|
Mortensen,
Ole V.
Research Assistant Professor
Ph.D. in Molecular Biology (1999) Aarhus University, Denmark
Address: 6068 Biomedical Science Tower 3
Phone: 412-648-9748
Fax: 412-383-5267 or 412-383-8663
Email: mortense@pitt.edu
Regulation of biogenic monoamine transporters
The biogenic monoamine transporters are the primary mechanism for clearance of their respective neurotransmitter from the extracellular space and serve as important regulators of signal amplitude and duration at synapses. They are targets of psychostimulants, such as cocaine and amphetamines, and of antidepressants such as SSRIs and thus provide a compelling clinical rationale for understanding the function and regulation of these carriers. These drugs either block transport of substrates as is the case for SSRIs and cocaine, or are carrier substrates, such as amphetamines, which both inhibit uptake and stimulate efflux of intracellular neurotransmitter. The result is an increase in levels of extracellular biogenic monoamine augmenting neuronal receptor signaling.
My research is focused
on enhancing our understanding of the processes by which the dopamine
transporter and other biogenic monoamine transporers are regulated and
to identify other proteins that are involved in this process. One mechanism
for acute presynaptic regulation of dopamine transport is modulation of
transporter number through the trafficking of carriers to and from the
cell surface.
Others and we have found this process and also other biochemical and pharmacological
properties of biogenic monoamine transporters seem to vary with the expression
system used. For example we have found that the sensitivity to protein
kinase C activation vary greatly with almost no reduction in transporter
numbers on the surface of human neuroblastoma cells but on the other hand
a complete removal of essentially all transporters when expressed in frog
Xenopus oocytes. This suggests that although a single gene product confers
dopamine transport activity, the transporter itself may not function in
isolation.
To identify molecules responsible for these differences we have successfully used functional co-expression cloning in Xenopus oocytes. This led to the identification of a MAP kinase phosphatase, MKP3, which appears responsible for the modulatory activity. Surprisingly conventional MAP kinase families are not involved in the PMA-stimulated internalization of DAT, as MAP kinase inhibitors had no effect on carrier internalization, nor did the activity state of different MAP kinases correlate with the PMA-induced down regulation of DAT. These results suggest that MAP kinase phophatases modulate a novel signaling transduction pathway involved in the trafficking of neurotransmitter transporters.
Our lab is currently using several different techniques such as substrate trapping and yeast two-hybrid screening to identify what other molecules are substrates for the identified MAP kinase phosphatase. We believe this will identify novel and important proteins that are involved in this central mechanism of regulating membrane protein trafficking. We are also continuing our successful functional co-expression screening method to isolate novel proteins involved in the regulation and modulation of dopamine transporter activity.
Another project of our lab involves the use of DNA micro-arrays to investigate the differential gene expression patterns in the brains of rats treated chronically with inhibitors of biogenic monoamine transporter. These inhibitors include both psychostimulants such as cocaine and antidepressants such as prozac.
Sample Publications:
© Copyright 2001 - University
of Pittsburgh Department of Neurobiology
Webmaster S
Hunter Simpson