Citation
Chan, Lee Chin
(2018)
Transcriptomic analysis of EJ28 bladder cancer cells persistently infected with Newcastle disease virus.
Masters thesis, Universiti Putra Malaysia.
Abstract
Newcastle disease virus (NDV) is a highly contagious avian virus which leads to
tremendous economy loss in poultry industry. Nevertheless, NDV shows good oncolytic
activities on cancer cells by inducing apoptosis and therefore, it has been assessed in
clinical trials for cancer treatment. Despite their promising potential, NDV was found to
be able to persistently infect cancer cells in vitro without causing any cell death. The
morphological characteristics of the cancer cells persistently infected by NDV has been
described in the previous studies but the exact mechanism involved has yet to be
elucidated. Hence, the objective of this study is to investigate the transcriptomic profiles
of cancer cells persistently infected by NDV. By challenging with three rounds of
infection with Malaysian velogenic strain AF2240, the NDV persistently infected
bladder cancer cells EJ28 was established and was designated as EJ28P. The persistency
of EJ28P was confirmed when they have grown to 4-fold of the original seeding number
after 5 days post NDV infection; whilst its parental cells was nearly diminished in the
same condition. Annexin V apoptosis assay revealed that approximately 60% of parental
cells underwent apoptosis at 48 h post infection while the EJ28P was about 30%, which
was insignificantly different from mock-infection. EJ28P reinfected with recombinant
NDV AF2240 with green fluorescent protein (rAF-GFP) exhibited green fluorescent
even after 25 passages. This further confirmed the persistency of NDV in EJ28P.
Subsequently, total RNA of EJ28 and EJ28P were extracted and subjected to microarray
analyses. A total of 355 genes, which were differentially expressed in EJ28P compared
to EJ28, were identified using edgeR program, with their log2 fold change of 2 or more.
Among them, 222 genes were up-regulated while 133 genes were down-regulated. Gene
ontology (GO) of these genes were obtained using PANTHER Classification System and
Database for annotation, visualisation and Integrated Discovery (DAVID). Genes
associated to cytokine and apoptosis such as IL6, IL8, GBP2, CXCL8, HER5 and TNF
were down-regulated. Pathway analysis revealed that TGF-β signalling was
downregulated in EJ28P, which could lead suppression of apoptotic pathway and
promotion of cell proliferation. However, the anti-virus responses of EJ28P were not
completely suppressed as interferon-induced transmembrane (IFITM1), an anti-viral protein gene was up-regulated. On the other hand, genes associated to solute carrier
families that are responsible for glucose and amino acids transportation across the
membrane, were significantly up-regulated, suggesting that high demand of energy for
virus activities or for the cancer cell’s metabolism, or for both. In addition, genes related
to keratin group were overexpressed possibly involved in maintaining the cell structural
integrity. Since these expressed genes were not only beneficial to cell but also to virus,
it may either reflect a competition on both cell and virus for each survival, or an
interaction from both sides in order to maintain a co-existing form. Based on these
analyses, it is postulated that impairment of apoptosis and defective in pro-inflammatory
response, together with over expression of solute carrier families and keratin groups,
contribute to NDV persistent infection in bladder cancer cells. This study expands our
understanding on persistent NDV infection in bladder cancer cells.
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