Somatic variants of the level of expression of a cell surface antigen

Somatic variants with constitutive changes in the expression of the cortical thymocyte differentiation antigen HTA 1 were derived from the T-cell leukemia line Molt 4 using monoclonal antibody NA1/34 and the fluorescent activated cell sorter. Cells with the highest and lowest fluorescence were sorted and expanded. After several cycles, high expressor variants, with 10- to 12-fold increased surface HTA 1 and low expressors, with a level of one third relative to the wild-type, were obtained. The stability of the high expressors was improved by cloning. In spite of the large differences in the level of HTA 1 between the various mutants and the wild-type, the expression of HLA-A,B,C or its increase following interferon-alpha stimulation, remained unchanged. Although in HTA 1 there was only a trace of beta2-microglobulin (beta2m) detected by lactoperoxidase labelling of the high expressor variants, significant levels of both beta2m and HTA 1 light chain beta(t) were observed in gels stained with Coomassie blue. The physiological association of beta(t) with HTA 1 was confirmed by the substantial increase of beta(t) which parallels the increase of HTA 1.     

Loss of phylogenetic information in chorion gene families of Bombyx mori gene conversion

The silkmoth chorion has provided a stimulating model for the study of evolution and developmental regulation of gene families. Previous attempts at inferring relationships among chorion sequences have been based on pairwise comparisons of overall similarity, a potentially problematic approach. To remedy this, we identified the alignable regions of low sequence variability and then analyzed this restricted database by parsimony and neighbor-joining methods. At the deepest level, the chorion sequence tree is split into two branches, called "alpha" and "beta." Within each branch, early- and late-expressing genes each constitute monophyletic groups, while the situation with middle-expressing genes remains uncertain. The HcB gene family appears to be the most basal beta-branch group, but this conclusion is qualified because the effect of gene conversion on branching order is unknown. Previous studies by Eickbush and colleagues have strongly suggested that ErA, HcA, and HcB families undergo gene conversion within a gene family, whereas the ErB family does not. The occurrence of conversion correlates with a particular tree structure; namely, branch lengths are much greater at the base of the family than at higher internodes and terminal branches. These observations raise the possibility that chorion gene families are defined by gene conversion events (reticulate evolution) rather than by descent with modification (synapomorphy).      

THE CHEMICAL REGULATION OF THE DORMANCY PHASES OF BUD DEVELOPMENT

literature pertaining to the development and regulation of dormancy in the buds of woody species is reviewed and interpreted as follows. Morphological observations, the effects of environmental factors, and other evidence support the concept that bud dormancy involves a cycle of 3 separate phases of development. Beginning at the developmental pattern of spring, the 3 phases are: (1) dormancy development leading to the dormant state; (2) release from dormancy leading to the non-dormant state; and (3) the initiation of spring burst leading again to spring development. The regulation of dormancy is, therefore, discussed in terms of the regulation of development of the apex within each phase and the regulation of transitions between phases. The principal existing theory of dormancy regulation implies that dormancy consists, in total, of merely the inhibition of spring development, and that regulation involves first the accumulation of an inhibitor then its disappearance. The conceptual basis of this inhibitor theory is argued to be inadequate as is the experimental evidence for the existence of a specific inhibitor and for a correlation between its concentration and dormancy induction or release. There is little direct evidence on the mechanism of the regulation of bud development within any developmental phase. Circumstantial evidence suggests the developmental patterns arise from chemical patterns resulting from the interactions of classes of growth regulator such as auxin, kinin, and gibberellin. Some evidence exists concerning the regulation of the transitions between the phases of dormancy. A substance has recently been detected which may be a hormone regulating the initiation of dormancy development. The production of this substance may be photoperiodically determined. A role for gibberellins in the regulation of dormancy release has been postulated.     

Mitogen‐activated protein kinase dependency in BRAF/RAS wild‐type melanoma: A rationale for combination inhibitors

Inhibitors targeting the mitogen‐activated protein kinase (MAPK) pathway and immune checkpoint molecules have dramatically improved the survival of patients with BRAF^V600‐mutant melanoma. For BRAF/RAS wild‐type (WT) melanoma patients, however, immune checkpoint inhibitors remain the only effective therapeutic option with 40% of patients responding to PD‐1 inhibition. In the present study, a large panel of 10 BRAF^V600‐mutant and 13 BRAF/RAS WT melanoma cell lines was analyzed to examine MAPK dependency and explore the potential utility of MAPK inhibitors in this melanoma subtype. We now show that the majority of BRAF/RAS WT melanoma cell lines (8/13) display some degree of sensitivity to trametinib treatment and resistance to trametinib in this melanoma subtype is associated with, but not mediated by NF1 suppression. Although knockdown of NF1 stimulates RAS and CRAF activity, the activation of CRAF by NF1 knockdown is limited by ERK‐dependent feedback in BRAF‐mutant cells, but not in BRAF/RAS WT melanoma cells. Thus, NF1 is not a dominant regulator of MAPK signaling in BRAF/RAS WT melanoma, and co‐targeting multiple MAP kinase nodes provides a therapeutic opportunity for this melanoma subtype.     

