Research Highlights
The research interests of Cell Signaling and Growth Control members are grouped into four areas: basic mechanisms of cell signaling and mitogenic control; tissue development and cell differentiation; cell injury and responses to carcinogens; and apoptosis and immunobiology. One of the most exciting findings made under this program was in the laboratory of former Program Leader Nicholas Heintz, PhD. The Heintz research team discovered that under conditions of oxidative stress, where there is cell cycle arrest and no expression of cyclin D1, there is discordance between normal DNA binding activity of E2F and NF-kB transcription factor complexes and the binding of these complexes to chromatin. This effect is related to the formation of a novel complex between the p65 subunit of NF-kB and E2F-6, a complex that appears to prevent activation of gene expression.
"We're finding that the trafficking of transcription factors, on and off of chromatin, is exceedingly different under conditions of arrest and conditions of growth," says Heintz. "It's a redox-dependent process. We can show that the promoter regions of cyclin D1 are affected under oxidative stress, linking redox-dependent signaling to growth control."
Russell Hovey, PhD, assistant professor of animal science, cloned several isoforms of the human prolactin receptor spliced from a new exon 11, including two forms of the receptor that are thought to act in a dominant negative fashion to inhibit receptor function. These new isoforms have been identified in both colon and breast cancers.“ Hovey looked at expression of these isoforms during development in mice and found a relationship between various stages of mammary gland development and receptor expression,” says Heintz. “Next, he will try to figure out their role in human breast cancer.”
Wolfgang Dostmann, PhD, assistant professor of pharmacology, developed novel and highly specific inhibitors of cGMP-dependent protein kinase (PKG), one of the major intracellular second messenger signaling targets. The inhibitors are cell permeable and show great promise in dissecting the cGMP specific signaling events in a variety of cell types. In cultured rat aortic vascular smooth muscle cells, the use of these PKG-inhibitors demonstrated a physiologically important role for PKG in regulating phenotypic modulation. In small intact cerebral arteries, the inhibitors effectively inhibited NO-induced vasodilation, further emphasizing the central role for PKG in the modulation of vascular contractility.
“I believe the whole concept of using peptide inhibitors conjugated to delivery agents is really important,” says Dostmann. “It’s a very efficient way of delivering peptides and peptide conjugates into cells and raises the possibility of conjugating peptides that would inhibit other pathways in cancer.”
Douglas Johnson, PhD, professor of microbiology and molecular genetics, examined the cell-cycle specific localization of the Cdc24p guanine-nucleotide exchange factor (GEF) in the budding yeast S. cerevisiae. His laboratory determined that the localization of Cdc24p to sites of polarized growth is a function of both polarized targeting to cellular membranes as well as efficient anchoring of the GEF in a cytoskeletal complex, components of which were previously unknown. As Cdc24p is homologous to numerous mammalian GEFs that are involved in oncogenesis, these studies may provide new insight into regulation of these important signaling pathways.
In continued studies of how T helper cells make differentiating decisions, Mercedes Rincón, PhD, assistant professor of medicine, and her colleagues identified the role of IL-6 in T helper type 2 differentiation via induction of NFATc2.
Karen Lounsbury, PhD, assistant professor of pharmacology; Brooke Mossman, PhD, professor of pathology; and Douglas Taatjes, PhD, research associate professor of pathology, collaborated on studies of how asbestos alters, at the local level, cell growth properties and cell cycle and signal events that can eventually lead to lung cancer. This year, the researchers concentrated on a large family of protein kinase Cs (PKCs) that respond to a wide range of extracellular stimuli. They found that one family member, PKC delta, is activated by exposure to asbestos.
“This project nurtures our mutual interests in cell signaling through protein kinases,” says Lounsbury. “Our recent data indicate that asbestos signaling, leading to outcomes of both cell proliferation and programmed cell death, requires the activity of PKC delta. These new findings are exciting because they establish PKC delta as a central link between asbestos-mediated cell injury and its downstream pathologic effects.”
Additional work that took place in Mossman’s laboratory this year focused on an area of intense interest in environmental toxicology—how ultrafine airborne particles act as a major cause of human disease, including cancer. The researchers showed that such particles increase protooncogene expression and proliferation in alveolar epethelial cells.
