L. Burton Nabors

Loss of protein inhibitors of activated STAT-3 expression in glioblastoma multiforme tumors: implications for STAT-3 activation and gene expression.

Purpose: STATs activate transcription in response to numerous cytokines, controlling proliferation, gene expression, and apoptosis. Aberrant activation of STAT proteins, particularly STAT-3, is implicated in the pathogenesis of many cancers, including GBM, by promoting cell cycle progression, stimulating angiogenesis, and impairing tumor immune surveillance. Little is known about the endogenous STAT inhibitors, the PIAS proteins, in human malignancies. The objective of this study was to examine the expression of STAT-3 and its negative regulator, PIAS3, in human tissue samples from control and GBM brains. Experimental Design: Control and GBM human tissues were analyzed by immunoblotting and immunohistochemistry to determine the activation status of STAT-3 and expression of the PIAS3 protein. The functional consequence of PIAS3 inhibition by small interfering RNA or PIAS3 overexpression in GBM cells was determined by examining cell proliferation, STAT-3 transcriptional activity, and STAT-3 target gene expression. This was accomplished using [3H]TdR incorporation, STAT-3 dominant-negative constructs, reverse transcription-PCR, and immunoblotting. Results and Conclusions: STAT-3 activation, as assessed by tyrosine and serine phosphorylation, was elevated in GBM tissue compared with control tissue. Interestingly, we observed expression of PIAS3 in control tissue, whereas PIAS3 protein expression in GBM tissue was greatly reduced. Inhibition of PIAS3 resulted in enhanced glioblastoma cellular proliferation. Conversely, PIAS3 overexpression inhibited STAT-3 transcriptional activity, expression of STAT-3–regulated genes, and cell proliferation. We propose that the loss of PIAS3 in GBM contributes to enhanced STAT-3 transcriptional activity and subsequent cell proliferation.

The ING4 Tumor Suppressor Attenuates NF-κB Activity at the Promoters of Target Genes

ABSTRACT The NF-κB family mediates immune and inflammatory responses. In many cancers, NF-κB is constitutively activated and induces the expression of genes that facilitate tumorigenesis. ING4 is a tumor suppressor that is absent or mutated in several cancers. Herein, we demonstrate that in human gliomas, NF-κB is constitutively activated, ING4 expression is negligible, and NF-κB-regulated gene expression is elevated. We demonstrate that an ING4 and NF-κB interaction exists but does not prevent NF-κB activation, nuclear translocation, or DNA binding. Instead, ING4 and NF-κB bind simultaneously at NF-κB-regulated promoters, and this binding correlates with reductions in p65 phosphorylation, p300, and the levels of acetylated histones and H3-Me3K4, while enhancing the levels of HDAC-1 at these promoters. Using a knockdown approach, we correlate reductions in ING4 protein levels with increased basal and inducible NF-κB target gene expression. Collectively, these data suggest that ING4 may specifically regulate the activity of NF-κB molecules that are bound to target gene promoters.

Lyn kinase activity is the predominant cellular SRC kinase activity in glioblastoma tumor cells.

Cellular Src activity modulates cell migration, proliferation, and differentiation, and recent reports suggest that individual members of the Src family may play specific roles in these processes. As we have found that Lyn, but not Fyn, activity promotes migration of glioblastoma cells in response to the cooperative signal generated by platelet-derived growth factor receptor beta and integrin alpha(v)beta3, we compared the activity and expression of Lyn and Fyn in glioblastoma (grade IV) tumor biopsy samples with that in anaplastic astrocytoma (grade III) tumors, nonneoplastic brain, and normal autopsy brain samples. Lyn kinase activity was significantly elevated in glioblastoma tumor samples. Notably, the Lyn kinase activity accounted for >90% of pan-Src kinase activity in glioblastoma samples but only approximately 30% of pan-Src kinase activity in the other groups. The levels of phosphorylation of the autophosphorylation site were consistent with significantly higher Lyn activity in glioblastoma tumor tissue than nonneoplastic brain. Although the normalized levels of Lyn protein and the relative levels of Lyn message were significantly higher in glioblastoma samples than nonneoplastic brain, the normalized levels of Lyn protein did not correlate with Lyn activity in the glioblastoma samples. There was no significant difference in the normalized levels of c-Src and Fyn protein and message in the glioblastoma and nonneoplastic brain. Immunostaining revealed that Lyn is located primarily in the glioblastoma cells in the tumor biopsies. These data indicate that Lyn kinase activity is significantly elevated in glioblastoma tumors and suggest that it is the Lyn activity that promotes the malignant phenotype in these tumors.

