Gastrointestinal (GI) peptides, including mammalian bombesin-like peptides, integrate secretory, contractile and proliferative functions in the GI tract. The broad, long term objective of this proposal remains to elucidate the signal transduction pathways that mediate GI peptide-mediated cell proliferation. GI peptides elicit their characteristic effects on cellular processes by binding to specific G protein-coupled receptors (GPCR) on the surface of their target cells. Protein kinase C (PKC) occupies a pivotal role in the signal transduction pathways that mediate numerous cellular responses elicited by GI peptides including cell proliferation. However, the events occurring downstream of specific isoforms of PKC remain elusive. The present challenge is to identify downstream targets for PKCs that transmit signals to the cell interior and participate in the regulation of processes that control cell function, including cell proliferation. We cloned a novel serine/threonine protein kinase, termed protein kinase D (PKD), with distinct structural and enzymological properties that has emerged as a downstream target of novel isoforms of PKC. During the past funding period, our studies established that the PKC/PKD pathway is operational in a variety of cell types stimulated with many different stimuli, generated experimental evidence supporting a model that envisages PKD activation as a dynamic multi-step process and indicated that PKD plays a role in the mediation of GPCR-induced cell proliferation. Based on these findings, our central hypothesis is that GI peptide receptors activate a novel PKC/PKD phosphorylation cascade that plays a critical role in the signal transduction of GI peptide-induced cellular proliferation. An additional hypothesis is that this novel PKC/PKD phosphorylation cascade is operational in gastrointestinal cells. We will examine these hypotheses pursuing the following specific aims: 1) Characterize the sequential multi-step mechanism of phosphorylation-dependent PKD activation in response to GPCR activation; 2) Identify the PKD domains necessary for potentiation of GPCR-induced cell proliferation; 3) Characterize the role of MAPK pathways in PKD potentiation of GPCR-induced cell proliferation; and 4) Characterize the regulation and function of PKD in intestinal epithelial cells.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
Project #
Application #
Study Section
General Medicine A Subcommittee 2 (GMA)
Program Officer
May, Michael K
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of California Los Angeles
Internal Medicine/Medicine
Schools of Medicine
Los Angeles
United States
Zip Code
Sinnett-Smith, James; Ni, Yang; Wang, Jia et al. (2014) Protein kinase D1 mediates class IIa histone deacetylase phosphorylation and nuclear extrusion in intestinal epithelial cells: role in mitogenic signaling. Am J Physiol Cell Physiol 306:C961-71
Rozengurt, Enrique; Soares, Heloisa P; Sinnet-Smith, James (2014) Suppression of feedback loops mediated by PI3K/mTOR induces multiple overactivation of compensatory pathways: an unintended consequence leading to drug resistance. Mol Cancer Ther 13:2477-88
Ni, Yang; Sinnett-Smith, James; Young, Steven H et al. (2013) PKD1 mediates negative feedback of PI3K/Akt activation in response to G protein-coupled receptors. PLoS One 8:e73149
Sinnett-Smith, James; Kisfalvi, Krisztina; Kui, Robert et al. (2013) Metformin inhibition of mTORC1 activation, DNA synthesis and proliferation in pancreatic cancer cells: dependence on glucose concentration and role of AMPK. Biochem Biophys Res Commun 430:352-7
Yoo, James; Rodriguez Perez, Citlali Ekaterina; Nie, Wenxian et al. (2013) TNF-? and LPA promote synergistic expression of COX-2 in human colonic myofibroblasts: role of LPA-mediated transactivation of upregulated EGFR. BMC Gastroenterol 13:90
Kisfalvi, Krisztina; Moro, Aune; Sinnett-Smith, James et al. (2013) Metformin inhibits the growth of human pancreatic cancer xenografts. Pancreas 42:781-5
Soares, Heloisa P; Ni, Yang; Kisfalvi, Krisztina et al. (2013) Different patterns of Akt and ERK feedback activation in response to rapamycin, active-site mTOR inhibitors and metformin in pancreatic cancer cells. PLoS One 8:e57289
Yoo, James; Rodriguez Perez, Citlali Ekaterina; Nie, Wenxian et al. (2012) TNF-ýý induces upregulation of EGFR expression and signaling in human colonic myofibroblasts. Am J Physiol Gastrointest Liver Physiol 302:G805-14
Waldron, Richard T; Innamorati, Giulio; Torres-Marquez, M Eugenia et al. (2012) Differential PKC-dependent and -independent PKD activation by G protein ? subunits of the Gq family: selective stimulation of PKD Ser??? autophosphorylation by G?q. Cell Signal 24:914-21
Young, Steven H; Rozengurt, Nora; Sinnett-Smith, James et al. (2012) Rapid protein kinase D1 signaling promotes migration of intestinal epithelial cells. Am J Physiol Gastrointest Liver Physiol 303:G356-66

Showing the most recent 10 out of 111 publications