Control of nitrogen regulated virulence traits of the human fungal pathogen Candida albicans [Elektronische Ressource] = Steuerung von stickstoffregulierten Virulenzeigenschaften des human-pathogenen Pilzes Candida albicans / submitted by Neelam Dabas

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• Publié par: julius-maximilians-universitat_wurzburg
• Publié le: 01 janvier 2008
• Nombre de lectures: 16
• Langue: English
• Poids de l'ouvrage: 9 Mo

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Control of Nitrogen Regulated Virulence Traits of the
Human Fungal Pathogen Candida albicans

Steuerung von stickstoffregulierten Virulenzeigenschaften
des human-pathogenen Pilzes Candida albicans



Thesis for submission to a doctoral degree
at the Graduate School of Life Sciences,
Julius-Maximilians-Universität Würzburg,
Section: Infection and Immunity




submitted by
Neelam Dabas

from
Delhi, India



Würzburg, 2008



















Submitted on: …………………………………………………………..……..
Office stamp

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Chairperson: ……………………………………………………………….......

Primary Supervisor: …………………………………………………………..

Supervisor (Second): ………………………………………………….…......

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Date of Public Defence: …………………………………………….…………

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Affidavit



I hereby declare that my thesis entitled “Control of Nitrogen Regulated Virulence Traits of the
Human Fungal Pathogen Candida albicans” is the result of my own work. I did not receive
any help or support from third parties, i.e., commercial consultants or others. All sources and /
or materials applied are listed and specified in the thesis.

Furthermore, I verify that this thesis, neither in identical nor in similar form, has not yet been
submitted as part of another examination process.

I confirm that the information which I have given in this application is complete and true.





Würzburg
(Date) (Signature)




































Dedicated to
My mother








Acknowledgements

This thesis reports the results of my work that was done at the Candida workgroup, Institute
for Molecular and Infections biology since August, 2004. However, the responsibility to
represent the unswerving support system that I have received during this time in translating
my efforts into its current form is left to this single page.
My deepest gratitude is due to Prof. Dr. Joachim Morschhäuser for his incessant
encouragement and meticulous guidance all throughout this period. He not only provided me
the opportunity to join his group but also played the role of a teacher, motivator and guide, all
through these years. His untiring efforts and patience have enabled me to complete this work
successfully. Thank you, Joachim, for all the intense discussions and also the lighter
moments. I value them all.
I sincerely thank Prof. Dr. Dr. h. c. J. Hacker and Prof. Dr. med. Matthias Frosch for
providing the excellent working facilities at the institute. Special thanks to my promotion
committee members Prof Dr. Sven Hammerschmidt and PD Dr. Sven Krappmann for their
guidance and help, especially in bringing this thesis to its present form.
I wish to thank all my lab mates who have been a constant source for help and
friendship. Initial days at the lab and in Würzburg were made enjoyable in the company of
Kajal and Manjishtha. Thanks to Davina, Julia, Nim, Oliver, Peter and Ulrich for their support
and also for making labwork a lively experience. I would also like to thank Aditi, Bernardo,
Michael, Satheesh, Tina and Sabrina (both of them!) for their help. I express my gratitude
towards all members of the institute who have time and again helped me with my work.
The stay at beautiful city Würzburg has given me many friends who have helped me
during difficult times. I am grateful to Amna for all her efforts in the crucial first few months;
Narayan for all the discussions throughout these years and especially for his help with
Northern experiment. Thanks to Aru, Jaya, Naresh, Padma, Vijay and everyone at
Wuerzburgindians for many wonderful evenings together. Also, thanks to Kumari for being
around!
The blessings of Maa in every step of my life cannot be acknowledged in words and I
would not attempt to do so. I acknowledge her as my driving force. The determination to
begin this journey and reach its final destination has a lot to do with the unconditional and
unfailing support of my family, especially Annu di, Monu and Sumit. I hope to have lived up
to your expectations.
TABLE OF CONTENTS

