Biomedical subjects

Brad Bryan

Publications and source records attributed to Brad Bryan.

5 recordsLinked to original sources

PubMed2007

Transforming growth factor-beta-independent regulation of myogenesis by SnoN sumoylation.

Recent progress has been made on the role of oncoproteins c-Ski and related SnoN in the control of cellular transformation. c-Ski/SnoN potently repress transforming growth factor-beta (TGF-beta) antiproliferative signaling through physical interaction with signal transducers called Smads. Overexpression of c-Ski/SnoN also induces skeletal muscle differentiation, but how c-Ski/SnoN function in myogenesis is largely unknown. During our investigation on the role of sumoylation in TGF-beta signaling, we inadvertently found that SnoN is modified by small ubiquitin-like modifier-1 (SUMO-1). Here, we biochemically characterize SnoN sumoylation in detail and report the physiological function of the modification. Sumoylation occurs primarily at lysine 50 (Lys-50). PIAS1 and PIASx proteins physically interact with SnoN to stimulate its sumoylation, thus serving as SUMO-protein isopeptide ligases (E3) for SnoN sumoylation. SnoN sumoylation does not alter its metabolic stability or its ability to repress TGF-beta signaling. Notably, loss of sumoylation in the Lys-50 site (via a Lys-to-Arg point mutation) potently activates muscle-specific gene expression and enhances myotube formation. Our study suggests a novel role for SUMO modification in the regulation of myogenic differentiation.

Cell Line↗

PubMed2005

Ubiquitination of RhoA by Smurf1 promotes neurite outgrowth.

The Rho-family of small GTPases consists of essential regulators of neurite outgrowth, axonal pathfinding, and dendritic arborization. Previous work has demonstrated in non-neuronal cell types that Smurf1, an E3 ubiquitin ligase, regulates cell polarity and protrusive activity via PKCzeta-dependent recruitment to cellular protrusion sites, and subsequent ubiquitination and proteasomal degradation of RhoA. In this study, we show that Smurf1 enhances neurite outgrowth in Neuro2a neuroblastoma cells. We demonstrate that RhoA is ubiquitinated, and that Smurf1 and RhoA physically interact in vivo. Interestingly, Smurf1 overexpression in Neuro2a cells dramatically reduces RhoA protein levels during dibutyric cyclic AMP, but not retinoic acid induced neurite outgrowth. This Smurf1-dependent reduction in RhoA protein levels was abrogated using the general proteasome inhibitor MG132, suggesting that RhoA is targeted for ubiquitination and degradation via Smurf1. Together, our data suggest that localized regulation of different subsets of Rho GTPases by specific guidance signals results in an intracellular asymmetry of RhoA activity, which could regulate neurite outgrowth and guidance.

Animals↗

PubMed2005

Sarcoidosis.

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Humans↗

PubMed2004

GEFT, a Rho family guanine nucleotide exchange factor, regulates neurite outgrowth and dendritic spine formation.

The Rho family of small GTPases controls a wide range of cellular processes in eukaryotic cells, such as normal cell growth, proliferation, differentiation, gene regulation, actin cytoskeletal organization, cell fate determination, and neurite outgrowth. The activation of Rho-GTPases requires the exchange of GDP for GTP, a process catalyzed by the Dbl family of guanine nucleotide exchange factors. We demonstrate that a newly identified guanine nucleotide exchange factor, GEFT, is widely expressed in the brain and highly concentrated in the hippocampus, and the Purkinje and granular cells of the cerebellum. Exogenous expression of GEFT promotes dendrite outgrowth in hippocampal neurons, resulting in spines with larger size as compared with control spines. In neuroblastoma cells, GEFT promotes the active GTP-bound state of Rac1, Cdc42, and RhoA and increases neurite outgrowth primarily via Rac1. Furthermore, we demonstrated that PAK1 and PAK5, both downstream effectors of Rac1/Cdc42, are necessary for GEFT-induced neurite outgrowth. AP-1 and NF-kappaB, two transcriptional factors involved in neurite outgrowth and survival, were up-regulated in GEFT-expressing cells. Together, our data suggest that GEFT enhances dendritic spine formation and neurite outgrowth in primary neurons and neuroblastoma cells, respectively, through the activation of Rac/Cdc42-PAK signaling pathways.

Animals↗

PubMed2003

A Rac/Cdc42-specific exchange factor, GEFT, induces cell proliferation, transformation, and migration.

The Rho family of small GTPases, including Rho, Rac, and Cdc42, play essential roles in diverse cellular functions. The ability of Rho family GTPases to participate in signaling events is determined by the ratio of inactive (GDP-bound) and active (GTP-bound) forms in the cell. The activation of Rho family proteins requires the exchange of bound GDP for GTP, a process catalyzed by the Dbl family of guanine nucleotide exchange factors (GEFs). The GEFs have high affinity for the guanine nucleotide-free state of the GTPases and are thought to promote GDP release by stabilizing an intermediate transition state. In this study, we have identified and characterized a new Rac/Cdc42-specific Dbl family guanine nucleotide exchange factor, named GEFT. GEFT is highly expressed in the excitable tissues, including brain, heart, and muscle. Low or very little expression was detected in other nonexcitable tissues. GEFT has specific exchange activity for Rac and Cdc42 in our in vitro GTPase exchange assays and glutathione S-transferase-PAK pull-down assays with GTP-bound Rac1 and Cdc42. Overexpression of GEFT leads to changes in cell morphology and actin cytoskeleton re-organization, including the formation of membrane microspikes, filopodia, and lamilliopodia. Furthermore, expression of GEFT in NIH3T3 cells promotes foci formation, cell proliferation, and cell migration, possibly through the activation of transcriptional factors involved in cell growth and proliferation. Together, our data suggest that GEFT is a Rac/Cdc42-specific GEF protein that regulates cell morphology, cell proliferation, and transformation.

Amino Acid Sequence↗