Extracellular ATP in cancer: mechanism study of ATP internalization and ATP-induced drug resistance in cancer cells and tumors - ABSTRACT
ATP is one of the most versatile biological molecules in all organisms. It provides readily available energy for
almost all enzymatic reactions and phosphorylates proteins and enzymes in almost all signal transduction
cascades. It also functions as an extracellular messenger. Although all of these biological processes cannot
function without ATP, ATP has almost been taken for granted in performing these essential functions, and
research focuses have been much more on other molecules involved in these reactions. Recent research has
shown that ATP plays some very important but previously unrecognized functions in cancer. Intratumoral
extracellular ATP (eATP) is found to be more than 1,000 times higher than that in normal tissues, in the range
of 100-500 µM, but the sources, destination and functions of the high levels of eATP are still largely unclear.
Our recent studies have revealed that eATP can function either extracellularly or intracellularly because eATP
can be internalized by cancer cells by different types of endocytotic processes, particularly macropinocytosis.
Once inside cells, ATP elevates intracellular ATP levels; promotes cell metabolism, growth and proliferation;
enhances signal transduction for cell survival and proliferation; and augments drug resistance. However,
exactly how eATP is internalized and then released by cancer cells is far from fully understood. It is also
presently unknown if the eATP internalization is a general phenomenon and phenotype among different cancer
types. Furthermore, how and if internalized eATP-induced drug resistance is regulated at transcriptional and
translational levels is largely unclear. There is a big gap in our current understanding of eATP and our ultimate
goal of more effectively treating cancer by disrupting eATP traffic and functions. The long-term research goal
of my lab is to understand how eATP affects cancer at molecular, cellular and animal levels and use gained
knowledge to design novel therapies to more effectively treat cancer. The objectives of this proposed study
are to determine the prevalence and mechanisms that control and regulate ATP's cross-membrane
internalization and intracellular release, and drug resistance in cancer. The central hypothesis of this study is
that eATP is internalized by most cancer types and then released inside cells to perform diverse functions such
as promoting cell survival and drug resistance not only at the signaling level but also at transcriptional and
translational levels. To test this hypothesis, three specific aims are proposed: Specific Aim 1. Determine the
prevalence of eATP internalization among difference cancer cell lines and cancer types. Specific Aim 2. Use
various ATP analogs and endosome markers to study mechanisms of internalization and release of eATP in
cancer cells. Specific Aim 3. Use reverse genetics and bioluminescence imaging to study eATP-mediated
drug resistance in cancer cells and xenografted tumors in mice. The completion of the study will provide
insights into how eATP gets into cancer cells and performs functions such as promotion of drug resistance,
and identification of novel targets for reducing drug resistance and improving cancer patients' survival.
