An integrative gene expression signature analysis identifies CMS4 KRAS-mutated colorectal cancers sensitive to combined MEK and SRC targeted therapy.

BACKGROUND: Over half of colorectal cancers (CRCs) are hard-wired to RAS/RAF/MEK/ERK pathway oncogenic signaling. However, the promise of targeted therapeutic inhibitors, has been tempered by disappointing clinical activity, likely due to complex resistance mechanisms that are not well understood. This study aims to investigate MEK inhibitor-associated resistance signaling and identify subpopulation(s) of CRC patients who may be sensitive to biomarker-driven drug combination(s). METHODS: We classified 2250 primary and metastatic human CRC tumors by consensus molecular subtypes (CMS). For each tumor, we generated multiple gene expression signature scores measuring MEK pathway activation, MEKi "bypass" resistance, SRC activation, dasatinib sensitivity, EMT, PC1, Hu-Lgr5-ISC, Hu-EphB2-ISC, Hu-Late TA, Hu-Proliferation, and WNT activity. We carried out correlation, survival and other bioinformatic analyses. Validation analyses were performed in two independent publicly available CRC tumor datasets (n = 585 and n = 677) and a CRC cell line dataset (n = 154). RESULTS: Here we report a central role of SRC in mediating "bypass"-resistance to MEK inhibition (MEKi), primarily in cancer stem cells (CSCs). Our integrated and comprehensive gene expression signature analyses in 2250 CRC tumors reveal that MEKi-resistance is strikingly-correlated with SRC activation (Spearman P < 10-320), which is similarly associated with EMT (epithelial to mesenchymal transition), regional metastasis and disease recurrence with poor prognosis. Deeper analysis shows that both MEKi-resistance and SRC activation are preferentially associated with a mesenchymal CSC phenotype. This association is validated in additional independent CRC tumor and cell lines datasets. The CMS classification analysis demonstrates the strikingly-distinct associations of CMS1-4 subtypes with the MEKi-resistance and SRC activation. Importantly, MEKi + SRCi sensitivities are predicted to occur predominantly in the KRAS mutant, mesenchymal CSC-like CMS4 CRCs. CONCLUSIONS: Large human tumor gene expression datasets representing CRC heterogeneity can provide deep biological insights heretofore not possible with cell line models, suggesting novel repurposed drug combinations. We identified SRC as a common targetable node--an Achilles' heel--in MEKi-targeted therapy-associated resistance in mesenchymal stem-like CRCs, which may help development of a biomarker-driven drug combination (MEKi + SRCi) to treat problematic subpopulations of CRC.

Case series: CTLA4-IgG1 therapy in minimal change disease and focal segmental glomerulosclerosis.

BACKGROUND: Minimal Change Disease (MCD) in relapse is associated with increased podocyte CD80 expression and elevated urinary CD80 excretion, whereas focal segmental glomerulosclerosis (FSGS) has mild or absent CD80 podocyte expression and normal urinary CD80 excretion. METHODS: One patient with MCD, one patient with primary FSGS and three patients with recurrent FSGS after transplantation received CD80 blocking antibodies (abatacept or belatacept). Urinary CD80 and CTLA-4 levels were measured by ELISA. Glomeruli were stained for CD80. RESULTS: After abatacept therapy, urinary CD80 became undetectable with a concomitant transient resolution of proteinuria in the MCD patient. In contrast, proteinuria remained unchanged after abatacept or belatacept therapy in the one patient with primary FSGS and in two of the three patients with recurrent FSGS despite the presence of mild CD80 glomerular expression but normal urinary CD80 excretion. The third patient with recurrent FSGS after transplantation had elevated urinary CD80 excretion immediately after surgery which fell spontaneously before the initiation of abatacept therapy; after abatacept therapy, his proteinuria remained unchanged for 5 days despite normal urinary CD80 excretion. CONCLUSION: These observations are consistent with a role of podocyte CD80 in the development of proteinuria in MCD. In contrast, CD80 may not play a role in recurrent FSGS since the urinary CD80 of our three patients with recurrent FSGS was only increased transiently after surgery and normalization of urinary CD80 did not result in resolution of proteinuria.

Minimal change disease: a dysregulation of the podocyte CD80-CTLA-4 axis?

