Oncogene 22:9007C9021 [PubMed] [Google Scholar] 9. of hundreds of genes involved in cell cycle progression, adhesion, metabolism, and apoptosis (1C4). Overexpression of MYC is a hallmark of human cancer, contributing to the expression of numerous groups of genes involved in transformation, metastasis, and overall poor prognosis (5, 6). MYC has been estimated to be active in nearly 70% of human cancers; the mechanisms of activation include amplification, translocation, deregulated translation, and protein turnover (7, 8). As such, MYC has been the subject of extensive study in the search for treatment modalities (reviewed in references 3, 9, and 10). Activation of MYC is induced by mitogenic stimuli to promote cell cycle progression (11C17). To prevent aberrant MYC expression from driving unsafe proliferation in Rabbit polyclonal to CNTF the animal, a safeguard has evolved whereby MYC activation in the absence of mitogenic survival signals is opposed by cellular responses of apoptosis and/or cell cycle arrest, depending on the cellular context and p53 status (18C25). Despite these observations of almost 20 years ago and the realization that other growth-promoting transcription factors, such as E1A and E2F1, act similarly (26C29), the mechanism of MYC-induced apoptosis and cell cycle arrest is still poorly understood. Expression of prosurvival oncogenes, the earliest example of which is Bcl-2, has been shown previously to counteract the death function of MYC (30C32). Additionally, activation of phosphoinositide-3-kinase (PI3K) and its downstream target AKT can protect against apoptosis induced by MYC (33). PI3K and AKT were shown in the mid-1990s to convey a strong prosurvival signal downstream of receptor tyrosine kinases (34C36) by impacting the apoptosis machinery directly (37C40) and by regulating FOXO transcription factors (41C45). Furthermore, loss of the tumor suppressor MMAC1/PTEN results in constitutive PI3K signals (46, 47) and can lead to tumors in humans (48, 49). Thus, aberrant MYC activation together with overactive AKT, a condition that is often achieved in tumor cells, can provide the cooperative growth and antiapoptotic signals necessary to promote tumorigenesis. A recently identified protein, cell division control protein A7 (CDCA7; also called JPO1), is expressed Merck SIP Agonist from the MYC- and E2F-responsive gene (50C52). MYC and E2F1 bind to the promoter of to drive CDCA7 expression (50, 52), causing CDCA7 mRNA to be widely expressed, Merck SIP Agonist with high levels in the colon, Merck SIP Agonist thymus, and small intestine and lower levels in the testis, stomach, and bone marrow (52). High levels of CDCA7 mRNA have been found in patients with acute myeloid leukemia (AML) and blast crisis-stage chronic myeloid leukemia (CML) (51), while solid tumors displaying high levels of MYC have also been shown to be positive for CDCA7 (51). While CDCA7 has weak transformation properties when expressed alone, coexpression rescues the transformation of a transformation-defective MYC mutant with a MYC box II (MBII) deletion (52). Furthermore, recent work by Penn and colleagues has shown that JPO2, a protein with some homology with CDCA7, can associate directly with MYC, and this increases MYC-dependent transformation (53). Both CDCA7 and JPO2 contain a highly conserved cysteine-rich carboxyl-terminal region that might allow binding to DNA (50). However, it is not known whether CDCA7 also associates with MYC. In the present study, we show that CDCA7 and MYC interact physically. We have mapped the domains of interaction and have discovered that AKT phosphorylates CDCA7 near this contact region, leading to loss of its association with MYC, binding to 14-3-3 proteins, and exclusion from the nucleus. Coexpression of CDCA7 with MYC sensitized cells to serum withdrawal-induced apoptosis, and this proapoptotic activity required the MYC-binding region. Short hairpin RNA interference (shRNAi)-mediated knockdown of CDCA7 rescued cells from MYC-dependent apoptosis following removal from serum. These findings point.