Disease relevance of MAP1B

• Postmortem changes in the levels and localization of microtubule-associated proteins (tau, MAP2 and MAP1B) in the rat and human hippocampus [1].
• Focal cerebral ischemia, produced by reversible occlusion of the right middle cerebral artery, resulted in a large decrease in the expression of both MAP1B and MAP2 in the infarct core at the messenger ribonucleic acid and protein levels [2].
• MAP1B in AEFs and membrane fractions from cultured dorsal root ganglion neurons (DRGNs) remains membrane-associated following high-salt washes and contains sialic acid [3].
• Mapping of human microtubule-associated protein 1B in proximity to the spinal muscular atrophy locus at 5q13 [4].
• Immunohistochemical expression of microtubule-associated protein 5 (MAP5) in glial cells in multiple system atrophy [5].

Psychiatry related information on MAP1B

• Immunochemical evidence that fragments of phosphorylated MAP5 (MAP1B) are bound to neurofibrillary tangles in Alzheimer's disease [6].

High impact information on MAP1B

• The protein MAP-1B links GABA(C) receptors to the cytoskeleton at retinal synapses [7].
• Furthermore, GABA(C) receptors and MAP-1B co-localize at postsynaptic sites on bipolar cell axon terminals [7].
• Recognized now as one of the most abundant axonal microtubule-associated proteins, a convergence of evidence implicates an overlapping in vivo role of tau with other axonal microtubule-associated proteins (e.g. MAP1B) in establishing microtubule stability, axon elongation and axonal structure [8].
• The interaction of MAG with MAP1B is relevant to the known role of MAG in affecting the cytoskeletal structure and stability of myelinated axons [9].
• In addition, expression of the phosphorylated isoform of MAP1B was increased significantly when DRGNs were cocultured with MAG-transfected COS cells [9].

Chemical compound and disease context of MAP1B

• Interestingly, lithium, which is a potent inhibitor of glycogen synthase kinase 3, suppresses this mode of MAP1B phosphorylation in differentiated neuroblastoma cells and cerebellar granule neurons [10].

Biological context of MAP1B

• Binding sites for a MAG-Fc chimera on DRGNs colocalized with MAP1B on neuronal varicosities, and MAG and MAP1B also colocalized in the periaxonal region of myelinated axons [9].
• The gene includes seven exons, and the third exon contains sequence not represented in mouse or rat MAP1B [11].
• The exon/intron organization underlying the alternative transcripts and the N-terminal amino acid sequence of the putative truncated MAP1B isoforms resemble those of MAP1A, providing further evidence for an evolutionary relationship [12].
• Moreover, we show that overexpression of MAP1B in wild-type cortical neurons leads to cell death characteristic of GAN-null neurons, whereas reducing MAP1B levels significantly improves the survival rate of null neurons [13].
• Mammalian genomes usually contain three family members, MAP1A, MAP1B and a shorter, more recently identified gene called MAP1S [14].

Anatomical context of MAP1B

• The expression of some MAP1B as a neuronal plasma membrane glycoprotein (Tanner, S.L., R. Franzen, H. Jaffe, and R.H. Quarles. 2000. J. Neurochem. 75:553-562.), further documented here by its immunostaining without cell permeabilization, is consistent with it being a binding partner for MAG on the axonal surface [9].
• C19ORF5 is a sequence homologue of microtubule-associated proteins MAP1A/MAP1B of unknown function, except for its association with mitochondria-associated proteins and the paclitaxel-like microtubule stabilizer and candidate tumor suppressor RASSF1A [15].
• MAP2 and MAP1B also accumulated in neuronal cell bodies prior to a loss of immunostaining in some regions, notably subiculum [1].
• Microtubule-associated proteins 1A (MAP1A) and MAP1B are abundant neuronal MAPs thought to be involved in neurite formation and stabilization [16].
• Contact with astroglial membranes induces axonal and dendritic growth of human CNS model neurons and affects the distribution of the growth-associated proteins MAP1B and GAP43 [17].

