Lab Research Projects

The Merajver research group is devoted to understanding the molecular genetics and associated functions of very aggressive breast cancer types. The primary areas of focus are systems biology, mathematical oncology, biophysics, cell biology, genetics, and drug development. A summary of the research currently underway in the lab is provided below.


p38 regulation of cellular motility in breast cancer

P38g Uninformative Figure

One hallmark of breast cancer progression is a shift from a slow epithelial mode of motion to a rapid mesenchymal-like form of motility. Understanding the genes and behaviors catalyzing this transition is therefore essential to targeting breast cancer metastasis. We discovered that a particular isoform of p38 MAPK, p38 gamma, regulates this motility transition by altering cytoskeletal architecture--in part due to regulation of RhoC expression. When p38 gamma is inhibited in aggressive breast cancer cells it dramatically impairs their ability to move, which appeared to be due to improperly aligned stress fibers. Significantly, high p38 gamma expression is associated with a worse patient prognosis, and inhibiting p38 gamma significantly restricts metastasis in a xenograft model.

Through collaborations with the Garikipati and Arruda labs in the Mechanical Engineering department we developed a computational model of cell motility that revealed that the improper stress fiber alignment was in fact responsible for the motility phenotype we observed. Surprisingly, the model predicted and subsequent biological experiments validated a novel leading edge behavior--leading edge protrusion oscillations--that allows cells to accommodate modified cytoskeletal architectures.

Future work will focus on dissecting the detailed molecular mechanisms by which p38 gamma influences breast cancer cell motility while concurrently expanding the capabilities of the computational model of motility.

P38g Informative Figure
(Image from Rosenthal et al. Cancer Res. 2011 Oct 15;71(20):6338-49. Epub 2011 Aug 23.)

Rosenthal DT, Iyer H, Escudero S, Bao L, Wu Z, Ventura AC, Kleer CG, Arruda EM, Garikipati K, Merajver SD
p38y promotes breast cancer cell motility and metastasis through regulation of RhoC GTPase, cytoskeletal architecture, and a novel leading edge behavior.
Cancer Res. 2011 Oct 15;71(20):6338-49. Epub 2011 Aug 23.

Retroactivity: an underappreciated property of covalently modified signaling networks

The Meravjer lab and other groups have shown in both experimental and theoretical work that covalently modified signaling cascades naturally exhibit bidirectional signal propagation via a phenomenon known as retroactivity. An important consequence of retroactivity, which arises due to enzyme sequestration in covalently modified signaling cascades, is that a downstream perturbation can produce a response in a component upstream of the perturbation without the need for explicit feedback connections. Retroactivity may, therefore, play an important role in the cellular response to a targeted therapy. Kinase inhibitors are a class of targeted therapies designed to interfere with a specific kinase molecule in a dysregulated signaling pathway. While extremely promising as anti-cancer agents, kinase inhibitors may produce undesirable off-target effects by non-specific interactions or pathway cross-talk.

In the figure, a simple signaling cascade is depicted, where each sequential cycle represents the activation (denoted by *) and inactivation of protein Yi. As a direct result of enzyme sequestration, a perturbation in one cycle can affect the amount of protein available to participate in the previous cycle. Thus, a reverse response can propagate upstream to a preceding cycle.

(Figure from Wynn ML et al BMC Sys Bio 2011)

Jiang P, Ventura AC, Sontag ED, Merajver SD, Ninfa AJ, Del Vecchio D.
Load-induced modulation of signal transduction networks.
Sci Signal. 2011 Oct 11;4(194):ra67. doi: 10.1126/scisignal.2002152.

Wynn ML, Ventura AC, Sepulchre JA, GarcĂ­a HJ, Merajver SD.
Kinase inhibitors can produce off-target effects and activate linked pathways by retroactivity.
BMC Syst Biol. 2011 Oct 4;5:156.

Ventura AC, Jiang P, Van Wassenhove L, Del Vecchio D, Merajver SD, Ninfa AJ.
Signaling properties of a covalent modification cycle are altered by a downstream target.
Proc Natl Acad Sci U S A. 2010 Jun 1;107(22):10032-7. Epub 2010 May 17.

Ventura AC, Sepulchre JA, Merajver SD.
A hidden feedback in signaling cascades is revealed.
PLoS Comput Biol. 2008 Mar 21;4(3):e1000041.

The role of energy metabolism in regulating aggressive phenotypes in breast cancer

Cancer cells exhibit an altered metabolic phenotype, known as the Warburg effect, which involves high rates of glucose uptake and lactate production, even under aerobic conditions. The Warburg effect appears to be an intrinsic component of most cancers and there is evidence linking cancer progression to mutations, translocations, and alternative splicing of genes that directly code for or have downstream effects on key metabolic enzymes. Many of the same signaling pathways are routinely dysregulated in cancer and a number of important oncogenic signaling pathways play important regulatory roles in central carbon metabolism. The Merajver lab is combining mathematical, computational, and experimental systems biology approaches to help further our understanding of the complex regulatory relationship between cancer metabolism and signal transduction. In collaboration with the Burant Lab and Schnell Lab at the University of Michigan, we are using both targeted (with 13-carbon tracers) and non-targeted mass spectrometry methods to understand metabolic differences in an in vitro model of breast cancer progression.

In the figure, glucose metabolism is depicted, which drives important biosynthetic pathways in cells. Glucose and glutamine are important extracellular substrates of central carbon metabolism and lactate, the primary product of glycolysis, is exported from the cell, contributing to acidification.

