Disease relevance of Pcmt1

• The fatal seizure disorder in Pcmt1-/- mice can be mitigated but not eliminated by antiepileptic drugs [1].
• Mice lacking this enzyme (Pcmt1-/- mice) have elevated levels of damaged residues and die at a mean age of 42 days from massive tonic-clonic seizures [2].
• PIMT-deficient mice died from progressive epileptic seizures with grand mal and myoclonus between 4 and 12 weeks of age [3].
• The gene coding for prenylated-protein carboxyl methyltransferase (PPMT) of the protozoan parasite Trypanosoma brucei has been cloned and expressed in the baculovirus/Sf9 cell system [4].
• Methylation of 21-23 kD membrane proteins by a membrane-associated protein carboxyl methyltransferase in neuroblastoma cells. Increased methylation in differentiated cells [5].

High impact information on Pcmt1

• We conclude that methylation of modified proteins with isoaspartyl residues is essential for the maintenance of a mature CNS and that a deficiency in PIMT results in fatal progressive epilepsy in mice [3].
• The brains of PIMT-deficient mice started to enlarge after 4 weeks of age when the apical dendrites of pyramidal neurons in cerebral cortices showed aberrant arborizations with disorganized microtubules [3].
• PIMT knock-out (KO) mice exhibit brain enlargement and fatal epileptic seizures [6].
• We therefore studied the D/L ratio of aspartic acid at specific sites in histone H2B, a known target of PIMT in vivo [7].
• Because PIMT has numerous substrates in cells, these findings also suggest that D-aspartate may be more common in cellular proteins than hitherto imagined and that its occurrence, in some proteins at least, is independent of animal age [7].

Chemical compound and disease context of Pcmt1

• Previous studies have shown that mice deficient in the gene encoding this enzyme (Pcmt1-/-) accumulate damaged proteins, have altered levels of brain S-adenosylmethionine (AdoMet) and S-adenosylhomocysteine (AdoHcy), and suffer from epileptic seizures that result in death at an average age of about 42 days [8].

Biological context of Pcmt1

• Pcmt1-/- mice manifest two key phenotypes: a fatal seizure disorder and retarded growth [1].
• The higher number of granule cells was accompanied by a greater number of cells undergoing mitosis in the dentate gyrus, suggesting that an increase in neuronal cell proliferation occurs in this neurogenic zone of adult Pcmt1-/- mice [9].
• These observations, coupled with the fact that humans have polymorphisms in the pcmt gene, suggest that isoaspartyl self-proteins may alter the maintenance of peripheral immune tolerance [10].
• Two overlapping clones containing the entire 684-nucleotide (nt) sequence encoding murine protein beta-aspartate methyltransferase (EC 2.1.1.77) were isolated from a genomic library [11].
• Comparison of the genomic sequence information with the 3'-untranslated regions (UTRs) of two cDNA clones from a murine testis library indicated that PCMT mRNA precursors undergo alternative splicing [11].

Anatomical context of Pcmt1

• The concentration of damaged residues in heart, testis, and brain proteins in transgenic Pcmt1-/- mice initially increased with age but unexpectedly reached a plateau by 100 days of age [2].
• In addition, these levels appear to be most significantly altered in the hippocampus of the Pcmt1-/- mice [12].
• PCMT(-/-) CD4(+) T cells exhibit increased proliferation in response to mitogen and Ag receptor stimulation as compared with wild-type CD4(+) T cells [10].
• We show here that PIMT is upregulated in neurodegenerative neurons and colocalizes in neurofibrillary tangles (NFTs) in AD [13].
• We were able to show that pJP-A was the isomerized isoaspartyl form by demonstrating that pJP-A but not pJP-B was a substrate for the protein carboxyl methyltransferase enzyme (L-isoaspartyl/D-aspartyl protein methyltransferase; EC 2.1.1.77) purified from bovine erythrocytes [14].

Associations of Pcmt1 with chemical compounds

• Because changes in the AdoMet/AdoHcy ratio could potentially alter the overall excitatory state of the brain, this effect may play a role in the progressive epilepsy seen in the Pcmt1-/- mice [12].
• Recent studies have demonstrated that mice lacking protein L-isoaspartate (D-aspartate) O-methyltransferase (Pcmt1-/- mice) have alterations in the insulin-like growth factor-I (IGF-I) and insulin receptor pathways within the hippocampal formation as well as other brain regions [9].
• There were no significant differences in plasma insulin levels for adult Pcmt1-/- mice during glucose tolerance tests [15].
• Pcmt1-deficient mice present with abnormal AdoMet/AdoHcy homeostasis [16].
• To identify major targets of PIMT action we cultured rat PC12 cells with adenosine dialdehyde (AdOx), a methyltransferase inhibitor that promotes accumulation of isoAsp in vivo [17].

Other interactions of Pcmt1

• Examination of upstream elements of this pathway in the hippocampus revealed that Pcmt1-/- mice have increased activation of insulin-like growth factor-I (IGF-I) receptor and/or insulin receptor [15].
• Western blot analysis revealed an approximate 200% increase in insulin receptor protein levels and an approximate 50% increase in IGF-I receptor protein levels in the hippocampus of Pcmt1-/- mice [15].
• Here we show that components of this pathway, including Akt, GSK3beta and PDK-1, are more highly phosphorylated in the brains of Pcmt1-/- mice, particularly in cells of the hippocampus, in comparison with Pcmt1+/+ mice [15].
• On the accelerating rotorod, we found Pcmt1-/- mice actually perform significantly better than their heterozygous and wild-type littermates, a situation that has only been infrequently described in the literature and has not been described to date for epilepsy-prone mice [8].
• Interestingly, synapsin I, which was extensively modified posttranslationally in PIMT-deficient mice, was specifically repaired in a partially rescued, but symptom-improved, Tg line [18].

Analytical, diagnostic and therapeutic context of Pcmt1

• In addition, double immunofluorescence studies demonstrated that phosphorylated IGF-I/insulin receptors in the subgranular zone were localized on immature neurons, suggesting that the increased activation of one or both of these receptors in Pcmt1-/- mice could contribute to the growth and survival of these cells [9].
• Multiple PCMT mRNAs were detected on Northern blots of RNA extracted from murine brain, testis, liver and kidney [11].
• Partial nt sequence analysis of the two clones revealed that the protein carboxyl methyltransferase (PCMT)-encoding sequence is distributed among seven exons, ranging from 32 to 339 bp in length, within 25 kb of genomic DNA [11].
• The gene therapy presented in this report provided a better prognosis for the survival of PIMT-deficient mice than the previously reported anti-epileptic drug therapy [19].
• We have been particularly interested in this enzyme since addition of the compound CGP3466 to primary rat astroglia cell cultures resulted in an upregulation of Pimt at the mRNA level, as shown here by semi-quantitative RT-PCR [20].

References