ABT-510, a modified type 1 repeat peptide of thrombospondin, inhibits malignant glioma growth in vivo by inhibiting angiogenesis

Anti-angiogenic therapies would be particularly beneficial in the treatment of malignant gliomas. Peptides derived from the second type 1 repeat (TSR) of thrombospondin-1 (TSP-1) have been shown to inhibit angiogenesis in non-glioma tumor models and a modified TSR peptide, ABT-510, has now entered into Phase II clinical trials of its efficacy in non-glioma tumors. As microvascular endothelial cells (MvEC) exhibit heterogeneity, we evaluated the ability of the modified TSR peptide (NAcSarGlyValDalloIleThrNvaIleArgProNHE, ABT-510) to inhibit malignant glioma growth in vivo and to induce apoptosis of brain microvessel endothelial cells (MvEC) propagated in vitro. We found that daily administration of ABT-510 until euthanasia (days 7 to 19), completely inhibited the growth of human malignant astrocytoma tumors established in the brain of athymic nude mice. The microvessel density was significantly lower and the number of apoptotic MvEC was significantly higher (3-fold) in the tumors of the ABT-510-treated animals. Similar results were found using a model in which the established tumor is an intracerebral malignant glioma propagated in a syngeneic mouse model. ABT-510 treatment of primary human brain MvEC propagated as a monolayer resulted in induction of apoptosis in a dose- and time-dependent manner through a caspase-8-dependent mechanism. It also inhibited tubular morphogenesis of MvEC propagated in collagen gels in a dose- and caspase-8 dependent manner through a mechanism that requires the TSP-1 receptor (CD36) on the MvEC. These findings indicate that ABT-510 should be evaluated as a therapeutic option for patients with malignant glioma.

Rare TP53 genetic variant associated with glioma risk and outcome

Validation of a recent finding linking a rare variant in TP53 to the risk of glioma, the most common primary brain tumour, is reported here. This study genotyped the single nucleotide polymorphism (SNP) rs78378222 in 566 glioma cases and 603 controls. The variant ‘C’ allele (with an allelic frequency of 1.1% in controls) was associated with a 3.5-fold excess in glioma risk (odds ratio 3.54; p=0.0001). Variant carriers had significantly improved survival (hazard ratio 0.52; p=0.009) when compared to non-carriers. The rs78378222 SNP is the first confirmed rare susceptibility variant in glioma. Results may shed light on the aetiology and progression of these tumours.

1p/19q chromosome deletions in metastatic oligodendroglioma

Extracranial metastasis of primary brain tumors is a rare phenomenon. Of the few cases reported of metastatic oligodendroglioma, only two have evaluated genetic alterations, specifically deletions of chromosomes 1p and 19q. Herein, we report two additional patients with metastatic anaplastic oligodendroglioma to bone, both followed until death. All available pathology specimens were reviewed and genetic analysis was performed in one of the cases. Although the bone metastasis was non-informative, the primary intracranial tumor revealed codeletions of the 1p and 19q chromosomal arms, commonly recognized as the genetically favorable profile of oligodendrogliomas. Both patients died of complications related to their systemic disease and did not have any radiologic evidence of intracranial progression at the time of their last MRI studies. Along with the reported literature, our data suggest that despite their generally favorable behavioral profiles, oligodendroglial tumors with 1p/19q deletions may be more prone to metastasis as they progress. Genetic analysis serves a valuable ancillary role in the diagnostic workup of such cases.

SWI/SNF gene variants and glioma risk and outcome.

