[Show abstract][Hide abstract] ABSTRACT: Dysregulation of the WNT and insulin-like growth factor 2 (IGF2) signaling pathways has been implicated in sporadic and syndromic forms of adrenocortical carcinoma (ACC). Abnormal β-catenin staining and CTNNB1 mutations are reported to be common in both adrenocortical adenoma and ACC, whereas elevated IGF2 expression is associated primarily with ACC. To better understand the contribution of these pathways in the tumorigenesis of ACC, we examined clinicopathological and molecular data and used mouse models. Evaluation of adrenal tumors from 118 adult patients demonstrated an increase in CTNNB1 mutations and abnormal β-catenin accumulation in both adrenocortical adenoma and ACC. In ACC, these features were adversely associated with survival. Mice with stabilized β-catenin exhibited a temporal progression of increased adrenocortical hyperplasia, with subsequent microscopic and macroscopic adenoma formation. Elevated Igf2 expression alone did not cause hyperplasia. With the combination of stabilized β-catenin and elevated Igf2 expression, adrenal glands were larger, displayed earlier onset of hyperplasia, and developed more frequent macroscopic adenomas (as well as one carcinoma). Our results are consistent with a model in which dysregulation of one pathway may result in adrenal hyperplasia, but accumulation of a second or multiple alterations is necessary for tumorigenesis.
American Journal Of Pathology 07/2012; 181(3):1017-33. · 4.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Knowledge of factors and mechanisms contributing to the inherent radioresistance of pancreatic cancer may improve cancer treatment. Irradiation inhibits glycogen synthase kinase 3beta (GSK3beta) by phosphorylation at serine 9. In turn, release of cytosolic membrane beta-catenin with subsequent nuclear translocation promotes survival. Both GSK3beta and beta-catenin have been implicated in cancer cell proliferation and resistance to death.
We investigated pancreatic cancer cell survival after radiation in vitro and in vivo, with a particular focus on the role of the function of the GSK3beta/beta-catenin axis.
Lithium chloride, RNAi-medicated silencing of GSK3beta, or the expression of a kinase dead mutant GSK3beta resulted in radioresistance of Panc1 and BxPC3 pancreatic cancer cells. Conversely, ectopic expression of a constitutively active form of GSK3beta resulted in radiosensitization of Panc1 cells. GSK3beta silencing increased radiation-induced beta-catenin target gene expression as measured by studies of AXIN2 and LEF1 transcript levels. Western blot analysis of total and phosphorylated levels of GSK3beta and beta-catenin showed that GSK3beta inhibition resulted in stabilization of beta-catenin. Xenografts of both BxPC3 and Panc1 with targeted silencing of GSK3beta exhibited radioresistance in vivo. Silencing of beta-catenin resulted in radiosensitization, whereas a nondegradable beta-catenin construct induced radioresistance.
These data support the hypothesis that GSK3beta modulates the cellular response to radiation in a beta-catenin-dependent mechanism. Further understanding of this pathway may enhance the development of clinical trials combining drugs inhibiting beta-catenin activation with radiation and chemotherapy in locally advanced pancreatic cancer.
Neoplasia (New York, N.Y.) 05/2010; 12(5):357-65. · 5.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Telomere dysfunction and shortening induce chromosomal instability and tumorigenesis. In this study, we analyze the adrenocortical dysplasia (acd) mouse, harboring a mutation in Tpp1/Acd. Additional loss of p53 dramatically rescues the acd phenotype in an organ-specific manner, including skin hyperpigmentation and adrenal morphology, but not germ cell atrophy. Survival to weaning age is significantly increased in Acd(acd/acd) p53(-/-) mice. On the contrary, p53(-/-) and p53(+/-) mice with the Acd(acd/acd) genotype show a decreased tumor-free survival, compared with Acd(+/+) mice. Tumors from Acd(acd/acd) p53(+/-) mice show a striking switch from the classic spectrum of p53(-/-) mice toward carcinomas. The acd mouse model provides further support for an in vivo role of telomere deprotection in tumorigenesis.
Cancer cell 07/2009; 15(6):465-76. · 25.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Scientists have long hypothesized the existence of tissue-specific (somatic) stem cells and have searched for their location in different organs. The theory that adrenocortical organ homeostasis is maintained by undifferentiated stem or progenitor cells can be traced back nearly a century. Similar to other organ systems, it is widely believed that these rare cells of the adrenal cortex remain relatively undifferentiated and quiescent until needed to replenish the organ, at which time they undergo proliferation and terminal differentiation. Historical studies examining cell cycle activation by label retention assays and regenerative potential by organ transplantation experiments suggested that the adrenocortical progenitors reside in the outer periphery of the adrenal gland. Over the past decade, the Hammer laboratory, building on this hypothesis and these observations, has endeavored to understand the mechanisms of adrenocortical development and organ maintenance. In this review, we summarize the current knowledge of adrenal organogenesis. We present evidence for the existence and location of adrenocortical stem/progenitor cells and their potential contribution to adrenocortical carcinomas. Data described herein come primarily from studies conducted in the Hammer laboratory with incorporation of important related studies from other investigators. Together, the work provides a framework for the emerging somatic stem cell field as it relates to the adrenal gland.
[Show abstract][Hide abstract] ABSTRACT: Drug therapy for adrenocortical carcinoma (ACC), a rare and lethal malignancy, is largely empirical and ineffective. New treatments directed at molecular targets critical to the pathophysiology of ACC may prove more efficacious.
