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1.  Germline Mutations in Mtap Cooperate with Myc to Accelerate Tumorigenesis in Mice 
PLoS ONE  2013;8(6):e67635.
Objective
The gene encoding the methionine salvage pathway methylthioadenosine phosphorylase (MTAP) is a tumor suppressor gene that is frequently inactivated in a wide variety of human cancers. In this study, we have examined if heterozygosity for a null mutation in Mtap (MtaplacZ) could accelerate tumorigenesis development in two different mouse cancer models, Eμ-myc transgenic and Pten+/−.
Methods
Mtap Eμ-myc and Mtap Pten mice were generated and tumor-free survival was monitored over time. Tumors were also examined for a variety of histological and protein markers. In addition, microarray analysis was performed on the livers of MtaplacZ/+ and Mtap+/+ mice.
Results
Survival in both models was significantly decreased in MtaplacZ/+ compared to Mtap+/+ mice. In Eµ-myc mice, Mtap mutations accelerated the formation of lymphomas from cells in the early pre-B stage, and these tumors tended to be of higher grade and have higher expression levels of ornithine decarboxylase compared to those observed in control Eµ-myc Mtap+/+ mice. Surprisingly, examination of Mtap status in lymphomas in Eµ-myc MtaplacZ/+ and Eµ-myc Mtap+/+ animals did not reveal significant differences in the frequency of loss of Mtap protein expression, despite having shorter latency times, suggesting that haploinsufficiency of Mtap may be playing a direct role in accelerating tumorigenesis. Consistent with this idea, microarray analysis on liver tissue from age and sex matched Mtap+/+ and MtaplacZ/+ animals found 363 transcripts whose expression changed at least 1.5-fold (P<0.01). Functional categorization of these genes reveals enrichments in several pathways involved in growth control and cancer.
Conclusion
Our findings show that germline inactivation of a single Mtap allele alters gene expression and enhances lymphomagenesis in Eµ-myc mice.
doi:10.1371/journal.pone.0067635
PMCID: PMC3694069  PMID: 23840755
2.  Chemical Genetic Screening for Compounds that Preferentially Inhibit Growth of Methylthioadenosine Phosphorylase (MTAP) Deficient Saccharomyces Cerevisiae 
Methylthioadenosine phosphorylase (MTAP), a key enzyme in the methionine salvage pathway, is inactivated in a variety of human cancers. Since all human tissues express MTAP, it would be of potential interest to identify compounds that selectively inhibit the growth of MTAP deficient cells. To determine if MTAP inactivation could be targeted, we have performed a differential chemical genetic screen in isogenic MTAP+ and MTAP− S. cerevisiae. A low molecular weight compound library containing 30,080 unique compounds was screened for those that selectively inhibit growth of MTAP− yeast using a differential growth assay. One compound, containing a 1,3,4-thiadiazine ring, repeatedly showed a differential dose response, with MTAP− cells exhibiting a four-fold shift in IC50 compared to MTAP+ cells. Several structurally related derivatives of this compound also showed enhanced growth inhibition in MTAP− yeast. These compounds were also examined for growth inhibition of isogenic MTAP+ and MTAP− HT1080 fibrosarcoma cells, and four of the five compounds exhibited evidence of modest, but significant, increased potency in MTAP− cells. In summary, these studies show the feasibility of differential growth screening technology and have identified a novel class of compounds that can preferentially inhibit growth of MTAP− cells.
doi:10.1177/1087057110386371
PMCID: PMC3019245  PMID: 21131597
Methionine Salvage Pathway; Drug screening; Yeast; Genetic-chemical interaction
3.  Mice Heterozygous for Germline Mutations in Methylthioadenosine Phosphorylase (MTAP) Die Prematurely of T-cell Lymphoma 
Cancer research  2009;69(14):5961-5969.
Large homozygous deletions of 9p21 that inactivate CDKN2A, ARF, and MTAP are common in a wide variety of human cancers. The role for CDKN2A and ARF in tumorigenesis is well established, but whether MTAP loss directly affects tumorigenesis is unclear. MTAP encodes the enzyme methylthioadenosine phosphorylase, a key enzyme in the methionine salvage pathway. To determine if loss of MTAP plays a functional role in tumorigenesis, we have created an MTAP-knockout mouse. Mice homozygous for a MTAP null allele (MtaplacZ) have an embryonic lethal phenotype dying around day 8 post-conception. Mtap/MtaplacZ heterozygotes are born at Mendelian frequencies and appear indistinguishable from wild-type mice during the first year of life, but they tend to die prematurely with a median survival of 585 days. Autopsies on these animals reveal that they have greatly enlarged spleens, altered thymic histology, and lymphocytic infiltration of their livers, consistent with lymphoma. Immunohistochemical staining and FACS analysis indicate that these lymphomas are primarily T-cell in origin. Lymphoma infiltrated tissues tend to have reduced levels of Mtap mRNA and MTAP protein, and unaltered levels of methyldeoxycytidine. These studies show that Mtap is a tumor suppressor gene independent of CDKN2A and ARF.
doi:10.1158/0008-5472.CAN-09-0145
PMCID: PMC2757012  PMID: 19567676
Cancer; Tumor Suppressor Gene; Methionine; Embryonic Lethal

Results 1-3 (3)