The mechanism of histatin 5 induced cell death in Saccharomyces cerevisiae

Thesis (M.A.)--Boston UniversityHistatin 5 is a potent antifungal peptide endogenously produced by the parotid, sublingual and submandibular glands in humans. The potent antifungal properties afforded provide histatin 5 as an enticing biological therapeutic in treating oral candidiasis as well as other opportunistic yeast infections in immunocompromised individuals. As Candida albicans gains resistance to the current pharmacotherapies, it is pertinent to elucidate novel approaches in treating this pathogen. While a plethora of research has been performed studying histatin 5, its mechanism of action within C. albicans and other yeast species remains unresolved. Herein, we report on histatin 5 and suggest a mechanism of killing within a Saccharomyces cerevisiae model. Using haploid genetic knockouts, several genes of interested were tested in viable culture at the 50% lethal dose of histatin 5. Cells were further analyzed as being resistant or hypersensitive to histatin 5. Genes of interest and protein gene products were categorized in six distinct categories including cell surface transport, ion channels and osmoregulation, ionic/osmotic stress response, calcineurin regulation, oxidative stress response and finally cell wall and plasma membrane integrity. Histatin 5 internalizes via interactions with Ssa1, an Hsp70 family member, via initial binding then subsequent transfer to polyamine transporters Dur3 and Ptk2. Once inside the cell, histatin 5 operates through at least two pathways. Histatin 5 causes a deregulation of ionic gradients and membrane potential through cell surface ion channels Pma1 and Trk1. Initial osmotic stress activates regulatory pathways including high osmolarity glycerol (Hog1) pathways as well as the calcium dependent phosphatase calcineurin. While the osmotic stress is the immediate response to histatin 5 internalization, it is believed that histatin 5 also travels to the actively respiring mitochondria via interactions with cytosolic Ssa1. Histatin 5 enters the mitochondria and disrupts the electron transport chain ultimately producing highly reactive free radicals and reactive oxygen species. These species consequently damage DNA, lipids and proteins and are the main factors involved cell death. While further research is necessary, the establishment of necessary gene products for histatin 5 induced killing in S. cerevisiae grants mechanistic clarity, hopefully allowing for the development and advancement of histatin 5 mediated therapies in the future

Cholangiocarcinoma: Epidemiology and risk factors

Cholangiocarcinoma (CCA) is a heterogeneous disease arising from a complex interaction between host-specific genetic background and multiple risk factors. Globally, CCA incidence rates exhibit geographical variation, with much higher incidence in parts of the Eastern world compared to the West. These differences are likely to reflect differences in geographical risk factors as well as genetic determinants. Of note, over the past few decades, the incidence rates of CCA appear to change and subtypes of CCA appear to show distinct epidemiological trends. These trends need to be interpreted with caution given the issues of diagnosis, recording and coding of subtypes of CCA. Epidemiological evidences suggest that in general population some risk factors are less frequent but associated with a higher CCA risk, while others are more common but associated with a lower risk. Moreover, while some risk factors are shared by intrahepatic and both extrahepatic forms, others seem more specific for one of the two forms. Currently some pathological conditions have been clearly associated with CCA development, and other conditions are emerging; however, while their impact in increasing CCA risk as single etiological factors has been provided in many studies, less is known when two or more risk factors co-occur in the same patient. Moreover, despite the advancements in the knowledge of CCA aetiology, in Western countries about 50% of cases are still diagnosed without any identifiable risk factor. It is therefore conceivable that other still undefined etiologic factors are responsible for the recent increase of CCA (especially iCCA) incidence worldwide

A DNA methylation biomarker of alcohol consumption.

The lack of reliable measures of alcohol intake is a major obstacle to the diagnosis and treatment of alcohol-related diseases. Epigenetic modifications such as DNA methylation may provide novel biomarkers of alcohol use. To examine this possibility, we performed an epigenome-wide association study of methylation of cytosine-phosphate-guanine dinucleotide (CpG) sites in relation to alcohol intake in 13 population-based cohorts (ntotal=13 317; 54% women; mean age across cohorts 42-76 years) using whole blood (9643 European and 2423 African ancestries) or monocyte-derived DNA (588 European, 263 African and 400 Hispanic ancestry) samples. We performed meta-analysis and variable selection in whole-blood samples of people of European ancestry (n=6926) and identified 144 CpGs that provided substantial discrimination (area under the curve=0.90-0.99) for current heavy alcohol intake (⩾42 g per day in men and ⩾28 g per day in women) in four replication cohorts. The ancestry-stratified meta-analysis in whole blood identified 328 (9643 European ancestry samples) and 165 (2423 African ancestry samples) alcohol-related CpGs at Bonferroni-adjusted P<1 × 10-7. Analysis of the monocyte-derived DNA (n=1251) identified 62 alcohol-related CpGs at P<1 × 10-7. In whole-blood samples of people of European ancestry, we detected differential methylation in two neurotransmitter receptor genes, the γ-Aminobutyric acid-A receptor delta and γ-aminobutyric acid B receptor subunit 1; their differential methylation was associated with expression levels of a number of genes involved in immune function. In conclusion, we have identified a robust alcohol-related DNA methylation signature and shown the potential utility of DNA methylation as a clinically useful diagnostic test to detect current heavy alcohol consumption.Medical Research Council (Grant IDs: MC_UU_12015/1, MC_UU_12015/2), Wellcome Trust. Detailed acknowledgements are included in the Supplementary Information that accompanies the paper on the Molecular Psychiatry website

Revisiting the association between candidal infection and carcinoma, particularly oral squamous cell carcinoma

Background: Tobacco and alcohol are risk factors associated with cancer of the upper aerodigestive tract, but increasingly the role of infection and chronic inflammation is recognized as being significant in cancer development. Bacteria, particularly Helicobacter pylori, and viruses such as members of the human papilloma virus family and hepatitis B and C are strongly implicated as etiological factors in certain cancers. There is less evidence for an association between fungi and cancer, although it has been recognized for many years that white patches on the oral mucosa, which are infected with Candida, have a greater likelihood of undergoing malignant transformation than those that are not infected. Objective: This article reviews the association between the development of oral squamous cell carcinoma in potentially malignant oral lesions with chronic candidal infection and describes mechanisms that may be involved in Candida-associated malignant transformation