This has been established in tumors of different tissue origins and in particular those derived from the breast [28,29]. phosphorylation of Akt(ser473) can be regulated by more than 90 kinases. Interestingly, phosphorylation of Akt(ser473), but not thr308, can be severely reduced by inhibition of Choline kinase activityviasiRNA or KT 5720 small molecule inhibitors. We show here that the regulation of Akt phosphorylation by Choline kinase is PI3K-independent. In addition, xenograft tumors treated with Choline kinase inhibitors demonstrated a statistically significant decrease in Akt(ser473) phosphorylation. Importantly, the reduction in phosphorylation correlates with regression of these xenograft tumors in the mouse model. == Conclusion == High Choline kinase expression and activity has previously been implicated in tumor development and metastasis. The mechanism by KT 5720 which Choline kinase is involved in tumor formation is still not fully resolved. From our data, we proposed that Choline kinase plays a key role in regulating Akt(ser473) phosphorylation, thereby promoting cell survival and proliferation. == Background == Akt or Protein kinase B, is a serine/threonine kinase that plays an important role in regulating a number of cellular processes such as growth, metabolism and survival (reviewed in [1]). The importance of the Akt pathway is highlighted by the mutation of various components of the pathway in human cancers such as the PTEN and PI3-kinase (P110), which occur in more than 30% of human tumors (reviewed in [2]). In recent years, much has been invested in the search for other Akt substrates in the hope of understanding the different cellular processes controlled by Akt. Currently over fifty Akt substrates have been identified. For Akt to achieve full activation, phosphorylation is needed at both serine 473 (ser473) of the hydrophobic tail and threonine 308 (thr308) of the activation motif, upon growth factor ligation to the receptor tyrosine kinases [3]. The extra-cellular growth signal is transducedviathe Ras protein resulting in the activation of PI3K. The lipid kinase phosphorylates phosphatidylinositol 4,5-bisphosphate (PIP2) to phosphatidylinositol (3,4,5)-trisphosphate (PIP3) which acts as a secondary messenger to recruit Aktviaits PH domain KT 5720 to the peripheral membrane. Similarly, PDK1 is also recruitedviaits PH domain to phosphorylate thr308 of Akt. To date, there are several candidate kinases fulfilling the role of PDK2, for the ser473 residue, the most likely candidate being the mTORC2 [4]. Others include DNA-PK, ILK and some PKCs [5-9]. Choline kinase (ChoK), is a lipid kinase that phosphorylates choline to generate phosphoryl choline (PCho). PCho serves as the first step in the Kennedy pathway for the generation of phosphatidylcholine [10], a major lipid component of the cellular membrane. In the last few years, high PCho and ChoK activity has been found in several human tumor types including breast, lung, colon and prostate [11,12]. There is a strong clinical correlation between ChoK expression level and tumor malignancy in breast, lung and bladder cancer [13,14]. Several reports have also demonstrated that with the inhibition of ChoK either by siRNA or small molecule inhibitors, there is a marked reduction in proliferation and mitogenic properties and Rabbit polyclonal to Myocardin a decrease in breast cancer cell viability has being reported in combination with 5-fluorouracil [15,16]. A full understanding of how this lipid kinase and its downstream substrates contribute to tumorigensis has yet to be disclosed, although some previous studies clearly correlate ChoK regulation with Rho A signaling, and transcriptome analysis of ChoK overexpression demonstrates its effects on cell cycle regulation and apoptosis impairment [17-19]. Previously, it has been shown that PCho confers mitogenic properties to mouse fibroblasts upon stimulation by PDGF or FGF [20,21]. In this work, we searched for kinases that could regulate Akt activity specifically at ser473. Using a human kinome siRNA library, we silenced individual kinases systematically in.