Tang, Amy

Abstract Hyperactive K-RAS signaling is a major menace that drives aggressive tumor growth and metastasis in human cancer. Currently, there are no effective ways to treat human cancers that have oncogenic K-RAS mutations that confer drug resistance, aggressive tumor growth, systemic metastasis, and poor clinical outcome. Therefore, finding novel approaches and new drug targets to inhibit oncogenic K-RAS is an urgent goal and the major challenge in cancer therapy and treatment. Instead of targeting an upstream signaling module such as EGFR/HER2/KRAS/B-RAF/MEK/MAPK/AKT/mT0R, we targeted the most downstream signaling module in the EGFR/HER2/K-RAS pathway called the SIAH-dependent proteolytic machinery. SIAHs are the human homologs of seven-in-absentia (SINA), an evolutionarily conserved RING E3 ligase, an essential downstream signaling module, and a critical gatekeeper required for proper ERBB/RAS/RAF signal transduction. Guided by the insights and principles learned from Drosophila RAS signaling pathway, we conducted preclinical studies to dissect SIAH function in the context of ERBB/K-RAS-mediated tumorigenesis and metastasis in human cancer cells and tumor specimens. We found that: 1) SIAH is a novel biomarker for human cancer, i.e., SIAH specifically decorates proliferating tumor cells (not stromal or immune cells in the tumor microenvironment). SIAH expression is progressively and markedly upregulated as human cancer progresses to the advanced stages in human pancreatic, lung, breast, and prostate cancers; and 2) inhibiting SIAH function is highly effective to abolish tumorigenesis and metastasis in multiple of the most aggressive human cancer cell lines known in the literature that include pancreatic cancer cells (MiaPaCa and Panc-1), lung cancer cells (A549, H727, and UMC11), invasive breast cancer cells (MDA-MB-231, MDA-MB-468, and MDA-MB-435), colorectal cancer cells (SW620 and HCT116) and hormonal-refractory prostate cancer cells (PC-3 and DU-145) in our preclinical studies. These findings demonstrate that SIAH is an attractive and logical new therapeutic target for novel anti-K-RAS and anticancer therapy in human cancer. Through our work, SIAH has emerged as a new and effective drug target against oncogenic K-RAS activation in human cancer cells. Using anti-SIAH molecules to block K-RAS signaling in human cancer is an excellent example of science going from the bench (basic research in fruit flies) to the bedside (preclinical studies and ultimately clinical trials). As a highly evolutionarily conserved E3 ligase and the most downstream gatekeeper of EGFR/HER2/K-RAS/B-RAF signaling pathway, SIAH is uniquely and logically positioned to become a next-generation anti-K-RAS drug target. Our preclinical studies have demonstrated that SIAH-dependent proteolysis is an Achilles' heel for human cancer cells. Albeit at an early preclinical stage, knowledge gained from our study has great promise that has generated many excitements with immediate translational values. Anti-SIAH-based small molecule inhibitors may aid in expanding our arsenal of novel anticancer therapies. By attacking the oncogenic ERBB/K-RAS/B-RAF pathway using multipronged synergistic inhibitions at upstream (EGFR/HER2 membrane receptors), midstream (K-RAS/B-RAF/MEK/mTOR), and downstream (SIAH E3 ligase) signaling modules in parallel, we will be in a great position to halt the genesis, progression, and metastasis of the most aggressive and the deadliest forms of human cancers. If successful, we hope to translate our findings to the cancer clinics to treat many cancer patients with metastatic diseases in the near future. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr B14.