The objective of the study was to profile human adrenal tumors and ACC cell lines to assess activated IGF signaling and determine the efficacy of two IGF receptor (IGF-1R) antagonists alone and in combination with mitotane.
ACC cell lines that display or lack activated IGF signaling are used to assess the effects of two IGF-1R antagonists in cultured cells and ACC xenograft tumors.
Transcriptional profiling data derived from DNA microarray analysis of human adrenal tumors implicate IGF2 as the single highest up-regulated transcript in the vast majority of carcinomas. We show that the majority of ACC cell lines tested display constitutive IGF ligand production and activation of downstream effector pathways. Both IGF-1R antagonists cause significant dose-dependent growth inhibition in ACC cell lines. Furthermore, we observe that mitotane, the first-line adrenolytic drug used in patients with ACC, results in enhanced growth inhibition when used in combination with the IGF-1R antagonists. We next examined the activity of IGF-1R antagonists against ACC xenografts in athymic nude mice. IGF inhibition markedly reduced tumor growth greater than that observed with mitotane treatment, and combination therapy with mitotane significantly enhanced tumor growth suppression.
These findings establish a critical role of IGF signaling in ACC pathophysiology and provide rationale for use of targeted IGF-1R antagonists to treat adrenocortical carcinoma in future clinical trials.
[Show abstract][Hide abstract] ABSTRACT: The nuclear receptor steroidogenic factor 1 (Sf1, Nr5a1) is essential for adrenal development and regulates genes that specify differentiated adrenocortical function. The transcriptional coactivator beta-catenin reportedly synergizes with Sf1 to regulate a subset of these target genes; moreover, Wnt family members, signaling via beta-catenin, are also implicated in adrenocortical development. To investigate the role of beta-catenin in the adrenal cortex, we used two Sf1/Cre transgenes to inactivate conditional beta-catenin alleles. Inactivation of beta-catenin mediated by Sf1/Cre(high), a transgene expressed at high levels, caused adrenal aplasia in newborn mice. Analysis of fetal adrenal development with Sf1/Cre(high)-mediated beta-catenin inactivation showed decreased proliferation in presumptive adrenocortical precursor cells. By contrast, the Sf1/Cre(low) transgene effected a lesser degree of beta-catenin inactivation that did not affect all adrenocortical cells, permitting adrenal survival to reveal age-dependent degeneration of the cortex. These results define crucial roles for beta-catenin--presumably as part of the Wnt canonical signaling pathway--in both embryonic development of the adrenal cortex and in maintenance of the adult organ.
Development 09/2008; 135(15):2593-602. · 6.27 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Aberrant activation of protein kinase Cbeta (PKCbeta) by pancreatic cancer cells facilitates angiogenesis and tumor cell survival. Targeting PKCbeta with enzastaurin, a well-tolerated drug in clinical trials, would be expected to radiosensitize pancreatic tumors through direct antitumor and antivascular effects.
We tested the hypothesis that enzastaurin radiosensitizes pancreatic cancer cells in culture and in vivo through inhibition of PKCbeta. We analyzed pancreatic cancer xenografts for growth delay and microvessel density after treatment with enzastaurin, radiation, or both. We determined the effect of radiation and enzastaurin on glycogen synthase kinase 3beta, a mediator of cell death in culture and in vivo.
At concentrations attained in patients, enzastaurin reduced levels of active PKCbeta measured by phosphorylation at Thr(500) in culture and in xenografts. Enzastaurin alone did not affect pancreatic cancer cell survival, proliferation, or xenograft growth. However, enzastaurin radiosensitized pancreatic cancer cells in culture by colony formation assay. Enzastaurin alone decreased microvessel density of pancreatic cancer xenografts without appreciable effects on tumor size. When combined with radiation, enzastaurin increased radiation-induced tumor growth delay with a corresponding decrease in microvessel density. Enzastaurin inhibited radiation-induced phosphorylation of glycogen synthase kinase 3beta at Ser(9) in pancreatic cancer cells in culture and in tumor xenografts, suggesting a possible mechanism for the observed radiosensitization.
Enzastaurin inhibits PKCbeta in pancreatic cancer cells in culture, enhancing radiation cytotoxicity. Additional antivascular effects of enzastaurin were observed in vivo, resulting in greater radiosensitization. These results provide the rationale for a clinical trial in locally advanced pancreatic cancer combining enzastaurin with radiation.
Clinical Cancer Research 12/2007; 13(22 Pt 1):6827-33. · 8.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The existence and location of undifferentiated cells with the capability of maintaining the homeostasis of the adrenal cortex have long been sought. These cells are thought to remain mostly quiescent with a potential to commit to self-renewal processes or terminal differentiation to homeostatically repopulate the organ. In addition, in response to physiologic stress, the undifferentiated cells undergo rapid proliferation to accommodate organismic need. Sufficient adrenocortical proliferative capacity lasting the lifespan of the host has been demonstrated through cell transplantation and enucleation experiments. Labeling experiments with tritium, BrdU, or trypan blue, as well as transgenic assays support the clonogenic identity and location of these undefined cells within the gland periphery. We define undifferentiated adrenocortical cells as cells devoid of steroidogenic gene expression, and differentiated cells as cells with steroidogenic capacity. In this review, we discuss historic developmental studies together with recent molecular examinations that aim to characterize such populations of cells.
Molecular and Cellular Endocrinology 03/2007; 265-266:10-6. · 4.24 Impact Factor