Modulation of the Deubiquitinating System in Viral Infection, Lymphoid Cell Activation and Malignant Transformation
Year: 2007
Type: dissertation
Abstract: Most cellular proteins are affected by the conjugation of Ubiquitin (Ub),\nwhich may regulate their stability, activity or localization. The family\nof deubiquitinating enzymes (DUBs) removes Ub from conjugates and\nregulates the production and recycling of Ub. DUBs are thereby critically\ninvolved in the control of important functions such as cell growth,\ndifferentiation and apoptosis. Increasing evidence implicates\nderegulation of DUBs in malignant transformation. The human genome\ncontains many putative DUB-encoding genes but little is known about their\ntissue distribution, pattern of expression, activity and substrate\nspecificity. This thesis describes the use of a chemistry-based\nfunctional proteomics approach to identify active DUBs in human tumor\ncells of different tissue origin, in primary resting and mitogen\nstimulated cells, in Epstein-Barr virus (EBV) infected B lymphocytes, as\nwell as in human papilloma virus (HPV) E6/E7 immortalized keratinocytes.\nThe role of the ubiquitin C-terminal hydrolase (UCH)-L1 in the\nEBV-related B cell tumor Burkitt´s lymphoma (BL) is further investigated.\n\nBoth tumor specific and tissue specific patterns of DUB activity were\nidentified in a panel of tumor cell lines of different tissue origin. HPV\ncarrying cervical carcinomas showed a diverse activity pattern when\ncompared to the adjacent normal tissue, suggesting a role for some of the\nDUBs in the development of this tumor. The activity of specific enzymes,\nincluding USP5, -7, -9, -13, -15 and -22, was upregulated by mitogen\nactivation or virus infection in normal T- and B-lymphocytes. UCH-L1 was\nhighly expressed in tumor cell lines of epithelial and hematopoietic cell\norigin but was not detected in freshly isolated and mitogen activated\ncells. Upregulation of this DUB was a late event in the establishment of\nEBV immortalized lymphoblastoid cell lines (LCLs) and correlated with\nenhanced proliferation suggesting a possible role in growth\ntransformation.\n\nUCH-L1 was shown to regulate lymphocyte function-associated antigen\n(LFA)-1 dependent homotypic adhesion in B-lymphocytes. Integrin-mediated\ncell adhesion is essential in the development and activation of B-cells,\nand tight LFA-1 mediated adhesion may hinder malignant cell growth and\ninvasion. LFA-1 dependent homotypic adhesion was activated following\nUCH-L1 knockdown in BL cells and this correlated with slow-down of BL\ncell proliferation in suspension and in semisolid agar and an\naccumulation in the G1 phase of the cell cycle. This suggests that UCH-L1\nis required for maintaining LFA-1 in a low-avidity, non-adhesive state\nthat favors the proliferation of malignant B-cells.
Source: Figshare
Author: Ulrika Rolén
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2143642025