Disease relevance of AFF1

• The human AF4 (ALL-1 fused gene on chromosome 4) gene (4q11) is recurrently involved in reciprocal translocations to the MLL (mixed lineage leukemia) gene (11q23), correlated with high-risk acute lymphoblastic leukemia (ALL) in infants and early childhood [1].
• The AF4 protein interacts with the product of another gene, AF9, which is also fused to MLL in acute leukemias [2].
• Transfection of leukemic cells with MLL-AF4 siRNAs reduces leukemia-associated morbidity and mortality in SCID mice that received a xenotransplant, suggesting that MLL-AF4 depletion negatively affects leukemia-initiating cells [3].
• As concerning studies on minimal residual disease, data on PCR monitoring of the ALL1/AF4 fusion transcript, resulting from the t(4;11) translocation, show the clinical relevance of this molecular test in predicting outcome and, as a consequence, in designing individual post-remission therapies [4].
• A set of recombinant phage carrying genomic fragments for the coding region and flanking sequences of the AF-4 gene were isolated [5].

Psychiatry related information on AFF1

• However, Q-RT-PCR is more accurate in assessing the molecular response after induction treatment and could be more useful in clinical decision-making in ALL1-AF4-positive ALL patients [6].
• Members of the AF4/FMR2 family of nuclear proteins are involved in human diseases such as acute lymphoblastic leukemia and mental retardation [7].

High impact information on AFF1

• The gene is novel, expressed in adult brain and placenta, and shows similarity with another human protein, MLLT2, expressed from a gene at chromosome 4q21 involved in translocations found in acute lymphoblastic leukaemia (ALL) cells [8].
• We explored downstream target genes of the most prevalent MLL fusion protein, MLL-AF4 [9].
• MLL-AF4 binds to the CDKN1B promoter in vivo and regulates CDKN1B promoter activity [9].
• This finding may have implications in terms of leukemia stem cell resistance to chemotherapy in MLL-AF4 leukemias [9].
• We found that in the MLL-AF4-induced cell lines, the expression of the cyclin-dependent kinase inhibitor gene CDKN1B was dramatically changed at both the RNA and protein (p27kip1) levels [9].

Biological context of AFF1

• We cloned and sequenced cDNAs derived from transcripts of the AF-4 and AF-9 genes involved in the most common chromosome abnormalities, t(4:11)(q21:q23) and t(9:11)(p22:q23), respectively [10].
• To further evaluate the 4q21 gene and its role in t(4;11) acute leukemia, we have cloned a 38-kb genomic region and mapped exons of the AF-4 gene [11].
• We provide evidence that this peptide is able to inhibit the proliferation of leukemia cells with t(4;11) chromosomal translocations expressing MLL-AF4 fusion genes [2].
• The synthetic peptide PFWT disrupts AF4-AF9 protein complexes and induces apoptosis in t(4;11) leukemia cells [2].
• Overexpression of MLL-AF4 does not lead to increased proliferation in either cell line, but rather, cell growth was slowed compared with similar cell lines inducibly expressing truncated MLL [9].

Anatomical context of AFF1

• The AF-4 gene was expressed in all cell lines as a major and a minor transcript [11].
• B-cell development in the presence of the MLL/AF4 oncoprotein proceeds in the absence of HOX A7 and HOX A9 expression [12].
• We have previously established a novel MLL/AF4-positive cell line, B-lineage 3 (BLIN-3), which retains several features of normal B-lineage development (functional Ig gene rearrangement and apoptotic sensitivity to stromal cell withdrawal) not generally observed in infant ALL [12].
• No evidence for MLL/AF4 expression in normal cord blood samples [13].
• Young Mll-AF4 mice had lymphoid and myeloid deregulation manifest by increased lymphoid and myeloid cells in hematopoietic organs [14].

Associations of AFF1 with chemical compounds

• FEL contains guanosine triphosphate-binding and nuclear localization consensus sequences and uses one of two possible 5' exons encoding the first 12 or 5 amino acids [15].
• By varying the concentration of tetracycline in growth media, we found that increasing levels of MLL-AF4 expression result in a progressive decrease in growth rate and fraction of S phase cells, paralleled by an increase in percentage of cells expressing CD11b [16].
• Cleavage of DNA substrates containing the normal homologues of the MLL and AF-4 translocation breakpoints was examined in vitro upon incubation with human DNA topoisomerase IIalpha and etoposide, etoposide catechol, etoposide quinone, or dactinomycin [17].
• The expression level of MLL-AF4 fusion protein was not reduced by 17-AAG in human leukemia cells [18].
• An H. pylori VacA-deficient mutant, AF4(vacA::kan), was cultured in significantly lower numbers from AGS cells after 24 h incubation with gentamicin added to the culture medium than were the type I wild-type strain AF4 (P<0.03) and an isogenic cagA mutant (P<0.01) [19].

Physical interactions of AFF1

• In two-hybrid studies, ENL interacted with AF4 and AF5q31 as well as with a fragment of AF10 [20].

Other interactions of AFF1

• Interaction of AF4 wild-type and AF4.MLL fusion protein with SIAH proteins: indication for t(4;11) pathobiology [1]?
• Expression of the AF-4 gene was studied in a total of 28 various nonhematopoietic, hematopoietic, and t(4;11) leukemic cell lines [11].
• To explore whether CDKN1B might be a direct target of MLL and of MLL-AF4, we used chromatin immunoprecipitation (ChIP) assays and luciferase reporter gene assays [9].
• RESULTS: In all cell lines, the ENL gene is significantly closer to the MLL gene than the AF4 gene (with P value < 0.0001) [21].
• The LAF4 gene was identified previously by its high sequence homology to the AF4 protein and encodes a protein of 1,227 amino acids [22].

Analytical, diagnostic and therapeutic context of AFF1

• Using primer sets derived from ALL-1 and AF4 cDNAs by reverse transcription-polymerase chain reaction (RT-PCR), we were able to amplify the breakpoint sites of the fusion transcript of all 15 ALL cases with karyotypic or molecular evidence of the t(4;11) [23].
• Using Western blotting analysis, we demonstrated that the AF4 gene encodes proteins with apparent molecular weight of 125 and 145 kD [24].
• A 45-kD protein coprecipitated with AF4 protein in immunoprecipitation [24].
• ALL1 gene breakpoint distribution was determined by Southern blot hybridization and/or reverse transcription-PCR of the ALL1/AF4 fusion cDNA in 70 patients [25].
• We now use microarray analysis to identify patterns of gene expression in BLIN-3 that may modulate MLL/AF4 oncogenesis and contribute to the retention of normal B-lineage developmental characteristics [12].

References