Members of the Kahn lab conduct basic research into the mechanisms of cell regulation by GTP binding proteins, particularly the Arf family of 21 kDa GTPases and their associated partners. The Arf family is comprised of both the six mammalian Arfs(1-6) and 22 Arf-like (Arl) proteins with more divergent functions and conservation in primary sequences. The two main areas of current research include the role of Arfs and Arf-dependent adaptors in regulation of protein export from the Golgi and the role of Arl2 and Arl3 in regulating mitochondria, microtubules, cilia, and cell division.

Arf1-6 are ubiquitous, essential proteins which function as regulators of membrane traffic at multiple locations but most prominently in budding of carriers from the TGN. We have developed siRNA reagents to specifically deplete cells of each of the Arfs in efforts to determine the levels of redundancy and roles of each Arf in membrane traffic. In a related project are examining the regulation of export from the Golgi of Alzheimer’s disease (AD)relevant proteins; including the amyloid precursor protein (APP), b-secretase (BACE1), γ-secretase, and LR11/SorLa. Together these studies are revealing new levels of complexity and regulation of cargo sorting and export at this critical step of membrane traffic. A molecular model for the regulation of AD-relevant protein traffic is expected to provide insights into the site and regulation of generation of the neurotoxic Ab peptides, and hopefully lead to novel targets for intervention in AD pathogenesis.

The second major project underway in our lab is the study of the Arl2 GTPase, which is present (i) in cytosol in an inactive form complexed with the tubulin co-chaperone Cofactor D and protein phosphatase PP2A, (ii) in mitochondria where it is predicted to bind BART and the adenine nucleotide translocase (ANT1) and impact ATP levels in cells, (iii) at centrosomes where it is implicated in regulation of the microtubule cytoskeleton, and (iv) in the nucleus. The closely related GTPase, Arl3, is also under study and overlaps with locations and binding partners with Arl2, though is also found in cilia, on the mitotic spindle and in midbodies. Knockdown of Arl3 results in failure in cytokinesis and increases in multinucleated cells. Because Arl2 and Arl3 are found in the earliest eukaryotes and have been very highly conserved throughout eukaryotic evolution we expect that a molecular understanding of their functions and mechanisms will bring new insights into energy metabolism, microtubule dynamics, and the integration of cell signaling between several essential cell processes that may be involved in one or more chronic diseases such as diabetes or cancer.

 

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