BACKGROUND: Minimal Change Disease (MCD) is associated with CD80 expression in podocytes and elevated urinary CD80 excretion during active renal disease. We have evaluated the urinary excretion of CTLA-4 and CD80 during different stages of the nephrotic syndrome in patients with MCD to test the hypothesis that persistent increased urinary CD80 excretion in patients with MCD in relapse is due to an ineffectual CTLA-4 response of the host to curtail the activation of CD80. METHODS: Thirty-two children with biopsy-proven MCD were studied during relapse and/or remission. Eleven healthy subjects served as controls. RESULTS: Urinary CD80 excretion was significantly increased in MCD patients in relapse relative to that in MCD patients in remission (p < 0.001) and controls (p < 0.001). Although urinary CTLA-4 excretion was higher in MCD patients in relapse than in MCD patients in remission (p = 0.01) and controls (p = 0.03), no significant correlation was observed between urinary CD80 excretion and urinary CTLA-4 level in MCD patients at the time of relapse (p = 0.06). At the time of remission, CD80 had decreased significantly in all patients, but CTLA-4 levels either decreased or remained unchanged in all but five patients, and no correlation was observed between urinary CD80 excretion and CTLA-4 level (p = 0.7). CONCLUSIONS: Urinary CTLA-4 levels do not correlate with urinary CD80 excretion, suggesting the possibility that the CTLA4 response may be suboptimal in this disease during relapse.

Restraint of angiogenesis by zinc finger transcription factor CTCF-dependent chromatin insulation.

Angiogenesis is meticulously controlled by a fine balance between positive and negative regulatory activities. Vascular endothelial growth factor (VEGF) is a predominant angiogenic factor and its dosage is precisely regulated during normal vascular formation. In cancer, VEGF is commonly overproduced, resulting in abnormal neovascularization. VEGF is induced in response to various stimuli including hypoxia; however, very little is known about the mechanisms that confine its induction to ensure proper angiogenesis. Chromatin insulation is a key transcription mechanism that prevents promiscuous gene activation by interfering with the action of enhancers. Here we show that the chromatin insulator-binding factor CTCF binds to the proximal promoter of VEGF. Consistent with the enhancer-blocking mode of chromatin insulators, CTCF has little effect on basal expression of VEGF but specifically affects its activation by enhancers. CTCF knockdown cells are sensitized for induction of VEGF and exhibit elevated proangiogenic potential. Cancer-derived CTCF missense mutants are mostly defective in blocking enhancers at the VEGF locus. Moreover, during mouse retinal development, depletion of CTCF causes excess angiogenesis. Therefore, CTCF-mediated chromatin insulation acts as a crucial safeguard against hyperactivation of angiogenesis.

Serum from minimal change patients in relapse increases CD80 expression in cultured podocytes.

BACKGROUND: Minimal change disease (MCD) is the most common cause of nephrotic syndrome in children and is associated with the expression of CD80 in podocytes and the increased excretion of CD80 in urine. We hypothesized that serum from patients with MCD might stimulate CD80 expression in cultured podocytes. METHODS: Sera and peripheral blood mononuclear cells (PBMCs) were collected from subjects with MCD in relapse and remission and from normal controls. Immortalized human podocytes were incubated with culture media containing patient sera or supernatants from patient and control PBMC cultures. CD80 expression was measured by quantitative PCR and western blot analysis. RESULTS: Sera collected from patients with MCD in relapse, but not in remission, significantly increased CD80 expression (mean ± standard deviation: 1.8 ± 0.7 vs. 0.8 ± 0.2; p < 0.004) and CD80 protein secretion by podocytes (p < 0.05 between relapse and normal controls). No such CD80 increase was observed when podocytes were incubated with supernatants of PBMC cultures from patients in relapse. CONCLUSIONS: Sera from MCD patients in relapse, but not in remission, stimulated CD80 expression in cultured podocytes. Identifying this factor in sera could provide insights into the pathogenesis of this disorder. No role in CD80 expression by podocytes was found for cytokines released by PBMCs.

Ras Pathway Activation and MEKi Resistance Scores Predict the Efficiency of MEKi and SRCi Combination to Induce Apoptosis in Colorectal Cancer.

