For more than 2 decades, epidemiologic studies have been reported on the effect of dietary fat on the risk of prostate cancer. Experimental data indicate that n-3 polyunsaturated fatty acids (PUFAs) inhibit whereas n-6 PUFAs stimulate prostate cancer cell growth. However, the mechanism of PUFA's effect is unknown. n-3 and n-6 PUFAs are essential fatty acids and necessary for survival. Mammals cannot synthesize these fatty acids cte novo, neither can convert n-6 to n-3 or vice versa. Therefore they have to be taken in from diet. Fish oil is a rich source of n-3 polyunsaturated fatty acids. We hypothesize that n-3 PUFAs incorporate into the sn-2 position of phospholipids, and the n-3 PUFA-enriched phosphoinositides affect the Akt signaling pathway, regulate expression of genes resulting in prostate cell growth inhibition. In this project, we will study the suppression of prostate cancer progression by n-3 fatty acid enriched diet and its mechanism of action. Our specific aims are: Determine the effect of n-3 fatty acids on prostate cancer proliferation, progression and metastasis. We will assess the n-3 diet on prostate cancer proliferation, histological progression, expression of biomarkers (genes, proteins and lipids), survival and metastasis;Determine whether the timing of n-3 fatty acid intake differentially affects prostate cancer. We will determine whether early- and/or lateintake will have a similar effect on prostate cancer to life-long intake of n-3 fatty acids. Clinically, it is important to know whether childhood intake of n-3 fatty acids and whether n-3 fatty acids supplementation after the development of prostate cancer are beneficial;Determine the effect of n-3 fatty acids on the localization of phosphoinositides and on the Akt signaling pathway. We will determine whether n-3 fatty acid containing PIPs affect Pdk and Akt protein localization, activation and downstream signaling. We take advantage of our strengths of in vivo and in vitro, mouse and human model systems. For the first time, molecular changes (mRNA and lipid) associated with fish oil diet in the prostate will be comprehensively and systematically analyzed. In addition, conventional pathway dissection approach will also be applied to study the mechanism of action of fish oil on prostate cancer.