect on progression of established metastatic ovarian cancer without normal tissue toxicity. These results offer the first genetic validation of GAS6/AXL targeting as an effective strategy for inhibition of metastatic tumor progression in vivo. Furthermore, this study defines the soluble AXL receptor as a therapeutic candidate agent for treatment of metastatic ovarian cancer, for which current therapies are ineffective.

The Metastasis-Associated Gene Prl-3 Is a p53 Target Involved in Cell-Cycle Regulation

The p53 tumor suppressor restricts tumorigenesis through the transcriptional activation of target genes involved in cell-cycle arrest and apoptosis. Here, we identify Prl-3 (phosphatase of regenerating liver-3) as a p53-inducible gene. Whereas previous studies implicated Prl-3 in metastasis because of its overexpression in metastatic human colorectal cancer and its ability to promote invasiveness and motility, we demonstrate here that Prl-3 is an important cell-cycle regulator. Consistent with a role in DNA damage-induced cell-cycle arrest, Prl-3 overexpression induces G(1) arrest downstream of p53 by triggering a PI3K-Akt-activated negative feedback loop. Surprisingly, attenuation of Prl-3 expression also elicits an arrest response, suggesting that basal level Prl-3 expression is pivotal for normal cell-cycle progression. Our findings highlight key dose-dependent functions of Prl-3 in both positive and negative regulation of cell-cycle progression and provide insight into Prl-3s role in cancer progression.

Direct regulation of GAS6/AXL signaling by HIF promotes renal metastasis through SRC and MET

Significance Here we report a fundamental and previously unknown role for the receptor tyrosine kinase AXL as a direct hypoxia-inducible transcription factor target driving the aggressive phenotype in renal clear cell carcinoma through the regulation of the SRC proto-oncogene nonreceptor tyrosine kinase and the MET proto-oncogene receptor tyrosine kinase. Of therapeutic relevance, we demonstrate that inactivation of growth arrest-specific 6 (GAS6)/AXL signaling using a soluble AXL decoy receptor reversed the invasive and metastatic phenotype of clear cell renal cell carcinoma (ccRCC) cells. Furthermore, we define a pathway by which GAS6/AXL signaling utilizes lateral activation of MET through SRC to maximize cellular invasion. Our data provide an alternative model for SRC and MET activation by GAS6 in ccRCC and identify AXL as a therapeutic target driving the aggressive phenotype in renal clear cell carcinoma. Dysregulation of the von Hippel–Lindau/hypoxia-inducible transcription factor (HIF) signaling pathway promotes clear cell renal cell carcinoma (ccRCC) progression and metastasis. The protein kinase GAS6/AXL signaling pathway has recently been implicated as an essential mediator of metastasis and receptor tyrosine kinase crosstalk in cancer. Here we establish a molecular link between HIF stabilization and induction of AXL receptor expression in metastatic ccRCC. We found that HIF-1 and HIF-2 directly activate the expression of AXL by binding to the hypoxia-response element in the AXL proximal promoter. Importantly, genetic and therapeutic inactivation of AXL signaling in metastatic ccRCC cells reversed the invasive and metastatic phenotype in vivo. Furthermore, we define a pathway by which GAS6/AXL signaling uses lateral activation of the met proto-oncogene (MET) through SRC proto-oncogene nonreceptor tyrosine kinase to maximize cellular invasion. Clinically, AXL expression in primary tumors of ccRCC patients correlates with aggressive tumor behavior and patient lethality. These findings provide an alternative model for SRC and MET activation by growth arrest-specific 6 in ccRCC and identify AXL as a therapeutic target driving the aggressive phenotype in renal clear cell carcinoma.

Genome-Wide Analysis of p53 under Hypoxic Conditions

ABSTRACT Hypoxia is an important nongenotoxic stress that modulates the tumor suppressor activity of p53 during malignant progression. In this study, we investigated how genotoxic and nongenotoxic stresses regulate p53 association with chromatin, p53 transcriptional activity, and p53-dependent apoptosis. We found that genotoxic and nongenotoxic stresses result in the accumulation and binding of the p53 tumor suppressor protein to the same cognate binding sites in chromatin. However, it is the stress that determines whether downstream signaling is mediated by association with transcriptional coactivators. In contrast to p53 induced by DNA-damaging agents, hypoxia-induced p53 has primarily transrepression activity. Using extensive microarray analysis, we identified families of repressed targets of p53 that are involved in cell signaling, DNA repair, cell cycle control, and differentiation. Following our previous study on the contribution of residues 25 and 26 to p53-dependent hypoxia-induced apoptosis, we found that residues 25-26 and 53-54 and the polyproline- and DNA-binding regions are also required for both gene repression and the induction of apoptosis by p53 during hypoxia. This study defines a new role for residues 53 and 54 of p53 in regulating transrepression and demonstrates that 25-26 and 53-54 work in the same pathway to induce apoptosis through gene repression.

Cross-talk between hypoxia and insulin signaling through Phd3 regulates hepatic glucose and lipid metabolism and ameliorates diabetes

Signaling initiated by hypoxia and insulin powerfully alters cellular metabolism. The protein stability of hypoxia-inducible factor-1 alpha (Hif-1α) and Hif-2α is regulated by three prolyl hydroxylase domain–containing protein isoforms (Phd1, Phd2 and Phd3). Insulin receptor substrate-2 (Irs2) is a critical mediator of the anabolic effects of insulin, and its decreased expression contributes to the pathophysiology of insulin resistance and diabetes. Although Hif regulates many metabolic pathways, it is unknown whether the Phd proteins regulate glucose and lipid metabolism in the liver. Here, we show that acute deletion of hepatic Phd3, also known as Egln3, improves insulin sensitivity and ameliorates diabetes by specifically stabilizing Hif-2α, which then increases Irs2 transcription and insulin-stimulated Akt activation. Hif-2α and Irs2 are both necessary for the improved insulin sensitivity, as knockdown of either molecule abrogates the beneficial effects of Phd3 knockout on glucose tolerance and insulin-stimulated Akt phosphorylation. Augmenting levels of Hif-2α through various combinations of Phd gene knockouts did not further improve hepatic metabolism and only added toxicity. Thus, isoform-specific inhibition of Phd3 could be exploited to treat type 2 diabetes without the toxicity that could occur with chronic inhibition of multiple Phd isoforms.

