Studies on Polyoma Middle T Antigen Signaling.
development of tumors in mice expressing transgenic polyomavirus middle T (MT) antigen
in mammary cells has been intensively studied because it closely matches the progression
of human breast cancer. Here I have examined the regulation of ERK by MT in mouse
mammary gland epithelial cells. Stress responses are important in both the development
and treatment of cancer. MT suppress... read morees the strong activation of ERK by many stress
conditions (serum starvation, oxidative stress, UV radiation, hypoxia or drugs causing
ER stress). This is an unexpected result, since MT activates RAS, an upstream activator
of ERK. This suppression is specific in that MT does not affect all aspects of response
to a particular stress. MT affects ERK activation at multiple points: involvement of the
ERK kinase MEK1/2 and ERK phosphatases. MT genetic analysis and gain of function assays
indicated PI3K/AKT is required but not sufficient for ERK suppression by MT. In
addition, based on human mammary epithelial cells MCF10A experiments, MT also uses Y322
to regulate ERK dephosphorylation. ERK suppression by MT subjected to stress is involved
in multiple cell phenotypes. Suppression of ERK improves cell survival exposed to
peroxide and reduces COX2 expression caused by hypoxia. Suppression of ERK caused NMuMG
cells accumulated in G1 cycle while MT-NMuMG cells can overcome ERK suppression via
constitutively activated PI3K pathway. More importantly, ERK suppression also
contributes to MT regulation of cytokine expression and cytokine responses. Because ERK,
which can regulate cytokine response, is affected by MT, I looked more generally at the
role of MT in regulating cytokine. I found MT induces cytokines such as IL-6, CCL2 and
CCL5 production. MT attenuates ERK activation induced by TNFá and sensitizes
TNFá-induced apoptosis. MT enhances IL-6, CCL2 and CCL5 while reduces COX2
induction by TNFá. Gene Array study showed MT regulates cytokine expression at
least at RNA level both under basal activities and after TNFá treatment. Together,
this work gives a new insight of polyomavirus MT signaling in regulation of ERK in
response to stress and emphasizes the importance of MT regulating cytokine expression
and cytokine response. In chapter IV, I described some experiments directed at the
possibilities that there is a second target for the MT Y315 site. These experiments did
not reach any final conclusions.
Thesis (Ph.D.)--Tufts University, 2011.
Submitted to the Dept. of Biochemistry.
Advisors: Brian Schaffhausen, and Akiko Hata.
Committee: Larry Feig, and Alexei Degterev.
Keyword: Biochemistry.read less