Effects of BRAF inhibitors on human melanoma tissue before treatment,early during treatment,and on progression

Selective BRAF inhibitors (BRAFi) are a standard of care for the treatment of BRAF^V600‐mutant metastatic melanoma. We analyzed a unique set of serial triplicate human metastatic melanoma tumor biopsies to identify biomarkers of BRAFi response and resistance. Morphologic features and immunohistochemical biomarkers were analyzed in 37 metastatic melanoma biopsies at pretreatment (PRE), early during treatment (EDT), and on progression (PROG) from 15 patients treated with a BRAFi and correlated with response and outcome. At EDT, proliferative markers decreased regardless of response, whereas markers of cell death increased in responders. High expression of nuclear p27 at baseline was the strongest predictor of a poorer OS and predicted worse response. The results show that BRAFi are universally antiproliferative, regardless of clinical response, whereas markers of cell death increased only in responders. The addition of therapies targeting the cell cycle machinery may improve the response and duration of BRAFi, and investigation of the mechanisms of apoptosis may provide additional therapeutic targets.     

Paradoxical oncogenesis: are all BRAF inhibitors equal?

Cutaneous squamous cell carcinoma (cSCC) is a concerning toxicity with BRAF inhibitors in the treatment for melanoma. While the two drugs shown to improve survival, vemurafenib, and dabrafenib, have similar efficacy, the reported rates of cSCC are quite different. Drawing upon preclinical and clinical trial data, this article discusses the potential factors behind the different cSCC incidences reported with the two BRAF inhibitors and provides a strategic approach to understand this issue further.     

Targeted BRAF Inhibition Impacts Survival in Melanoma Patients with High Levels of Wnt/β-Catenin Signaling

Unprecedented clinical responses have been reported in advanced stage metastatic melanoma patients treated with targeted inhibitors of constitutively activated mutant BRAF, which is present in approximately half of all melanomas. We and others have previously observed an association of elevated nuclear β-catenin with improved survival in molecularly-unselected melanoma patients. This study sought to determine whether levels of Wnt/β-catenin signaling in melanoma tumors prior to treatment might predict patient responses to BRAF inhibitors (BRAFi). We performed automated quantification of β-catenin immunohistochemical expression in pretreatment BRAF-mutant tumors from 32 BRAFi-treated melanoma patients. Unexpectedly, patients with higher nuclear β-catenin in their tumors did not exhibit the survival advantage previously observed in molecularly-unselected melanoma patients who did not receive BRAFi. In cultured melanoma cells treated with long-term BRAFi, activation of Wnt/β-catenin signaling is markedly inhibited, coinciding with a loss of the enhancement of BRAFi-induced apoptosis by WNT3A observed in BRAFi-naïve cells. Together, these observations suggest that long-term treatment with BRAFi can impact the interaction between BRAF/MAPK and Wnt/β-catenin signaling to affect patient outcomes. Studies with larger patient cohorts are required to determine whether nuclear β-catenin expression correlates with clinical responses to BRAFi and to specific mechanisms of acquired resistance to BRAFi. Understanding these pathway interactions will be necessary to facilitate efforts to individualize therapies for melanoma patients.     

What is Meant by “95% of Species”? An Argument for the Inclusion of Rapid Tolerance Testing

It is increasingly common for water quality guidelines and risk assessments to consider the proportion of species at risk from a particular toxicant, based on the species sensitivity distribution (SSD) for that toxicant. There is a premise that the sensitivity data from species included in the SSD are sufficient to predict the effect on species for which there are no data. We discuss and review assumptions that follow this premise and find that for most toxicant SSDs include too few species, and that component species are biased toward particular taxonomic groups, common species and species from North America and western Europe. Consequently, protecting a given percentage, for example, 95%, of species in an SSD will likely protect more or less than 95% of species in nature, by an unknown amount. For the assumptions of SSDs to be better met, there is a need for tolerance data on more species, from more taxonomic and other groups, including rare species and those from widespread localities. In order to achieve this, we argue for the inclusion of rapid tests, which we define as toxicity tests designed to require less effort to conduct, relative to traditional tests, so sensitivity can be quickly and approximately determine in many species. Their use will allow for more species, more representative of natural communities, to be tested and therefore allow the construction of less biased SSDs and thus more accurate guidelines and assessments of risk.