PACSIN family members regulate intracellular vesicle trafficking via their ability to regulate cytoskeletal rearrangement. These processes are known to be involved in trafficking of GLUT1 and GLUT4 in adipocytes. In this study PACSIN3 was observed to be the only PACSIN isoform that increases in expression during 3T3-L1 adipocyte differentiation. Overexpression of PACSIN3 in 3T3-L1 adipocytes caused an elevation of glucose uptake. Subcellular fractionation revealed that PACSIN3 overexpression elevated GLUT1 plasma membrane localization without effecting GLUT4 distribution. In agreement with this result, examination of GLUT exofacial presentation at the cell surface by photoaffinity labeling revealed significantly increased GLUT1, but not GLUT4, after overexpression of PACSIN3. These results establish a role for PACSIN3 in regulating glucose uptake in adipocytes via its preferential participation in GLUT1 trafficking. They are consistent with the proposal, which is supported by a recent study, that GLUT1, but not GLUT4, is predominantly endocytosed via the coated pit pathway in unstimulated 3T3-L1 adipocytes.
Keywordsadipocyte; endocytosis; GLUT1; GLUT4; PACSIN3; membrane trafficking; syndapin The need to transport glucose from outside to inside the cell is a fundamental feature of cellular survival and growth. In mammals glucose transport of the facilitated diffusion type is mediated by a group of transporters known as the GLUT family (SLC2A gene symbol). The GLUT's comprise a 13-member family of 12-trans-membrane spanning 50-60 kD proteins [1]. Among these, GLUT1 and GLUT4 are of central relevance to peripheral glucose disposal and have been extensively studied. Nevertheless, the mechanisms involved in controlling the trafficking of GLUT1 and GLUT4 to and from the plasma membrane, and the differences between the trafficking of the two GLUT's, are not completely understood [2,3]. It is possible that proteins involved in integrating cytoskeletal rearrangements with membrane trafficking participate in these mechanisms. Recent studies have identified adaptor proteins that do coordinate membrane trafficking events with alterations in the cytoskeleton. Major examples are the amphiphysin, cortactin, endophilin, intersectin and syndapin/PACSIN families [4][5][6][7]. These proteins contain multiple protein-protein interaction domains, which allow them to *Address correspondence to William Roach at present address: Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755-3844. william.roach@dartmouth.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. In thi...