Disease relevance of MLLT4

• Cloning of the ALL-1 fusion partner, the AF-6 gene, involved in acute myeloid leukemias with the t(6;11) chromosome translocation [1].
• AF6 gene on chromosome band 6q27 maps distal to the minimal region of deletion in epithelial ovarian cancer [2].
• Monitoring of minimal residual disease in patients with MLL-AF6-positive acute myeloid leukaemia by reverse transcriptase polymerase chain reaction [3].

High impact information on MLLT4

• To understand the molecular mechanism of the specific localization of l-afadin at ZA in epithelial cells and at cell-cell AJ in nonepithelial cells, we attempted here to identify an l-afadin-binding protein(s) and isolated a protein, named ponsin [4].
• The AF-6/afadin protein, which contains a single PDZ domain, forms a peripheral component of cell membranes at specialized sites of cell-cell junctions [5].
• The junction-associated protein AF-6 interacts and clusters with specific Eph receptor tyrosine kinases at specialized sites of cell-cell contact in the brain [5].
• Furthermore, AF-6 is a substrate for a subgroup of Eph receptors and phosphorylation of AF-6 is dependent on a functional kinase domain of the receptor [5].
• Immunohistochemical analysis in the adult rat brain reveals coclustering of AF-6 with Eph receptors at postsynaptic membrane sites of excitatory synapses in the hippocampus [5].

Biological context of MLLT4

• This localization is in part due to the interaction of the C-terminal part of these receptors (ended by the consensus sequence A/EXYV) and the PDZ domain of afadin [6].
• The disruption of cell-cell AJs in MDCK cells by culturing at a low Ca2+ concentration caused rapid endocytosis of cadherin, but not that of nectin or afadin [7].
• These results suggested that AF-6 could control integrin-mediated cell adhesion by regulating Rap1 activation through the recruitment of both SPA-1 and Rap1GTP via distinct domains [8].
• We have identified the PDZ domain protein AF-6 as an intracellular binding partner of the junctional adhesion molecule (JAM), an integral membrane protein located at cell contacts [9].
• Bcr increases the affinity of AF-6 to Ras, and a mutant of AF-6 that lacks a specific phosphorylation site for Bcr shows a reduced binding to Ras [10].

Anatomical context of MLLT4

• Afadin is an actin filament-binding protein which associates nectin with the actin cytoskeleton [7].
• Nectin-2 is a component of cell-cell adherens junctions and interacts with l-afadin, an F-actin-binding protein [11].
• Our results suggest that JAM can be recruited to intercellular junctions by its interaction with the PDZ domain-containing proteins AF-6 and possibly ZO-1 [9].
• Full-length mouse JAM co-distributed with endogenous AF-6 in human Caco-2 cells at sites of cell contact independent of whether adjacent cells expressed mouse JAM as an extracellular binding partner [9].
• AF-6 as well as ZO-1 could be coprecipitated with JAM from endothelial cell extracts, demonstrating the association of the endogenously expressed molecules in vivo [9].

Associations of MLLT4 with chemical compounds

• RYK, a catalytically inactive receptor tyrosine kinase, associates with EphB2 and EphB3 but does not interact with AF-6 [12].
• Mammalian Ras proteins associate with multiple effectors, including Raf, Ral guanine nucleotide dissociation stimulator, phosphoinositide 3-kinase and AF-6 [13].

Physical interactions of MLLT4

• In this report we demonstrate that the nectin3/PRR3 receptor carries the A/EXYV consensus sequence and interacts in vivo with both long and short isoforms of afadin [6].
• Overexpression of a truncated form of nectin-2 incapable of interacting with afadin failed to form cell-cell adhesion [14].
• We used the yeast two-hybrid system to identify novel Lmo2 interacting proteins and found that the AF6 protein binds to Lmo2 [15].
• In vitro binding studies using truncated fragments and their mutants suggested that SPA-1 was bound to the PDZ domain of AF-6 via probable internal PDZ ligand motif within the GAP-related domain [8].
• Chimeric MLL products with a Ras binding cytoplasmic protein AF6 involved in t(6;11) (q27;q23) leukemia localize in the nucleus [16].

Co-localisations of MLLT4

• Immunostaining analysis revealed that SPA-1 and RapV12 were co-localized with AF-6 at the cell attachment sites [8].

Regulatory relationships of MLLT4

• In vivo interaction of AF-6 with activated Ras and ZO-1 [17].

Other interactions of MLLT4

• These results suggest that the human nectin3/PRR3 is a new afadin-associated molecule [6].
• We show here that AF-6 does not bind to human RYK in vitro or in vivo [12].
• In the present study, we showed that SPA-1, a Rap1 GTPase-activating protein (GAP), was bound to a cytoskeleton-anchoring protein AF-6 [8].
• Afadin, which did not bind Rap1, was inactive in this capacity [18].
• SPA-1 and AF-6 were co-immunoprecipitated in the 293T cells transfected with both cDNAs as well as in normal thymocytes [8].
• This can be overcome by overexpression of CSK or strong activation of c-Src. c-Src is recruited by AF-6 to cell-cell contact sites, suggesting that c-Src is regulated by a PDZ protein in special cellular locations [19].

Analytical, diagnostic and therapeutic context of MLLT4

• Thereafter, cytogenetical analysis and reverse transcriptase polymerase chain reaction (RT-PCR) analysis of bone marrow showed t(6;11)(q27;q23) translocation and MLL/AF6 fusion products, respectively [20].
• Sequence analysis of the derivative chromosomes revealed that a 186-bp segment of MLL intron 6, downstream of the breakpoint, had been duplicated, inverted, and inserted between MLL and AF6 on the der(11) chromosome [21].
• The detailed genetic map of AF6 was determined by in situ chromosome hybridization and radiation hybrid mapping [22].
• In these five patients, the MLL-AF6 transcripts were detected in every sample tested after induction and consolidation chemotherapy [3].
• Monitoring minimal residual disease in patients with MLL-AF6 fusion transcript-positive acute myeloid leukemia following allogeneic bone marrow transplantation [23].

References