Abstract The central importance of the ERBB/RAS signal transduction cascade has been well established in human cancer. As such, novel approaches to counteract activated ERBB/RAS signals constitute important measures to reverse tumorigenesis and metastasis in human cancers. Instead of targeting an upstream signaling module such as ERBB/RAS/MEK/MAPK/AKT/mTOR, we targeted the most downstream signaling module in the ERBB/RAS pathway called the SIAH-dependent proteolytic machinery. SIAHs are the human homologs of Seven-In-Absentia (SINA), an evolutionarily conserved RING E3 ligase, an essential downstream signaling module and a critical “gatekeeper” required for proper Drosophila RAS signal transduction. Guided by the insights and principles learned from Drosophila RAS signaling pathway, we conducted preclinical studies to examine SIAH function in the context of RAS-mediated tumorigenesis and metastasis in human cancer cells.We found that (1) SIAH is a novel biomarker for human cancer, i.e. it specifically decorates proliferating tumor cells (not stromal cells in the tumor microenvironment). SIAH expression is progressively and markedly upregulated as human cancer progresses to the advanced stages in human pancreatic, lung, breast and prostate cancers; and (2) inhibiting the proteolytic function of SIAH is highly effective to abolish tumorigenesis and metastasis in eight of the most aggressive human cancer cell lines known in the literature that include pancreatic cancer cells (MiaPaCa and Panc-1), lung cancer cells (A549), invasive breast cancer cells (MDA-MB-231, MDA-MB-468 and MDA-MB-435) and hormonal-refractory prostate cancer cells (PC-3 and DU-145) in soft agar as well as in athymic nude mice. These findings suggest that SIAH may be an attractive new therapeutic target for novel anti-RAS and anti-cancer therapy in human cancer. As a highly evolutionarily conserved E3 ligase and consistent with its “gatekeeper” function identified in the ERBB/RAS signaling pathway, SIAH is well positioned to become a next-generation and potent anticancer drug target to block the tumor-promoting RAS pathway and to treat the most aggressive types of human cancers. “Using anti-SIAH molecules to block active RAS signaling in human cancer” may be another example of “from the bench [basic science from fruitflies (model organism) to human cancers] to the bedside story [translational medicine in the near future]”. Anti-SIAH-based anticancer strategy may aid in expanding our arsenal of novel anticancer therapies. By attacking the oncogenic ERBB/RAS pathway using multi-pronged synergistic inhibitions at upstream (EGFR/HER2 membrane receptors), midstream (RAS/RAF/MEK/mTOR) and downstream (SIAH E3 ligase) signaling modules in parallel, we may be in a great position to halt the genesis, progression and metastasis of the most aggressive and lethal types of human cancers. If successful, we hope to translate our findings to the cancer clinics to treat many cancer patients with metastatic diseases in the future. Citation Information: Cancer Res 2009;69(23 Suppl):A1.

Abstract A better understanding of the antagonistic interaction and cross-talk between the pivotal oncogenic and tumor suppressor signaling pathways, and the concerted cancer signaling networks that control tumorigenesis and metastasis should give rise to novel therapeutic interventions. Hyperactivated ERBB/RAS is known to drive neoplastic transformation, tumorigenesis and metastasis in a large percentage of human cancers, and thus finding novel measures to countervail activated EGFR/HER2/RAS signals to reverse tumorigenesis and metastasis remains an important goal in cancer biology. Instead of targeting an upstream signaling component, we targeted the most downstream signaling module in the ERBB/RAS pathway, the SIAH-dependent proteolytic machinery. SIAHs are evolutionarily conserved RING E3 ligases that are the critical downstream “gatekeeper” signaling modules in the RAS signal transduction pathway. We show that human SIAH E3 ligase is upregulated in proliferating tumor cells in human tumor specimens, and that proper SIAH function is required for RAS signal transduction. By inhibiting SIAH2 E3 ligase, we have blocked both tumorigenesis and metastasis in eleven of the most aggressive human cancer cell lines known in athymic nude mice. Our observations highlight the important roles that SIAH2 plays in RAS-dependent tumorigenesis and metastasis in human cancer. In this study, we aim to identify the molecular mechanism underlying SIAH2 deficiency-mediated growth inhibition in human cancer cells. We have found that SMAD2/3/4 - the essential downstream mediators of TGFβ signaling, are novel SIAH2 substrates in that SIAH2 physically interacts with, ubiquitinates and degrades SMAD2/3/4 (not SMAD1). The identification of SIAH2-mediated SMAD2/3/4 modulation may provide an additional molecular mechanism to explain the well documented, but less understood RAS-TGFβ antagonism described in normal development, tumorigenesis and metastasis. We propose that the tumor promoting activity of SIAH2 may be mediated through the degradation of SMAD2/3/4 proteins which enhancing the growth-promoting activity of the RAS pathway while suppressing the growth inhibitory action of the TGFβ pathway. Since the substrate specificity of ubiquitin-mediated proteolysis is primarily determined by the E3 ligase, our results provide new insights into the role of altered proteolysis in mediating the RAS-TGFβ antagonism and cross-talk observed in the genesis and progression of human cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5073.

