Ras-related protein Rab35 is a member of the large Rab GTPase family. Rab35 is involved in many cellular functions, including endocytic recycling, cytokinesisis and endosomal trafficking []. It is one of several Rab proteins to be found to participate in the regulation of osteoclast cells in rats []. In addition, Rab35 has been identified as a protein that interacts with nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) in human cells. Overexpression of NPM-ALK is a key oncogenic event in some anaplastic large-cell lymphomas; since Rab35 interacts with NPM-ALK, it may provide a target for cancer treatments []. Rabs are regulated by GTPase activating proteins (GAPs), which interact with GTP-bound Rab and accelerate the hydrolysis of GTP to GDP. Guanine nucleotide exchange factors (GEFs) interact with GDP-bound Rabs to promote the formation of the GTP-bound state. Rabs are further regulated by guanine nucleotide dissociation inhibitors (GDIs), which facilitate Rab recycling by masking C-terminal lipid binding and promoting cytosolic localization. Most Rab GTPases contain a lipid modification site at the C terminus, with sequence motifs CC, CXC, or CCX. Lipid binding is essential for membrane attachment, a key feature of most Rab proteins [, ].
This entry includes proteins containing an N-terminal tripartite DENN domain, including DENND1A (also known as connecdenn 1), DENND1B (connecdenn 2) and DENND1C (connecdenn 3). These proteins act as guanine-nucleotide exchange factors for Rab35 through the DENN domain. Inactive GDP-bound RAB35 is converted into its active GTP-bound form by the exchange of GDP to GTP. The DENN domains of DENND1A and DENND1B, but not DENND1C, bind Rab35, indicating that binding and activation are separate. The C-termini of DENND1A, DENND1B and DENND1C differ significantly, but each binds to clathrin and to the clathrin adaptor AP-2. This is a means to regulate clathrin-mediated endocytosis of synaptic vesicles and exit from early endosomes [].
MICAL (molecule Interacting with CasL) family is a group of multifunctional proteins that contain the calponin homology (CH), a LIM and a coiled-coil (CC) domains []. They interact with receptors on the target cells, help recruiting other proteins, and promote the modulation of their activity with respect to the downstream events []. There is only one MICAL protein found in Drosophila [], while there are 5 MICAL (MICAL1/2/3, MICAL-like1/2) isoforms found in vertebrates []. Drosophila MICAL and vertebrate MICAL1/2/3 contain an extra N-terminal FAD (flavin adenine dinucleotide binding monooxygenase) domain, whose structure resembles that of a flavo-enzyme, p-hydroxybenzoate hydroxylase []. Drosophila MICAL has an NADPH-dependent actin depolymerising activity []. Vertebrate MICALs are also shown to be effectors of small Rab GTPases, which play important roles in vesicular trafficking []. MICAL-like protein 1 (MICAL-L1) interacts with small G proteins and regulates endocytic recycling of receptors [, ]. It forms a complex with Rab13 that regulates EGFR trafficking at late endocytic pathways []. MICAL-L1 also forms a complex with Arf6 that regulates Rab8a function. MICAL-L1 can be regulated by Rab35 [].MICAL-like protein 2 (MICAL-L2, also known as JRAB) interacts with Rab13 []and Rab8 to regulate the endocytic recycling of occludin, claudin and E-cadherin to the plasma membrane. It may thereby regulate the establishment of tight junctions and adherens junctions []. MICAL-L2/JRAB also regulates the reorganisation of the actin cytoskeleton through interactions with actinin-1, actinin-4, and filamentous actin [], and via filamins during cell spreading [].
