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David W Dawson

Publications and source records attributed to David W Dawson.

5 recordsLinked to original sources
PubMed2006

Mammalian polynucleotide phosphorylase is an intermembrane space RNase that maintains mitochondrial homeostasis.

We recently identified polynucleotide phosphorylase (PNPase) as a potential binding partner for the TCL1 oncoprotein. Mammalian PNPase exhibits exoribonuclease and poly(A) polymerase activities, and PNPase overexpression inhibits cell growth, induces apoptosis, and stimulates proinflammatory cytokine production. A physiologic connection for these anticancer effects and overexpression is difficult to reconcile with the presumed mitochondrial matrix localization for endogenous PNPase, prompting this study. Here we show that basal and interferon-beta-induced PNPase was efficiently imported into energized mitochondria with coupled processing of the N-terminal targeting sequence. Once imported, PNPase localized to the intermembrane space (IMS) as a peripheral membrane protein in a multimeric complex. Apoptotic stimuli caused PNPase mobilization following cytochrome c release, which supported an IMS localization and provided a potential route for interactions with cytosolic TCL1. Consistent with its IMS localization, PNPase knockdown with RNA interference did not affect mitochondrial RNA levels. However, PNPase reduction impaired mitochondrial electrochemical membrane potential, decreased respiratory chain activity, and was correlated with altered mitochondrial morphology. This resulted in FoF1-ATP synthase instability, impaired ATP generation, lactate accumulation, and AMP kinase phosphorylation with reduced cell proliferation. Combined, the data demonstrate an unexpected IMS localization and a key role for PNPase in maintaining mitochondrial homeostasis.

Adenosine Triphosphate↗
PubMed2006

The TCL1 oncoprotein binds the RNase PH domains of the PNPase exoribonuclease without affecting its RNA degrading activity.

TCL1 is an AKT kinase coactivator that, when dysregulated, initiates mature lymphocyte malignancies in humans and transgenic mice. While TCL1 augments AKT pathway signaling, additional TCL1 interacting proteins that may contribute to cellular homeostasis or transformation are lacking. Here, an exoribonuclease, PNPase, was identified in a complex with TCL1. The AKT interaction domain on TCL1 bound either RNase PH repeat domain of PNPase without influencing its RNA degrading activity, which was compatible with predicted docking models for a TCL1-PNPase complex. Our data provide a novel protein interaction for mammalian PNPase that may impact TCL1 mediated transformation.

Blotting, Western↗
PubMed2005

T cell leukemia-1 modulates TCR signal strength and IFN-gamma levels through phosphatidylinositol 3-kinase and protein kinase C pathway activation.

A signaling role for T cell leukemia-1 (TCL1) during T cell development or in premalignant T cell expansions and mature T cell tumors is unknown. In this study, TCL1 is shown to regulate the growth and survival of peripheral T cells but not precursor thymocytes. Proliferation is increased by TCL1-induced lowering of the TCR threshold for CD4(+) and CD8(+) T cell activation through both PI3K-Akt and protein kinase C-MAPK-ERK signaling pathways. This effect is submaximal as CD28 costimulation coupled to TCL1 expression additively accelerates dose-dependent T cell growth. In addition to its role in T cell proliferation, TCL1 also increases IFN-gamma levels from Th1-differentiated T cells, an effect that may provide a survival advantage during premalignant T cell expansions and in clonal T cell tumors. Combined, these data indicate a role for TCL1 control of growth and effector T cell functions, paralleling features provided by TCR-CD28 costimulation. These results also provide a more detailed mechanism for TCL1-augmented signaling and help explain the delayed occurrence of mature T cell expansions and leukemias despite tumorigenic TCL1 dysregulation that begins in early thymocytes.

Animals↗
PubMed2003

Virilization in bilateral macronodular adrenal hyperplasia controlled by luteinizing hormone.

We report a case of a virilized 59-yr-old woman with elevated serum testosterone levels and bilateral macronodular adrenal hyperplasia. The patient underwent laparoscopic right adrenalectomy, after which the elevated testosterone level transiently normalized. The immediate postoperative depression of the testosterone level suggested that the process was driven by gonadotropins that were suppressed by the stress of surgery. The excised right adrenal mass contained testosterone by immunohistochemistry and LH receptor mRNA by in situ hybridization. The recurrence of hyperandrogenemia suggested that the enlarged left adrenal was also secreting testosterone. The serum testosterone level increased in response to im injection of human chorionic gonadotropin, suggesting control by aberrant LH receptors. Injection of leuprolide acetate (7.5 mg im) to suppress LH levels resulted in normalization of the testosterone level 12 d later that persisted for several weeks. Ectopic receptors mediating Cushing's syndrome have been described in several cases of bilateral adrenal hyperplasia and adrenal adenoma. This is the first case to our knowledge in which pure androgen overproduction in adrenal hyperplasia has been shown to be controlled by LH receptors. In our patient, the control of androgen secretion by LH may explain the postmenopausal onset of virilization and the transient postoperative normalization of the serum testosterone level.

Adrenal Gland Diseases↗