Colorectal cancer (CRC) is the second leading cause of cancer death in the United States. The RAS pathway is activated in more than 55% of CRC and has been targeted for therapeutic intervention with MEK inhibitors. Unfortunately, many patients have de novo resistance, or can develop resistance to this new class of drugs. We have hypothesized that much of this resistance may pass through SRC as a common signal transduction node, and that inhibition of SRC may suppress MEK inhibition resistance mechanisms. CRC tumors of the Consensus Molecular Subtype (CMS) 4, enriched in stem cells, are difficult to successfully treat and have been suggested to evade traditional chemotherapy agents through resistance mechanisms. Here, we evaluate targeting two pathways simultaneously to produce an effective treatment by overcoming resistance. We show that combining Trametinib (MEKi) with Dasatinib (SRCi) provides enhanced cell death in 8 of the 16 tested CRC cell lines compared to treatment with either agent alone. To be able to select sensitive cells, we simultaneously evaluated a validated 18-gene RAS pathway activation signature score along with a 13-gene MEKi resistance signature score, which we hypothesize predict tumor sensitivity to this dual targeted therapy. We found the cell lines that were sensitive to the dual treatment were predominantly CMS4 and had both a high 18-gene and a high 13-gene score, suggesting these cell lines had potential for de novo MEKi sensitivity but were subject to the rapid development of MEKi resistance. The 13-gene score is highly correlated to a score for SRC activation, suggesting resistance is dependent on SRC. Our data show that gene expression signature scores for RAS pathway activation and for MEKi resistance may be useful in determining which CRC tumors will respond to the novel drug combination of MEKi and SRCi.

Involvement of estrogen-related receptors in transcriptional response to hypoxia and growth of solid tumors.

The development of intratumoral hypoxia is a universal hallmark of rapidly growing solid tumors. Adaptation to the hypoxic environment, which is critical for tumor cell survival and growth, is mediated primarily through a hypoxia-inducible factor (HIF)-dependent transcriptional program. HIF activates genes that facilitate crucial adaptive mechanisms including increased glucose uptake and glycolysis and tumor angiogenesis, making it an important therapeutic target. However, the HIF-dependent transcriptional mechanism remains incompletely understood, and targeting HIF is a difficult endeavor. Here, we show that the orphan nuclear receptor estrogen-related receptors (ERRs) physically interact with HIF and stimulate HIF-induced transcription. Importantly, ERRs appear to be essential for HIF's function. Transcriptional activation of hypoxic genes in cells cultured under hypoxia is largely blocked by suppression of ERRs through expression of a dominant negative form of ERR or treatment with a pharmacological ERR inhibitor, diethylstilbestrol. Systematic administration of diethylstilbestrol severely diminished growth and angiogenesis of tumor xenografts in vivo. Because nuclear receptors are outstanding targets for drug discovery, the findings not only may offer mechanistic insights into HIF-mediated transcription but also may open new avenues for targeting the HIF pathway for cancer therapy.

APC and TP53 Mutations Predict Cetuximab Sensitivity across Consensus Molecular Subtypes.

Recently, it was suggested that consensus molecular subtyping (CMS) may aide in predicting response to EGFR inhibitor (cetuximab) therapies. We recently identified that APC and TP53 as two tumor suppressor genes, when mutated, may enhance cetuximab sensitivity and may represent easily measured biomarkers in tumors or blood. Our study aimed to use APC and TP53 mutations (AP) to refine the CMS classification to better predict responses to cetuximab. In total, 433 CRC tumors were classified into CMS1-4 subtypes. The cetuximab sensitivity (CTX-S) signature scores of AP vs. non-AP tumors were determined across each of the CMS classes. Tumors harboring combined AP mutations were predominantly enriched in the CMS2 class, and to a lesser degree, in the CMS4 class. On the other hand, AP mutated CRCs had significantly higher CTX-S scores compared to non-AP CRCs across all CMS classes. Similar results were also obtained in independent TCGA tumor collections (n = 531) and in PDMR PDX/PDO/PDC models (n = 477). In addition, the in vitro cetuximab growth inhibition was preferentially associated with the CMS2 cell lines harboring A/P genotypes. In conclusion, the AP mutation signature represents a convenient biomarker that refines the CMS classification to identify CRC subpopulations predicted to be sensitive to EGFR targeted therapies.

Protein kinase C epsilon is overexpressed in primary human non-small cell lung cancers and functionally required for proliferation of non-small cell lung cancer cells in a p21/Cip1-dependent manner.