In the figure an in vitro model of breast cancer is depicted. 3D breast cell growth is imaged with fluorescent confocal microscopy: (A) The HME normal-like mammary epithelial cells form well-organized acini with empty central lumen resembling normal mammary ducts. In contrast, (B) the tumorigenic MCF-7 cancer cells form defined acini with filled lumen resembling ductal carcinoma in situ; (C and D) Both metastatic cell lines exhibit forms of invasion and loss of acinar organization.

Energy utilization in cancer cells is very different from that of normal cells. Identifying the molecular and metabolic changes that promote metastasis may lead to the development of new drugs that prevent disease progression. We are studying the cellular energy balance in different cell lines that provide an in vitro model of tumor progression. We are looking for metabolic changes that correlate with the switch between cell proliferation and motility. This switch is expected to be important as it relates to primary tumor formation, where rapid proliferation is crucial, and to secondary metastasis, where motility to new sites is essential. In order to learn more about the switch from proliferation to motility, we are studying a wide variety of key metabolic pathways, as well as a variety of important motility regulators in these cells.

In the figure, MDA-MB-231 breast cancer cells are stained for DNA with DAPI in blue, top left; triosephosphate isomerase (a glycolytic enzyme) in green, top right; and actin (which makes up the cytoskeleton) in red, bottom left. The bottom right shows all images merged together.

Wynn ML, Merajver SD, Schnell S.
Unraveling the complex regulatory relationships between metabolism and signal transduction in cancer.
Adv Exp Med Biol. 2012;736:179-89.

NF-KB and an anti-angiogenic drug

A link between deregulated NF-kB activity and oncogenesis has recently been shown. Frequently, this uncontrolled activity is due to either constitutive activation of NF-kB or inactivation of IkB, which are responsible for activation of NF-kB. The Merajver lab has shown that the copper chelator tetrathiomolybdate (TM) is able to suppress the NF-kB signaling cascade and downregulate many pro-angiogenic factors including VEGF, IL-1, IL-6 and IL-8 in SUM149 cells. SUM149 cells treated with TM showed decreased cell invasion and motility, and tumor volume and lung metastasis were decreased in SUM149 xenografted mice. Furthermore, we have shown that TM is an effective chemopreventative agent that acts through modulation of the mammary stem cell compartment. Our lab has played an integral role in identifying the importance of TM, which is planned for Phase III clinical trials.

Pan Q, Rosenthal DT, Bao L, Kleer CG, Merajver SD.
Antiangiogenic tetrathiomolybdate protects against Her2/neu-induced breast carcinoma by hypoplastic remodeling of the mammary gland.
Clin Cancer Res. 2009 Dec 1;15(23):7441-6. Epub 2009 Nov 24.

Pan Q, Bao LW, Merajver SD.
Tetrathiomolybdate inhibits angiogenesis and metastasis through suppression of the NFkappaB signaling cascade.
Mol Cancer Res. 2003 Aug;1(10):701-6.

Pan Q, Bao LW, Kleer CG, Brewer GJ, Merajver SD.
Antiangiogenic tetrathiomolybdate enhances the efficacy of doxorubicin against breast carcinoma.
Mol Cancer Ther. 2003 Jul;2(7):617-22.

Redman BG, Esper P, Pan Q, Dunn RL, Hussain HK, Chenevert T, Brewer GJ, Merajver SD.
Phase II trial of tetrathiomolybdate in patients with advanced kidney cancer.
Clin Cancer Res. 2003 May;9(5):1666-72.

Pan Q, Kleer CG, van Golen KL, Irani J, Bottema KM, Bias C, De Carvalho M, Mesri EA, Robins DM, Dick RD, Brewer GJ, Merajver SD.
Copper deficiency induced by tetrathiomolybdate suppresses tumor growth and angiogenesis.
Cancer Res. 2002 Sep 1;62(17):4854-9.

Anti-RhoC Metastatic Compounds

The Merajver lab was the first to discover that RhoC is consistently overexpressed in inflammatory breast cancer (IBC) tumors compared to stage-matched non-IBC tumors. Research from the Merajver lab and others has revealed that RhoC is overexpressed in a broad range of aggressive cancers and that its increased expression is associated with tumor cell metastasis and poor patient prognosis. Furthermore, we have found that RhoC is both necessary and sufficient for cancer stem cells metastasis. Based on the broad role of RhoC in cancer metastasis and the dearth of anti-metastatic therapies, the Merajver lab has worked to discover and design an anti-RhoC small molecule inhibitor. Currently in preclinical testing, a promising drug continues to show remarkable efficacy both in vitro and in vivo at preventing breast cancer metastasis with no apparent off-target effects.

Macrophages and Breast Cancer

There is an ever increasing link between cancer and sites of chronic inflammation in the body. Within the environment of smoldering inflammation that surrounds tumors, macrophages play an important role in promoting many aspects of cancer. These tumor-associated macrophages have been shown to support angiogenesis, promote tumor cell invasion and migration, suppress antitumor immune responses, and even enhance metastasis. It is evident that the tumor marcophages and tumor cells are communicating to one another via secreted signals in order to serve these pro-tumor functions. The Merajver Lab recently began a new study to understand the signals that cancer cells send to macrophages. Our goal is to discover potential therapeutic targets for future anti-cancer compounds and to better understand the role that non-cancerous cells play in promoting cancer.