Chemoresistant metastatic disease presents the most serious threat to cancer patients despite the increased arsenal of targeted therapeutic options available to clinicians. While intense study into late-stage cancer progression has revealed a number of mechanisms that contribute to chemoresistance, little is known about the intracellular signaling mechanisms that desensitize cells to cytotoxic chemotherapy. In an effort to address this knowledge gap, we recently performed a large-scale RNA-interference (RNAi) screen intended to comprehensively identify critical kinases and phosphatases in the human genome that alter or modify tumor cell sensitivity to chemotherapeutic agents. In this RNAi screen, we identified a novel phosphatase, MK-STYX, which potently suppressed the response of tumor cells to a wide variety of chemotherapeutic drugs. Our central hypothesis is that MK-STYX specifically controls mitochondrial function by regulating phosphorylation of the machinery required for ATP synthesis, and thereby serves an essential role in the induction of chemotherapeutic-induced cell death. The objective of this project is to determine how MK-STYX regulates cellular ATP levels, and thus modulates intrinsic apoptosis. We propose the following specific aims to address this hypothesis and to understand its significance in the context of metastatic colorectal carcinoma: (1) Identify the catalytic mechanism of MK-STYX in the mitochondria;(2) Identify the mechanism whereby MK-STYX regulates chemoresistance;(3) Establish the role of MK-STYX in colorectal cancer progression and chemoresistance. Consistent with our central hypothesis, we have shown that loss of MK-STYX increases ATP production. Therefore, we predict that the elevation in cellular ATP due to loss of MK-STYX is sufficient to inhibit apoptosome formation and entry into apoptosis. We have shown that MK-STYX interacts with two additional mitochondrial proteins and we will mechanistically determine the mitochondrial function and the molecular consequences of each of these interactions. We have also shown that loss of MK-STYX expression correlates with colorectal cancer progression. To determine whether loss of MK-STYX mediates chemoresistance in vivo, we will test the efficacy of standard chemotherapies on a colorectal xenograft model using cell lines that demonstrate variable expression of MK-STYX, or have been manipulated to decrease endogenous MK-STYX levels. We will also determine the prognostic significance of MK-STYX protein levels in a cohort of patients with colorectal cancer.

Public Health Relevance

Our recent identification of thirteen phosphatases that suppress chemoresistance, or whose expression drives chemosensitivity, has provided an avenue for a better understanding of the molecular basis of chemoresistance. If we can determine how loss of expression of these phosphatases leads to the development of chemoresistance, we will be better able to screen for chemoresistance and design rational drug strategies to treat chemoresistant tumors in cancer patients.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
Project #
Application #
Study Section
Basic Mechanisms of Cancer Therapeutics Study Section (BMCT)
Program Officer
Salnikow, Konstantin
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Van Andel Research Institute
Grand Rapids
United States
Zip Code
Wang, Tong; Goodall, Megan L; Gonzales, Paul et al. (2015) Synthesis of improved lysomotropic autophagy inhibitors. J Med Chem 58:3025-35
Niemi, Natalie M; Sacoman, Juliana L; Westrate, Laura M et al. (2014) The pseudophosphatase MK-STYX physically and genetically interacts with the mitochondrial phosphatase PTPMT1. PLoS One 9:e93896
Westrate, Laura M; Drocco, Jeffrey A; Martin, Katie R et al. (2014) Mitochondrial morphological features are associated with fission and fusion events. PLoS One 9:e95265
Lanning, Nathan J; Looyenga, Brendan D; Kauffman, Audra L et al. (2014) A mitochondrial RNAi screen defines cellular bioenergetic determinants and identifies an adenylate kinase as a key regulator of ATP levels. Cell Rep 7:907-17
Martin, Katie R; Narang, Pooja; Medina-Franco, José L et al. (2014) Integrating virtual and biochemical screening for protein tyrosine phosphatase inhibitor discovery. Methods 65:219-28
Goodall, Megan L; Wang, Tong; Martin, Katie R et al. (2014) Development of potent autophagy inhibitors that sensitize oncogenic BRAF V600E mutant melanoma tumor cells to vemurafenib. Autophagy 10:1120-36
Westrate, Laura M; Sayfie, Aaron D; Burgenske, Danielle M et al. (2014) Persistent mitochondrial hyperfusion promotes G2/M accumulation and caspase-dependent cell death. PLoS One 9:e91911
Martin, Katie R; Barua, Dipak; Kauffman, Audra L et al. (2013) Computational model for autophagic vesicle dynamics in single cells. Autophagy 9:74-92
Niemi, Natalie M; MacKeigan, Jeffrey P (2013) Mitochondrial phosphorylation in apoptosis: flipping the death switch. Antioxid Redox Signal 19:572-82
Niemi, Natalie M; Lanning, Nathan J; Westrate, Laura M et al. (2013) Downregulation of the mitochondrial phosphatase PTPMT1 is sufficient to promote cancer cell death. PLoS One 8:e53803

Showing the most recent 10 out of 15 publications