The protein kinase C (PKC) family of proteins plays important roles in growth regulation and is implicated in tumorigenesis. It has become clear that the role of PKC in tumorigenesis is cell context dependent and/or isoform specific. In this study, we showed for the first time by immunohistochemistry that overexpression of PKC epsilon was detected in the vast majority (>90%) of primary human non-small cell lung cancers (NSCLC) compared with normal lung epithelium. Inhibition of the PKC epsilon pathway using a kinase-inactive, dominant-negative PKC epsilon, PKC epsilon(KR), led to a significant inhibition of proliferation and anchorage-independent growth of human NSCLC cells in a p53-independent manner. This was accompanied by a specific induction of the cyclin-dependent kinase (cdk) inhibitor p21/Cip1 but not p27/Kip1. In response to serum stimulation, PKC epsilon(KR)-expressing cells showed a prolonged G(1)-S transition and delayed and reduced activation of cdk2 complexes, which was likely attributed to the increased binding of p21/Cip1 to cdk2. Furthermore, inhibition of PKC epsilon function either by expressing PKC epsilon(KR) or by small interfering RNA (siRNA)-mediated gene knockdown resulted in c-Myc down-regulation, which, in turn, regulated p21/Cip1 expression. Knockdown of PKC epsilon or c-Myc expression using siRNA led to induction of p21/Cip1 and attenuation of G(1)-S transition in NSCLC cells. Using p21(+/+) and p21(-/-) HCT116 isogenic cell lines, we further showed that growth inhibition by PKC epsilon(KR) required the function of p21/Cip1. Collectively, these results reveal an important role for PKC epsilon signaling in lung cancer and suggest that one potential mechanism by which PKC epsilon exerts its oncogenic activity is through deregulation of the cell cycle via a p21/Cip1-dependent mechanism.

PTPRS drives adaptive resistance to MEK/ERK inhibitors through SRC.

PTPRS is the most commonly mutated receptor tyrosine phosphatase in colorectal cancer (CRC). PTPRS has been shown to directly affect ERK and regulate its activation and nuclear localization. Here we identify that PTPRS may play a significant role in developing adaptive resistance to MEK/ERK inhibitors (MEKi/ERKi) through SRC activation. Moreover, we demonstrate a new clinical approach to averting adaptive resistance through the use of the SRC inhibitor, dasatinib. Our data suggest the potential for dasatinib to enhance the efficacy of MEKi and ERKi by preventing adaptive resistance pathways operating through SRC.

PTPRS Regulates Colorectal Cancer RAS Pathway Activity by Inactivating Erk and Preventing Its Nuclear Translocation.

Colorectal cancer (CRC) growth and progression is frequently driven by RAS pathway activation through upstream growth factor receptor activation or through mutational activation of KRAS or BRAF. Here we describe an additional mechanism by which the RAS pathway may be modulated in CRC. PTPRS, a receptor-type protein tyrosine phosphatase, appears to regulate RAS pathway activation through ERK. PTPRS modulates ERK phosphorylation and subsequent translocation to the nucleus. Native mutations in PTPRS, present in ~10% of CRC, may reduce its phosphatase activity while increasing ERK activation and downstream transcriptional signaling.

Angiopoietin-like-4 and minimal change disease.

BACKGROUND: Minimal Change Disease (MCD) is the most common type of nephrotic syndrome in children. Angiopoietin-like-4 (Angplt4) has been proposed as mediator of proteinuria in MCD. The aim of this study was to evaluate the role of Angptl4 as a biomarker in MCD. METHODS: Patients with biopsy-proven primary MCD, focal segmental glomerulosclerosis, membranous nephropathy (60, 52 and 52 respectively) and 18 control subjects had urinary and serum Angptl4 measured by Elisa. Frozen kidney tissue sections were stained for Angptl4. RESULTS: Angptl4 was not identified in glomeruli of MCD patients in relapse. Urinary Angptl4 levels were elevated in MCD in relapse as well as in patients with massive proteinuria due to other glomerular diseases. CONCLUSION: Neither serum nor urine Angptl4 appear to be good biomarkers in MCD. Elevated urinary Angptl4 n glomerular disease appears to reflect the degree of proteinuria rather than any specific disease.

Cooperation between PKC-alpha and PKC-epsilon in the regulation of JNK activation in human lung cancer cells.