Abstract The dismal prognosis of patients diagnosed with invasive and metastatic cancer points to our limited arsenal of effective anticancer therapies. The central importance of EGFR/HER2/RAS pathway activation has been well established in neoplastic transformation and tumorigenesis. An important goal in cancer biology is to identify novel and effective means to inhibit activated EGFR/HER2/K-RAS signals and reverse malignant transformation, tumor growth and cancer metastasis. SIAHs are the human homologs of Drosophila Seven-In-Absentia (SINA), an evolutionarily conserved RING E3 ligase that is an essential downstream signaling module and critical “gatekeeper” required for RAS signal transduction in human cancer cells. By targeting the most downstream signaling module identified in the RAS pathway - the SIAH2 proteolytic machinery, we are able to block tumorigenesis and metastasis in multiple of the most aggressive forms of human cancer cells known in athymic nude mice. Although we are fully cognizant of the systemic limitation in the xenograft models and incomplete mimicry of the full-spectrum metastatic processes observed in athymic nude mice, we are encouraged by the impressive anti-SIAH2-based tumor suppression in these preclinical studies. In this study, we aim to identify the molecular mechanism(s) of SIAH2 action in human cancer cells. To delineate SIAH2 function in cancer, through a proteomic approach, we identified three endogenous LIM domain proteins, TRIP6/FHL2/LPXN, as the bona fide SIAH2-interacting proteins isolated from the most aggressive human cancer cell lines (A549, MiaPaCa and MDA-MB-435 cells) in parallel. We provide extensive biochemical evidence to show that TRIP6/FHL2/LPXN are bona fide SIAH2 substrates. These new SIAH2 substrates can successfully rescue cell motility and viability defects observed in SIAH2-deficient cancer cells, suggesting that these focal adhesion proteins may represent one of many diverse signaling modules that function downstream of SIAH2 in mediating aspects of RAS-dependent signaling in normal development and cancer. Our results suggest In response to ERBB/RAS activation, SIAH2 E3 ligase modulates cell junction, adhesion and migration by targeting focal adhesion proteins for ubiquitin-mediated proteolysis to promote cell migration, tumorigenesis and metastasis in human cancer cells. The identification of SIAH2-mediated focal adhesion and cell junction modulation may have important implications in cancer biology to explain the well-documented modulations in focal adhesion, cell junction and motility in response to ERBB/RAS activation in human cancer cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4808.

Abstract Breast cancer is the most common form of cancer diagnosed and the second leading cause of cancer death among women in the United States. Cancer metastases are the major cause of morbidity and mortality among breast cancer patients. The central importance of the HER2/Neu/EGFR/RAS signaling pathway has been well established in the growth, invasion and metastasis of human breast cancer, even though oncogenic RAS mutations are rare in breast cancer, activation of the tumor-promoting ERBB/RAS pathway has been consistently documented in high-grade breast tumors. As such, novel approaches to inhibit activated ERBB/RAS signals constitute important measures to block tumor growth and metastasis in mammary tumors. In this study, instead of targeting an upstream signaling component such as HER2/EGFR/RAS, we targeted the most downstream signaling module identified in the RAS pathway - the SIAH proteolytic machinery. SIAH is an evolutionarily conserved RING E3 ligase that is a critical “gatekeeper” required for RAS signal transduction in human cancer cells. SIAH is specifically expressed in tumor cells in 120 human breast cancer patients examined so far. The increased SIAH expression is correlated with increased grades and aggressiveness of human breast cancer. We then asked whether inhibiting the gatekeeper function of SIAH would be effective in blocking mammary tumorigenesis and metastasis in human breast cancer. Our results indicated that SIAH2-deficiency successfully abolished tumor growth of three breast cancer cell lines (MDA-MB-231, MDA-MB-435 and MDA-MB-468) in soft agar assays as well as in athymic nude mice. Importantly, by inhibiting SIAH2 function in highly aggressive human breast cancer cells, we are able to completely block tumorigenesis and metastasis of two highly invasive and metastatic human breast cancer cell lines (MDA-MB-231 and MDA-MB-435). These findings suggest that SIAH2 may be an attractive new therapeutic target for novel breast cancer therapy and developing anti-SIAH molecules will aid in expanding our arsenal of effective anticancer therapies. More effective breast cancer treatments may be obtained by multi-pronged synergistic inhibitions at upstream (HER2/EGFR membrane receptors), midstream (RAS/RAF/MEK/mTOR) and downstream (SIAH E3 ligase) signaling modules in the HER2/EGFR/RAS pathway in parallel. Thus, by attacking the growth-promoting ERBB/RAS pathway at multiple signaling modules simultaneously, we may be in a great position to halt the genesis, progression and metastasis of human breast cancer. If successful, this study has the promise to be translated to the cancer clinics to alleviate tumor burdens, inhibit cancer metastasis, improve the efficacy for the treatment of breast cancer, and in particularly help cancer patients with metastatic diseases. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4518.