1 SUMMARY 1
1 ZUSAMMENFASSUNG 4
2 INTRODUCTION 7
2.1 Determinants of pathogenicity: Virulence factors 8
2.1.1 Adhesins 8
2.1.2 Extracellular hydrolytic enzymes 9
2.1.3 Morphogenetic switching 12
2.1.4 Phenotypic 17
2.2 Nitrogen regulation and fungal virulence 17
2.2.1 Nitrogen regulatory genes: GATA transcription factors 19
2.2.2 Ammonium permease mediated filamentous growth in C. albicans 21
2.3 Aims of the study 23
3 MATERIALS AND METHODS 24
3.1 Bacterial strain 24
3.2 Plasmids 24
3.3 C. albicans strains 29
3.4 Primers 45
3.5 Materials 47
3.6 Methods 48
3.6.1 Growth and maintenance of E. coli strains 49
3.6.2 aC. albicans strains 49
3.6.3 Selection media for C. albicans transformants 49
3.6.4 Phenotypic assays 49
3.6.5 Small scale plasmid DNA isolation (Miniprep) 50
3.6.6 Polymerase Chain Reaction (PCR) 51
3.6.7 DNA digestion with restriction enzymes 51
3.6.8 Gel electrophoresis and gel elution of DNA fragments 51
3.6.9 Elution of inserts from agarose gel 52
3.6.10 Cloning gene of interest in vectors 52
3.6.11 Screening of recombinants 53 3.6.12 C. albicans transformation 54
3.6.13 Genomic DNA isolation from C. albicans 54
3.6.14 Southern hybridization 55
3.6.15 RNA isolation from C. albicans 56
3.6.16 Northern hybridization 57
3.6.17 5'-Rapid amplification of cDNA ends (5' RACE) assay 58
3.6.18 SDS polyacrylamide gel electrophoresis (SDS PAGE) and
Western blotting 58
3.6.19 GFP expression analysis 60
3.6.20 Ammonium uptake assays 60
4 RESULTS 61
4.1 Mutational analysis of ammonium permease Mep2p of C. albicans 61
4.1.1 Identification of the minimal region in the C-terminal cytoplasmic
tail of Mep2p required for induction of filamentous growth 61
4.1.2 Expression pattern and ammonium uptake capacity of mutated Mep2p
proteins 65
4.1.3 Signaling activity of mutated Mep2p proteins 70
4.1.4 An F239A mutation abolishes ammonium uptake and induction of
filamentous growth by Mep2p 74
4.2 Control of ammonium permease expression and nitrogen starvation-
induced filamentous growth in C. albicans 76
4.2.1 Two putative GATA factor binding sites in the MEP2 promoter are
essential for the upregulation of MEP2 expression under limiting
nitrogen conditions 76
4.2.2 Filamentous growth is correlated with MEP2 expression levels 80
4.2.3 GATA factors GLN3 and GAT1 in C. albicans 81
4.2.4 Construction of GLN3 and GAT1 deletion mutants 82
4.2.5 GATA factors Gln3p and Gat1p control MEP2 expression 88
4.2.6 Ammonium permease MEP1 expression is also regulated by GATA
factors 91
4.2.7 Gln3p regulates nitrogen starvation-induced filamentous growth in
C. albicans 92
4.2.8 Inactivation of GAT1 activates MEP2-independent filamentation
pathways 94
4.2.9 Forced MEP2 expression bypasses the requirement of GLN3 for
filamentous growth 96
4.3 Secreted aspartic protease expression in C. albicans is controlled by a
transcription factor regulatory cascade 98
4.3.1 The GATA transcription factors Gln3p and Gat1p are required for
growth of C. albicans on proteins 98
4.3.2 Functional analysis of the GAT1 gene 100 4.3.3 GLN3 and GAT1 control expression of the secreted aspartic protease
SAP2 and oligopeptide transporters OPT1 and OPT3 102
4.3.4 Forced expression of SAP2 overcomes the growth defect of
gln3 Δ gat1 Δ mutants 104
4.3.5 Forced expression of the transcription factor STP1 bypasses the
requirement of GATA transcription factors for growth on proteins 105
4.3.6 Expression of the transcription factor STP1 is controlled by Gln3p
and Gat1p 108
4.3.7 Nitrogen catabolite repression of SAP2 is mediated by regulation of
STP1 expression 109
5 DISCUSSION 112
5.1 Mutational analysis of Mep2p 112
5.2 The GATA transcription factors Gln3p and Gat1p control MEP2
expression and filamentous growth 117
5.3 A transcription factor regulatory cascade controls secreted aspartic
protease expression in C. albicans 121
6 REFERENCES 127
7 APPENDIX 138

7.1 Publications and Presentations 138
7.2 Curriculum Vitae 139


Summary
1 Summary
The yeast Candida albicans is a member of the normal mic