Phorbol esters can induce activation of two mitogen-activated protein kinase (MAPK) pathways, the extracellular signal-regulated kinase (ERK) pathway and the c-Jun N-terminal kinase (JNK) pathway. Unlike ERK activation, JNK activation by phorbol esters is somehow cell-specific. However, the mechanism(s) that contribute to the cell-specific JNK activation remain elusive. In this study, we found that phorbol 12-myristate 13-acetate (PMA) induced JNK activation only in non-small cell lung cancer (NSCLC) cells, but not in small cell lung cancer (SCLC) cells, whereas ERK activation was detected in both cell types. In NSCLC cells, PMA induced JNK activation in a time- and dose-dependent manner. JNK activation was attenuated by protein kinase C (PKC) down-regulation through prolonged pre-treatment with PMA and significantly inhibited by PKC inhibitors Gö6976 and GF109203X. Subcellular localization studies demonstrated that PMA induced translocation of PKC-alpha, -betaII, and -epsilon isoforms, but not PKC-delta, from the cytosol to the membrane. Analysis of various PKC isoforms revealed that PKC-epsilon was exclusively absent in the SCLC cell lines tested. Ectopic expression of PKC-epsilon in SCLC cells restored PMA activation of JNK signaling only in the presence of PKC-alpha, suggesting that PKC-alpha and PKC-epsilon act cooperatively in regulating JNK activation in response to PMA. Furthermore, using dominant negative mutants and pharmacological inhibitors, we define that a putative Rac1/Cdc42/PKC-alpha pathway is convergent with the PKC-epsilon/MEK1/2 pathway in terms of the activation of JNK by PMA.

Response of estrogen receptor-positive breast cancer tumorspheres to antiestrogen treatments.

Estrogen signaling plays a critical role in the pathogenesis of breast cancer. Because the majority of breast carcinomas express the estrogen receptor ERα, endocrine therapy that impedes estrogen-ER signaling reduces breast cancer mortality and has become a mainstay of breast cancer treatment. However, patients remain at continued risk of relapse for many years after endocrine treatment. It has been proposed that cancer recurrence may be attributed to cancer stem cells (CSCs)/tumor-initiating cells (TICs). Previous studies in breast cancer have shown that such cells can be enriched and propagated in vitro by culturing the cells in suspension as mammospheres/tumorspheres. Here we established tumorspheres from ERα-positive human breast cancer cell line MCF7 and investigated their response to antiestrogens Tamoxifen and Fulvestrant. The tumorsphere cells express lower levels of ERα and are more tumorigenic in xenograft assays than the parental cells. Both 4-hydroxytamoxifen (4-OHT) and Fulvestrant attenuate tumorsphere cell proliferation, but only 4-OHT at high concentrations interferes with sphere formation. However, treated tumorsphere cells retain the self-renewal capacity. Upon withdrawal of antiestrogens, the treated cells resume tumorsphere formation and their tumorigenic potential remains undamaged. Depletion of ERα shows that ERα is dispensable for tumorsphere formation and xenograft tumor growth in mice. Surprisingly, ERα-depleted tumorspheres display heightened sensitivity to 4-OHT and their sphere-forming capacity is diminished after the drug is removed. These results imply that 4-OHT may inhibit cellular targets besides ERα that are essential for tumorsphere growth, and provide a potential strategy to sensitize tumorspheres to endocrine treatment.

Protein kinase C-epsilon promotes survival of lung cancer cells by suppressing apoptosis through dysregulation of the mitochondrial caspase pathway.

The serine/threonine protein kinase C (PKC) has been implicated in the regulation of drug resistance and cell survival in many types of cancer cells. However, the one or more precise mechanisms remain elusive. In this study, we have identified and determined the mechanism by which PKC-epsilon, a novel PKC isoform, modulates drug resistance in lung cancer cells. Western blot analysis demonstrates that expression of PKC-epsilon, but not other PKC isoforms, is associated with the chemo-resistant phenotype of non-small cell lung cancer (NSCLC) cell lines. Northern blotting and nuclear run-on transcription analysis further reveals that the failure of expression of PKC-epsilon in the chemo-sensitive phenotype of small cell lung cancer (SCLC) cells results from transcriptional inactivation of the gene. Importantly, forced expression of PKC-epsilon in NCI-H82 human SCLC cells confers a significant resistance to the chemotherapeutic drugs, etoposide and doxorubicin. Resistance is characterized by a significant reduction in apoptosis in PKC-epsilon-expressing cells. Treatment of NCI-H82 cells with etoposide induces a series of time-dependent events, including the release of cytochrome c from the mitochondria to the cytosol, activation of caspase-9 and caspase-3, and cleavage of poly(ADP-ribose) polymerase (PARP). All of these events are blocked by PKC-epsilon expression. Furthermore, caspase-specific inhibitors, z-VAD-fmk and z-DEVD-fmk, significantly attenuate the accumulation of sub-G(1) population and block the PARP cleavage in response to etoposide. These results suggest that PKC-epsilon prevents cells from undergoing apoptosis through inhibition of the mitochondrial-dependent caspase activation, thereby leading to cell survival. Finally, down-regulation of PKC-epsilon expression by the antisense cDNA in NSCLC cells results in increased sensitivity to etoposide. Taken together, our findings suggest an important role for PKC-epsilon in regulating survival of lung cancer cells.

