Normal function of human cells requires coordination of many different external stimuli and the cells' subsequent responses. Cells must detect if there are appropriate nutrients and mitogens available for them to grow or proliferate. Cells are also bombarded with various DNA damaging agents and must respond by stopping cell proliferation, fixing DNA damages, and then resuming their normal function. These two pathways, mitogen response and DNA repair, have often been studied as separate pathways. There are however data to suggest that the two pathways may communicate with each other. The goal of this project is to study how the enzymes inside a cell that regulate mitogenic responses may interact with the enzymes that are responsible for DNA damage repair. The goal of this project is to learn if S6 kinases play a role in the DNA repair pathways. S6 kinases are regulated by the enzymes mTOR (mammalian target of rapamycin) and PI3K (Phosphoinositide-3 kinase). mTOR came to the forefront of cell proliferation research when rapamycin, a cell proliferation inhibitor used as an immunosuppressant in organ transplantation, was found to inhibit mTOR. mTOR regulates many of the cellular processes including transcription, translation, proliferation, and cell size determination. PI3K is found to be mutated in many human cancers, and it also regulates many cellular processes such as metabolism and proliferation. S6 kinases are regulated by both mTOR and PI3K and are thought to mediate some of the mTOR and PI3K functions. Recently there have been data to suggest that S6 kinases may also be regulated by ATM and ATR, enzymes that are activated during DNA damage responses and activate DNA repair mechanisms. This proposal will begin to lay out the fundamental pieces in assessing whether S6 kinases are indeed regulated by the ATM/ATR pathway. There are two specific aims in this proposal. In the first aim, we will assess whether ATM or ATR are involved in activating S6 kinases (sub-aim 1A) as well as studying if serine 356, a potential site on S6 kinases modified by ATM/ATR, is important for S6 kinase function (sub-aim 1B). In the second aim we will study if S6 kinases are found in the DNA damage areas of a cell (sub-aim 2A), assess whether the absence of S6 kinases has an effect on DNA damage responses (sub-aim 2B), and assess whether S6 kinase activation following DNA damage results in inhibition of the PI3K and mTOR signaling (sub-aim 2C). With the previous SCORE funding our laboratory has been able to assess what activates an S6 kinase. The professional developmental objective of this proposal is to reach the next goal of our laboratory, which is to understand what S6 kinases do in cells once they become activated, as well as to increase our productivity and competitiveness.