Associations of MAP1B with chemical compounds

• Consistently with this hypothesis, a major pool of MAP1B HC is rapidly degraded after blocking protein synthesis with cycloheximide, whereas LC1 levels remain constant even after 24 hr of cycloheximide treatment [18].
• Furthermore, the endogenous degradation of MAPs in neonate brain homogenates was calcium-dependent and inhibited by leupeptin, and the pattern of degradation products for MAP1B and MAP2 was similar to that of calpain-mediated proteolysis [19].
• Distinct from all other MAPs, the MAP1B light chain-induced formation of stable but apparently flexible microtubules resistant to the effects of nocodazole and taxol [20].
• Betamethasone exposure resulted in decreased immunoreactivity (IR) of MAP1B by 34.3 % and MAP2abc by 34.1 % (P < 0.05) [21].
• Furthermore, MAP1B in intact DRGNs is readily degraded by extracellular trypsin and is labeled by the cell surface probe sulfosuccinimidobiotin [3].

Physical interactions of MAP1B

• C19ORF5 is a homologue of microtubule-associated protein MAP1B that interacts with natural paclitaxel-like microtubule stabilizer and candidate tumor suppressor RASSF1A [22].
• MAP-1B also bound in vitro assembled alpha-synuclein fibrils [23].
• Diminished protein levels of the microtubule-associated protein MAP1B and increased levels of the GTP-binding protein RND2 were confirmed in the developing cortex in vivo and in primary hippocampal neurons in vitro [24].
• In addition, we found posttranscriptional regulation of MAP1B mRNA by the selective RNA-binding protein QKI in oligodendroglia [25].
• This suggests that SCG10 is more potent to destabilize microtubules than MAP1B to rescue them [26].

Regulatory relationships of MAP1B

• Furthermore, forced expression of exogenous QKI was sufficient for promoting MAP1B expression [25].

Other interactions of MAP1B

• Microtubule-associated protein 1B: a neuronal binding partner for myelin-associated glycoprotein [9].
• Immunoblots confirmed a loss of MAP2 and MAP1B within a few hours after death [1].
• The amino acid sequence of VCY2IP-1 shows 59.3% and 41.9% homology to two human microtubule-associated proteins (MAPs), MAP1B and MAP1A, respectively [27].
• The results, together with the recent finding of an interaction between gigaxonin and MAP1B, a MT associated protein, suggests that gigaxonin plays an important role in the crosstalk between the IF and MT networks [28].
• Consistent with this, we isolated and partially characterized a multiprotein complex from the hippocampus of patients with AD that contains phosphorylated MAP1B, collapsin-response mediator protein 2 (CRMP-2), Plexins A1 and A2, and a processed form of Sema3A [29].

Analytical, diagnostic and therapeutic context of MAP1B

• MAP1B heavy chain (HC) and light chain (LC1), as well as the light chain of MAP1A (LC2), were prepared in purified form for use as standards and/or immunogens for generation of antibodies for immunoblotting [18].
• In situ hybridization with MAP1B antisense riboprobe showed markedly increased hybridization signal intensities in the large neurons, whereas neurons in the normal-appearing cortex and most of the normal-sized neurons in the dysplastic cortex had faint signals [30].
• By immunoelectron microscopy, the products of the reaction with the anti-S 100 antibody appeared as heterogeneous granular deposits and with the antibody to MAP 1B they were randomly scattered throughout the astrocytic inclusions [31].
• Here we have analyzed the effects of the MAP1B light chain in the absence or presence of the heavy chain by immunofluorescence microscopy of transiently transfected cells [20].
• Confirmation of induced expression of MAP1B mRNA was obtained by PCR with specific primers and by immunocytochemical analysis in cultured RPE cells and in surgically removed epiretinal membranes from patients with proliferative vitreoretinopathy [32].

References