James C Clemens

Assistant Professor of Biochemistry

Department: Biochemistry
Phone: 765.494.1087
Fax: 765.494.7897
Office: BCHM 5
E-mail: jclemens@purdue.edu

Area of Expertise: Molecular mechanisms of neuron connection specificity
Curriculum Vitae

Lab Members

Programmed cell death (PCD) is an important biological process used developmentally by multi-cellular organisms to pattern tissue structures and post-developmentally as a means to maintain homeostasis. Disruption of programmed cell death signaling post-developmentally contributes to human diseases ranging from cancer initiation and progression to neurodegenerative diseases.

PCD is utilized as a means to eradicate damaged precancerous cells to prevent tumor formation. Mutations that impair PCD processes create a cellular state in which precancerous cells are not destroyed allowing them to proliferate and progress to a cancerous state. As a result of this, the elucidation of PCD pathways has become a major goal of cancer research with the hope of identifying therapeutic targets for small molecules to activate PCD in cancer cells.

Activation of PCD has been linked to the neuronal cell death that is observed in neurodegenerative diseases including Alzheimer’s disease (AD), Parkinson’s disease (PD), Amyotrophic Lateral Sclerosis (ALS) and Huntington’s disease (HD). The etiology of non-familial forms of these neurodegenerative diseases is largely unknown, but it is speculated that the mechanisms that lead to the ultimate death of neurons in these diseases is similar. A common theme in neurodegenerative diseases is mitochondrial dysfunction and oxidative stress leading to neuron loss through PCD. Because of this, there is great interest in defining PCD signaling mechanisms with the goal of developing strategies to rescue neurons from PCD fates and prolong their lives.

While it may seem that cancer and neurodegeneration are unrelated problems, recent findings by our lab and others have determined that axon guidance receptor signaling plays a role in both of these types of human disease in addition to their classical roles in nervous system patterning. Using Drosophila as a model organism, our studies have identified a link between the Netrin binding axon guidance receptors and the anti-apoptotic properties of Activated cdc42 kinase (Ack). The Ack family comprises structurally related non-receptor tyrosine kinases that are evolutionarily conserved from worms to humans. Activating mutations in Ack1 and increased Ack1 protein levels have been found in many human cancers, where their presence correlates with a poor prognosis. In spite of these findings, it is unclear what the physiological functions of Ack are.

Our current focus is in defining the signaling pathways and molecular mechanisms that converge upon Ack to control PCD from both a cancer and neurodegenerative perspective. To accomplish these goals, we combine biochemical, molecular biological and molecular genetic approaches within the Drosophila system.

- Recent Publications

Abdallah, A. M., Zhou, X., Kim, C., Shah, K. K., Hogden, C., Schoenherr, J. A., . . . Chang, H. C. (2013). Activated Cdc42 kinase regulates Dock localization in male germ cells during Drosophila spermatogenesis. Dev. Biol., 378, 141-153. Retrieved from http://www.sciencedirect.com/science/article/pii/S0012160613001504

Gunnar, N., Drennan, J. M., Lamanuzzi, M., Walker, K., Clemens, J. C., & Kidd, T. (2013). Blocking apoptotic signaling rescues axon guidance in Netrin mutants. Cell Rep., 3, 595–606. Retrieved from http://www.sciencedirect.com/science/article/pii/S2211124713000934#

Schoenherr, J. A., Drennan, J. M., Martinez, J. S., Chikka, M. R., Hall, M. C., Chang, H. C., & Clemens, J. C. (2012). Drosophila activated Cdc42 kinase has an anti-apoptotic function. PLoS Genet, 8, 5. Retrieved from http://www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.1002725

Yang, Z., Huh, S. U., Drennan, J. M., Kathuria, H., Martinez, J. S., Tsuda, H., . . . Clemens, J. C. (2012). Drosophila Vap-33 is required for axonal localization of Dscam isoforms. J. Neurosci., 32, 17241-17250. Retrieved from http://www.jneurosci.org/content/32/48/17241.long

Matthews, B. J., Kim, M. E., Flanagan, J. J., Hattori, D., Clemens, J. C., Zipursky, S. L., & Grueber, W. B. (2007). Dendrite self-avoidance is controlled by Dscam. Cell, 129, 593-604.

Wojtowicz, W. M., Flanagan, J. J., Millard, S. S., Zipursky, S. L., & Clemens, J. C. (2004). Alternative splicing of Drosophila Dscam generates axon guidance receptors that exhibit isoform-specific homophilic binding. Cell, 118, 619-633.

Zhan, X. L., Clemens, J. C., Neves, G., Hattori, D., Flanagan, J. J., Hummel, T., . . . Zipursky, S. L. (2004). Analysis of Dscam diversity in regulating axon guidance in Drosophila mushroom bodies. Neuron, 43, 673-686.

Graveley, B. R., Kaur, A., Gunning, D., Zipursky, S. L., Rowen, L., & Clemens, J. C. (2004). The organization and evolution of the Dipteran and Hymenopteran Down syndrome cell adhesion molecule (Dscam) genes. RNA, 10, 1499-1506.

Hummel, T., Vasconcelos, M. L., Clemens, J. C., Fishilevich, Y., Vosshall, L. B., & Zipursky, S. L. (2003). Axonal targeting of olfatory receptor neurons in Drosophila is controlled by Dscam. Neuron, 37, 221-231.

Muda, M., Worby, C. A., Simonson-Leff, N., Clemens, J. C., & Dixon, J. E. (2002). Use of double-stranded RNA mediated interference to determine the substrates of protein tyrosine kinases and phosphatases. Biochem. J., (366), 73-77.