Biomedical subjects

Steven F Dowdy

Publications and source records attributed to Steven F Dowdy.

23 records · Page 2Linked to original sources

PubMed2003

Novel p27(kip1) C-terminal scatter domain mediates Rac-dependent cell migration independent of cell cycle arrest functions.

Hepatocyte growth factor (HGF) signaling via its receptor, the proto-oncogene Met, alters cell proliferation and motility and has been associated with tumor metastasis. HGF treatment of HepG2 human hepatocellular carcinoma cells induces cell migration concomitant with increased levels of the p27(kip1) cyclin-cdk inhibitor. HGF signaling resulted in nuclear export of endogenous p27 to the cytoplasm, via Ser-10 phosphorylation, where it colocalized with F-actin. Introduction of transducible p27 protein (TATp27) was sufficient for actin cytoskeletal rearrangement and migration of HepG2 cells. TATp27 mutational analysis identified a novel p27 C-terminal domain required for cell migration, distinct from the N-terminal cyclin-cyclin-dependent kinase (cdk) binding domain. Loss or disruption of the p27 C-terminal domain abolished both actin rearrangement and cell migration. The cell-scattering activity of p27 occurred independently of its cell cycle arrest functions and required cytoplasmic localization of p27 via Ser-10 phosphorylation. Furthermore, Rac GTPase was necessary for p27-dependent migration but alone was insufficient for HepG2 cell migration. These results predicted a migration defect in p27-deficient cells. Indeed, p27-deficient primary fibroblasts failed to migrate, and reconstitution with TATp27 rescued the motility defect. These observations define a novel role for p27 in cell motility that is independent of its function in cell cycle inhibition.

Actins↗

PubMed2003

Modulation of cellular function by TAT mediated transduction of full length proteins.

Due to the barrier imposed by the cell membrane, delivery of macromolecules in excess of 500 Daltons directly into cells remains problematic. However, proteins, which have been evolutionarily selected to perform specific functions, are therefore an attractive therapeutic agent to treat a variety of human diseases. In practice, the direct intracellular delivery of these proteins has, until recently, been difficult to achieve due primarily to the bioavailability barrier of the plasma membrane, which effectively prevents the uptake of the majority of peptides and proteins by limiting their passive entry. However, recent work using small cationic peptides, termed protein transduction domains (PTDs), derived from nucleic acid binding proteins, such as HIV TAT protein or the Dros. m. transcription factor Antp. or synthetic poly-Arginine, have now been shown to deliver a myriad of molecules, including synthetic small molecules, peptides and proteins, into animal models in vivo. Here, we focus on the delivery of biologically active, full length proteins to treat pre-clinical disease models.

Animals↗

PubMed2002

Protein transduction technology.

Intracellular delivery of macromolecules remains problematic because of the bioavailability restriction imposed by the cell membrane. Recent studies on protein transduction domains have circumvented this barrier, however, and have resulted in the delivery of peptides, full-length proteins, iron beads, liposomes, and radioactive isotopes into cells in culture and animal models in vivo.

Animals↗

PubMed2002

Regulation of G(1) cell-cycle progression by oncogenes and tumor suppressor genes.

Progression of resting quiescent G(0) cells into early G(1) and transition across the restriction point are highly regulated processes. Mutation of proto-oncogenes and tumor suppressor genes regulating these transitions are targeted during oncogenesis. Recent work has underscored the importance of the G(0) to early G(1) transition and metabolism to neoplastic cells.

Animals↗

PubMed2002

c-Rel regulation of the cell cycle in primary mouse B lymphocytes.

Surface-expressed BCR mediates the proliferation and expansion of antigen-specific B lymphocytes during a humoral immune response. Although several studies extensively characterize BCR proliferative signaling, the mechanisms linking these pathways to the cell cycle remain elusive. Using knockout mice, we show that c-Rel, a proto-oncogenic member of the NF-kappaB transcription factor family, is essential to BCR-mediated proliferation and cell cycle progression. Splenic B cells obtained from gene-targeted c-Rel knockout mice display a defective proliferation response to antigen receptor cross-linking, resulting in G(1) arrest. At the molecular level, we see that BCR stimulation of resting c-Rel(-/-) B cells fails to induce proper cyclin D3 and cyclin E expression, thereby negatively impacting G(1) phase cyclin-dependent kinase (CDK) activity. c-Rel-deficient B cells also exhibit incomplete phosphorylation of the Retinoblastoma protein (pRb) and poor expression of E2Fs, thus impeding the G(1) to S phase transition. Down-regulation of the pRb-related p130 protein during the G(0) to G(1) transition and removal of the CDK inhibitor p27(KIP1) in late G(1) parallel that of wild-type cells, suggesting that Rel-deficient B cells can exit the G(0) resting state and enter G(1) phase normally. Finally, we demonstrate that restoration of proliferation can be achieved partially upon reintroduction of cyclin E using a protein transduction method to reconstitute primary B cells. Collectively, these studies emphasize the importance of c-Rel in lymphocyte proliferation and oncogenesis, and highlight a requirement for c-Rel in establishing an effective humoral immune response.

Animals↗