The neuronal RhoA GEF, Tech, interacts with the synaptic multi-PDZ-domain-containing protein, MUPP1.

Tech is a RhoA guanine nucleotide exchange factor (GEF) that is highly enriched in hippocampal and cortical neurons. To help define its function, we have conducted studies aimed at identifying partner proteins that bind to its C-terminal PDZ ligand motif. Yeast two hybrid studies using the Tech C-terminal segment as bait identified MUPP1, a protein that contains 13 PDZ domains and has been localized to the post-synaptic compartment, as a candidate partner protein for Tech. Co-transfection of Tech and MUPP1 in human embryonic kidney 293 cells confirmed that these full-length proteins interact in a PDZ-dependent fashion. Furthermore, we confirmed that endogenous Tech co-precipitates with MUPP1, but not PSD-95, from hippocampal and cortical extracts prepared from rat brain. In addition, immunostaining of primary cortical cultures revealed co-localization of MUPP1 and Tech puncta in the vicinity of synapses. In assessing which PDZ domains of MUPP1 mediate binding to Tech, we found that Tech can bind to either PDZ domain 10 or 13 of MUPP1 as mutation of both these domains is needed to disrupt their interaction. Taken together, these findings demonstrate that Tech binds to MUPP1 and suggest that it regulates RhoA signaling pathways in the vicinity of synapses.

Satisfying the requirements of the Food and Drug Administration and Centers for Medicare and Medicare Services.

Clinical studies of new imaging technologies conducted for regulatory purposes have traditionally focused on satisfying the standards of the US Food and Drug Administration (FDA) for marketing clearance or approval of a new product. However, given the increased scrutiny that is being directed at diagnostic imaging by third-party payers, obtaining clinical data that can support Medicare coverage of a new imaging technology is increasingly important to ensure the maximum diffusion of that technology. This article describes the regulatory requirements of both the FDA and Centers for Medicare and Medicare Services and explains how sponsors may approach clinical studies to secure both FDA clearance or approval and Centers for Medicare and Medicare Services coverage and payment.

Medical devices and the US Food and Drug Administration: regulating the tools of radiology.

The radiology community has an ever-expanding array of technologies to use in the care of patients. Regulated by the US Food and Drug Administration, these technologies often raise complex regulatory and legal questions in everyday practice that can be daunting for practicing radiologists. This article reviews the federal medical device regulatory framework pertinent to the practice of radiology, with the aims of highlighting the potential impact of federal regulation on everyday practice and minimizing misunderstandings about enforcement exposure.

The food and drug administration and molecular imaging agents: potential challenges and opportunities.

Molecular imaging, which combines the use of traditional imaging modalities with pharmaceutical and biologic imaging agents, holds considerable promise, particularly in light of recent advances in genomics and new applications beyond diagnosis toward the earlier detection and characterization of disease, the reliable assessment of treatment efficacy, and imaging-link therapeutic applications. Its potential notwithstanding, the current U.S. Food and Drug Administration (FDA) regulatory framework governing imaging agents sets a high bar for marketing approval, which may slow the pace at which molecular imaging becomes routinely available. Understanding the FDA's regulatory framework, the issues surrounding molecular imaging agents, and potential opportunities will allow the radiology community to more effectively collaborate with the FDA to address these regulatory barriers and ensure that the full potential of molecular imaging is realized.

Nuclear translocation of the SRF co-activator MAL in cortical neurons: role of RhoA signalling.

Although it is well established that RhoA signaling pathways play key roles in regulating neuronal morphology, their involvement in other aspects of neuronal function has received little attention. Recent studies have elucidated a novel intracellular signaling pathway used by RhoA to elicit activation of serum response factor (SRF)-mediated transcription. In this pathway, activation of RhoA triggers nuclear translocation of the SRF co-activator, megakaryocytic acute leukemia (MAL). In assessing whether RhoA regulates transcription in neurons via this pathway, we have found that a constitutively active form of Tech (transcript-enriched in cortex and hippocampus), a RhoA guanine nucleotide exchange factor (GEF) that is expressed in forebrain neurons, stimulates SRF reporter activity in extracts of primary cortical cultures and induces nuclear translocation of MAL in cortical neurons. Both of these responses appear to be mediated by Tech's activation of RhoA as they are not mimicked by a mutant Tech construct lacking RhoA GEF activity and are blocked by C3 transferase, a selective inhibitor of RhoA. Furthermore, Tech-induced increases in SRF activity are suppressed by a dominant negative MAL construct. These findings demonstrate that RhoA signaling pathways are able to regulate transcription in neurons by triggering translocation of the SRF co-activator MAL.