Disease relevance of RAB4A

• In order to evaluate the role of Rab proteins in ENaC function, Rab4 wild-type (WT), the GTPase-deficient mutant Rab4Q67L, and the dominant negative GDP-locked mutant Rab4S22N were over-expressed in the colon cancer cell line, HT-29 and amiloride-sensitive currents were recorded [1].
• After global ischemia there was a marked increase in immunoreactivity of both endocytic markers, rabaptin-5 and rab4, in neurons, and to a lesser extent in glia compared to controls [2].
• Human rab4 and rab5 were expressed in chicken embryo fibroblasts using a Sindbis virus expression vector [3].
• Stimulation by HIV-1 of HRES-1/Rab4 expression and its regulation of CD4 recycling reveal novel coordinate interactions between an infectious retrovirus and the human genome [4].
• Regulation of CD4 Expression via Recycling by HRES-1/RAB4 Controls Susceptibility to HIV Infection [4].

High impact information on RAB4A

• Wild-type rab4 caused a redistribution of Tfn-R's from endosomes to the plasma membrane [5].
• To determine its role during endocytosis, we generated stable cell lines that overexpressed mutant or wild-type rab4 [5].
• We now present biochemical evidence for a mitosis-specific p34cdc2 phosphorylation of Rab1Ap and Rab4p [6].
• We also show that the distribution of Rab1Ap and Rab4p between cytosolic and membrane-bound forms is different in interphase and mitotic cells [6].
• In particular, detailed descriptions have emerged of the mechanisms that recruit integrins and growth factor receptors to Rab4- and Rab11-driven pathways [7].

Biological context of RAB4A

• RCP was therefore suggested to serve a dual function as Rab4 and Rab11 binding protein [8].
• The small GTPase Rab4 is involved in endocytosis through sorting and recycling early endosomes [9].
• The Rab4 specific residue His39 modulates the nucleotide binding pocket giving rise to a reduced rate for nucleotide hydrolysis and exchange [10].
• The study suggests that Rab4 regulates the channel through multiple mechanisms that include protein-protein interaction, GTP/GDP exchange, and channel protein trafficking [11].
• Biotinylation with cell impermeant NHS-Sulfo-SS-Biotin implies that Rab4 impairs CFTR expression at cell surface [11].

Anatomical context of RAB4A

• Rab4 regulates recycling from early endosomes [12].
• The enhanced cytosolic CFTR indicates that Rab4 expression restrains CFTR appearance at the cell membrane [11].
• Rab4 over-expression in HT-29 cells inhibits both basal and cAMP-stimulated CFTR-mediated currents [11].
• Finally, dephosphorylation and reassociation of soluble rab4 with membranes occurred upon exit of cells from mitosis [13].
• Thus, phosphorylation of Ser196 is directly responsible for the reversible translocation of rab4 into the cytosol of mitotic cells [13].

Associations of RAB4A with chemical compounds

• These data suggest that abnormal membrane recycling in NPFs results from specific inhibition of rab4 function by excess cholesterol in EEs [14].
• Mutation of Ser196 to glutamine or aspartic acid completely prevented rab4 phosphorylation in mitotic cells and also blocked its appearance in the cytosol [13].
• Taken together, our data provide evidence that Rabip4s, possibly via their interaction with Rab4, regulate integrin trafficking and are involved in the migration of NIH 3T3 fibroblasts [15].
• We propose that the subcellular localization of the protein is primarily driven by the RUN domain to endosomal microdomains characterized by Triton X-100 insolubility and that the FYVE domain and the Rab4-binding domain then allow for the recruitment of the protein to lipophilic microdomains enriched in phosphatidylinositol 3-phosphate [16].
• Furthermore, association of Rab4 with the latex bead-containing phagosomes was revealed by flow cytometry [17].

Physical interactions of RAB4A

• These effects depend on the ability of Rabenosyn-5 to interact with Rab4 [18].
• Distinct Rab-binding domains mediate the interaction of Rabaptin-5 with GTP-bound Rab4 and Rab5 [19].
• RCP interacts with Rab4 in addition to Rab11 [20].
• The pull-down and immunoprecipitation experiments suggest that Rab4 physically interacts with CFTR through protein-protein interaction [11].
• Instead, phosphorylated rab4 is in a complex with the peptidyl-prolyl isomerase Pin1 during mitosis, but not during interphase [21].

Enzymatic interactions of RAB4A

• We found a pronounced increase of the Rab4 soluble form and its soluble complexes with the tyrosine-phosphorylated GDI-2 [22].

Co-localisations of RAB4A

• We recently demonstrated that epitope-tagged Rab15 (HArab15) co-localizes with Rab4, -5, and -11 on early endosomal membranes in CHO cells (Zuk, P. A., and Elferink, L. A. (1999) J. Biol. Chem. 274, 22303-22312) [23].

Regulatory relationships of RAB4A

• CD2AP/CMS regulates endosome morphology and traffic to the degradative pathway through its interaction with Rab4 and c-Cbl [9].

Other interactions of RAB4A

• We investigated the role of the rab4 effector rabaptin-5alpha and its putative partner gamma(1)-adaptin in membrane recycling [12].
• We have identified a novel 80-kDa protein that interacts specifically with the GTP-bound conformation of Rab4, and subsequent work has shown that it also interacts strongly with Rab11 [24].
• Differentiation of MEG-01 cells induced by 100 nM 12-O-tetradecanoylphorbol-13-acetate revealed the considerable increases in mRNA expression of rap1B, rab3B, rab4, ram and ran whereas the levels of rap2B, rhoA and rac1 decreased [25].
• We propose that CD2AP/CMS, through interactions with Rab4 and c-Cbl, controls early endosome morphology and may play a role in traffic between early and late endosomes, and thus in the degradative pathway [9].
• To address the mechanisms that regulate communication between such domains, we searched for proteins that interact with both Rab5 and Rab4 [18].

Analytical, diagnostic and therapeutic context of RAB4A

• Active status of Rab4 was confirmed by GTP overlay assay, while its expression was verified by Western blotting [11].
• Confocal immunofluorescence microscopy showed that the early endosomal GTPases Rab4 and Rab5 both do not codistribute with Rab7 within the same cell [26].
• Peptide mapping of Rab4 was performed to take advantage of additional scissile bonds within Switch II to determine more precisely the limits of the nucleotide-dependent protease-accessible region [27].
• Confocal and electron microscopic immunocytochemistry revealed that rab4 colocalized with the actin terminal web and microvilli in the apical region of the exocrine acinar cells [28].
• Following high-speed centrifugation of postnuclear supernatants prepared from 1-day neonatal pancreatic homogenates, rab4 partitioned into a Triton X-100 insoluble particulate fraction and was partially solubilized upon extraction with 0.1 M Na2CO3, pH 11.5, or 1 M KCl, suggesting that rab4 was not an integral membrane protein [28].

References