Phospholipase D stabilizes HDM2 through an mTORC2/SGK1 pathway.

Phosphatidic acid (PA), the primary metabolite of the phospholipase D (PLD)-mediated hydrolysis of phosphatidylcholine, has been shown to act as a tumor promoting second messenger in many cancer cell lines. A key target of PA is the mammalian target of rapamycin (mTOR), a serine-threonine kinase that has been widely implicated in cancer cell survival signals. In agreement with its ability to relay survival signals, it has been reported that both PLD and mTOR are required for the stabilization of the p53 E3 ubiquitin ligase human double minute 2 (HDM2) protein. Thus, by stabilizing HDM2, PLD and mTOR are able to counter the pro-apoptotic signaling mediated by p53 and promote survival. mTOR exists in at least two distinct complexes-mTORC1 and mTORC2-that are both dependent on PLD-generated PA. Although PLD and its metabolite PA are clearly implicated in the transduction of survival signals to mTOR, it is not yet apparent which of the two mTOR complexes is critical for the stabilization of HDM2. We report here that the PLD/mTOR-dependent stabilization of HDM2 involves mTORC2 and the AGC family kinase serum- and glucocorticoid-inducible kinase 1 (SGK1). This study reveals that mTORC2 is a critical target of PLD-mediated survival signals and identifies SGK1 as a downstream target of mTORC2 for the stabilization of HDM2.

Suppression of cell migration by protein kinase Cdelta.

The ability of cancer cells to migrate is strongly correlated with malignant progression and metastasis. Survival signals that suppress apoptosis have also been linked to increased cell motility. We previously reported that suppression of protein kinase Cdelta (PKCdelta) provided survival signals in a rat fibroblast model system. These studies have been extended to human breast cancer cells with differential cell motilities and PKCdelta levels. BT-549 cells, which lack detectable expression of PKCdelta, migrate very efficiently, whereas MCF-7 cells, which express high levels of PKCdelta, migrate very poorly. Ectopic expression of PKCdelta suppressed cell migration in the BT-549 cells, and downregulation of PKCdelta enhanced cell migration in the MCF-7 cells. Downregulation of PKCdelta in the MCF-7 cells also led to increased secretion of the matrix metalloprotease MMP-9. The migration of mouse embryo fibroblasts (MEFs) from wild type and PKCdelta knockout mice was also examined and MEFs from PKCdelta knockout mice had a five-fold increase in cell migration relative to the wild-type MEFs. These data provide evidence that PKCdelta suppresses cell migration in both human breast cancer cells and in primary mouse fibroblasts, and indicate that the loss of PKCdelta in human cancers could contribute to both cell survival and metastasis.

Rat pups reduce ultrasonic vocalization after exposure to an adult male rat.

We examined how the experience of a threatening stimulus alters subsequent behavior in a situation where the immediate threat is absent. A small huddle of 12-day-old rats was exposed to a potentially infanticidal adult male rat for 5 min. During male exposure, pups were significantly more immobile than control pups. Thirty, 60, and 180 min after male exposure, the pups were isolated for 5 min from litter and dam in an unfamiliar environment. When isolated, pups that had been previously exposed to the male emitted significantly fewer ultrasonic vocalizations than controls, but did not differ in immobility. Low levels of vocalization were apparent 30 and 60 min after male exposure and were not evident at 180 min. The pups seemed to have adjusted their behavior to a potential male threat in a different context for a limited period of time.