BACKGROUND The human SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complex plays essential roles in a variety of cellular processes and has been implicated in human cancer. However, the role of germline genetic variants in this complex in relation to cancer risk is not well studied. METHODS We assessed the association of 16 variants in the catalytic subunits (SMARCA2 and SMARCA4) of the SWI/SNF complex with the risk of glioma subtypes (lower grade astrocytoma, oligodendroglioma and glioblastoma [GBM]) and with mortality from high-grade tumors (GBM) in a multicenter US case-control study that included 561 cases and 574 controls. Associations were estimated with odds ratios (OR, for risk) or hazards ratios (HR, for mortality) with 95% confidence intervals (CI). False discovery rate (FDR-q) was used to control for multiple testing in risk associations. RESULTS None of the investigated SNPs was associated with overall glioma risk. However, analyses according to histological subtypes revealed a statistically significant increased risk of oligodendroglioma in association with SMARCA2 rs2296212 (OR = 4.05, 95% CI = 1.11-14.80, P = 0.030, q = 0.08) and rs4741651 (OR = 4.68, 95% CI = 1.43-15.30, P = 0.011, q = 0.08) and SMARCA4 rs11672232 (OR = 1.90, 95% CI = 1.01-3.58, P = 0.048, q = 0.08) and rs12232780 (OR = 2.14, 95% CI = 1.06-4.33, P = 0.035, q = 0.08). No significant risk associations were observed for GBM or lower grade astrocytoma. Suggestive associations with GBM mortality were not validated in the Cancer Genome Atlas. CONCLUSION Our findings suggest that genetic variants in SMARCA2 and SMARCA4 influence the risk of oligodendroglioma. Further research is warranted on the SWI/SNF complex genes and epigenetic mechanisms more generally in the development of glioma in adults.

A novel technique to quantify glioma tumor invasion using serial microscopy sections.

Here we present a new technique to quantitatively characterize malignant glioma invasion in a syngeneic mouse model. The GL261 mouse malignant glioma cell line was injected intracerebrally into the C57B1/6 black mouse and allowed to propagate for 10 or 17 days, followed by euthanasia of the animal, harvesting of the brain, fixation, and serial sectioning. Histologic examination was performed and the primary tumor mass and discontinuous sites of tumor invasion were traced on digital images of serial microscopy sections, followed by analysis of the invasion characteristics using a custom-written MATLAB program. We found a significant increase in the number of discontinuous tumor invasion sites and in the distance of these sites from the tumor centroid in mice that were euthanized at 17 days post-tumor cell injection, as compared to mice euthanized at 10 days. Furthermore, a scatter plot analyses indicated that the invasion site data could be grouped based on the characteristics of area and distance from the tumor centroid to reveal significant differences between the two experimental groups of mice. This quantitative method will allow a future in vivo analysis of invasion characteristics in glioma cells expressing altered levels or function of invasion genes, and of new therapy targeting invading glioma cells.

Brain tumor risk according to germ-line variation in the MLLT10 locus

Genome-wide association studies have recently identified a cancer susceptibility locus at 10p12 mapping to MLLT10 associated with the onset of diverse tumors. We genotyped two tightly linked single-nucleotide polymorphisms (SNPs) at MLLT10 associated with meningioma (rs12770228) or ovarian cancer (rs1243180), and tested for associations among 295 meningioma cases, 606 glioma cases and 646 noncancer controls, all of European descent. The variant ‘A’ allele in MLLT10 rs12770228 was associated with an increased risk of meningioma (per allele odds ratio: 1.25; 95% confidence interval: 1.02, 1.53; P=0.031). Similar associations were observed for rs1243180. MLLT10 variants were unrelated to glioma. Functional investigation identified 22 candidate functional SNPs mapping to this region. The present study further validates 10p12 as a meningioma risk locus.

Toenail selenium, genetic variation in selenoenzymes and risk and outcome in glioma

BACKGROUND Selenium is an essential trace element obtained through diet that plays a critical role in DNA synthesis and protection from oxidative damage. Selenium intake and polymorphisms in selenoproteins have been linked to the risk of certain cancers though data for glioma are sparse. METHODS In a case-control study of glioma, we examined the associations of selenium in toenails and genetic variants in the selenoenzyme pathway with the risk of glioma and patient survival. A total of 423 genetic variants in 29 candidate genes in the selenoenzyme pathway were studied in 1547 glioma cases and 1014 healthy controls. Genetic associations were also examined in the UK Biobank cohort comprised of 313,868 persons with 322 incident glioma cases. Toenail selenium was measured in a subcohort of 300 glioma cases and 300 age-matched controls from the case-control study. RESULTS None of the 423 variants studied were consistently associated with glioma risk in the case-control and cohort studies. Moreover, toenail selenium in the case-control study had no significant association with glioma risk (p trend = 0.70) or patient survival among 254 patients with high grade tumors (p trend = 0.70). CONCLUSION The present study offers no support for the hypothesis that selenium plays a role in the onset of glioma or patient outcome.