The function of the dopamine transporter (DAT) to terminate dopamine neurotransmission is regulated by endocytic trafficking of DAT. To elucidate the mechanisms of DAT endocytosis, we generated a fully functional mutant of the human DAT in which a hemagglutinin epitope (HA) was incorporated into the second extracellular loop. The endocytosis assay, based on the uptake of an HA antibody, was designed to study constitutive-and protein kinase C (PKC)-dependent internalization of HA-DAT expressed in non-neuronal cells and rat dopaminergic neurons. Large-scale RNA interference analysis of PKC-dependent endocytosis of HA-DAT revealed the essential and specific role of an E3 ubiquitin ligase, Nedd4 -2 (neural precursor cell expressed, developmentally downregulated 4 -2), as well as the involvement of adaptor proteins present in clathrin-coated pits, such as epsin, Eps15 (epidermal growth factor pathway substrate clone 15), and Eps15R (Eps15-related protein). Depletion of Nedd4 -2 resulted in a dramatic reduction of PKC-dependent ubiquitination of DAT. Endogenous Nedd4 -2, epsin, and Eps15 were coimmunoprecipitated with heterologously expressed human HA-DAT and endogenous DAT isolated from rat striatum. A new mechanistic model of DAT endocytosis is proposed whereby the PKC-induced ubiquitination of DAT mediated by Nedd4 -2 leads to interaction of DAT with adaptor proteins in coated pits and acceleration of DAT endocytosis.

Despite commendable progress in the prevention, detection, and treatment of a wide variety of solid tumor types, oral squamous cell carcinoma (OSCC) remains a significant health burden across the globe. OSCC carcinogenesis involves accumulation of genetic alterations that coincide with the multistep malignant transformation of normal oral epithelium. OSCC is often first diagnosed at late stages of the disease (advanced regional disease and/or metastasis). Delayed diagnosis precludes successful treatment and favorable outcomes. In clinical practice, opportunities exist to identify patients with oral potentially malignant disorders (OPMDs), which precede the development of cancer. This review addresses the current status of laboratory and clinical research on OPMDs, with emphasis on leukoplakia and erythroplakia. OSF is also presented, though there is a paucity of published studies on this disorder. We focus on findings that could translate into earlier diagnosis and more efficacious treatment of those lesions with significant malignant potential. We explore how markers of OPMD malignant transformation might be implemented into current diagnostic practice to help clinicians objectively stratify patients into treatment/follow-up groups according to relative risk. We provide an overview of recently concluded and ongoing OPMD chemoprevention trials. We describe laboratory OPMD models that can be used to not only to reveal the genetic and molecular intricacies of oral cancer but also to develop novel screening methods and therapeutic approaches. Finally, we call for targeted screening programs of at-risk populations in order to facilitate diagnosis and treatment of OPMD and early OSCC.Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide, with 600,000 new cases reported annually. 1,2 Approximately half of these cases present as squamous cell carcinoma on the lip or within the oral cavity. 3 While the detection and treatment of most malignancies has improved over the last several decades, the prognosis associated with oral squamous cell carcinoma (OSCC) has remained unchanged. [4][5][6] As a result, more than 120,000 deaths can be attributed to OSCC per annum. 7 Oral cancer does not currently satisfy criteria for a screenable disease, 8 however, theory 9 suggests that most cases are preceded by asymptomatic clinical lesions collectively referred to as oral potentially malignant disorders (OPMDs). 10 Herein, we review basic and clinical research on OPMDs and suggest possible approaches to effectively address this public health burden. Particular attention is placed on how understanding OPMD might translate into earlier diagnosis and more efficacious treatment. Nomenclature and EpidemiologyThere are several OPMDs that precede the development of OSCC. Those most commonly encountered are erythroplakia