Faculty Bibliography

Background: Most skin cancer-related deaths are due to malignant melanoma. Risk assessment criteria for melanoma currently include skin phenotype, family and sun exposure history, factors that are subject to observer and recall bias. Genetic markers of susceptibility have been identified in association studies; however little progress has been made in developing them to improve screening and identification of individuals at risk of melanoma. Tyrosinase (TYR), a known susceptibility gene and a determinant of skin pigmentation, was thus investigated further to characterize its association with melanoma susceptibility and to identify markers which can be used in a risk assessment model. Methods: The cohort consisted of 326 individuals diagnosed with melanoma and 400 control subjects. TYR was interrogated using fifteen tag single nucleotide polymorphisms (SNPs) spanning the gene and statistical association tests performed. Additionally, ancestry informative markers were utilized to correct for population genetic sub-structure. Haplotype analysis was performed to determine if specific regions of the gene contributed more significantly to susceptibility. Coding regions of the gene are currently being sequenced and identified variants will be tested for impact on enzymatic function. Results: Of the 15 SNPs, 8 were associated with melanoma; 4 with decreased risk (Odds ratios 0.41-0.71) and 4 with increased risk (Odds ratios 1.43-1.96). SNPs localized to 2 regions of the gene (spanning exon 1 to intron 2 and intron 3 to 4) with markers of increased as well as decreased susceptibility present in both areas. With the exception of one coding region variant, SNPs were localized to introns. Conclusions: SNPs localized to TYR may serve as useful biomarkers for determining susceptibility to melanoma. We are currently sequencing the gene in our population in order to identify additional and potentially more potent markers of melanoma susceptibility. Coding region variants are being characterized for their effect on protein stability and enzyme activity such that functional active variants (most likely to affect susceptibility to melanoma) can be identified and assessed for their utility in melanoma risk assessment

Background/Aims: Patients with myelofibrosis have increased risk of bleeding and thrombosis. Increased numbers of platelet microparticles (PMP) and/or pathological platelet-neutrophil interactions has been suggested to underlie this trait. Megakaryocytes from patients, as well as from mice expressing low levels of Gata1(the Gata1low model of myelofibrosis) is characterized by an abnormal localization of P-selectin (P-sel). Whether these mice also develop thrombosis is not known. Aims: The aim of this study was to determine whether Gata1low mice develop thrombosis with age and, in this case, the role played by P-sel. Materials and methods: Gata1low mice were crossed with P-selnull mice according to standard protocols and Gata1lowP-selWT, Gata1lowP-selnull and Gata1WTPselnull or Gata1WTP-selWT littermates obtained. Blood platelet counts (ptl) and PMP counts were compared among the four experimental groups (Table). The presence of thrombosis was determined according to standard histological criteria. Results: Gata1WT mice had significantly greater platelet levels than Gata1low mice regardless of P-sel (Wilcoxon rank test, p <=0.0001). PMP were found to be reduced in Gata1low mice compared to Gata1WT littermates (Table I). Gata1WTP-selnull and Gata1low/P-selnull littermates had also reduced numbers of PMP. P-sel was only expressed by PMP from Gata1WTP-selWT mice. Thrombosis was only found in adult (5-9 months) and old (10-16 months) Gata1lowP-selWT mice. The majority of the thrombi were found in adult mice (67% vs 33% of organs affected). Conclusions: The maturation defect induced in megakaryocytes by the Gata1low mutation leads to a pro-thrombotic state detectable from 5 months of age. The presence of the P-selnull mutation rescues the thrombotic phenotype but not the ptl or PMP deficiency induced by the Gata1low mutation. Thus, abnormal P-sel localization, rather than altered PMP numbers, appears to be responsible for the thrombogenicity induced by the Gata1low mutation. These results suggest P-sel as possible target for therapeutic prevention of thrombosis in PMF

OBJECTIVE: JAK2V617F occurs in approximately 93% of patients with polycythemia vera and approximately 50% of patients with either primary myelofibrosis or essential thrombocythemia. Chromosomal abnormalities are detected in 50% of patients with primary myelofibrosis, 29% with polycythemia vera, and 8% to 10% with essential thrombocythemia. The relationship between the presence of such chromosomal abnormalities and the JAK2V617 allele burden, and the role that each of these genetic events play in the origins and progression of the myeloproliferative neoplasms (MPNs), remain unclear. MATERIALS AND METHODS: Individual hematopoietic colonies were assayed in vitro from the CD34(+) cells of six JAK2V617F-positive MPN patients with marker chromosomal abnormalities. Colonies were simultaneously analyzed for JAK2 genotype and chromosomal abnormalities. RESULTS: Among the 248 colonies assayed from cultures containing 500 CD34(+) cells, chromosomal abnormalities were detected in 5% of colonies with wild-type JAK2, 32% of JAK2V617F heterozygous colonies and 56% of JAK2V617F homozygous colonies. Overall, 92% of chromosomally abnormal colonies were also JAK2V617F homozygous. Although 54 colonies contained wild-type JAK2 exclusively, 4 of these colonies were characterized by chromosomal abnormalities. CONCLUSION: This study indicates that MPN hematopoietic progenitor cells do not necessarily always acquire genetic events in the same sequence. (Chromosomally abnormal progenitor cells are closely associated with JAK2V617F homozygosity; p=0.0001.). Chromosomal abnormalities such as +8, +9 can occasionally precede acquisition of JAK2V617F. These findings support the existence of earlier genetic events that precede JAK2V617F or cytogenetic abnormalities in MPN hematopoietic progenitor cells

Inflammatory breast cancer (IBC) is the most lethal form of primary breast cancer. IBC lethality derives from generation of tumour emboli, which are non-adherent cell clusters that rapidly spread by a form of continuous invasion known as passive metastasis. In most cancers, expression of E-cadherin, an epithelial marker, is indicative of low metastatic potential. In IBC, E-cadherin is overexpressed and supports formation of tumour emboli by promoting tumour cell interactions rather than adherence to stroma. E-cadherin, a surface component of adherens junctions, is anchored by interaction with p120 catenin (p120). We show that the unique pathogenic properties of IBC result in part from overexpression of the translation initiation factor eIF4GI in most IBCs. eIF4GI reprograms the protein synthetic machinery for increased translation of mRNAs with internal ribosome entry sites (IRESs) that promote IBC tumour cell survival and formation of tumour emboli. Overexpression of eIF4GI promotes formation of IBC tumour emboli by enhancing translation of IRES-containing p120 mRNAs. These findings provide a new understanding of translational control in the development of advanced breast cancer