The Drosophila immune deficiency (IMD) pathway, homologous to the mammalian tumor necrosis factor (TNF‐α) signaling pathway, initiates antimicrobial peptide (AMP) production in response to infection by gram‐negative bacteria. A membrane‐spanning peptidoglycan recognition protein, PGRP‐LC, functions as the receptor for the IMD pathway. This receptor is activated via pattern recognition and binding of monomeric peptidoglycan (DAP‐type PGN) through the PGRP ectodomain. In this article, we show that the receptor PGRP‐LC is down‐regulated in response to Salmonella/Escherichia coli infection but is not affected by Staphylococcus infection in vivo, and an ectodomain‐deleted PGRP‐LC lacking the PGRP domain is an active receptor. We show that the receptor PGRP‐LC regulates and integrates two host defense systems: the AMP production and melanization. A working model is proposed in which pathogen invasion and tissue damage may be monitored through the receptor integrity of PGRP‐LC after host and pathogen are engaged via pattern recognition. The irreversible cleavage or down‐regulation of PGRP‐LC may provide an additional cue for the host to distinguish pathogenic microbes from nonpathogenic ones and to subsequently activate multiple host defense systems in Dro‐sophila, thereby effectively combating bacterial infection and initiating tissue repair.—Schmidt, R. L., Trejo, T. R., Plummer, T. B., Platt, J. L., Tang, A. H. Infection‐induced proteolysis of PGRP‐LC controls the IMD activation and melanization cascades in Drosophila. FASEB J . 22, 918–929 (2008)

Abstract Constitutively active RAS small GTPases promote the genesis of human cancers. An important goal in cancer biology is to identify means of countervailing activated RAS signaling to reverse malignant transformation. Oncogenic K-RAS mutations are found in virtually all pancreatic adenocarcinomas, making the RAS pathway an ideal target for therapeutic intervention. How to best contravene hyperactivated RAS signaling has remained elusive in human pancreatic cancers. Guided by the Drosophila studies, we reasoned that a downstream mediator of RAS signals might be a suitable anti-RAS target. The E3 ubiquitin ligase seven in absentia (SINA) is an essential downstream component of the Drosophila RAS signal transduction pathway. Thus, we determined the roles of the conserved human homologues of SINA, SIAHs, in mammalian RAS signaling and RAS-mediated tumorigenesis. We report that similar to its Drosophila counterpart, human SIAH is also required for oncogenic RAS signaling in pancreatic cancer. Inhibiting SIAH-dependent proteolysis blocked RAS-mediated focus formation in fibroblasts and abolished the tumor growth of human pancreatic cancer cells in soft agar as well as in athymic nude mice. Given the high level of conservation of RAS and SIAH function, our study provides useful insights into altered proteolysis in the RAS pathway in tumor initiation, progression, and oncogenesis. By targeting SIAH, we have found a novel means to contravene oncogenic RAS signaling and block RAS-mediated transformation/tumorigenesis. Thus, SIAH may offer a novel therapeutic target to halt tumor growth and ameliorate RAS-mediated pancreatic cancer. [Cancer Res 2007;67(24):11798–810]

AbstractTLRs are usually thought to recognize substances produced by microorganisms and thus, to initiate host defenses. This concept, however, fails to explain some functions of this family of receptors. Recognition of endogenous substances may explain the broader functions of TLRs in physiology and disease. Activation of TLRs by endogenous substances necessitates vigorous control of the function of the receptors. This communication will summarize a line of research, which points to an endogenous agonist for TLR4 and a putative mechanism for controlling the function of that receptor.