New Route to Nuclear Signaling

Science's STKE  17 Feb 2004:
Vol. 2004, Issue 220, pp. tw61-TW61
DOI: 10.1126/stke.2202004TW61

Miaczynska et al. identified a pathway involving an endosomal compartment containing the small guanosine triphosphatase (GTPase) Rab5 that linked signaling from the cell membrane to the nucleus. Although the endocytosis of plasma membrane receptors has traditionally been viewed as a mechanism for terminating signals, various lines of evidence suggest that endosomes may also fulfill a signaling function. Miaczynska et al. used mass spectrometry together with affinity chromatography to identify two proteins from HeLa cell extracts--APPL1 and APPL2 (for adaptor protein containing PH domain, PTB domain, and leucine zipper motif)--that specifically bound to activated (GTP-bound) Rab5 (which has been implicated in regulating endocytosis). APPL1 and APPL2 were localized in membranous structures found beneath the plasma membrane (where they colocalized with each other and with Rab5 but not with the canonical endosome marker EEA1) and in the nucleus. Treatment of cells with epidermal growth factor, some of which briefly localized to APPL-containing structures, or with H2O2 stimulated the release of APPL1 from these endosomes and its translocation to the nucleus. This release depended on GTP hydrolysis by Rab5. Immunoprecipitation of proteins from nuclear extracts as well as affinity chromatography indicated that APPL1 associated with components of the NuRD/MeCP1 nucleosome remodeling and histone deacetylase complex, which is involved in regulating chromatin structure and gene expression. Knockdown of APPL1 and APPL2 inhibited DNA synthesis and cell proliferation, and mutational analysis indicated that APPL1 binding to Rab5 was required for its functional effects. Thus, these data identify an endosomal compartment from which Rab5 and its effectors act to transmit extracellular signals to the cell nucleus.

M. Miaczynska, S. Christoforidis, A. Giner, A. Shevchenko, S. Uttenweiler-Joseph, B. Habermann, M. Wilm, R. G. Parton, M. Zerial, APPL proteins link Rab5 to nuclear signal transduction via an endosomal compartment. Cell 116, 445-456 (2004). [Online Journal]