Enzootic transmission of yellow fever virus in Peru.

The prevailing paradigm of yellow fever virus (YFV) ecology in South America is that of wandering epizootics. The virus is believed to move from place to place in epizootic waves involving monkeys and mosquitoes, rather than persistently circulating within particular locales. After a large outbreak of YFV illness in Peru in 1995, we used phylogenetic analyses of virus isolates to reexamine the hypothesis of virus movement. We sequenced a 670-nucleotide fragment of the prM/E gene region from 25 Peruvian YFV samples collected from 1977 to 1999, and delineated six clades representing the states (Departments) of Puno, Pasco, Junin, Ayacucho, San Martin/Huanuco, and Cusco. The concurrent appearance of at least four variants during the 1995 epidemic and the genetic stability of separate virus lineages over time indicate that Peruvian YFV is locally maintained and circulates continuously in discrete foci of enzootic transmission.

Phylogeny of the Simbu serogroup of the genus Bunyavirus.

The Simbu serogroup of the genus Bunyavirus, family Bunyaviridae contains 25 viruses. Previous serological studies provided important information regarding some but not all of the relationships among Simbu serogroup viruses. This report describes the nucleotide sequence determination of the nucleocapsid (N) gene of the small genomic segment of 14 Simbu serogroup viruses and partial nucleotide sequence determination of the G2 glycoprotein-coding region (encoded by the medium RNA segment) of 19 viruses. The overall phylogeny of the Simbu serogroup inferred from analyses of the N gene was similar to that inferred from analyses of the G2 protein-coding region. Both analyses revealed that the Simbu serogroup viruses have evolved into at least five major phylogenetic lineages. In general, these phylogenetic lineages were consistent with the previous serological data, but provided a more detailed understanding of the relatedness amongst many viruses. In comparison to previous phylogenetic studies on the California and Bunyamwera serogroups of the Bunyavirus genus, the Simbu serogroup displays much larger genetic variation in the N gene (up to 40% amino acid sequence divergence).

Genetic relationships and evolution of genotypes of yellow fever virus and other members of the yellow fever virus group within the Flavivirus genus based on the 3' noncoding region.

Genetic relationships among flaviviruses within the yellow fever (YF) virus genetic group were investigated by comparing nucleotide sequences of the 3' noncoding region (3'NCR). Size heterogeneity was observed between members and even among strains of the same viral species. Size variation between YF strains was due to duplications and/or deletions of repeated nucleotide sequence elements (RYF). West African genotypes had three copies of the RYF (RYF1, RYF2, and RYF3); the Angola and the East and Central African genotypes had two copies (RYF1 and RYF3); and South American genotypes had only a single copy (RYF3). Nucleotide sequence analyses suggest a deletion within the 3'NCR of South American genotypes, including RYF1 and RYF2. Based on studies with the French neurotropic vaccine strain, passage of a YF virus strain in cell culture can result in deletion of RYF1 and RYF2. Taken together, these observations suggest that South American genotypes of YF virus evolved from West African genotypes and that the South American genotypes lost RYF1 and RYF2, possibly in a single event. Repeated sequence elements were found within the 3'NCR of other members of the YF virus genetic group, suggesting that it is probably characteristic for members of the YF virus genetic group. A core sequence of 15 nucleotides, containing two stem-loops, was found within the 3'NCR of all members of the YF genetic group and may represent the progenitor repeat sequence. Secondary structure predictions of the 3'NCR showed very similar structures for viruses that were closely related phylogenetically.

Epidemiología Molecular del Virus de la Fiebre Amarilla / Molecular Epidemiology of the Virus of Yellow Fever

Los datos genéticos surgieron que el virus de la fiebre amarilla no se presentan en ondas pizoóticas ni en el Perú ni en Bolivia,sino que tiene naturaleza permanente y focalizada,las clases de virus de fiebre amarilla que se encontraron en Perú y Bolivia,son miembros del genotipo II de América del Sur,en tanto que los virus encontrados en otros lugares de este continente pertenecen al genotipo I de América del Sur.(au)