Functional analysis of p53 binding under differential stresses

ABSTRACT Hypoxia and DNA damage stabilize the p53 protein, but the subsequent effect that each stress has on transcriptional regulation of known p53 target genes is variable. We have used chromatin immunoprecipitation followed by CpG island (CGI) microarray hybridization to identify promoters bound by p53 under both DNA-damaging and non-DNA-damaging conditions in HCT116 cells. Using gene-specific PCR analysis, we have verified an association with CGIs of the highest enrichment (>2.5-fold) (REV3L, XPMC2H, HNRPUL1, TOR1AIP1, glutathione peroxidase 1, and SCFD2), with CGIs of intermediate enrichment (>2.2-fold) (COX7A2L, SYVN1, and JAG2), and with CGIs of low enrichment (>2.0-fold) (MYC and PCNA). We found little difference in promoter binding when p53 is stabilized by these two distinctly different stresses. However, expression of these genes varies a great deal: while a few genes exhibit classical induction with adriamycin, the majority of the genes are unchanged or are mildly repressed by either hypoxia or adriamycin. Further analysis using p53 mutated in the core DNA binding domain revealed that the interaction of p53 with CGIs may be occurring through both sequence-dependent and -independent mechanisms. Taken together, these experiments describe the identification of novel p53 target genes and the subsequent discovery of distinctly different expression phenomena for p53 target genes under different stress scenarios.

VHL loss in renal cell carcinoma leads to up-regulation of CUB domain-containing protein 1 to stimulate PKCδ-driven migration

A common genetic mutation found in clear cell renal cell carcinoma (CC-RCC) is the loss of the von Hippel-Lindau (VHL) gene, which results in stabilization of hypoxia-inducible factors (HIFs), and contributes to cancer progression and metastasis. CUB-domain-containing protein 1 (CDCP1) was shown to promote metastasis in scirrhous and lung adenocarcinomas as well as in prostate cancer. In this study, we established a molecular mechanism linking VHL loss to induction of the CDCP1 gene through the HIF-1/2 pathway in renal cancer. Also, we report that Fyn, which forms a complex with CDCP1 and mediates its signaling to PKCδ, is a HIF-1 target gene. Mechanistically, we found that CDCP1 specifically regulates phosphorylation of PKCδ, but not of focal adhesion kinase or Crk-associated substrate. Signal transduction from CDCP1 to PKCδ leads to its activation, increasing migration of CC-RCC. Furthermore, patient survival can be stratified by CDCP1 expression at the cell surface of the tumor. Taken together, our data indicates that CDCP1 protein might serve as a therapeutic target for CC-RCC.

Interactions of high mobility group box proteins with DNA and chromatin

Publisher Summary This chapter describes the interactions of high-mobility group box proteins with DNA and chromatin. The experimental methods described in the chapter make use of a Drosophila melanogaster ( D. melanogaster ) chromosomal protein, HMG-D, which was isolated as the major HMG-l-like chromosomal protein in D. melanogaster and from a screen of a Drosophila λgt11 expression library with a DNA region from the fushi tarazu upstream element DNA fragment (fiz-SAR) under conditions that were favorable for the selection of a sequence-specific protein. HMG-D is a homolog of HMG1, which has a role in embryonic chromatin at a time when the chromatin is transcriptionally silent but is undergoing rapid rounds of replication. HMG-D contains only a single copy of the DNA-binding domain followed by a tail region that has a basic motif similar to the C-terminal domain of histone H1 and a C-terminal acidic stretch similar to that seen in HMG1/2 proteins.

Targeting the loss of the von Hippel-Lindau tumor suppressor gene in renal cell carcinoma cells.

Late-stage clear cell renal carcinoma poses a formidable clinical challenge due to the high mortality rate associated with this disease. Molecular and genetic studies have identified functional loss of the von Hippel-Lindau (VHL) gene as a frequent and crucial event in the development of the malignant phenotype of clear cell renal carcinomas. Loss of VHL function thus represents a pathognomonic molecular defect for therapeutic exploitation. The objective of this study was to evaluate the possibility of targeting VHL loss through pharmacologic means. Chromomycin A3 (ChA3) was identified through in silico analysis of existing publicly available drug profiles from the National Cancer Institute as an agent that seemed to selectively target VHL-deficient clear cell renal carcinoma cells. Genotype-selective toxicity was first determined through short-term viability assays and then confirmed with clonogenic studies. Coculture of fluorescently labeled VHL-deficient and VHL-positive cells showed discriminate killing of the VHL-deficient cells with ChA3. Mechanistically, overexpression of hypoxia-inducible factor (HIF)-2alpha in VHL-positive clear cell renal carcinoma cells phenocopied loss of VHL with respect to ChA3 toxicity, establishing ChA3 as a HIF-dependent cytotoxin. This study shows the feasibility of selectively targeting the loss of the VHL tumor suppressor gene in clear cell renal carcinoma for potential clinical benefit and may have greater ramifications in the development of new targeted therapies for the treatment of cancer and other genetic diseases.