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Vol. 17, Issue 5, 2223-2235, May 2006

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Factors Controlling Fibroblast Growth Factor Receptor-1's Cytoplasmic Trafficking and Its Regulation as Revealed by FRAP Analysis

Star M. Dunham-Ems ^* , Haridas E. Pudavar , Jason M. Myers ^*, Pamela A. Maher , Paras N. Prasad , and Michal K. Stachowiak ^* 

^* Molecular and Structural Neurobiology and Gene Therapy Program, Department of Pathology and Anatomical Sciences, State University of New York at Buffalo, Buffalo, NY 14214; Institute for Lasers, Photonics, and BioPhotonics, Department of Chemistry, State University of New York at Buffalo, Buffalo NY 14260; and The Salk Institute, La Jolla, CA 92037

Submitted August 11, 2005; Revised February 3, 2006; Accepted February 8, 2006
Monitoring Editor: Suzanne Pfeffer

Biochemical and microscopic studies have indicated that FGFR1 is a transmembrane and soluble protein present in the cytosol and nucleus. How FGFR1 enters the cytosol and subsequently the nucleus to control cell development and associated gene activities has become a compelling question. Analyses of protein synthesis, cytoplasmic subcompartmental distribution and movement of FGFR1-EGFP and FGFR1 mutants showed that FGFR1 exists as three separate populations (a) a newly synthesized, highly mobile, nonglycosylated, cytosolic receptor that is depleted by brefeldin A and resides outside the ER-Golgi lumen, (b) a slowly diffusing membrane receptor population, and (c) an immobile membrane pool increased by brefeldin A. RSK1 increases the highly mobile cytosolic FGFR1 population and its overall diffusion rate leading to increased FGFR1 nuclear accumulation, which coaccumulates with RSK1. A model is proposed in which newly synthesized FGFR1 can enter the (a) "nuclear pathway," where the nonglycosylated receptor is extruded from the pre-Golgi producing highly mobile cytosolic receptor molecules that rapidly accumulate in the nucleus or (b) "membrane pathway," in which FGFR1 is processed through the Golgi, where its movement is spatially restricted to trans-Golgi membranes with limited lateral mobility. Entrance into the nuclear pathway is favored by FGFR1's interaction with kinase active RSK1.

Abbreviations used: AII, angiotensin II; BAMC, bovine adrenal medullary cells; BFA, brefeldin A; BMP7, bone morphogenetic protein-7; EGFR1, epidermal growth factor receptor 1; ER, endoplasmic reticulum; FGF, fibroblast growth factor; FGFR1, FGF receptor-1; FRAP, fluorescent recovery after photobleaching; GFP, green fluorescent protein; EGFP, enhanced GFP; SP, signal peptide; NLS, nuclear localization signal; PI3K, phosphoinositol 3-kinase; RSK1, p90 ribosomal S6 kinase-1; SP, signal peptide; SRP, signal-recognition particle; TK, tyrosine kinase; TMD transmembrane domain.

Address correspondence to: M. K. Stachowiak (mks4{at}buffalo.edu).

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